Still having tuning problems with my 66GL. I think the valve lash is wrong. I tried adjusting it by following the instructions in the shop manual, but a combination of that and the carb needing tuned is causing the car to not run. It is backfiring through the carb and out the intake. I've replaced all the vac lines I can find in the engine, and replaced all the upper gaskets in the head. I've got the exhaust manifold to exhaust pipe gasket off the car so my exhaust shop can build me a 1.5" exhaust to replace my rusted one. would that little exhaust leak cause the car to not run very well?

-Collan in USA

Those engines are very sensitive to not having a decent exhaust fitted. They seem to rely quite a bit on scavenging for smooth running...so a leaking manifold to DP joint, for example, introduces a significant lope into the idle.

Firing through the carb is usually an indication that it's lean. It can be other things, of course, but that's the usual one. Vacuum leak?

cheers

James