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MG MGB Technical - Still the same bad idle

I cannot beleive it i have rebuilt every thing.After finding Valve Timing out i have replaced with . New timing chain ,dizzy,coil, rocker shaft,buckets, push rods, carb rebuild and done it all by the book and double checking every thing i only had the rebuilt carbs to put on today and i thought i had the problem sorted. Put the rebuilt carbs on after cleaning and checking all the faces and used new gaskets ,nuts etc. It started straight away on choke set the fast idle it was running superb . The linkage was not connected so i could synchro and balance the carbs up when the temp got to the proper level .Pushed choke in got them balanced around 800 rpm set mixture not running to bad . Then it started again idle all over the place and trying to set up the rear carb no chance i have had to screw mixture screw nearly all the way in so whether some dirt has got into it i don't know. But i have put brand new petrol into the car and the fuel pump is showing 6psi pressure( I give up) I rebuilt the carbs with the greatest of care all new o rings ,needle valves,needles,seals and spindles so if it is the carbs cannot understand why unless it has got a bit of dirt in it . If i pull the choke out it runs ok. Got 170psi now on every cylinder ,Have rechecked timing ,tappets, I really dont know what to do now apart from taking the carbs off again.Plus the same trouble is here when the electric fan comes in it pulls the idle really down any ideas please regards Tony
A Basham

Tony. I responded to your e-mail with a recommendation to visit my website at www.custompistols.com/ and read the tech articles on the fuel system which David DuBois has written. Your first problem to correct is the fuel pump pressure which, if the gauge is reading correctly, is about twice what it should be for the SU carbs. Correct that, either with an SU fuel pump or a pressure regulator and clean your spark plugs.

After that, please let us know what carbs you are using. With the HS-4, you need to set the jet about .060" below the bridge as an initial starting point. A dial caliper is useful for this. It would also be useful to know what needles you are using. I find the AAA needle works best.

Les
Les Bengtson

Les,It is a genuine SU fuel pump for a MGB that is fitted to the car i have rechecked it with a proper low pressure gauge the fist was a cheap dual purpose one , it is at 3 to 3-1/2 psi. I did try to get into your site but cannot for some reason. I have already replaced the plugs with new ones thinking the one could have gone down, no chance even put the old ones back

The carbs are HIF4's and even though people have laughed when they have seen me do it .I do check the depth of the jets with a Dial Caliper like your self so both carbs are identical to the thou instead of the 2 turns down from bridge , more so since i have rebuilt them following the instructions to the letter.The needles fitted are the ones given by Burlen (ACD) ones . I have double checked every thing . When i found the Valve Timing out i thought found the problem . More so when the cylinder compressions shot up to 170psi-173psi on a compression test from the original 150 psi when checked when the valve timing was out.

I wonder if there is a problem with these carbs or i have got a bit of dirt stuck i expect i will have to strip them again.I have replaced the fuel with fresh 4 star into a empty tank,it has an in line filter fitted. When it first started every thing seemed to be going superb then when it got to temperature and the electric fan cut in the same old problem. Fan pulls the tick over right down.But i have done every electrical check possible and cleaned and re soldered every connection on the fan system

It is impossible to get the carbs tuned when the engine is at the correct temperature as when the fan cuts in the idle just goes to pot BUT even when the fan is not running i cannot adjust the rear carb it seems to want more fuel i have all the correct equipment to tune and set the carbs and engine up i am not just guessing things

Things done or replaced
New rocker shaft,Push Rods,Buckets
New Timing Chain and Tensioner.plus have checked cam lift with DTI dial seems to be standard cam fitted
New Distributor 45D- 4160
New Coil Sports ballast type as stated
All new Ignition Parts .plus have changed them all at least once again as may be new ones may have been faulty
Carb's rebuilt with Burlen rebuild kit ,new Needles,Jets,Solid discs,Etc
New Exhaust
Head crack tested and valves lapped in
Block has new .020 pistons ,crank reground
All new water pipes,thermostat,replaced radiator
New oil, filter's oil pressure superb
New breather pipes Y piece and tappet chests cleaned out

