CR 250 RC Valve

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#1
First of all, I have previously run a thread with this very same issue, being that my by occasionally goes bwahh at times, when coming out of slow sections and rolling the throttle on for longer straights.

The former thread was all about jetting, and I beleive this is all sorted, but I still have this same issue - My bike is not sputtering, not drooling, dosn't foul plugs, starts easily and is normally right up there in all wether and temperatures.

Now reasently I had a local dealer try to diagnose the problem, he said he never tried anything like it, but out of his 20 something years of experience he would think it was an electrical problem - due to it being right when the engine is suppose to hit the powerband he would think it could have something to do with the rc valve control.

I have disassembled the rc servo and checked both the electrical motor and pot-control, both appear in perfect condition and the servo gears are nice - no wear.

Tonight I tried starting the bike with the rc valve cover removed, and I could see stuttering movement when the powervalve engaged (but it does engage rather rapidly) - at one time I thought I saw that the powervalve actuator arm actually closed the valve shortly while pinning the throttle, but I am not 100% sure as I could not recreate this scenario. When I touch the actuator arm, I can feel juttering movement as it opens the powervalve (going little steps back and forth, while going through the entire motion) - is this normal ?

Have any of you had a similar issue ?
 

cnielse5

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#2
I have heard the cables can get worn or loose. My 03 Had a similar problem and I just took the slack out of the cables.
 
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#3
Thanks,

Yes I have noticed that too, I recently took a little slack out myself, but unfortunately it didn't solve my issue. Does your valve move smoothly or will it judder/small erratic movements, do you know ?

I am thinking that maybe I have a bad soldering in the CDI, but I am reluctant in buying a new since they are $600 in this country ????.
 

DieselTech

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#4
Possibly carbon build-up on the powervalves, requiring disassembly and cleaning? Maybe they are binding or not closing all the way?
 
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#5
I don't think the power valve would cause a bog. It would certainly cause a lack of power while exiting the turns if it were stuck open, but not a bog. I would go back to looking at your jetting and reeds.
 
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#6
Thanks for input,

It is not like a real bog, it exits turns fine but right before hitting the powerband in the midrange it occasionally dwells at a certain rpm for 1-4 seconds before suddenly kicking into the powerband and pulling strong.

It never misfires, as far as i can tell from the sound of the exhaust - it doesn't resemble pressing the kill button in anyway. It simply just doesn't pull as strong as it usually does, but otherwise ok - like turning the throttle down to 1/3 power for a couple of seconds, then pinning it.

I just have no good way of testing whats wrong, any ideas ?

Reeds, piston, gaskets are new (2 hours) and the change did not affect the symptom - which by the way has been there for a couple of years now.
 

cnielse5

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#7
I have not ever pulled the cover off the side yet. so I don't know what the power valve does. Sorry.
 
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#8
Tonight I tried starting the bike with the rc valve cover removed, and I could see stuttering movement when the powervalve engaged (but it does engage rather rapidly) - at one time I thought I saw that the powervalve actuator arm actually closed the valve shortly while pinning the throttle, but I am not 100% sure as I could not recreate this scenario. When I touch the actuator arm, I can feel juttering movement as it opens the powervalve (going little steps back and forth, while going through the entire motion) - is this normal ?
the rc servo motor is a type of electric motor known as a "stepper motor", they dont spin around continously like a normal motor but rather they move in either direction in small steps a few degrees at a time or in a whole circle. same sort of thing as used in radio control cars for the steering etc..
so what you describe is more or less normal operation.
as a foot note if you suspect the powervalve could be your problem then why not try disconect the cables and jam the powervalve arm (where the cables attach) in a midway postion using some cable ties or something and see how the bike rides.... ok i know it wont have the same bottom or top end power, but if it fixes the hesitation you talk about then you know you're on the right track with fault tracing.
good luck.
 
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#9
Thanks steve.emma

I disassembled the RC controller and found that it is a normal 12v DC motor, not a stepper motor. The position detection mechanism is a normal 5k Ohm potentiometer similar to the type found in older stereo's. Both items appear to be operating ok, when connected to 12 VDC - I find no error.

I have tried jamming the arm, but only when the engine was cold (neighbours!!!), I will try it with a warm engine on tuesday, out on the track - The cold trial run did display lack of top end power similar to what I have experienced, but the engine started sputtering and I couldn't tell whether it was because it was cold or because the powervalve was jammed.