engine misfires once hot!?

[carlofiori91]

Okay, so I got the coils tested two days ago and no problems there so it seems! So i bought a new ignition module thinking it would solve all my problems! However, it did nothing, same problem occurred! So does this means the coils are faulty even though the tests showed them to be fine!? I pulled out the plugs after the engine went bad and tested for sparks, sparking both sides but not a blue spark both sides were yellow. Plugs looked in good condition. feels like I am throwing money and time at this bike!

[Rebel]

You mentioned a "yellow" spark. That could be indicative of a low battery that is not firing the coils at the proper voltage resulting in a weak spark. Is your gap "too wide" on the plugs? You've almost replaced the entire system, so there's not much else it really can be.

[ME 109]

What color is the spark when the bike is running ok? Have you checked for blue color spark with a cold engine?
Not sure where I'm going with this but.....

To quote, "once the engine gets hot it suddenly misfires and looses all of its power"

This could apply to a magic carpet, too.

More information needed as too what occurs. Does it misfire once, and bog down continuously or does it misfire erratically, such as surging?

[Rebel]

To me it still seems like your exhaust valves are too tight. I had this issue with a John Deere tractor some years ago and once the engine heated up the valves were too tight on the exhaust side and the engine would lose compression and shut off. Once cold again, it would start fine and repeat the process.

[jagarra]

I guess we need some further clarification on the symptom. Does it fire erratically after it warms up or does it just sort of poop out where it looses power??
I had a problem that drove me nuts in diagnosing it. It was on a Fiat that I had that would run great for about 10 minutes then fire erratically when warmed up. turned out to be the coil.
The question I would have is when the coils were checked, were they operated long enough to get them hot internally?

[carlofiori91]

Its as I say once the engine gets really hot say like a 15 minute ride you pull the throttle back and just complete misfiring loose of power but idles okay really weird! Then runs fine when its cold until it gets hot again. It cant be the battery as its only a few months old, also I don't think it is the valves as I set them loose and the same problem occured, I have reset them back since. I purchased some new coils today thinking that would be the end of my problem but it didn't solve the problem same thing happened. I am now more clueless than ever!

[Rob]

I keep a new set of coils in stock against the time when I have another bout with coils that crap out when warm and work again when cool. I know they are rather pricy, but my peace of mind and freedom from aggravations is apparently worth the price for me.

(Now if I could buy 'insurance' for other things that vex me life would be even better.)

Ken

You are also hedging against inflation...although when you use your stock, you will need to resupply, of course.

[jagarra]

On my old Triumph, when the battery is not hooked up, it will idle OK, but when I give it the gas it misfires. You mentioned your battery was relatively new. Is it fully charged like from an external charger. Can you take it to a shop for a load test. (maybe where you bought it) Do your cables have a good tight clean connection. I have seen corrosion creep up the cable under the insulation and present problems, especially in the area where the ends are swaged on.

[Rob]

On my old Triumph, when the battery is not hooked up, it will idle OK, but when I give it the gas it misfires. You mentioned your battery was relatively new. Is it fully charged like from an external charger. Can you take it to a shop for a load test. (maybe where you bought it) Do your cables have a good tight clean connection. I have seen corrosion creep up the cable under the insulation and present problems, especially in the area where the ends are swaged on.

Wow - over 3 years ago: viewtopic.php?f=1&t=3974&start=0#p47505

[jagarra]

Rob,

Interesting that you dug up that old post. Problem seems so similar. The way I figured out what was going on was I used an oscilloscope to look at the output of the of the electrics after rectification. The electrical pulses feeding the system were very erratic, the distance between them kept changing. Once a battery was added, the timing of the pulses stayed stable and the misfire was gone. Part of the batteries job is to level these pulses out, that is why I am questioning the battery condition.

gg