04 Honda CR250 Powervalve not fully closing

[DKT735]

I have an 04 Honda CR250 that I noticed hasn't been running as good as is used to. I pulled the powervalve cover and discovered that it is about 1/8 of an inch shy of fully closing. I checked for carbon buildup but there wasn't much and the powervalve operates smoothly from stop to stop when the cables are unhooked. I suspect the servo motor. Has anyone had a servo motor go out?

Thanks

 

[NO HAND]

...I suspect the servo motor. Has anyone had a servo motor go out?...

There was someone here on DRN with the same problem and it was the servo motor being contaminated with water and debris, perhaps it is not totally waterproof, and may be allergic to frequent washing.

 

[Wilky]

Here is a quick test of your servo motor.

Take the RC cover off, start the bike and rev it for a second or two. Do this five or six times while watching the valve. If it rotates counterclockwise when revved high (fully open and 8500 RPMs according to the manual) and goes back at idle, then the servo motor is at least responding to some kind of command from the computer.

Another thing to check is the cable tension. Too tight or loose could cause erratic results. I adjusted mine so that if I push horizontally on the cable (right side when the valve is closed (or rotated fully clockwise) and visa versa for the left ) with a screwdriver the cable will move about half the distance to the case (1/8 inch maybe). If it doesn’t move it is too tight if it touches the case it is too loose. I have done some experimenting (nothing major) with the RC valve, let me know if you want to know my findings and I will do a write-up.

What are the symptoms of your sick bike?

 

[DKT735]

The powervalve moves when the motor is reved up. when the bike returns to idle the powervalve is about 1/8 of an inch from closing. You can let the bike die and it still is open about an 1/8 of an inch.

The motor isn't as responsive and has less low and mid-range power than it used to have. I had Eric Gorr to a low-mid port job for me and until about a month ago the bike was pretty responsive for a CR. It has good compression and the piston and rings are new.

I adjusted the cables and they are tight but not too tight if you know what i mean. I'd like to read your findings on the power valve cable adjustments. Sound like you put some work into it.

Thanks

 

[Wilky]

I like you (among many others I am sure) was/am on a quest for more low to mid power from the case reed CR250 (mine is a 04). Sense I am on a fairly tight budget as far as the bike is concerned I started looking for some low cost/no cost mods. While doing some research (mainly here on DRN this place is great) I ran across and article about the RC valve that basically mirrors what I motioned in my previous post. While messing with the valve and cable adjustments I noticed like you that the valve was not completely closing so I attempted to adjust the valve to close completely. The manual even notes that while running at idle the valve should be completely closed (turned fully clockwise) touching the stop pin. Try as I might I could not achieve this condition. I adjusted the right side as far down and the left as far up as I could trying to force the valve to rotate more clockwise (closing the valve) during idle. I was able to close the gap a little by doing this but I could not get it do completely close I went from a 1/8 inch to 1/16 inch gap. In my test I would manually close the valve, start the engine to idle (no revving whatsoever) and then kill the engine and lo and behold the valve would open back to that 1/16 inch gap revving it resulted in the valve opening and returning to the same 1/16 inch gap. After messing with it for an hour I took the bike out to see if what I was able to achieve made any difference to the power delivery. And………..no discernable power gains were achieved. This however was not the end of the RC valve story. I did do some more experimenting with the valve but not until after my next attempt for more low-end.

In chapter two I tuned my attention to the carburetor, jetting to specific. In my research I found that most guys that went down this road found that the Mikuni’s were crap, at least as far as jetting was concerned, and the Keihin’s were gold. Many dished out $150-$200 for the Mikuni/Keihin swap, easy for and 02-03 but no so for the 04-05 because of the throttle position sensor. Read the thread “Attn: 2002/2003 CR250 Keihin PWK Converts” for more info on this. Just before I was going to say “screw the TPS I’m going to plop down my $150 and give it a try” along came James Dean and his custom jetting kit that addresses the very problem I was trying to solve. After a quick thought of hmmm $70 bucks for the jetting kit is less that half the price of the $150 Keihin plus concerns about the TPS would be gone I ordered the kit strait away. BTW the JD Kit comes with a money back guarantee so you truly have nothing to lose.

A couple of days later I had the kit in my hands and had it took all of 15 minutes to install. Let me tell you a little about the nettles before I go on. First they look a lot different from the stockers. The JD nettle is made of what looks like brass not the aluminum looking stock nettles. The tapers are very different especially near the tip where the stock nettles have a short strait section, the JD’s do not. I also found, after I broke out my micrometer, that the stock nettles do not really have strait section near the clip and the JD’s do. Anyways I wanted to do a good A/B back to back test so I took the bike out and rode it for about 20 minutes with the stock nettle in. Then I installed the JD kit following the instructions. First thing I noticed that bike started easier, it felt like half way through my normal kick it lit up. While sitting on the bike and revving it seemed to rev a lot cleaner. With in the first 20 feet I new it was $70 well spent. The power came on right off idle and built up fast. This was a big improvement in the low end on the CR. On the track less clutch work is involved everywhere. After riding the bike for about three weeks including a couple trips to the track I reinstalled the stock nettle to see if the performance gains where in my head or in the bike. After ten minutes on the stock nettle I had enough and the JD nettle was back in. The gains were definitely not in my head.

More experimentation with the RC valve was prompted by a post I read here on DRN about a guy that adjusted his valve to 12mm on a 05 CR250. Basically what you do is adjust the right side cable adjuster so that the bottom of the adjustment bolt is 12mm from the top of the butterfly valve (that is what I call it) when the valve is closed. This mod had me doing the exact opposite of what I did when I tried to get the valve to close completely during idle. This mod actually had a desirable effect for me. It has moved the hit from the high-mid RPM range down to the low-mid to mid RMP range without effecting the low end. This is where I do most of my riding, I hardly ever rev my bike out.

One more thing to add. I just did my first top end complete with a new Wiesco piston and rings and this seams to have added even more power everywhere. While a the shop picking up my parts I was talking to the guy there and he told me to keep the RC valve cables lubed because he had heard of a couple of guys that had the plastic gear in the servo motor strip out because the valve was too hard for the motor to move. This may be something you should look into.

Back to your issue.

Other things I would check if you haven’t already.
Jetting
Reeds
Air leaks
Timing (key sheered off on flywheel shaft)

I hope you fine this information helpful or at least entertaining.

Scott