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MG Car Repair/74 HS4 carbs flooding saga


hi Barrie -thanks for your tips to question of 4\15\13- and my ongoing SU flooding issues. so..I have now had carbs professionally cleaned and all jets replaced, throttle linkage and butterfly valves etc..all made good and set up and tested.. The Fuel pump clicks and fully stops. When I crank engine it floods both carbs but rear is worse. Gas is not overflowing the bowls into the vapour lines but gas is puddling in throttle body floor and then pouring out front of air intake. Plugs are made wet. I do have fairly good spark from plug to engine block, and new electronic ignition, and good compression of 140 psi on all cyl. I am not choking it because that makes it worse. Any other troubleshooting ideas? Could I have a vapour lock somewhere? Can I bypass the gulp valve to rule it out as the culprit? help!

thanks much


Hi Paul.  No, I don't think you have a vapour lock.  My guess is that you have a problem with the inlet manifold.  If it is not airtight, then the car cannot suck in the correct mixture to fire and run properly.  

If you look at the inlet manifold it is basically 3 parts.  There are two inlet tracts and they are joined together by a balance tube.  Look carefully at everything that attaches to the balance tube, because I think that is where you have a problem.

Both ends of the balance tube should be sealed with a Welch Plug (Core Plug).  I have experienced one of them popping out when an engine backfired.  The result was a big air hole in the back of the inlet manifold and an engine that would not start.

Another possible culprit is the PCV valve on top.  As an experiment, just pull it off and seal the rubber hose underneath it with a cork.

Some export MGBs had an anti-run-on valve.  Remove it and block the hole.

Finally, you may have a brake servo.  If the large vacuum hose is split or perished, or if the servo has a fault, then this can stop the car from starting.  Once again, pull the hose from the manifold and seal it.  

Now try to start the car.  (Fingers crossed)

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Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

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