what causes sneezing, low rpm misfiring, and won't idle?

[pcrussell50]

this is on one of my v4 crossflows with an ordinary choke, not that newer quick start enrichment solenoid. it runs GREAT, at higher rpm if i can get it there without dying, but i can barely keep it running at 1500rpm--where it has an irregular miss, and occasional sneezing. i rebuilt the carbs, including changing the core plugs fairly recently. i did a compression test this afternoon and got:

128-134
125-128

as viewed from behind. i have not done a leak down test.

i'm seeking some guidance as to where to start my troubleshooting. i "feel" like it's a fuel problem, or an air leak or broken reed. i don't "feel" like it's electrical--but feelings aren't worth squat in a deterministic mechanical system.

i'm tempted to tear into the carbs again just to make sure--unless someone here advises me otherwise.

-peter

 

[kodibass]

Re: what causes sneezing, low rpm misfiring, and won't idle?

Most often a sneeze at low idle is one of the carb low jets dirty & causing a lean situation, the fact that you say it runs well at high rpm's would lead me to investigate the carbs low circuit area further.

 

[Bob_VT]

Re: what causes sneezing, low rpm misfiring, and won't idle?

Rebuild the carbs again and make sure you do a Lync & Sync (check the timing)....... I have seen a V-4 idle on one cylinder so the other part you need to verify is ALL 4 sparks at the plugs too.

 

[Haffiman]

Re: what causes sneezing, low rpm misfiring, and won't idle?

Check engine temperature balance. Defective, one or both, thermostats may cause what mentioned.