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Kawi 750 Turbo 6k RPM stumble 19 May 2019 10:10 #804171

  • Detrailers
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Greets all, posted this on 750turbo.com but I think its stumped everyone.

6k prm stumble, revs to 6k and will rev past but has a hard time and stumbles. Set the TPS and still the issue. Doesn't present itself every single time, really more when I'm hard on the throttle in 2nd and 3rd gear

Im wondering if when one of the injectors was unplugged and rode it for a while if it gummed up injector.

One thing odd is that the tach GOES CRAZY when its happening. Its an aftermarket tach so maybe that's its own issue.

Has new coils, New intake boots coming, new fuel filter, checked petcock flow and tank return line. I guess pull the injectors now?? Could this maybe be the ignitor or ignition. I pulled the cover off the pick up coil and I see oil made it onto the oil pressure sensor in there and there is a very small puddle but doesnt look like its getting to the contacts

Tell you what when I get this sorted out on probly gonna sell the bike they're just too finicky for my level of expertise and not a whole lot of people that know about them....
85 750 Turbo E2
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Last edit: by Street Fighter LTD.

Kawi 750 Turbo 6k RPM stumble 06 Jan 2020 01:26 #816529

  • Stu23
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Assuming the tach is driven by pulses at one of the coils, I'd suggest the problem is either in your ignition system or the tach itself.

The tach is either recording the problem or causing it.

Have you tried disconnecting the tach? If the problem continues, you'll know the tach isn't the problem and you've got a problem in the ignition or the coil is breaking down. If the problem goes away, the tach is causing it.

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Kawi 750 Turbo 6k RPM stumble 06 Jan 2020 14:04 #816579

  • loudhvx
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A particular combination of cylinder pressure and RPM could cause the spark to fail. The spark energy would then be absorbed in the coil as a "ring" (aka oscillation) which could make the tach go crazy (as Stu23 mentioned). This could happen if the cylinder pressure is higher than what would be expected from the factory, or if the spark-plug gap is too wide. Check the gaps and you can even try to reduce them a bit to see if the problem goes away.

Another thing that could cause it is if you are using aftermarket coils that are slightly higher resistance that stock... like using 3-ohm coils instead of 2.2-ohm coils.

It may not happen all the time because it requires the correct combination of turbo pressure, throttle opening, RPM, and engine load... being in just the right gear may play a role in engine loading.

As Stu23 mentioned, a tach which cannot handle the high voltage might cause the problem, rather than only indicating the problem. I would agree on disconnecting the tach as a test.

If the spark gap trick fixes it or greatly reduces it, but disconnecting the tach does not, then the solution may be a newer igniter, or newer coils, or different ignition.

If you are running a lot of boost, then as most drag racers and 2-stroke riders found, you may want an actual CDI ignition to give slightly higher voltage. Or better yet some sort of MSD type CDI to give better idle than standard CDI.

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Last edit: by loudhvx.
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