05 KDX 220 questions

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fullmetaljacket
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05 KDX 220 questions

Post by fullmetaljacket »

Hey all,,,first off,,great site,,,as soon as I seen it I had to register,,,,,got a couple of questions for ya's,,,I just bought a 05 KDX220R,,so far I love a lot about the bike but it seems like something isn't quite right,,,,if I pull out on the road and hit 6th gear there doesn't apper to be an RPM where the bike will run smooth,,,,no matter what RPM I try to run it at is seems jerky,,almost like theres a miss,,,it's more than just sound, I can feel it in the bike,,but as soon as you hit the throttle a bit more it runs smooth right until it levels out then jerky again,,,almost like it's trying to foul up,,changed the plug and no difference,,,is that normal???? I've had a lot of 2 strokes and never had one run like that,,,,,,,,question 2,,bottom and mid range power is beautiful but there seems to be nothing at the top,,,,revs go up but u can barely feel any pull at all at higher rpm,,,from riding other 2 strokes it doesn't seem right,,,if anybody can help it would be greatly appreciated
AZRickD
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Post by AZRickD »

I have an '03 KDX220R.

Same behavior when I'm riding it down the street to some local trails. I accelerate to speed and then back off the throttle to maintain the speed and it's as if the motor is balancing on a tight rope. Like the KIPS valve is being actuated and unactuated. In a turbo-charged airplane it's called "boot-strapping."

It's an equilibrium thing. Does yours sound like it's rattling?

As for the top end, mine does the same thing to. The motor revs freely up to a point, pulling nicely, and then it just makes more noise. If I'm accelerating in 5th and it does that, I upshift to sixth and it pulls nicely again and then it loses steam as if it needs a 7th gear.

What mods do you have on the bike, if any? (many will be suggested, rev pipe, carb mod, after-market reeds, head mods). They say a rev pipe will open up the bike more. How much more, I've never heard.

"Four-stroking" was mentioned. It ain't 4-stroking.

http://kdxrider.net/forums/viewtopic.ph ... r+stroking

I await the experts.

Rick
Last edited by AZRickD on 09:56 am Aug 31 2006, edited 1 time in total.
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Indawoods
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Post by Indawoods »

A 220 is made for tight trails... it is purpose built.

This is mainly due to the 33mm carb size and the port timing. These can be tweaked to great effect by sending your carb and head into http://www.rb-designs.com and have Ron work his magic. Ron will also get the jetting very close to what it needs to be.

Secondly get a FMF Desert pipe to get greater topend.
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Post by AZRickD »

All that will greatly improve a stock KDX 220.

The rattle will remain.

Rick
I done KX-ed QuailChaser's KDX220R
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Indawoods
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Post by Indawoods »

The rattle is the "KIPS".... if that stops.... your in trouble! :shock:
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****'95 KDX 200/****

"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
fullmetaljacket
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Post by fullmetaljacket »

Yes,,it does sound like it's rattling,,as for the bike,,it's bone stock right now,,,planning on new exhaust front to back,,carb work and reed valves this winter,,,gotta have a winter project,,,tks for the quick answers
AZRickD
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Post by AZRickD »

So, what do we make of the herky-jerky behavior of the engine at constant speed? I take mine down the road at moderate to higher speeds and I get that annoying boot-strapping.

Is this the nature power-valve 2-Ts or is this a peculiarity of the KIPS system??

Rick
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fuzzy
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Post by fuzzy »

It's not a street bike, and it is a 2-stroke. 2-stroke street bikes had valves in the exhaust that worked with the throttle to help cure this....among other things. This surging is common. I won't get into the theory behind it as I don't fully understand it myself, but any directly coupled drivetrain on a two stroke will do this(IE not a variable clutch on a sled, impeller on a ski, etc). I wonder how an auto-clutch equipped bike would act? I will say this...Here is a quote from one of the best kart engine builders in the country. He is a genious, and will blow your mind when talking 2T's....Builds his own pipes, stroker cranks, clutches, and all kinds of neat stuff.

"A four stroke is an air pump to the point that the same laws of physics apply...A 2-stroke has more physically in common with a brass or woodwind instrument" :rolleyes:
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
AZRickD
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Post by AZRickD »

2-stroke street bikes had valves in the exhaust that worked with the throttle to help cure this....
Sort of like a waste gate on a turbocharger that is tuned properly. Of course, a poorly set up waste gate (like a KIPS valve) will cause bootstrapping.

Looks like we'll have to live with it. After all, there is a forum here called "The KIPS Rattle."

Rick
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fuzzy
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Post by fuzzy »

Yeah, Kinda. It's mostly due to the fuel buildup when the slide closes on the carb, yet the engine is still turing xxx RPM. 2-strokes don't know how to decelerate as smoothly. :blink:
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
AZRickD
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Post by AZRickD »

Yep. The solution to boot-strapping in an airplane is to simply increase or reduce the throttle to escape that odd equilibrium.

That points to a fundemental difference between 4t piston airplanes and the venerable 2t with power valve. Airplane engines (piston or turbine) are designed and/or intended to operate at contant RPM (right down to the constant-speed propeller in somewhat more complex planes above the Cessna 172 level).

The dirtbike 2t is an on-off-on-off kind of thing. Whereas the airplane engine RPM can be changed to move away from the boot strapping, moving the 2t throttle to a new position/RPM just brings on another spot where it wants to wiggle the KIPS. A governor could be put in place to moderate that, but it would be more complex.

Rick
I done KX-ed QuailChaser's KDX220R
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