The car starts first time from cold pull choke out fully, start it then push choke in until it runs at 1200 rpm with choke on the cam arrow's it runs lovely. But then as soon as it gets hot and you push the choke in I cannot get it to idle evenly, or get the carbs tuned correctly.I can get them balanced and the mixture set the car runs OK for a few Min's then it starts running like a dog. The plugs are not fouling up i have checked

Again checked for air leaks even blocked of the servo
The car does not overheat. or over pressurize the cooling system ,no smoke does not use any oil or water. No crank case pressure
Sorry for such a long letter but you can understand my frustration and it is the only way to show i have done every thing plus i will be getting air leaks,ignition parts etc if i dont put down what i have checked
please help as i really am down and out now that i have put the valve timing back to the correct position and have not got the car any better

Regards TONY











A Bashamt

Tony - The one thing that you said that raised a red flag to me was "... i cannot adjust the rear carb it seems to want more fuel..." That, along withthe idle being dragged down by the cooling fan coming on, tells me that you have a problem with the rear carb. Since the HIF carbs usually have the fuel line running to the front carb first, then to the rear carb, I would suggest that the fuel is being restricted between the front and rear carb. this could happen inside the front carb, the line between the two,or at the rear carb. You could have an obstruction in the front carb that is restricting the fuel passage to the rear carb, a restriction in the line between the two carbs, or an obstruction in the rear carb. Another real possibility is a piston sticking in the rear carb, especially after the engine compartment heats up. Good luck - Dave
David DuBois

Tony-
Don't give up the ship! You don't have the *same* bad idle, you have a different one, and it sounds like things are actually much better.

It sounds like you've now got a carb problem.
HIF are prone to several difficulties.
Get a good light.
Start the car with air filters off, Raise engine speed enough that carb pistons are at least halfway up. They should be even as they rise, if not, the throttles are not in synch, or the pistons and vacuum chambers have been mixed up - Do you know how to do the drop test to check this?. Fix these two items first.

Beyond this point, check all the following before doing anything, as several of these things require removing carbs.

Look inside the carb throats, with the light. You will see fuel coming from the jets in a spray, which should be even.
If the back carb jet is spraying much less, there is a fuel feed problem at that carb. Check for obstruction in the feed line. If OK, then either the float level is wrong, or there is a problem with the float valve sticking due to dirt or poor manufacture - there are known issues with the plastic needle sticking in the guide, a little judicious sandpaper work on the plastic (to remove some extraneous flash from the moulding) will fix it.Be sure that there is not gas in the plastic floats, also a known problem, but that makes it rich or flooding.

If there is fuel spraying from one or two other holes in the bottom of the carb behind the jet, the cold start mechanism is either ON, or wrongly assembled. Check the linkage first. If OK, then you have to take the carbs off to get the cold start apart.
It is very hard to describe the inside of the cold start mechanism, and the books are not good on this, and I don't have one to look at, so here it is from memory - I always have to figure it out when I do one. It is a common problem, and it causes very strange things, some of which do not seem like excessively rich mixture - mostly it just doesn't make any sense! (If any SU is badly out, it will screw up the mixture readings on the OTHER carb, so your problem could actually be with the front one!) There is a small O ring on the coldstart spindle, if bad or missing, it causes this trouble. The spindle has a hole with a tapered groove connecting to it; this meters fuel for enrichment when the choke is ON, and the groove reduces that as you push the choke in,finally shutting the fuel OFF. As I recall, it is possible to install the spindle so that this passage is OPEN when the choke is OFF. You will have to examine the holes in the carb and spindle to figure out which way round it needs to be, so that with choke OFF the passage is CLOSED, and when choke is ON it is OPEN.

Before you put the vacuum bells back on, recheck that the jets move up and down as you turn the adjusting screws, and that the jets are even at about .055-.060 down from the bridge - it is possible to get them out of the little grooves in the thermo element. If you still have problems after you get it hot, remove the vacuum chambers and recheck the jet position hot - they will be slightly higher hot than cold, but should still be even if they start out that way.

Recheck that the mixture needles are correctly installed in the pistons, with the shoulders flush with the face of the piston.

Put it all back together and light it up!

Good luck,
FRM
FR Millmore

Tony,

if there are HIF 4 carbs on the car, the jet adusting screw must be screwed OUT for leaning the mixture! So it is just the other way than with 'normal' carbs. have jou checked this?

