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MG MGB Technical - HS 4 Carb

Hi
I fitted my MGB with recondiged HS4 Carb.on the original carbs there where tubes for the engine ventilation, on the recondiged one not.Is it nessesary to connect the car engine ventilation on the carbs, or can i live it in the air.On the original carbs where fx needles on the rec. carbs are No 5 needles, do i have to change them ?
I also fitted a new choke cable (old one was 72 type, new one is 62-68 type with the C on it),but now the choke is verry hard to pull (almost with 2 hands),does anybody maybe have a picture from the springs (4) attached on the heat shield.or does anyone now what it could be becaurse the choke is going that strong?

thanks
serge
serge

I have the same issue with Choke ('70 Roadster) I replaced the cable as it no longer 'locked' when pulled and I also replaced the return spring at the same time as the original was actually missing!. The first part of travel to about 1/2 way is OK then it gets tight Mind you I only go that far for starting. There is a good picture of the spring installation at
http://www.mgb-stuff.org.uk/choke.htm#11 (last 2 pictures) But I suspect its designed this way. More knowledgeable people will respond about the vent piping.
Bernie
B Anderson

Serge. What year is your B? Sounds like you have been supplied with early carbs. The choke shouldn't be hard to pull, have you got a photo of the carb end, then we can see.
Allan Reeling

If your carb doesn't have the breather port you will need to fit a PCV valve to the inlet manifold, and connect that to the hose coming from the front tappet chest cover. Failure to properly ventilate the crankcase will cause internal condensation, 'mayonnaise', and corrosion. As it is non-standard anyway I'd recommend a suitable generic PCV rather than the original used on early MGBs as they are more reliable and probably easier to fit.

If your choke cable comes up from below to the carbs as I suspect then it must be carefully routed so nothing obstructs it, as it is the outer that moves in the engine bay as the control is pulled, not the inner. Also when the control is half pulled, the inner must make a right-angle with the lever on the spindle. If it's at the wrong angle it can make the control very hard to pull at one end or the other. For example if it makes a right-angle at rest or only slightly pulled, it will get very hard when fully pulled. The cable inner should also be lubricated.
PaulH Solihull

I guess I'd better have another look at mine then! :)
Bernie
B Anderson

Also, I've done away with any springs on the choke, very easy to operate. The mechanism springs on the carbs are strong enough to return the jet.

Herb
Herb Adler

Hi,

The problem with the choke is solved, now its working fine. The Car is an 1968 mgb,european version. don't understand why i should put an PVC valve on the engine ventilation pipe, and run it to the manifold.Can i put little filter on the tube.I assume that for the carb mixure it it better without the ventilation pipe attached.

serge
serge

If you don't have a continual flow of air through the engine condensation will build up, with the mayonnaise that is basically a water and oil mix, and that will cause corrosion. The factory used a PCV valve from Feb 64 to Oct 68, then carb suction from then - for a reason.

Before that there was a tube from the rocker cover to the air filter, and a tube with an open end hanging down from the front tappet cover - the road draught tube. Which direction air flowed with that system, and whether any flowed at all, depended on circumstances. It was common to see oil splatter on the filter, which shows that wet and dirty air was going in at the road draught tube, or there was significant blow-by.

Both the PCV valve and the carb system ensure that the affect on mixture is minimal, and setting-up of the carb takes that into effect. A filter on the tube from the front tappet cover will do absolutely nothing for either pressure or satisfactory ventilation.

It's your choice, but I know what I'd be doing.
PaulH Solihull

Even the Moss supercharger kit comes with a provision for Positive Crankcase Ventilation. Simply running a length of hose, from the front tappet chest cover down to the base of the engine, is insufficient to provide the necessary ventilation of the crankcase as Paul has described. My '67 originally came with the mushroom shaped PCV valve. I ran it for many years with no problems at all. RAY
rjm RAY

On removing the rocker cover recently to adjust the tappets, there was quite a lot of foamy watery substance inside the cover. I thought this was due to short runs but after reading Pauls comment on lack of breathing I am thinking it could be this. It is an 18v engine in a 71 roadster and as far as I am aware all the vents etc are there, is there something else I should be looking at.
Trev
Trevor Harvey

Sounds like you do need to check the ventilation system, although if it only ever does short runs of a few miles you may still get it.

