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MG MGB Technical - Running Problem and I'm Frustrated

I am ready to drive my 1977 MGB over a cliff, but I live in Florida and we don't have cliffs. My car is backfiring thru the weber carb. So I had another weber and put it on and the same symptoms. It will only start if I pour gas in the carb and when it starts and I try to give it gas it backfires and also will pop fire in carb. I have changed distributers and set timing but the symptom continues. I have 160 compression in all 4 cylinders. I am thinking it could have jumped time. What does everyone think?

Please help a very frustrated owner.

Thanks, Tom
Tom

Had a similar thing. The wires were put on the distributer cap in the opposite order of rotation. Simple thing but easily overlooked.
tom

wires are fine. no problem there
Tom

Based on some advice I have received I would start with a new set of plugs, then check timing, points and condenser and condenser ground. I run my Weber about 20 degrees advanced.
Regards,
Dennis
D F Sexton

Sorry to insult you with this, but make sure you've got your plug wires on 1-3-4-2 Counter Clockwise. If you have them on 1-3-4-2 Clockwise, the car will run with the symptoms you describe. We get a car or two towed in with this problem every year.

--Carl
Carl Heideman

I believe that it was Chris who posted in one thread that getting the wires on 1-2-4-3, will allow the car to idle correctly, but not run well when it is given gas.
Good luck - Dave
David DuBois

Tom. I think you need to back off and listen to what people are telling you. There are a number of items which can cause this problem. Two of them are out of time, due to the wires being connected incorrectly, and the second is a carb problem. We cannot, over the internet, diagnose your specific problem. We can, however, give you the most common causes of your problem. As you test those diagnoses, we can focus more on what the more uncommon problems may be.

The term "jumped time" has no specific meaning. Does it mean that it has jumped ignition timing? Or, does it mean that it has jumped camshaft timing? If you have changed distributors and have, properly, set the ignition timing, you should be running well. Since you are not, let us see information, rather than attitude, presented to us. We are, as a group, very competent and can handle most problems that are presented to us. But, accurate information generates the most accurate response.

Do a dry, then wet, compression check and let us know what the readings are. Also, let us know what model Weber carb you are running. Both of these items will have an influence on how we can help you determine what your problem is. Les
Les Bengtson

Les, I don't have an attitude. Sorry you are so serious, lighten up. I have had numerous MG's in the past 25 years, have three now and really think they are great. It is okay to get frustrated with your car. As far as telling you everything in mechanic terms, not gonna happen as I am not a mechanic like some on this board. I try to explain it the best I can. If that isn't good enough for you DON"T REPLY, there are lots of people ready to give very good advise without the tone you implied.

Have a Nice Day!

Tom
Tom

Hi all.

I have learned to my cost that you have to be very careful when making jokey comments on the net, as the lack of visual feedback (expressions, body language, etc) can result in misunderstandings.

I once joked to a woman that I had a bizarre fetish, she took it seriously and wrote me a very understanding reply...

Don
Don

If the leads are connected incorrectly the car will neither idle nor run correctly, so, worth one final check.

Two things spring to mind, one being an induction leak so make sure that the manifold / head gasket is OK and that the manifold is tight.

Secondly, you changed the distributor but did you change the cap/leads and rotor arm. The cap in particular can create some very strange problems if it is faulty.

I've seen a cambelt jump a tooth but a chain no. Just as a check set No1 to TDC firing stroke and at this point valves 7&8 shoulod be "rocking" If this is the case valve timing is OK.
Iain MacKintosh

Tom,

If you have checked the wires and they are correctly connected then you have cocked up on the disi change or timing - just redo it from scratch and be methodical.
Chris at Octarine Services