May be there was a little misunderstanding that might be resposible for the bad idle?

Ralph
Ralph

Ralph, Yes i know how they should be set up and the directions for leaner - richer mixture , but thank you any how. It seems as if when hot i have to turn the rear carb to full richness IE Clock-wise. It makes me wonder if there is a fuel blockage or the float is sticking or needle valve. But i put new needle valves in and floats set the heights with a vernier caliper I have tried to calm down and it has just got to be the carbs so i will take them off and recheck them. Another member has suggested the choke spindles can be put back 180 degrees out. But i have checked another set of carbs and i am sure it does not matter as they are identical. Plus there is no mention in the instruction book or manual. The only part is the outer sleeve, the cut out must be at the top but the inner shaft that has the O ring on and the grooves and hole on , it seems that you can put it back in any position. If any one knows different please let me know. As i have said i will either do one of two things recheck these or put on the other set after re-newing gaskets O rings etc. As you will all have guessed i am gutted as i was 100% sure i had sorted every thing out but i will plod on. Any suggestions will be gratefully received TONY
A Basham

As previously sent to Tony, repeated here for completeness:

1. If the fuel pump is putting out 6psi that could well be too much. The original SU puts out about 1.5psi, aftermarket ones are often more than that and can overwhelm the float valves, so a pressure limiting valve has to be fitted. This *could* explain why it runs OK when warming up but not hot i.e. it is too rich, but doesn't explain why pulling the choke when it runs badly when hot makes it run better, that would tend to indicate a weak mixture (but see ignition comments below). I take it there is definitely no fuel flowing out of the overflow ports. How often does the fuel pump click with the engine stopped but the ignition left on (disconnect the coil -ve to avoid overheating the coil)? It should not click more than once every 30 secs once it has pressurised the system after first switching on. If more than that either the float valves are leaking, in which case I'd expect to see fuel eventually coming out of the overflow, or up through the main jet, but this could take several minutes if only slight. Another cause of clicking is the non-return valves in the pump itself leaking back, and this can contribute to weak mixture. What flow rate are you getting? With the supply pipe disconnected from a carb and directed into a container you should get *at least* one pint per minute, with negligible bubbles, and it should be very consistent. You may have to pump a pint or more before problems start happening.

2. You don't have to be so precise about the starting position of the jets, it is just that - a starting position. If one is higher or lower than the
other by even a couple of millimetres that is taken care of in the coarse and fine tuning. However it *is* useful to get them close to start with where you
are having problems, as if one takes noticeably more turns than the other to get it to the final correct
position it indicates something is wrong with one or other carb. Also if *both* have to be moved very far from the starting position it indicates a common problem.

3. Unfortunately HIFs are potentially more troublesome as they have extra valves and
passages to go wrong, the HS by comparison is an extremely simple device, and also things like float chambers and valves can be checked and replaced
with the carbs in-situ. Your biggest problem is that the whole of this engine is an unknown quantity to you, so there could be any number of things wrong with it, and if there are more than one they could well be interacting and giving conflicting indications, making it even more difficult to work out what is wrong. With the amount of problems you have had I think I would consider, if you have the option, swapping the carbs over with a pair from another correctly running engine to eliminate or prove the carbs as the issue, or one of them. Ditto the distributor for that matter.

4. You can check for blockages in the main fuel path of the carbs by removing the air filters (if fitted) and blowing gently in the overflow port with the engine switched off but the ignition on (to make sure the float chambers are full). This should push fuel up through the main jet and be visible looking in the air intake. Likewise if you suck gently on the overflow port with the engine running (use a long clear pipe so you don't get a mouth full of fuel) you should pull fuel *out* of the jet of that carb which will stop it contributing to engine running. You will probably have to do this test at a higher than normal idle speed or the engine will simply stall. Ideally you want it to be able to run on just one carb at a time to see if the speed drops by the same amount with each carb (as it should), if it drops by more or less with one than the other that indicates a carb problem on one or the other.

5. With the arrows under the fast-idle screws it is my understanding that is the fast-idle only position, there is no enrichment at that position. If you are saying that you can start the engine on choke then immediately reduce the choke to that position and the engine still runs well i.e. while still cold, I'd say that indicates the mixture is too rich as you *should* need gradually reducing enrichment until the temp gauge gets about half-way from C to N (although all cars are different in the amounts and timings).

