Not sure how to diagnose this miss at idle

[tz89]

I get an intermittent miss on cold idle with the choke on. Not constant but intermittent. Once the bike warms up it idles fine. Bike runs fine at speed.

 

I put on all new plug wires and caps (one was corroded with high resistance the rest were spec) and hoped it would clear up.

 

Is this more likely a carb, coil or other ignition issue?

 

Thanks

Edited August 12, 2014 by tz89

[utadventure]

take the temp of the header pipe of each cylinder with a laser temp gauge. That should tell you which cylinder you have to pay attention to.

[tz89]

I'm still trying to come up with a plausible theory for an intermittent misfire when cold.

[Neil86]

Check for any vacuum leaks around carbs and intake...probably more sensitive to

extra air at idle and cold.

[tz89]

I should have noticed and paid more attention to the wandering idle speed. A good indicator of an air leak.

 

This morning I replaced the cracked vacuum port caps. I noticed improved cold idle and didn't notice any missing, but I had to get to work so haven't done any real testing.

 

Could it be that simple?

[Neil86]

Yes very likely.

[tz89]

Done. It could use a sync now but until my brother sends back the digital carb sync I built (see write up) it will wait.

 

Thanks for the help. Best $12 ever.