Superjet 760 firing on one cylinder :(

[kieranm]

Hi,

Wondering if any one could advise, superjet has just had lot of work carried out on it over winter, bored out to 760, ported, msd cdi, msd coil, lightened flywheel, factory B, Wam waterbox etc

Worked fine for 2 outings, 4 hours ish. now firing on one cylinder.

Spark plugs both seem to be sparking, plugs are getting wet after turnover so fuel is getting in and have done compression test and both cylinders are within 10% of one another and right compression for mods. Poped carbs off valves working fine.

Before I strip back HT leads and swap out cdi to see if this is the fault anyone have any other suggestions or tests?

Any help would be great.

Kieran

 

[Big Kahuna]

the MSD Coils are hit or miss. Try installing your OEM could. Could be a bad connection or broken wire near the plug cap.
You could try cutting back the lead on that.

 

[blaster800]

start with a NEW set of plugs , I have seen new looking plugs not work under compression pressure ., then try to narrow down which cyl is ''possibly ''not working , Try to see which wire will throw the longest spark while cranking ??? are you still using the over temp sensor in your setup ? ? FWIW I had a wire work perfectly while visually looking at the spark while cranking , but under compression the spark would leak out of a small cut in the wire and cause a missfire . ..........have fun !

 

[kieranm]

Sorry didn't want to write essay in first post, have changed both spark plugs for new ones. The cylinder nearer the stern is the one not firing. Overtemp sensor is removed. Going to crank it in the dark tonight to see if I can see spark jumping. Next step cut back HT leads, reinstall original leads if not, then swap out cdi for oem I think...