6. I'd ignore the electric fan issue until you get the engine running properly, a poorly running engine *will* slow down more with the load of an electric fan than a correctly running engine. Other than that it is more likely to be a case of the fan pulling too much current, than not enough caused by bad connections. By improving bad connections you are actually making the effect worse :o) As an interim you can bridge the thermostatic switch to run the fan all the time and adjust the idle screws to compensate,
that will at least remove the fluctuation caused by the fans switching in and out while you are trying to work on the carbs. At the end remove the bridge and fine-tune the idle screws, making sure you *only* adjust both by the same amount in the same direction, and still making sure it idles OK when the fans switch in. On my V8 I have the idle set so that it is correct when the fans are running, which makes the idle a little high when they are not, but I would rather have the extra hot idle oil pressure which can be minimal on this engine.

7. You say you have a ballast type sports coil, have you measured the primary resistance? Original unballasted system coils (i.e. chrome bumper cars) measure about 3 ohms. Original ballasted system coils (i.e. rubber bumper cars) measure about 1.5 ohms. An unballasted system sports coil I have measures about 2.4 ohms i.e. a bit less than the standard coil. I'd expect a ballasted system sports coil to measure about 1.2 ohms. Ignore whatever it says on the coil itself, the indications are often confusing if not downright incorrect, always measure it. Whichever coil you have you must have the correct ignition feed. Chrome bumper cars had an unballasted system as I have said which has a direct ignition feed i.e. no harness ballast resistance. Rubber bumper cars had a ballasted system which included 1.5 ohms of pink resistance wire in between the white at the fuse box and the coil +ve. You must make sure you have the matching coil and ignition feed i.e. *either* a 3 (or 2.4) ohm coil with a direct feed, *or* a 1.5 (or 1.2) ohm coil with a ballasted feed, regardless of whether the car is chrome bumper or rubber, as a previous owner could have fiddled with the wiring on either. If you have a ballasted harness and the correct coil you should see about 6v on the coil +ve with the ignition on, engine stopped, and points closed. If you have a chrome bumper coil (i.e. 3 or 2.4 ohm) with a ballasted harness you will see about 9v on the coil +ve which is incorrect. If you see 12v on the coil +ve, regardless of whether you have a coil for a ballasted system or an unballasted system, then you do not have any harness ballast in circuit and must use a 3 ohm or 2.4 ohm coil, you will have to measure it. Note that with the points *open* all combinations result in 12v at the coil +ve. The incorrect combination can either result in weak sparking, or overheating of the coil and burning of the points, both which will cause running problems. Pulling the choke can mask some ignition problems.

8. Connect a voltmeter to the coil -ve terminal and start the engine, you should see about 9 or 10 volts. See if it is different between the engine
running well and running badly, or between the fan being off and the fan being on.

9. Connect a timing light to the coil lead and each plug lead when the engine is running well and make sure the flashes are regular and consistent, and that 1 and 4 are flashing at the correct time by pointing it at the timing marks. Then do the same when the engine is running badly and see if there is any difference.

10. With the engine running you should have slight negative pressure in the crankcase. When removing the oil filler cap at idle there should be a slight change in idle speed. If you lay a sheet of paper over the filler hole it should be sucked down onto it (make sure it is big enough not to get sucked inside) and the idle speed should restore. You may be able to get an indication off your vacuum gauge if you can connect it to the crankcase, i.e. by screwing it into an old filler cap, or possibly a piece of wood that
you then press down on to the filler hole to make a seal. If so, or just using the paper if not, disconnect the breather pipe from first one carb
(blocking the carb port) and then the other and check that the amount of suction stays the same. Will probably only be a couple of PSI. It's also
worth checking if the engine runs any differently with *both* breather pipes removed from the carbs and the ports sealed.
Paul Hunt 2

Paul many thanks for your detailed answer

I have done all the Electrical tests you have suggested and every thing is within your parameters.

