I just rebuilt my 1982 12a engine with almost all new parts. It does run. The problem is I go to start it in the morning and I pull the choke out and and crank it will start but i have to keep my foot on the gas and push the choke almost all the way back in or it will die. After its warmed up it will idle... at 1200 + rpm's. any lower and it will die. If I do turn it off it is Very hard to start again. I usually wait a few hours and try again or push start it. It has over 100 psi compression on each revolution so compression is not the problem. It's not ignition because thats all new. I put a different carb on it from another 1982 12A, same problem. It has about 13-15 hg of vacuum at 1200-1500 rpms?! I can't finf the leak. I have replaced all the gaskets almost twice. I'm out of ideas.
Even before I rebuilt it and it had a bad apex seal it started right up no problems. Now?
Any help is appreciated. Thanx

 

I think you have it sused out, vacuum leak. Only thing else I could offer is check the plugs and see how wet they are and recheck the timing.

 

Yup did that. The timing is perfect and the plugs were dry when i turn it off.

 

How's the fuel flow? You mentioned that the plugs were dry. If it was failing to start, seems like they should be wet?

 

Have you checked the bottom of the hose that goes from the #2 anti-afterburn valve to the intake manifold? It is directly above the exhaust and sometimes develops a split near the manifold where you can't see it..
http://intertron.com/ron/images/carb/c6.jpg

 

Thanx I'll check the fuel flow tomorrow but it runs perfect above 1500 rpm's all the way to 6000 no problem. As for under the intake i'll check that. It does however have NO emitions on it anymore.