Bonneville America Forums Forums Technical Forums Performance Mods spitting, backfiring, runs like crap

I rode the bike last Thursday and the bike ran great! the bike sat until this morning and when I fired her up, she is spitting through the carbs, backfiring through the pipes and generally running like crap. I suspect it is only running on one cylinder because when I gas it, it will backfire then run great for a second and then cut out again. I had this happen to me on the road one time, but it cured it self after I topped off with gas. I have a full tank now and have checked the four squirrel condoms and they are fine. All this is happening on the left side-the right sounds and runs great. I did check the plugs and they look a little black, but not bad. PLEASE HELP!

Sounds like a vacuum leak. Try swapping out the caps. Check your intake manifold too.

I'd also drain the bowl on that side and see what's in there.

possible hidden filter or tip over valve issue as well.

Swop coils or the two cables over under the tank and then see if itchanges sides..

can't swap just plug wires have to swap plug wires and the wires that power them up because our engines don't fire 360deg.

Phil and Ian are on their game! Vacuum leak sounds right. Tighten manifold clamps, replace four squirrel condoms, might as well hook up a tube and blow out your vent tube while you're at it and reset the tip over valve. Hidden filter, maybe, but more likely it would affect both sides (like mine did) instead of just one. Also, check the plug boot and make sure you've got a decent connection to the plug tip.

If the problem is one cylinder that is acting up or cutting out, I would as previsously suggested, swap the left and right coil. If after doing so, the problem changes to the other cylinder, you know that it is a bad coil. Check all connections - plugs to coils, and the CDI multi-pin connector.

Just came in from the bike. I pulled thw plug on the "good" side and tried to fire up the bike with only the "bad" side connected and the bike wouldnt fire up. I have drained the float bowl, and looked at all obvious wiring and dont see anything wrong. what is (and where is) this tip over valve and hidden filter. I also tried the old car trick to see if there was spark by grounding out the plug and didnt see any spark...however, I tried it also on the good side and didnt see any spark either. Would these things like the coil or tip valve go bad just by sitting for a few days?
THANK YOU ALL!!! PLEASE HELP!

would anyone that is familiar with this problem be willing to talk to me on the phone? I can call or you could me at 910-574-4248
Thanks again!

Thanks for all the help. I have done all the troubleshooting I can do and have isolated it down to a bad coil. If you know anyone that has one for sale, please PM me. It is also listed in the classifieds.
Thanks

I am having the exact same problems..carb spitting, big pops out of the left exhaust. power in and out.. if you get a new coil and it helps.. please let us know.. It's a long way to the dealer for me and no mechanics in the area.
Thanks

Jeff, did you check all connections to the suspect coil? I mean pull the connecting wires (high and low side) and make sure everything is clean and free of corrosion? How did you determine a bad coil, swap them? btw, did you try a new set of plugs, just in case?

I did swap them and everything worked as advertised on that particular side. I then tried the suspected bad coil with the good side's leads and no fire on the good side. Also tried new plugs, yes. This whole problem has happened to me before while going down the road, but after filling up and hitting a big pot hole, it righted itself. Suspect it may have been going out for a while and just finally gave in.

Good job on the troubleshoot!!

>You can do it. There is only 1 crank position sensor, so both coils have to fire for both cylinders.

If I follow this, & if I understand the 270 crank/cam timing, #2 is in the middle of an intake stroke when #1 is at TDC on compression.
Also, #1 is in the middle of a compression stroke when #2 is at TDC on exhaust (wasted spark time).
It seems unlikely that both coils fire in either of these situations;-)

>Firing both coils twice per revolution cuts down on the magnetic saturation time.

My belief is that the bottleneck here is at the pickup coil.

How can this be?
My guess is there's some magic in the CDI that sorts out The #1 & #2 triggers based on timing.

This belief system also helps explain a couple of other things:
1. No aftermarket CDI for 270.
2. Blown airbox on cranking (CDI initially confused @ cranking speed).

I still have identical symptoms on my '06.. right side runs great.. left side spits, farts and pops. also an occasional weird higher pitched popping sound from carb or vicinity.

Last night I..
checked coils.. good 1/2 inch spark string between each wire lead and coil.
Switched coil wires (right to left/left to right).. no engine start...
switched spark plugs (both clean).. no change.
What should I check next? Could it just be a bad plug wire?

Swap the good coil to the bad side (just 2 wires) and run plug to that side. See how it runs. Do the same with the popping side coil and see how the good side runs. This will tell you if you have a bad coil or not. However, if you have good spark on both, I suspect a vacuum leak somewhere. Replace 4 squirrel condoms, and tighten the clamps on the intake rubbers like previuosly stated.

Ha!
One missing squirrel rubber.
Growling on both sides now.
Thanks all.