G'day all, I've got a carby manual TP sedan that is struggling under load. When I drive up long hills on the freeway the car really feels like it's struggling (more than it used to anyway) and when I back off the throttle it makes a nasty jolt, almost like the engine has cut out and restarted again. Its worse when the air con is on.

The engine feels like it's being restricted, I've tied the choke OFF permanently which has helped but the problem is still there. The carby was fully rebuilt about 3 years ago and I've recently replaced all of the ignition system, and filters. The catalytic converter hasn't been replaced in about 100,000kms could this be causing the problem?

It is more likely that the secondary throttle of the carby is not opening either because of a vacuum problem or because the secondary diaphragm has deteriorated. I cured mine by buying a new diaphragm from Repco. It cost $180 which is very much overpriced for what it is. You can check the diaphragm by disconnecting the other end of the vacuum line that goes to it. Suck on the line and put your tongue over it to seal it off. If it holds vacuum (sticks onto your tongue), the diaphragm is OK. If not, it probably has a leak and needs replacing.

top carby gasket has a tear or not sealing
or you have a vaccume pot not working

or a vaccume hose joint leaking
next dissy cap coil then leads then plugs

I just tested the secondary diaphragm, it's fine, as are all the vacuum lines, but there is bugger all vacuum in the line running to the diaphragm. To test that everything else worked I ran a tube from the diaphragm out of the engine bay and into the car and sucked on it as I was driving, it hasn't spun wheels like that in a while! The car absolutely flew... well didn't hold up traffic anywaylol .

I reckon its a leak in the carby, thats probably causing the choke to stuff up as well. Thanks for the advice, you were both right, now i just have to pull the carby apart, bugger!

carby info in tm-tp posts

http://www.aussiemagna.com/forums/showthread.php?p=671775#poststop