QuestionHoward-I have a 79 MGB that I am having a problem with-it has a Weber 34
DGEC carb -it starts easy and idles at about 1500-2000 rpm -after about a
minute the exhaust header begins to glow cherry red. When I kick down the
(electric) choke the idle comes down to about 1000rpm and the exhaust
stops glowing. It will rev fine , but as soon as I put it in gear and start to drive
it begins to sputter and occasionally backfire and I can barely get it to 40
mph. I have done the following;1)replaced leaking intake manifold 2)replaced
plugs,wires,dist cap,rotor,gas filter 3) took it to a mechanic who specializes
in British cars-checked compression -175 psi on all cyls-checked timing
etc.(the vac adv has been disconnected and the timing advanced a couple
degrees), and he said the carb is the problem. 4) took it to a carb shop- he
tested it.rejetted, and leaned it out - I am taking it back to him tomorrow-
What do you think? Thanks
AnswerHi Howie,
I think you need to test exhaust back pressure. No more than 1.5 PSI is allowable. If you have a Weber carb then I take it you have a different exhaust manifold. I usually drill a hole forward of any CAT or muffler just a little smaller than the OD of a piece of brake line and I drive a one to two inch piece of brake line into the pipe and put a long hose on the pipe and run the pipe out to a gauge (a vacuum gauge usually has a section for testing fuel pressure) and place the gauge under a wiper arm so you can see it and drive the car and slowly drive up to the speed that it levels off at and read the gauge. I found that all the British cars I tested could not stand more than 1.5 PSI at any speed.
Howard