Coil test OK even when running rough the volts are OK both at coil and battery

Test of Ignition leads with strobe light,again rhythmic flashes no misses

Have done the paper test and to be honest it isnt pulled down, and it doesn't seem to effect the idle,The same if i blank the breather pipes to the carbs off

Fuel pump-It is a SU pump and it is showing 3psi,I have let it fill a gallon can up and it does it in the required time plus no dirt etc

I went to it this morning reset the jets to approx .60 thou down . Pulled choke out fully and it started first time pushed choke in half way running OK ,when temp gauge went up pushed it in to idle at 1200rpm off choke on fast idle it ran lovely.Then when temp gauge reached half way stopped engine took out plugs to check they were not soot-ed up they were OK. So i started it up without choke . (Bad Idle back) anything under 1000 rpm rough running. I put the Vacuum gauge onto the dizzy vacuum pipe with a tee piece got a vacuum reading of 12 Hg. Advanced the ignition timing by turning the distributor Vacuum went up to 15 Hg and engine runs a lot better , but still does not like to run under 1000 revs. Plus i have now started to notice blue smoke coming from the exhaust . More so if it has cut out during rough idle. But if i take the breather pipes off no excessive breathing or oil coming out of them even when revved . It is as if oil is being sucked up into the carbs from the tappet chest .I have got 15-40 oil in the engine but will try 20-50 oil tomorrow
I am wondering if the bad idle has something to do with the ignition timing or the new distributor. The Brand New distributor i bought is supposed to be the correct one for my engine, they are being sold on eBay now by a number of firms and are brand new items. Mine has no numbers on it to tell me if it is a 45D- 41610D model and i have asked the chap how he knows which model is which he cant tell me so be warned people. I have managed to get a reconditioned Lucas 41610 unit and will try this tomorrow. As for the oil being pulled into the engine i am at a loss as i could find no wear in the engine. Have put the uprated oil seals on all the valves.Could the carbs drag oil up the breather pipes when it cuts out during bad idle. Similar to when an engine chokes its self off if you leave the choke on to long then it throws smoke out for a time when started. Suggestions welcome as i really don't think it is breathing badly thru the breather pipes when i take them of and rev the engine all i get is a bit of breathing but no oil droplets.Many thanks every one of you for sticking with me i really do appreciate it regards TONY
A Basham

Tony. My newest book on SU carbs lists an ACD needle as being made, but does not show what the data points are. I would compare the data points to those of the AAA needle which seems to be the most commonly used needle for the MGB application.

In addition to the above recommendations, it might be good to test for some form of air leak as the system is warming up. Spraying the area around the joints with carb cleaner is one method of doing this. An air leak near the rear carb might cause you to have to enrichen the mixture to keep the engine running. With the engine warm, try removing the spark plug wires, one at a time and reconnecting after testing, to see what effect that has on the running of the engine. I once had a dead number three cylinder due to an air leak with weakened the mixture just enough to cause it not to fire. Good indications when a timing light was clamped to that spark plug wire, but no change in engine rpms when the plug wire was removed and a miss noted at idle.

Ideally, it would be best if you could set your rebuilt carbs up on an engine which is already running well, or get a set of carbs from an engine which is running and install them on your engine and see what happens.

Did you replace the throttle discs with the solid type or do you still have the poppet valves on yours? Do know some people have had problems with weak springs on the valves causing idle problems.

Stick with it, you are getting close now.

Les
Les Bengtson

Thanks Les
If the borrowed distributor does not work i have taken yours and others advice and borrowed a set of carbs from a car i know was running OK and will try them. As for the disc's yes i changed them when i rebuilt the carbs. As stated turning the distributor and advancing the timing put the Vacuum reading up from 12Hg to 16Hg and the car is ticking over much better. I will do the air leak test as suggested as i have seen signs of oil on the heat shield below the front carb if there is one it will be a miracle as i cleaned and checked all faces plus used Hermatite which i would not usually use. Also as i have said i would like to know if the carbs can suck oil up from the tappet chest. As oil smoke came out the exhaust today just like before, but i have blocked the breather pipes to the carbs off and checked to see if any oil is coming out off the tappet chest pipe. Nothing even if revved and only very slight breathing, plus the bores checked out perfect and i have put up rated oil seals on the valves . I have read about this problem and owners putting catch tanks onto the inner wing pipe coming from the tappet chest into the tank then out into the carbs oil is trapped in the tank . I am going to change the oil to 20/50 as i have used 15/40 if any one has any ideas please say something thanks every one TONY
A Basham

I'm a bit concerned that we are all giving Tony well-meaning but different advice. We should be focussing on the symptoms.

