Rich it all has to do with the cam used,assuming engine is dailed in at carb and timing. If you set the idle too low may run into a plug fouling situation where over time at extended idles,once you decide to smash the loud pedal misfires out the pipes are common. Too low an idle espeacally durring cold starts and durring warm up are probally biggest cause of fouled plugs.

 

interesting! Now I feel the need to check my plugs. It dose have good throttle response with no hesitation or backfiring.

 

The more radical the cam, the more radical the idle.

 

Rich:
Do you have the specs on the cam ( lift and duration)?
If it is a high lift cam as compared to stock your low end idle will be effected,but your top end usually improves.
It's like what 2fast said above.
Paul M.

 

It is a medium cam. I can look up the specs on the cam when I get home.

My question is why dose the pattern change? It goes from Rat-tat-tat to rat-tat-rat-tat to rat-tat-tat-tat-rat-tat-tat and so on. The cam and distributer control everything how can the pattern change? Maybe my MSD box doing 2 firings then 1 then 2?

 

It's the way the cam is. The lumpiness is caused by the the extra valve "overlap" which makes them sensitive to exhaust back pressure. Valve overlap happens when your engines inlet valve opens while the exhaust valve is still open. This aids airflow at high engine rpms but causes the lumpy idle.

Although it sounds cool, you're better off raising the idle until it smooths out.

The more radical the cam, the higher the idle needs to be to smooth it out

 

At low idle speeds with a "big" cam the gas velocity (air-fuel mix in the intake and the exhaust gases in the exhaust) is very low and there is a certain amount of the "wrong gas" going to the wrong location or a mixing of these gases resulting in cylinder to cylinder misfire. As you increase the engine speed the gas velocity/inertia increases and tends to flow to where is is supposed to go - no/less misfire.
auto10x
Bill