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MG MGB Technical - Vapour Lock (possibly)

Does this sound like vapour lock?

Car runs fine for about the first 20 minutes/10 miles, after this I start to notice a slight hesitancy at low revs. The hesitancy gets gradually worse and worse until applying anything over about an 1/8 throttle travel below about 3000rpm causes the engine to stall. Idle is still fine as is the high rev performance of the engine.

I have no insulation on my heat shield but the metal is intact. The ambient temperature is about 28 degrees centigade, but the temperature gauge is not going above normal.
Carl Kambites

Carl - Your problem sounds more like a clog in the fuel line, a clogged fuel tank vent or a fuel pump starting to go bad than vapor lock. I will send you a troubleshooting guide that may help you localize the problem, but for starters, try taking the fuel tank filler cap off, drive for awhile and if the problem goes away, you have found your problem. Good luck - Dave
David DuBois

if it's a generic fuel supply problem then why does the engine continue to run well at high revs?
Carl Kambites

Carl - Sorry, missed that part. Have you checked the advance weights in your distributor for any kind of sticking? Also check the pistons and vacuum chambers on the carbs for any kind of hang up. The pistons should move all the way up and down without any kind of hesitation. Finally, look at the needles and make sure they are not damaged or worn in any way. Good luck -Dave
David DuBois

This thread was discussed on 18/07/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.