Tony - the valve timing may well have been out, but general consensus has always been a carb problem, or at least a fuel mixture problem. I respectfully suggest that all of the well-meaning advice is leading to a scattergun-approach which is not getting you anywhere. That is clearly very frustrating! I know this will sound smart-arsed, but we need to look at one problem at a time.

First off, and according to the SU Manual, AAA was not an MGB needle in the UK or US. The UK spec is AAU for 1972-1974, ACD for 1974 and 1976 on. Not sure what happened to 1975, but ACD seems right according to the manual. Whatever, unless you have got the wrong type of needle for the jet, you'll be able to get the idle sorted.

Getting the bridges equalised to the thou is laudable but unless you have the jets in the pistons to the thou, and absolutely identical suction chambers in every respect, and thou-perfect throat dimensions, etc, etc, etc, is simply not necessary.

The carbs can suck oil from the tappet chest, at least they do with the HS type. That's the point of the system (I'm not sure they do it in the US because of emissions). If you disconnect the breathers you might lose some oil from the rear seal (due to crankcase pressurisation, you get the same effect if you fit one of those little K&N filters...) but the engine should run okay. A blockage in the front tappet chest (the one with the breather) could cause blue smoke, but that would obviously stop if you disconnected the breather system. The breather inlets are downstream of the butterflies so disconnecting the pipes could cause the mixture to go lean?

Paul is right that pulling out the choke is richening up the mixture, which fits with your feeling that it is too weak. Pulling out the choke also opens the throttle though so the increased revs could be your smoothness. If it is just the richening effect that is making the engine run better, then the engine must be running weak for some reason. If there are definitely no air leaks, then surely the problem must still be with the carb?

It varies from car to car, but you probably should not need any enrichment at idle once the car has started - ie you just need the extra revs to keep the engine going. You may need to pull the choke to drive away, but not to idle.

If the engine is struggling to idle, it is reasonable that the load from the electric fan is enough to pull the revs right down. However, if you cannot set the idle when the fan is not running then I cannot see how the fan is relevant.

It appears to me that you really need to try these known good carbs before messing with the ignition, etc.

Finally, have you contacted MGCC? The MGB Register or local MGCC Centre will probably know someone in your neck of the woods willing to come round and have a look. Amateur advice (well-meaning like the rest of us) it might be, but at least you could talk to someone and show them the problem 'in the flesh'.

Neil
Neil Lock

Many thanks Neil
I have asked if there is any one in my area who owns an MGB that would come down to give advice but cannot find any one. I have had a friend of mine who was a mechanic and is a time served Auto electrician, but has never owned an MGB to come today. We had all the diagnostic equipment available and as i have always said i will listen to anyone and he went thru all the tests that PAUL was good enough to send me in his reply. Every electrical test showed every thing A1. And yes he said exactly the same as you about the fan because the idle was so poor the fan made was making it worse. Then we went on to double check the tappets , Ignition timing, dwell , compression again every thing bang on to the book.

I know this sounds like i am saying this to prove i have done every thing i have posted but i swear on my granddaughters life this was done today. Like many others he could not believe i had not sorted it out as he came to my house when the engine was in bits to borrow some tools , and agreed every thing was spot on apart from the valve timing and when i put every thing together it would be OK

Any way i let him try to set the carbs from scratch.Two heads are better than one. He did every thing exactly the same as myself and got the same result.Then i suggested to do another Vacuum test as we knew the valve timing was OK now. The results are in a thread above we got it to idle much better by advancing the timing.As for air leak's i will recheck before i change carbs over to the ones i have borrowed , just to prove a point to myself for the time it will take to do i will just try the other dizzy .