I might as well add my two pence worth here. On my last trip to Florida in my 1977 "B" I was attempting to resolve a high speed miss that later I discovered was carb float related. In trying to resolve the problem I purchased a MSD high output coil. I swapped coils, and the B would only spit and sputter and backfire through the carb with the new coil. I never could drive it with the new coil. I don't know if it was deffective, shorted or what. After swapping back it ran as it had before the coil swap.
R Hill

re the high output coil: years ago I had a bugeye. I also lived in the middle of nowhere in south Texas. On a trip about an hour away from home, my coil gave up the ghost. As it happens in that part of the world, someone soon came by and offered assistance in the form of a used coil of unknown origin. The car ran, but not well. Got me home again. I pulled off the dist cap and was cranking the engine for some unknown reason, when I noticed the engine was firing randomly. A peek under the cap revealed that the spark was jumping randomly from the center to any of the cylinder contacts. Just another weird thing that LBC's can do.
Back to Tom's problem: the fact that it will only start when fuel is poured into the intakes, along with the misfiring would lead me to check for vacuum leaks. My favorite way is, wih the engine running, I move an unlit propane torch along all the obvious (and not so) places where a leak coud occur. Don't forget to check the vacuum advanve diaphram ans a leak point.
R. L Carleen

Tom, we are all friends here, right? Right!

Righty-o, could you tell us what the initial problem was (and how it came about). If I am understanding properly, the Weber (downdraft?) was "spitting" at speed? You then replaced it with another (similar) carb and had the same problem?
You then swapped distributors and now it barely runs at all?

1) I am biased against downdraft Webers on an MG but have used them with success. The carb nearly never "goes bad" so the problem was not likely initially with the carb.
2) Spitting back through the carb can be several things. Improper timing, improper ignition event (either wires in wrong order or a cross-connection from faulty insulation, carbon tracking, bad engine ground, etc), excessively lean, excessively rich, vaccum leak.
3) Go back to the original carb as at least it ran that way.
4) Do a "tune-up" on the original dizzy and replace it.
5) Replace the wires and plugs if you have not already done so.
6) Make certain the lead from the dizzy to the coil is OK and the power lead to the coil is OK.

7) Common mistake when static timing... Setting the dizzy to the point where the points are just closing instead of just opening (make this one myself from time to time).

To reiterate, common mistake and very easy to put ignition wires in wrong. Did this once on my Dodge v-8 and it would idle OK (lots of cylinders and rotating mass) but was a complete dog (ha ha) on the road. Took several attempts to get it right and then once I realized what I had done (wrong rotation direction) it was fixed in a jiffy. The fact that I had "checked it" 100 times didn't fix the initial problem... I was operating under a wrong assumption. Didn't help that I had "done it a dozen times" either!

Sigh.

Try these and tell us how it goes.

Mike!
mike!

Thanks to everyone for their help. Here is the situation after this weekend.
1. replaced the spark plugs
2. went back to the 25D dizzy
After this, the car started right up and after adjusting the carb and timing it ran much better. Got the car up to 40 but it seems sluggish and maybe even missing a little. The backfiring is 95% gone.

I have replaced the plugs and wires.

I have a 25d dizzy in the car now. Should I go with a 45D dizzy? I have the points, condensor to do both dizzys.

I also replaced the fuel pump because the old stopped working, with the little low pressure pump from NAPA. I am thinking this can be a problem? I was thinking of getting the high pressure pump and getting the fuel regulator. The reason I am thinking this can be a problem is because the fuel filter, which is new, never gets over 1/2 full and when the car is runnning there is very little if any fuel in the filter.

Thanks, Tom
Tom

I forgot to say that even though the car runs better you still have to feather the accelerator to get it going. You just can't giv it gas and go. When the car is idling and you give it gas it doesn' accelerate without hesitating.

Thanks, Tom
Tom

Tom I had the same problem last year with our 1966 MGB and spent alot of money on alot of new parts; new 45d dist. and electronic ignition. new coil and wires rebuild down draft weber; timed and re-timed and just kept throwing 100 dollar bills at it to no end;;;; replaced fuel pump and replaced ignition switch you name it I replaced it to no end and it still cut out and missed at about 3000 rpms and would not run well at idel either; I found the problem by ;;;;;; The fuel line had rust and rubber parts in the fuel and would pass into the carb and start the whole problem over again; Start the car spray carb-cleaner into the carb and burn it thru and see if it clears and runs right; also take a fuel line filter and install it at the carb gas line to catch any trash; Hope this helps it made our B run like a rocket with all the new parts;
Good luck
Ernie

<<<the little low pressure pump from NAPA. I am thinking this can be a problem? >>>
hmmmmmmmmmmmm, ya think maybe fuel starvation might be the issue?