You should have carb suction from both carbs, via a Y-pipe, to the front tappet cover. You could have a blockage in the pipes or hoses, but the filter and flame trap in the cover could also be completely gunged up. To check that part of the circuit remove the oil filler cap with the engine idling, and you should get a small change in engine speed, as you are effectively introducing a vacuum leak. If you put the palm of your hand, or a sheet of paper over the filler hole you should feel slight suction, i.e. the paper should be pulled down onto the hole. If you get that, the suction side is OK. If not then remove the hose from the tappet chest cover with the engine idling. If the revs change now then it looks like the cover filter is blocked, unfortunately, as it's not easy to get at.

The other half of the system is the air inlet which on cars without the American charcoal canister is the vented oil filler cap, which includes small holes to let air in and a filter to trap dust, this is why it is a service replacement item every 12k. There are non-vented versions for American cars with the canister, I've not seen those to compare, but I don't think they are as deep i.e. go down into the rocker cover as far as there is no filter. The vented one should have a small hole on the bottom of the cap, i.e. inside the rocker cover when it is fitted, through which you should be able to see the wire wool filter. I don't really know of a way of checking if that is blocked or not, but they are cheap enough to replace anyway, and how many of us have ever replaced it, I wonder.
PaulH Solihull

As I have an alloy rocker cover with a posh chrome filler cap I assume there is no vent system in this setup. Could be the cause of the sludge buildup, but I will check the rest of the breather system as reccomended. Thanks. Trev
Trevor Harvey

Almost all of the alloy rocker covers come with a stainless steel oil filler cap, that has a small hole drilled in the center, to allow air to enter the engine. RAY
rjm RAY

Can't comment on those caps, but really it should be filtered as well as restricted (the small hole).
PaulH Solihull

Whilst on the subject of crankcase ventilation, here's a slightly OT story.

Many moons ago I bought a new Morris 1100S, that's a Morris 1100, east west, detuned Cooper 1275 engine. I had problems with it stalling on longer runs, 10 miles or more. When it stalled, it would start OK immediately after. Roadside trouble shooting found that the float bowl was empty, so it was a fuel delivery problem. The fuel pump was a mechanical one, bolted to the side of the block. Pulled the pump, fitted a service kit, no better. Very frustrating.
One day having just got home and the engine started playing up. Rushed to pop the bonnet while the engine was still running and looked around to see what I could see. For some reason I removed the oil filler cap and all came good, with a great hiss. Turned out that this model was the first with PCV, but a non vented oil filler cap had been fitted, hence a build up of vaccuum in the crankcase, causing the diaphragm in the pump to be held down, stopping fuel pumping.
Fitting a vented cap solved this permanently.

Herb
Herb Adler

hi,

Thanks all, I fitted a PCV valve .The car was running good with the tubes fitted to the carbs, and no mayonnaise build up, so i want to keep it so

thanks serge
http://youtu.be/CXcYgvvOua0
serge

good on you SZerge. Problem resolved?
vem myers

Hi,

For the last few days i have some big oil los on the tappet covers on the side of the engine.I fitted some new gaskets a rubber one on the back coverplate (the cork one didn't fit and was to big) and a cork one on the front cover with the breather pipe.but after a run for about 20k the leak was there again.If fitted a new cork seal on the front cover (there was the leak, the oil dript along the engine on the exausht,you could smel it in the car).I pulled of the vent tube going to the PCV valve and drove for about 50k without a leak, i putted the vent tube back on and after 15k i smelled already burned oil, i pulled over and saw the oil dripping along the engine on the street.I pulled the vent pipe again and drove home for 30k ,home, i looked at the engine and there was no oil to see, and after 2 hours still no oil on the floor.The pvc valve, i tested it before and i could blow trough it, and the air came on top of the valve, and when i blow harder the valve opened and the air went in the direction of the carbs.Today i ran for 100k with the tube free in the air and the valve disconected.The car run fine and no oil leaks.I don't now what could be wrong,the difference to next year is that i put some new carbs on, and that instead of the engine tube going to the 2 carbs with a y piece, the engine tube now is going to the pvc valve.Last year i had now oil leaks.
serge