Both he and myself are worried about the oil smoke that started to appear after we had been messing trying different things. The car had cut out a good few times so like i said maybe it was then that the oil was pulled into the carbs. He double checked the breather system and agreed with me he didn't think it was breathing to bad plus there was no oil coming out of the pipes, he also agreed the vacuum from the carb should not be strong enough to pull the oil up from the tappet chest. Re your comment about tappet chest being blocked i cleaned every thing out and replaced all the hoses and Y piece. Plus i cannot see it being the valve stem oil seals as i fitted the uprated ones that fit on the guides. So why it should be blowing oil smoke out neither of us could understand but again i have read about this problem on other sites (But any one with any comments on this separate problem please reply)

Re- the needles you are right the ones i have in are the correct ones for my carbs this was double checked by Burlen they are ACD ones you can put AAA ones in, they are richer needles

Re- going onto fast idle within a few minutes of starting. My other 1976 MGB that runs perfect i have to do the same thing . Start on full choke then push in half way for a min then onto fast idle if i leave the choke on it chokes up this car runs like a clock and has passed an emissions test with flying colours
Well i will just keep plodding on if anyone thinks i am taking up to much space on this forum please say so as i realise i have posted a lot Regards TONY




Anthony Basham

Tony;
One small thing. What vibration damper do you have? If it has a rubber ring in the system it may have rotated slightly and unless you have checked TDC accurately and the pointer lines up then you may have a timing problem.This will offset all the cam and ignition timing if it is off.
Sandy
Sandy Sanders


I don't know if you have followed this saga but it has been a nightmare. Regarding the pulley yes I have double checked this when I re-set the Valve Timing and put a new timing chain and tensioner on. It was easy because I had the head off and did it by a DTI gauge and timing disc to get it spot on . I have managed to get it idling a lot better BUT have had to advance the ignition timing more than the book says ,which I really don't like doing and I have got the vacuum gauge to read 16Hg on idle which is a lot better than before but not as good as my other MGB. But I will be honest I really cannot think of anything else I can do. As I have rechecked every thing. Plus it now has nearly all new parts fitted it should be running like a Swiss watch with the readings I am getting and the new parts fitted . I have read about other MGB owners who have said they cannot get their cars to Tick over really smooth no matter what they do. But it really bugs me because my other 1976 MGB runs and Ticks over superb I will admit it is 100% better now than when I first got the car and it picks up fine and apart from the low Hg vacuum at idle shows every thing spot on when watching the vacuum gauge through the rev range.
To day even tried the other carbs and the other distributor but there was no change with the idle at all still not very smooth . So I put the old ones back on as i only borrowed them. I will now try to get it tested and give it a good blast to see if this can sort things out as it has been stood 9yrs and then take it from there because i will put my hands up and say i just cannot think of anything else i can do , anyway thanks for your input regards TONY
Anthony Basham

Im just curious who rebuilt your carbs? Did you put on the other running set of carbs to your car yet ?
James

Hi All

With reference to the difference between the AAA needle and the ACD, the ACD needle is leaner (i.e., it is a thicker needle) at all stations apart from 1 and 2.

As idling should be at station 1, as others have remarked, the difference between the needles should not be the cause of the problem.

There is a great spreadsheet called SUSEARCH3.xls which can be downloaded (Google susearch3 to find it) to allow needles to be compared.

James
James Reinhardt

Just to update every one on the Bad Idle saga. I have done and tried every thing that I have been advised to do or that I can think of to sort the problems out. Including trying another set of carbs and another distributor. Both known to be working perfectly, Plus re setting the valve timing. As for the needles nearly all are identical on idle.
I am now at the stage where to get the car to idle at any thing like acceptable I have, advanced the ignition timing to 11 degrees static, the carbs are set spot on with the balance and c/o readings within spec. With these settings and the idle at 1000rpm the idle is better than it has ever been although I do have times when hot the engine runs on when switched off. If I can ask just one more question on taking out the plugs I always find No 1 and No 4 plugs perfect. But No's-3 and No 2 plugs have always got oil residue on them more so on no3 plug. The valve stem oil seals fitted are the new advanced type and there is no bore wear the plugs have been swapped around and new ones also tried, but always the same result. If any member can give some idea's I would be most grateful. I cannot think apart than there is a mild performance cam fitted that would cause rough idle there is anything else I can do to to make the idle smooth at the correct rev's and ignition settings, so I hold my hands up I am now beaten. The car I will now get tested and give it a good run and then take it from there. So if any one can shed light on the plug problem I will have to say SORRY but it has beaten me . Many thanks every one for your time and help Regards TONY
Anthony Basham

Tony,

Sorry if I have lost the plot, but has oliy plugs come up before? I don't recall. If it's an old problem only just mentioned then we might be on to something. If it's a new problem then it must be something to do with the rebuild?

