pwr valve knock

[dustbuster]

I recently purchased a 2003 ec250. When I picked up the bike it hadnt been ridden for a few months and was running very rich, wouldnt rev out and had a lot of power valve knocking when grabbing any throttle. I replaced the fuel,spark plug, cleaned the air filter, replaced the 45 pilot jet with a 40, adjusted the pilot screw out from 1/2 turn open to 3 full turns. The bike has an Ltr pwr valve cover, moose reed spacer and I think the Ltr needle jet (stamped DDK) with clip currently 2nd position from top, a 180 main jet and #8 throttle slide. The spark plug is running closer to brown rather than oily black now, power feels better through throttle range and it really can rev out now but the pwr valve knock is still occurring although nowhere near as bad. It is most noticable on open sections of trail or on the road where I am cruising with some speed but not under much power and then opening the thottle. I live at almost sea level, temp. around 18 deg. centigrade and using premium unleaded fuel @ 50/1 mix with motorex. I'm wondering if i need to keep on with tuning or does a worn/faulty pwr valve act like this? If you have any experience with this or know how it can be corrected I'd appreciate your feedback.

[dionysis]

I have a 98 250 that did similar, however after taking the bike apart i found that it was not the power valve that was knocking but I actually had a broken gear in the transmission. I know that since 98 they improved the transmission but it is still something to look at.

I was absolutely amazed that the bike still ran well with a tooth missing. Only knocked when I got on the gas...

[dustbuster]

Hey, thanks for your input. The knocking I'm experiencing has been affected by playing with the carb. settings, but not eliminated. Also the noise isn't there all the time. Was it so with your 250's gear noise?

[jeffd]

There is a slight knock when the power valve flops open and closed. But, much louder is the chain slap against the hard plastic chain slider on the swingarm when the engine is under a "specific load". Actually, exactly the condition you describe ("some speed but not under much power and then opening the thottle") Not trying to spam for my friend Les too much - but an LTR chain guide quiets down the chain slap/noise quite a bit.

I am a bit confused by your post. Pre-detonation knock is usually caused by a lean condition. I wouldn't think a jetting change would affect operation of the power valve.. My guess is that your jetting changes are affecting how the engine behaves under a load with the conditions you describe ?? - thus changing the chain slap "harmonic"... ?

With a #8 slide and your other jetting specs - you should have been okay with a 45 pilot and having the air screw at 1/2 turn out seems odd, in similar conditions, I would have been about 2 1/2 turns out - seems like one of the passages might be obstructed. If it were me, I would disassemble the carb, remove all jets, spray in carb cleaner and blow out with compressed air. Where are you at on the idle screw? Make sure it isn't "in" near coil bind - if it is, you may want to richen back up your pilot and reset both idle and air screw settings (back out idle screw and start with air screw at 2 1/2 turns out.).

I got used to the chain slap, it is a characteristic of the bike - although an LTR chain guide helps alot. It would be nice if gasgas used a hard rubber like honda uses - it absorbs more of the impact. I have looked around for a "crossover part" for swingarm chain slider but have found nothing. Anyone else find anything? Might be nice to talk to the GasGas factory guys while they are here for the WEC races and ask them to change this...

jeff

[dustbuster]

Thanks, I'll definately watch out for the chain-slap thing but the noise seems to be coming from the cylinder/exhaust area and is a rapid series of knocks (or is that what the chain slapping sounds like?). As for the idle screw, I think I have one of the joke springs mentioned in another post on this site. It doesnt do anything, even if coilbound. When I pull up idle is too fast but will slowly reduce to almost stalling this is more severe with the air screw adjusted in. (faster idle that didnt seem to want to settle) Starting is easy, when cold choke on, no throttle two kicks. When warm no choke, no throttle and one kick. I agree that the carbie should get a good cleanout I've only cleaned the bits I've played with and a little compressed air sounds like a good thing.

[PEB]

Look Here:


http://www.smackovermotorsports.com/...ead.php?t=3573


Happy adjusting,

Paul B

[dustbuster]

Yes, yes, yes! This must be it. It sounds like the guys at smackover have had the same issue, so now I will check/adjust my pwr valve (and clean my carbie to sort out the idle- unless the pwr valve is affecting that as well) and see if we can put the 45 pilot jet back in and wind in the pilot air screw a little. I wonder would faulty pwr valve operation cause the plug to look like it's running rich due to inadequate discharge of exhaust gases? I'll post my results to let you know how it works out. Thanks for all the help and big manly hugs all round.

[dustbuster]

Just went for a ride before pulling anything apart. When looking ahead in normal riding posture, the noise seems to be coming from the front of the engine. Turning my head to check the chain makes the noise come from that area! I will be changing the chain guide. Jeff, as well as reducing noise, the Honda/LTR replacement looks like it would be much better than the standard unit anyway.Thanks again.

[GMP]

Remove the righ side PV cover and run the motor. You can cut down an M5 allen key to do this without removing the pipe. Observe the PV operation as you rev the motor, the plate should move from stop to stop. With the motor off, it should rest on the stop. If this looks OK, the PV is working properly. The PV will always rattle slightly, as PVs do on all bikes.

From my experience, #8 slide is lean for a 250 with a DDK or LTR needle unless your at very high altitude. I'd try a #7 after going through the carb.

[Boomhauer]

Dustbuster,
Here is something else for you to do when you get the power valve cover off. If it was me I would do this just to make sure the bearings are clean and in good shape being as how the bike was set up and not ridden for awhile.

This was written by my friend who got me into riding enduros.

http://www.gasgasrider.org/html/pv_disassembly.html