Hey guys. I know you guys are not fans of streetfighters, but i am on the verge of finishing my project. the only things still to be done are to upholster the seat and diagnose/fix my engine. It starts and idles fine, with k&n pod filters and a dynojet stage 3 jet kit. now the bike runs fine, and has plenty of power, but only for about 10-15 minutes, then cylinders 1&2 stop firing. the problem seems to be heat related because after pulling over and waiting a few minutes the bike will start and run fine but only for a short period of time. Spark plugs have been changed yesterday, carbs have been cleaned and re-cleaned. compression test showed 120 PSI on all four cylinders. Any help is much appreciated. Thanks in advance!

 

What do the plugs look like after it cuts out? How radically have you modified the cooling system (smaller radiator, different fan etc.)?

 

The plugs all look the same, from the cylinders that run and the ones that don't. they are a nice brown-ish colour (is good right?). the cooling system, and the engine in general, is un-modified aside from jets, filters, and exhaust. I'm starting to think it may have something to do with all of my electronics (icm, regulator, relays, flasher etc.) being packed into such a small space with little or no airflow for cooling. could a hot ignition control module possibly be causing it to not fire those cylinders?

i did take the paint off of the radiator... but i don't see that causing the slightest problem at all

 

I can't see the paint making that much difference. Black radiates heat much better than any other colour but there's no way that's causing your grief. Not sure about the heat in your electrics causing your problem either but the regulator would need some reasonable air flow to work properly..not much else would generate any significant heat. Is your fan cutting in and out? This would rule out a cooling system problem. Have you kept your temp gauge or put in an after market one? Either way, what's it saying?

Sorry to ask so many questions about your question but the problem needs narrowing down some. The plug colour sounds good and I'm a bit stumped as to why 1&2 would stop firing since they're on different coils. Even though the plug colour seems good, have you checked fuel lines etc.? Sometimes it's the really simple things that cause this kind of ****.

I'm going out of range (camping and fishing with the young bloke for a couple of days) but hopefully some of the other guys will help you sort this out.

One other thing, I've got no problem with street fighters...your bike, your choice.

 

A common problem is vacuum in the tank. When she's been running for a while shut her down and crack the filler cap with your ear next to it, see if you can hear an in-rush of air.

Worth a try?

 

If it were me, I would swap plug and coil wires to see it the problem go to #2&3 and #1&4 get fixed. This would help to narrow it down.

 

My vote is with the two replies above me.

Also coils that appear fine can break down when they get hot.

 

i had a coil do the samething on a race car when it got hot it just shut off when it was cold run great ....... i'd look at the coil

 

one more thing never run a plug with paint on it it will have a dead miss in it found that out the hard way also !

 

Thanks for the input guys. The fuel lines are all un-kinked and free flowing. I never noticed if the fans were cutting in and out, and i have no temp. guage :S. I will be working on it tonight so i will try to swap wires from 1&2 to 3&4, should be alright aslong as the same coil is connected to the same two cylinders as factory right? just backwards. Wouldn't vacuum in the tank cause a lack of fuel to all 4 carbs? (i'll check that out anyways because im running out of ideas). Thanks again. please keep the ideas coming!