For the plugs to be oiled, there must be oil in the combustion chamber - and that can only come past the rings or through the valve guides. I suppose it could come form the carb dashpot, but there's hardly any there... and unlikely to be on no 2 and 3 as they are mainly fuelled from different carbs and why aren't nos 1 and 4 affected.

So - worn rings, some kind of damage to the bore (unlikely to be on two cylinders), or oil coming past the valve guide oil seals. Or a dodgy head gasket I suppose. Crankcase pressure is another long shot.

Have you called the MGCC and asked for a contact in the MGB Register?

Neil
Neil Lock



Neal, Sorry if you have been mislead. I mentioned that I had oil residue in the breather pipes right from the start. When I posted my first threads weeks ago when the car was first bought, I found the breather system blocked. Cleaned it all out bought new pipes and Y piece. To be honest I thought this was the idle problem but it was not. Since cleaning the system out, I have always noticed oil residue in the pipes if I took them off. Yet if off and I run the engine no oil has ever came out of the pipe from the tappet chest just a slight pressure even if I revved the engine. I then took the head off to check the bores and valves. The engine had been rebuilt with plus .020 pistons had a full crank regrind before I bought the car, and has done less than 8000 miles since. On inspection, the bores were in perfect condition still crosshatched and within .001 thou of specification. The head was checked the valves lapped in and new style valve stem oil seals fitted. Then a new rocker shaft assembly, new push rods, and followers. The valve timing was found to be at least one tooth out (This we all thought on the forum was the culprit) so a new Timing Chain and tensioner and the Valve Timing reset. The compression rings must be ok I have between 173psi-175psi on a compression test. I did not want to take the pistons out as if you do they never go back in the same, and unless you are going to hone the bores and put new piston rings in, they are best left alone. I admit the oil rings could be broken but this would have to be on cylinders 2 and 3 as they both have oil on the plugs. Every thing was then put back together and not a lot of difference. Since then have tried another set of carb’s, another distributor just the same. I have advanced the ignition timing to 11 degrees static approx 23 degrees strobe at 1000 rpm and it is idling the best it has ever done. The only problem’s as stated it runs on some times when hot, and the oil residue on plugs 2 and 3. Just to confirm, my car has HIF4 carbs breathing system from front tappet chest to both carb’s no emission items fitted. If it is breathing into the carb’s why are number 1 and 4 plugs not affected and again the bores and compression rings must be ok with 170 psi plus on all cylinders. If oil rings, they must be damaged on both number 2 and 3 cylinders since both plugs have oil residue on them. This is why I give up as I have tried every suggestion and put new parts on every item showing the least sign of wear. Every test I and another mechanic both electrical and mechanical have done is showing every thing ok. I hold my hands up and say enough is enough. I admit I was told by at least two members to check valve timing and sure enough, it was out. But this has been rectified and its still as bad, again I have done what members have suggested try another set of carbs still the same, there is only so many times I can check for air leaks, carb’s, distributors when they have been checked or replaced with new, even the new stuff has been replaced with other new stuff. So I think you can realise why I have given up. No one would have liked to have sorted the problem out more than my self. Moreover, I will say this is the first time I have let an engine problem get the better of me. Unless some one can come up with something different than what has been suggested time after time then I cannot think of any thing else. I really do thank every one, but the same suggestions come time after time, and I have already tried them more than once. Please do not think me rude and I would be the first to admit that I have in my time missed silly things or done daft things but at the end of the day unless new suggestions come it will have to stop as it is. Many people would be happy with it as it is. I have driven many cars owned by long standing classic car owners that I could not have been happy with the way they ran, but they were quite happy with them. However, I like my cars to be right
Many thanks again every one kind regards TONY
Anthony Basham


Anthony;; A little light shone in my brain. Did this problem just start after you did the head work? ,. You mentioned 8000 miles since rebuild. You can still have good compression but with broken (damaged oil rings)you will have that blue smoke and fouled plugs.Did you install new pistons and rings back then and did it run well?Or has it been screwey ever since?
Sandy Sanders
Sandy Sanders

This thread was discussed between 18/02/2007 and 26/02/2007

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