No topend power

[highspeedsteel]

Hi all,

Had an interesting thing happen yesterday while racing the 1st round of the New Zealand GNCC series. I have just done a topend rebuild and have riden the bike a couple of times since (maybe 3 hours). Anyway I had/have a problem with my engine that happened right off the start. My bike has no topend, its like it dosn't hit the "powerband". The problem really was like a clogged airfilter, but that was fresh (had done one short ride). The bike has been running fine for for the 2 rides that I did since I replaced the piston/rings. My gut feeling is that the power valve isn't opening.

I rode the whole race (2hrs) like it, not sure if that was a good idea, the bike was fine in the really tight stuff because the low down power was still fine, the only problem was I was getting passed on wide open gravel road sections by 125 2-strokes Hopefully I haven't damaged anything, there were no other weird noises etc.

For the record I still did alright (22nd out of 66 in the clubmans class) 11 min behind the leader. I judged my fuel perfectly, I ran 2hrs 6min and didn't have to refuel at all. I switched to reserve 1/2 way round the 5th and final lap, and at the finish I have no visible fuel in the tank. Now I know the reserve is smallish.

Just thought I would sheer my experience. Will let you know what the problem is when I sort it out.

By the way the bike is an 2000 ec250.

 

[GMP]

Check the powervalve. I would suspect the actuator arm stud has broken off or something has come loose. It doesn't take much torque to break or weaken that stud. Its a cheap part though.

 

[highspeedsteel]

That was my guess too. In fact thats what I hope it is because thats relativly simple to fix.

 

[highspeedsteel]

Finally got some spare time and pulled the bike apart to fix the problem. The bolt holding the powervalve accuator plate on had come loose! It hadn't even fallen out. But the power valve could rotate and not work. Anyway fixed that problem. Haven't yet fired the bike up because I had to do something else the same day but I'm 99.99% certain that I have fixed the problem. A small bit of locktight should help also.

 

[GMP]

Good. Use a new M5 nylock nut, and only tighten enough to bottom the washer out on the stud shoulder, just snug.

 

[highspeedsteel]

Its the bolt that holds the plate to the powervalve, where the plate has a D shaped hole. I should have used loctight when reassembling the powervalve, but as typical I was in a hurry. The nyloc nut was still firmly on. The other one had just come undone far enough that the D shaped hole could move off the powervalve shaft. It was all smooth so should be fine, will give it a ride this weekend hopefully.

 

[GMP]

OK, I misunderstood. Blue loctite is fine. When you tighten the bolt with the PV rod attached to the plate, jam the plate to the cylinder so you can't pull up on the PV rod, otherwise you can dislodge the balls in the PV governer.