so my f3 decided it wanted to be a parallel twin today. was out riding and two cylinders stopped firing, dont know which(headers were too hot for me to want to touch them). Pulled over and made sure all the plug wires were connected and that she was getting fuel, both were good. ended up having my dad pick me up and haul the bike back to his garage and as soon as i got her off the truck she fired right up on all 4. i wont really be able to dig into her until saturday but i just want to get a list of what all i should check.

the obvious would be spark plugs, but i have a hard time believing that two fairly new plugs would go out at the same time.

so i figured i would check the coils, make sure they have the correct resistance make sure both coils have good grounds
and check the plug wires.

anything else i should look at or check?
anyone have this same issue and can point me directly to the problem?
thanks.

 

Sounds like fuel starvation to me. You could take the float bowls off the carbs after letting them fill up with the engine off and cold. Check each level to see if they are all the same. Also check any fuel filters for blockages. The fact that the engine fired up on all 4 cylinders when you were not riding the bike seems to confirm a lack of fuel once on the move. Let us know how you get on?

 

i highly doubt its fuel, ive had fuel starvation issues before and when that happened it was all the cylinders, not just two, and they sputtered out and didnt just quit firing. and also when she did fire up on all 4 there was quite a bit of white smoke coming out the back so that tells me it was still getting fuel.

but ill start working on it tonight or tomorrow morning and ill post what i find.

 

Found the problem, Coils are bad.
One coil had 12 ohms on the primary side(supposed to be 2.5-3.1) and had 24k ohms on the secondary( supposed to be 21k-25k)

and the other coild had 3.8 ohms on the primary which isnt too bad, and 28k on the secondary.

and since there was more resistance, that means less spark, which means all the tuning/jetting ive done in the past month will have to be redone

 

Really glad you found out what it was! Now you can enjoy riding again once you've replaced the coils. Well done!