<<<because the fuel filter, which is new, never gets over 1/2 full and when the car is runnning there is very little if any fuel in the filter.>>> hmmmm, might be on to something here...............so how much is a Weber anyway? And what made you decide to go with a 2 cent NAPA fuel pump instead of an SU? Just curious to the thought process.

Sure, we're all friends here so much that I can bust your stones for overlooking the obvious. Gas, it's required. And if there's any doubt, the tone is exactly as implied

Have a nice day!
Paul Hanley

Tom, Before buying the high pressure fuel pump and regulator you may want to read the thread,"Fuel supply"
about twenty threads down in this section. Notice the comments about low or empty fuel filters. FWIW, Clifton
Clifton Gordon

I have had my B for about a year now. As per the invoices I received one of the three POs (I found it changed owners 3 times in about a year and a half!) purchased the DGV Weber & manifold. I would assume it was bought & installed, then attempted to be adjusted. What I found (see one of my posts about 3 weeks ago) was that the float level was so low that it would literally run out of fuel while on an uphill grade and under any acceleration.

As a side note, I have noticed at some shows that some of the Weber DGV carbs were mounted in one direction, and others were turned 180 degrees around. That is to say some are set with the throttle cable to the front and other have the throttle cable at the rear. Basically, if the cable is at the front the main jets also will be at the front of the float bowl sitting at a 45 degree angle. Mine is set this way, which I believe only made the problem worse. Someone correct me if I am wrong here, but if the carb was turned 180 degrees (I know it would place the choke cable & the adjuster screw harder to get to) wouldn't this help fueling by putting the jets at the back where they would be less apt to starve out?

R Hill

Tom...from what I have read about the filters (loooonnnnggg discussions/threads) they usually look like that. Test the pump...as long as it is putting out the proper amount of fuel/pressure you "should" be all right but worth the test to elminate the possibility. Check around for amount it needs to put out (fills x size container in x minutes)...but the low pressure Facet pumps have a good rep....though a bit noisy from what I hear. I went through some issues and it took a new pump and rebuilt dizzy and new vac advance to clear it all up.

Sounds like fuel but lots of carb problems are really ignition problems. So if you can eliminate the ignition system next you can then focus on the problem. I have learned ..albeit very slowly.... to do the medical diagnostic theory...elminate things (systems) and what's left is it. Have you tested the dizzy advance at various rpms to be sure it is working properly? Look at the www.teglerizer.com site and at Paul Hunt's site www.mgb-stuff.uk.org to get the specs for your dizzy #. Also...is your vacuum advance working? Mine had a slow leak which was contributing to my problems.....sloppy dizzy, vac advance leak and failing 35 year old pump....it was a combo. Eliminate and fix one area at a time and you will get there and be driving. I am NOT a great mechanic by any means but am learning.

Dunno what got into Les. He is good guy and gives great advice. Sometimes you read someone's comments wrong or take it wrong, I guess.
J.T. Bamford

You are on the right track!

Fear not!

Testing the ignition circuit next would be wise as stated. Use of an adjustable timing light makes the process a home-job IF you have an accurate tach. The one in the dash is NOT always reliable. An alternative would be to take your dizzy(s) to a local shop with a Sun distributor tester and have them give you a chart of the advance at various RPM. (and have them tell you if that is Dizzy rpm or engine rpm!).
Easy to check vaccum advance for leaks, just suck on it or use a vaccum pump and watch the breaker plate (it should be rock-stable). If you suck on it just do it enough to move the plate then put your tongue over the end of the pipe and wait.

Low or no advance will definitely limit your top end!

Mike!
mike!

This thread was discussed between 23/07/2004 and 27/07/2004

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