Rebuilt Carb-Still Gassy

[Cliff Ruggles]

Nozzle drip would explain the carb being rich, or "gassy".  The idle system still needs some work, or the idle mixture screws are not out far enough?......Cliff

[batsong]

Thanks, Cliff.  Right now, I'm doing some driving and adjusting the idle mix and timing.  I'll try a richer mix at idle.  I've experienced subtle improvements, and all of the tests I've done have shown normal, if not very good, engine condition, but even so the exhaust and mpg is worrisome.  Given my lack of experience, I'm beginning to wonder if everything is normal.  It is a 70's engine with a carburetor.  What if the exhaust is supposed to be a little stinky given the cam I've put in?  I think right now I need to stop being afraid, drive it and adjust as I go.
Thanks, Gabe

[Cliff Ruggles]

The cam has everything to do with some unburnt fuel getting out the tailpipes.

Large duration camshafts, expecially those on relatively "tight" LSA's create overlap.  The overlap, or time both the intake and exhaust valves are open at the same time can allow quite a bit of unburnt fuel into the exhaust stream.

The effects of this are noted a "lope" from the engine, in contrast to a smooth/steady idle. 

It often helps to increase the base timing setting a bit, to start burning the compressed mixture sooner, which will often help smooth out the idle and reduce emissions.

We also have to add more idle fuel to provide an easier to ignite mixture, as cams with a lot of overlap, tight LSA's etc, reduce dynamic compression some at idle and low speeds.

These cams can also increase fuel consumption, at least in direct comparisons to smaller cams or similiar cams on a wider LSA......Cliff