It's certainly possible to get excessive oil consumption via the crankcase breather, so it's possible that is sucking oil into the cavity in the front tappet chest cover that should be filled with wire gauze, and leaking from there. Are you sure the cover or the pipe aren't cracked anywhere? Or the hose split? If it were the seals leaking I'd expect them to leak regardless as there is a lot of oil running down past those covers from the rockers. You need to clean the area thoroughly then watch it to see where the oil starts to come from. Talcum powder spread round the area is said to show oil well, clean oil can be difficult to see.

Incidentally you mention a PCV valve, and blowing air in the direction of the carbs. PCV valves were only used from Feb 64 to Oct 68, and they were connected to the inlet manifold. After that there was no PCV valve and the connection from the front tappet cover went to the carbs. I.e. you should either have a PCV valve, or a connection to the carbs, not both. Your last sentence does seem to say that, but conflicts with you saying earlier about blowing air towards the carbs.
PaulH Solihull

Hi,

Last year i can with a tube with a Y piece from the engine to the carbs.
In the winter i changed the carbs, these recondiged ones don't have the copper pipe to put the tube to.So i putted a PCV valve on the inlet manifold and connected to the engine breather pipe. Since this Tube is connected i got a big oil los.The last ride i made 100 kilometers, with the tube disconnected i have no oil los.I also tested the tapped cover by blowing air to the tappet cover ,there is also the wire gauze in there.If there is a crack in the cover or the tube (the tube is new) then it should also los oil with the tube from the engine to the PCV diconnected, with it didn't the last ride of 100K .Or not ?
serge

Are you using the stock Smiths PCV valve, used from'64 to '68, or did you fit a generic valve from another car? The air should flow only from the engine side cover to the intake manifold and not the other way. It's a one direction valve. If you are using the original style PCV valve, it's possible that the metering needle, under the diaphragm, is out of place and not centered in the orifice. This will allow large amounts of oil to enter the intake manifold. RAY
rjm RAY

Are you using the stock Smiths PCV valve, used from'64 to '68, or did you fit a generic valve from another car? The air should flow only from the engine side cover to the intake manifold and not the other way. It's a one direction valve. If you are using the original style PCV valve, it's possible that the metering needle, under the diaphragm, is out of place and not centered in the orifice. This will allow large amounts of oil to enter the intake manifold. A ruptured diaphragm will also cause this problem. RAY
rjm RAY

"then it should also los oil with the tube from the engine to the PCV diconnected"

Not necessarily. If the PCV is causing oil to be lifted into the pipe on the side cover, and that or the hose is cracked, then it will leak. If oil is not being lifted into the pipe i.e. when the crankcase breathing has ben disconnected then it will not leak. That's why I say to watch carefully when everything is clean to try and see where oil starts to come from.

These covers can be a factor in high oil consumption whether you have PCV ventilation or carb ventilation. There were two types as shown below and the one is more prone than the other. The replacement has much more of a restriction against oil flow. At least one person found the only cure was to change the cover. If the gauze, which is supposed to act as an oil-separator as well as a flame-trap, is poorly fitting, has large gaps round it, or is clogged up it can let oil past.


PaulH Solihull

Hi,

Mine cover is like the one on the Left (replacement ), i called some vendors, but these covers are no longer available, so thats a problem.
The cover was dry on the top, and on the screw where it is with connected to the engine, i could only found oil on the right bottem (there were the original has the square hole), there was no oil found abouve the cover, so the pipe and the tube are ok. The pcv valve is a replacement one (for the mgb ).
serge

Still looks like the gasket is leaking then, and it is the normal functioning of the crankcase ventilation system in pulling oil into the cover.
PaulH Solihull

This thread was discussed between 12/03/2013 and 06/04/2013

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