I know, this is the wrong forum, but it is kind of a general engine question. I am attempting to resurrect my MG TF (69 MGB engine) which has been dormant for 3 or 4 years. Idles OK, but when I step on the gas it immediately back fires through both carbs and dies. I have gone through the carbs, distributor (mechanical advance, vacuum advance, timing [petronix]), fuel pump (pressure & delivery), etc. - no joy. I checked the vacuum advance with a vacuum pump and while the dizzy plate does respond, the vacuum drops quickly when I stop pumping, which leads me to suspect a leak in the diaphragm. My question is, would a non operating vacuum advance account for that symptom?
I’m not one to complain about “cross-pollinating” on forums, so don’t take this that way, but if you’re not already a member of the “MG Experience” forum at mgexp.com, I highly recommend it. I’ve been a member for several years and its members are as friendly and knowledgeable about MGs as I am finding the folks here to be re: Jags.
No IMHO. You don’t need a vacuum advance at all except to get a bit better mileage whilst cruising. But lean conditions are the most common reason for spitting through the carbies. Since it’s both of them, a float problem is unlikely.
BUT, a vacuum leak can do it. I’d try capping off the hose to the dizzy. Seems unlikely, but perhaps the leaking diaphragm is sufficient to lean out the mixture in the manifold.
Problem solved! It was indeed a “too lean” problem. I had the carbs way too lean. The “B” engine in a “T” engine compartment is not a perfect marriage. The “T” engine compartment is much narrower than a “B”, and the HS carbs are adjusted with a nut under the jet, which requires a sawed off wrench. I think I lost track of the count of the nut flats, or perhaps the direction. Thanks for the replies, “lean” was the magic word.