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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Help: loss of power in 7000-10000rpm range
Post Info TOPIC: Help: loss of power in 7000-10000rpm range
lybker


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Help: loss of power in 7000-10000rpm range
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Dear all 

I am new to the forum, but post here as I hit a strange issue yesterday. 

 

I have fitted a TTR 250 engine in my daughters quad bike and have fitted a speeduino ECU and electronic fuel injection. During the mapping phase We did a number of high load runs (2-3 hours) on the dyno to ensure fueling is correct under any load. After 5-6 runs We suddenly lost power above 7000rpm (rpm limiter is set at 10500rpm) like 5 hp down and engine got a strange rattle during start and high rpm. from idle and up to 7000rpm power is still fine. CDI has been replaced with 36-2 tooth flywheel and bmw coil and pickup sensor.

Engine has high comp piston with max 5 hr run time on it and larger oil cooler. We had plenty of air blown directly at the engine during the power runs

Kindly share you knowledge and support on following questions:

 

  • Has anyone had similar issue with an engine loosing power in the high rpm range but still running normally ?
  • do this engine have any known weaknesses if put under high load for longer duration?
  • I have not had any time to investigate and was hoping it maybe was one valve not opening or closing due to maybe the spring being broken? 

Any info would help me dive into the problem, as We have a race coming up shortly and so my workshop time is limited - all guidance to getting to learn the engine better would be a benefit.

 

million thanks in advance

 

Before anyone asks - power is around 30hp ish...

kind regards

 

Lars



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mossproof


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I would suspect a sticking valve or broken spring.
As far as I know, noone on this forum has done an efi conversion so I would love to see more info and pictures.
Bear in mind the engine is much more stressed than usual with high comp piston and reduced air flow because of the quad front suspension.

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lybker


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Thanks - I will be tearing the engine down soon, as I had a to aggressive spark table causing a burn of the piston - this was just plain stupid. 

throttlebody is from a Yamaha WF250R and fuel pump from a Suzuki LTZ450. ECU in first edition was based on the Ecotrons.com small engine ECU including original CDI - taler updated with 36.2 tooth trigger and megasquirt ECU (speeduino)I have quite some pictures from the build, so just ask. Anyway here is a link to the folder Nothing secret there so feel free to take a peek:

https://photos.app.goo.gl/muw5GdtKUTAft2tT6

I hope the link works?

 

 



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lybker


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old thread but thought I should share the root cause of the power loss bein due to early ignition caused a meltdown of the the ignition bowl. Triggered by having a helicoil for the sparkplug as a heat collector

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