YAMAHA TRX850 with small hesitations

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Dominique D
Newbie
Posts: 3
Joined: Sat Jan 30, 2016 9:39 am

YAMAHA TRX850 with small hesitations

Post by Dominique D »

It has been about 7 years since I ues the scope, so I am verry rusty. I have a motorcycle Yamaha TRX850 here, parralel twin with 2 carburettors 2 coils. First problem was sometimes the bike hesitated at around 1800 rpm when turning the throttle slowly and would not go higher, when turning it fast it whent ok most of the time. Found the second spark plug cap to be defect also put in new spark plugs ans cleaned the carburettors but did not find annything special there. Now it sometimes has a verry small hesitation around 1800 , just a verry small stumble when keeping the gas constant.
Took a look at the secondary ignition picture and found the number 2 cylinder coil voltage peaking verry high and the firing line sometimes to be a lot highter then the the number 1 (excuse my Englisch)
The first cylinder is a lot richer CO 2.9% then the second CO 1.62%, what could explain the max voltage difference . Help me jump start my brain again to analyse these voltage lines
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Yamaha__20190912-0002.psdata
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sec-lichtjes gas.psdata
(14.69 MiB) Downloaded 391 times
sec-ontsteking-ralenti.psdata
(13.71 MiB) Downloaded 400 times
Yamaha_20190912-0006.psdata
(12.34 MiB) Downloaded 385 times

CycleImp
OneWave
OneWave
Posts: 15
Joined: Fri Oct 07, 2016 12:11 am

Re: YAMAHA TRX850 with small hesitations

Post by CycleImp »

I would do an in cylinder compression test or at least a leakdown test. Looks like you might have low compression on one cylinder(valve sealing problem - maybe a valve clearance issue?)

AndyM535
OneWave
OneWave
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Joined: Mon Aug 05, 2019 10:11 pm

Re: YAMAHA TRX850 with small hesitations

Post by AndyM535 »

I'd try balancing the carbs then check the throttle position sensor.

Dominique D
Newbie
Posts: 3
Joined: Sat Jan 30, 2016 9:39 am

Re: YAMAHA TRX850 with small hesitations

Post by Dominique D »

Before I started testing the ignition I did a compression test and leak down - TPS set ok - balanced the carbs .
Only the number 2 sparkplug cap was faulti.
A colleage said the pre ignition seemed a bit irregular with the throttle beeing s steady making the the CDI suspect

AndyM535
OneWave
OneWave
Posts: 15
Joined: Mon Aug 05, 2019 10:11 pm

Re: YAMAHA TRX850 with small hesitations

Post by AndyM535 »

If the coils are the same, would it be possible to swap them left-right and see it's related to the cylinder or the coil?

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