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05, 06, & 07 KX250. Check your powervalve!

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On the 05 to 07 KX250's. I have found the powervalve activation lever doesnt fully open the powervalve far enough to fully open the sub exhaust ports valve. This gets worse with age as the pivot points on the activation lever rod builds wear and slop to the point the sub ports dont even open at all. Maybe this is part of the pinging problem we all deal with (till a combination of things fixed mine including jetting, ignition pickup air gap, head work, and good fuel. But maybe this was the cause to begin with and maybe this is why when you think you fixed it, it seems to slowly come back and requires more fooling with. As the rod pivot points wear and slowly opening the sub ports less and less?).

 

 

To test yours just remove your pipe and powervalve activiation lever cover. look up the exhaust port at the powervalve sub ports, using a 8mm socket on the activition lever where it connects to the povervalve shaft open the valve till the sub valves fully open. Now note or somehow mark how far it must spin the shaft at the activator lever area to reach fully opening all 3 valves. Put the pipe back on but leave the activation lever cover off. Start the bike, warm her up and then rev the piss out of it while watching to see if it spins open the shaft as far as it needs to get all 3 valves open. What did you find?

 

To fix you can bend the activators arm upward some (check for clearance from the surrounding walls), but its best just to first replace the whole arm (as the pivot points do wear) and then only bend as far as needed to reach fully open while revving.

 

Enjoy!

Edited by UpAllNight

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To fix you can bend the activators arm upward some

 

Enjoy!

*Raises eyebrows* Um how about no.

 

And what about the people with pinging issues on a new bike? Think I just debunked this theory.  It's also a proven fact that the squish band is somewhat incorrect from the factory is the cause of most ping issues with th e05+ bikes.

Edited by moose_338

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Had two new. This ant the first time in history a bike has came off the assembly line with the powervalves not fully opening. Kawasaki has made this mistake a few times in history and it usually does lead to some pinging. I have had 6 different head profiles with squish clearance ranging from 0.038 to 0.050" and volumes from lower than stock to higher than stock. It does help but the bike is still always on the edge of a ping even with good fuel. Even with a new activator rod it came come up short of fully open which would explain why it happens when new. You don't have to take my word for it but have you actually check to see if yours is FULLY opening all 3 valves? AndI bet it is not. if not how would you fix this? I know i for surely want mine to open fully and i will not just assume Kawasaki got it right.

Edited by UpAllNight

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Had two new. This ant the first time in history a bike has came off the assembly line with the powervalves not fully opening. Kawasaki has made this mistake a few times in history and it usually does lead to some pinging. I have had 6 different head profiles with squish clearance ranging from 0.038 to 0.050" and volumes from lower than stock to higher than stock. It does help but the bike is still always on the edge of a ping even with good fuel. You don't have to take my word for it but have you actually check to see if yours is FULLY opening all 3 valves? And if not how would you fix this?

My sub valves fully open I checked them the last time I did a top end rebuild and had the KIPS valve apart for a cleaning. If this was as big a problem as you say it is I think we would have heard of it before now. Not saying your wrong but I cant see this being a widespread problem, It's just I cant see the sub valves not opening all the way causing a pinging issue. It's usually one or combination of these factors that contribute to pinging; compression, type of fuel, jetting and timing. 

 

Only out come I can see for the sub valves not opening enough is a slight change in the power band, as that's what they do by changing the port heights.

 

I'm also curious on how many hours you have on the bike and the extent of the wear you have on the actuation rods. And what kind of oil you use and if you have build up of gunk on your exhaust valve components?

Edited by moose_338

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Not an expert in porting or such but its my understanding the sub ports which increase the overall exhaust port opening helps exhaust heat escape from the combustion chamber to the pipe more efficiently. Did you actually check to make sure the bike was fully opening the sub ports on its own? On a bench everything will look good, its when its on the bike having to fully open it on it own.

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I have had two kx250. 2006. Both pinged new and(one worse than the other) i had to go through the normal steps of jetting, head work, air gap, and timing. Not sure of the hours on my current one but its still on its original crank and cylinder which is still good. I have run anywhere from 100% 110 octane race fuel to a 60/40 mix of race/pump. I run yamahalube at 32 over 1. Powervalves are actually very clean. I run wiseco pistons and replace then often as i usually keep the bike revved out here in Florida on sand tracks

Edited by UpAllNight

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Not an expert in porting or such but its my understanding the sub ports which increase the overall exhaust port opening helps exhaust heat escape from the combustion chamber to the pipe more efficiently. Did you actually check to make sure the bike was fully opening the sub ports on its own? On a bench everything will look good, its when its on the bike having to fully open it on it own.

