Here's a problem that just showed up on the modified GMC 302 I just built.
Once the engine is fully warmed up,it has a slight random misfire at idle.When the engine is warming up,the misfire is absent even with the engine unchoked.This engine has a moderate cam,idles at 700 rpm with a slight lope.It idles along normally for let's say 10 seconds,then has a putt putt misfire,then another few seconds,one misfire,then a few secons another misfire or two,no pattern to it,totaly random.But if I increase the idle speed to just above 1000 rpm,the misfire is gone
Everything is new or properly rebuilt,no vacuum leaks,points are fine,as is the plug wires and plugs.I checked the valve adjustment,even loosened the valves a little,no difference,No signs of a valve sticking in the guide,no worn cam lobes.I checked the compression with a warm engine several times,165 psi across the board,all cylinders with a few psi of each other.
On the road the engine runs very smooth and strong from idle to redline,it'll pull from 1000 rpm in high gear without a burp.No misfire during part throttle crusing or full wide open throttle.
I tried different plugs,no difference even with Iridium type.All the plug wires have less than 800 ohms resitance,no signs of carbon tracking on the cap.
If the misfire was consistant,I could put a finger on it,this problem just started,wasn't there for the first 800 miles.
The only thing I can suspect is a bad condensor(Mallory) on my home made dual point conversion.
Do you think the engine cylinder pressure simply is too much for a points type ignition to handle at idle?Ya know,with the hotter cam causing problems with the idle mixture as they often do,a cylinder or two fails to light on occasion?.Maybe now the rings are fully seated more compression than during the first 600-800 miles.
I'm old school,but maybe it's time for a MSD or similar multi spark ignition system?
