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I am getting baffled. I have two KDX 220s. Both bikes have vforce 3 reeds and fmf rev pipes. On my 04, I originally the stock carb get RB modified and head ported. Everything turned out great. Bike ran like a 4 stroke - great low down power. So when I upgraded my son's 03 bike, I purchased an RB air striker carb and put that on my bike and put my modified carb on his bike. His head also got ported. My son's bike also had a scratched cyclinder so it got resleaved and a new piston.

I was hoping that both bikes would run about the same since they have almost identical aftermarket parts. But . . . my son's bike accelerates much faster but has no low down torque. I have played with the air screw a lot and it helped but both bikes are still noticeably different. (Besides the carb on my son's bike was originally on mine and it worked fine). His bike sound's "zingy" much more like a KX 125 than a 220.

I was going to have my mechanic compare the porting on the two heads. He has now idea why both bikes run so differently. He wants to retard the ignition I am skeptical - seems to me I need to find the cause of what is going on as opposed to putting a band aid on it.

Its possible that resleaving the cyclinder increased the compression but honestly it does not seem like it has more compression. Both bikes are the same, such as to kick start.

What are your thoughts? I really love how my KDX works because of you and I want my son's bike to work the same.

I once had two identical brand new RM400's. One was much quicker than the other. I compared the porting, ignition timing etc. They were jetted exactly the same. I never did figure out what the significant difference was, but I always assumed it was manufacturing tolerance related. Mebbe one had just a little more head squish area, maybe one had reeds that flowed just a little more easily at low rpm... etc.
Mebbe one had less internal friction? Anyhow, I just thought I'd throw that out for drill.

One thing though, jetting affects low-end big time. During his last run for the world championship, without any other engine changes, Brad Lackey used to have his carburetor tuned differently on his RM500 for more or less low-end or top-end depending on the kind of track he would be on. I suspect that fuel distribution is the likely difference if the performance is markedly different at low rpm.

I don't believe either of your heads was "ported". 2 cycle cylinders are "ported": heads are shaved/milled/machined/cc'd and/or squish adjusted, etc.

When a sleeve in installed into a cylinder normally the machinist will match the ports between the aluminum and newly installed metal sleeve. This CAN affect the performance of the motor (a few thousands here and there can have a drastic impact and if in fact this was done intentionally or unintentionally you may have a "ported" cylinder.)

Installation of a sleeve which accepts an standard size piston should not increase your compression.

Retarding the ignition (within some acceptable parameters) will generally benefit the upper rpms range verses the lower end on a 2 cycle. Lower end rpm ranges may benefit from Advancing the timing a couple of degrees. (Of course if you go too far - denotation may become a problem)

P.S. Exact jetting may not work the same in each engine.

Opps - your right. I meant to say advance the ignition slightly to give it more low down.

Your right about the terms but what I meant to convey is that RB moddified both of the heads, but not drastically both use premium pump gas.

Maybe the sleaving is causing the difference and possibly the jetting . . . Thanks for the ideas. I will keep searching. Steve

RE "RM500"

Well . . . the god's must be smiling on me. Ron Black just called me a few minutes ago to offer some suggestions. He thinks that when the cyclinder got sleeved its possible that the powervalve area got damaged. Or basically, the powervalve got reassembled incorrectly.

The reason for why I have no bottom end is that the power valve is open. Hopefully, the cyclinder is ok and the power valve got reassembled wrong. I hope hope hope. Otherwise, anyone got an extra 220 cyclinder they want to sell?

Thanks again Ron for your assistance as well as everyone else who responded. Thanks for your time. Definately glad I did not listen to my local guy who just wanted to advance the ignition.

Ron you rock!!!

I'll second that about Ron. I've been e-mailing him some questions and he's always been polite and helpful. But more important, he's honest and truthful. I know I can trust his opinions that I am seeking and that he isn't just trying to sell me on something. Thanks Ron!!!

SteveWR450f wrote: But . . . my son's bike accelerates much faster but has no low down torque. (Besides the carb on my son's bike was originally on mine and it worked fine). His bike sound's "zingy" much more like a KX 125 than a 220.

Is the power valve working properly on the bike in question? Sounds like KIPS might be stuck in the open position. That would make it sound "zingy" down low, but not have much power.