I checked it on the bench and made a line with a paint marker to see it in operation too.

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I've heard of this issue some time ago and on KXriders.net and mine wasn't opening fully when we first got the bike. I did the same tweaking of the rod as well. So it's not unheard of, just very uncommon. I just never thought to mention it because I thought is was something I did during a rebuild.

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SAPPERS the only reason I mentioned it is because I went so long without even thinking to check. When I did I was surprised and figured there may be people like me that are riding around without the sub port valves fully opening. I rode YZ's for like 5 years before I switch to kawi and the YZ never seemed to have this issue so I kinda got lazy to ever check with the kawi. But between the last two 06 YZ250's I had a ton of other issues for me, trans breaking twice a year, stator going out, broken fork spring, crank wearing where it contacts crank bearing and more. All bikes have thier own issues though. I stuck with the KX's for now as the trans seems to be very well built. Digging in cases every 6 months gets old.

Its funny how the pinging is blamed soley on the head of the KX, yet the KX heads profile is actually slightly better out the box than the YZ250's head. The YZ comes with a squish clearance around 0.065" and the KX comes around 0.060". The comp ratio is similar. Yet the YZ's mild pinging is easily cured with either better fuel or jetting. The KX's pinging is not so easy to completely cure. The air gap helps as it basicly just retards the timing some, jetting richer and/or better fuel also helps. But all these attempts seem to aim at reducing combustion chamber temps. The head work also does this as well, by tightening the squish band clearance it keeps the what little charge that is located under the squish cooler by tranfering more heat to the piston and head. From what I been reading widening the exhaust ports opening transfers more of the combustion chambers heat to the pipe better which aids in controling pinging and also helps the pipe perform better at high RPM's. Unlike the main valve which raises the exhaust ports roof, the sub valves only offer more of a opening but at the same overall port height which has the same effect as just a wider exhaust port opening. This is where I came to the idea of the pinging's main culprit may just truly be the powervalves not opening the sub ports completely if at all and with this fixed it should be as easy to manage the pinging as the YZ.. This may be why other attemps help but its more of a big bag of band aids.

Edited by UpAllNight

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Real quick, when you guys say ping, what are you referring to exactly? What's this caused by?

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Pinging is a term used to describe detonation. Detonation is mainly a uncontrolled burn in the combustion chamber usually caused by too much heat in the head and piston area or a fuel with not enough octane. On the kx250 it sounds like a popping sound coming from the inside of the motor, happens while under power. Some people say it sounds like a rock inside the motor. It doesnt do it consistantly or non stop (at least mine havent), but will do it a few times per moto, depending on how much the particular bike suffers from it. The KX250 has been known to tear up lower rod bearings if this issue is not addressed.

Edited by UpAllNight
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Ohh, well in that case I know exactly what you're referring to. I guess for some reason I thought the ping being discussed was something besides detonation. Brain fart. Thanks.

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Just a update. After putting on two full days at the track on the KX with the powevalves fully opening the sub ports I can say this is noticable. Before I had the bike tuned just below the edge of its dreaded ping with the following setup...

 

Head work - 11mm wide squish with clearance set at 0.038" and angled to reach 0.046" just before the dom and using the stock overall CC for stock compression ratio.

air gap - Although I suspect all this does is retard timing. I was using just a hair more advancement to bring back some of the mid range that was lost after the air gap was set to 0.037" or whatever it was.

60% race- 40% pump fuel.

162 main, 50 pilot. Air screw set for day and weather.

 

After fixing the powervalve issue that some KX250's have I was able to add a hair more timing advancement and even go down to a 160 main jet without pinging. I did however go back up to 162 as 160 was on the edge of lean and I reather error slightly on the rich side.

 

The bike seems to extend its mid range torque into the top end revs better, kinda hard to explain. It doesnt rev any higher but the bike pulls quicker through its top end revs more briskly. On one corner with a double-double just out of it that I use 3rd coming out of, I could feel it pulling harder and quicker right before the face then it did before.

 

On another note. If you run the bike hard, staying wide open alot try using a 9 heat range plug. 8 is the stock range, but Kawi offers a optional 7 and 9 which indicates to me that in some situations it might be desired. I been using the 9 with good results, havent fouled one yet so alls good. Gotta remember they send them out the door setup for a ride range of riders.

Edited by UpAllNight

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