Well . . . I think the consensus is that the power valve is stuck in the open position. I have not done tear down yet to see if the power valve was reassembled incorrectly after the resleeving or if the cyclinder is messed up.

Anyway to start the bike see if the valve is working before I do the tear down?

Ron and everyone else, Thanks for the info!!!!!

Turned out that when the mechanic put in a fresh piston he bent teh actuator arm on the power valve. They replaced the part and now both bikes run the same. The torque is back - no longer runs like a KX 125.

The mechanic was scratching his head. He asked me why I could figure it out and he did not think there was a problem. He a is good mechanic but unfortunately he was testing the bike on a flat surface. I just told him I have good friends on the internet that are smart. Thanks guys I was really worringy that the cyclinder was damaged.

Steve

Good deal! Glad everything is back to normal.

RE: 'he bent teh actuator arm on the power valve..'

That makes this: 'He a is good mechanic..' contra-indicated.

Sorry...he may be a nice guy and all...but he's not a good mechanic. Not supporting that rod on disassembly IS common..it is also expressly cautioned against in the manual. It is also common sense mechancal sense to NOT force a small part via a large part...AND you sure-as-heck don't ever do such a thing 'backwards', that meaning forcing a 'driven' against a 'driver'. Example: A 'good' mechanic wants to evacuate the cooling system, so he puts an air ratchet on the impeller nut to manually activate the pump. As a consequence, he moves the crankshaft and transmission. That's not gonna work, 'eh? That's driving things 'backwards'.

Re: 'had a scratched cyclinder so it got resleaved'

Maybe I missed this...but 're-sleeved? Meaning it WAS sleeved? Is there a why for that? It shouldn't have BEEN sleeved in the first place. Sleeves DO change port timing, that dependent largely on the chamfering job done after the sleeve is put in. (IC said this already..I'm just agreeing with him..repeating for emphasis I guess).

You are lucky the part merely bent. Often it breaks off. Some riders have experienced completely grenaded engines as a result of such a break.

BTW...there is a flat machined into that shaft for the purpose of supporting it during maintenance.

I'd be wondering what the chances would be that your KIPS is timed correctly. given how it was damaged.

You need a new mechanic. Note** I'm assuming this person is a mechanic by trade and not the guy down the street that works out of his garage. Shop rates are not paid for him to learn how to do things. He's supposed to KNOW that already. If he doesn't know..he should find OUT before he breaks your stuff.

A bit of a rant maybe? Maybe. I'm real tired of folks called 'mechanics' that screw things up. I've 'enjoyed' that experience too many times to count. Your 'mechanic' owes you not only a fix for what he screwed up, but your money back for the 'job' he did in the first place.

Sorry for the delay in responding . . . Once I got the problem diagnosed I moved on to other issues. Anyway, I understand your comments about my "mechanic." I was not pleased. He runs/owns Extreme Cycle in Newberg. I typically have had good experience with their work and prices. Unfortunately, during my fresh top end job he was braking in a new kid. Turned out the kid broke the actuator arm on both my kdxs before he figured out the correct way.

As far as the sleave resleave confusion. I bought my son's bike used. The seller advertised that it had a fresh top end. Should have been a red flag to me. But I am not supermechanical and bought the bike after riding it. I did not take the top end off to see if the stock piston have ever exploded. Well . . . we rode the bike for a season and it did fine. But when it came time to put a fresh piston into it, it was discovered that the cyclinder was pretty scratched up. I reluctantly went ahead and paid to get it sleaved. In hindsight, next time I might try to get a cyclinder off ebay for about the same price.

Anyway, both bikes are back running good. Thanks for all the help.

Steve

It stinks to pay for other people to mess up your stuff.


Hey....it could've been worse!!!

(I've never been a fan of that view of things..but it is a fact most of the time).

Happy Trails!

This is why I work on my own stuff. "Breaking in the new kid", yup, a new kid that can't read the freaking manual, which very clearly states how to detach the KIPS rod.

I just rebuilt my kid's YZ that was "Maintained at xyz shop" which I bought from xyz shop. The Power valves in that were only half functional because the previous mechanic didn't put the actuator pawl in properly. And this is on a Yamaha, so simple it makes the KIPS system look like a newcular (sic) reactor.