ktm 2 stroke

have recently bought a KTM 125 motocross bike. I got this bike cheap as it starts and runs but will not rev to its full potential. I have
fitted a new plug, stripped and cleaned the carb, decoked the exhaust but to no avail. The bike starts first time without any trouble and will rev up to about 1/4 throttle but any more and the whole engine bogs down and will not rev any higher. By holding the throttle wide open it puffs and splutters and tries to blow the exhaust off, I believe this to be a backfire? does anyone have any ideas of where I should be looking to solve this problem. many thanks. nigel.
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head on over to rec.motorcycles.dirt- lots of very helpful 2strokers over there.
Dave
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snipped-for-privacy@yahoo.co.uk wrote:

Please get onto http://www.wikipedia.org and find out the difference between multiple posting and cross posting. One is very rude. The other can be a good thing in some circumstances. Since this post also appears in rec.models.rc.air, however, I suspect that you're well past the bounds of polite cross-posting, even.
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Tim Wescott
Wescott Design Services
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Leave the muffler off and try it... Ken.
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On Wed, 29 Mar 2006 18:08:07 GMT, Ken Sterling (Ken Sterling) wrote:

Excellent idea!!
Gunner
"The importance of morality is that people behave themselves even if nobody's watching. There are not enough cops and laws to replace personal morality as a means to produce a civilized society. Indeed, the police and criminal justice system are the last desperate line of defense for a civilized society. Unfortunately, too many of us see police, laws and the criminal justice system as society's first line of defense." --Walter Williams
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On Thu, 30 Mar 2006 08:54:12 GMT, with neither quill nor qualm, Gunner

While noise is fun, 2-strokes require a certain amount of backpressure (though slight) and a resonating chamber to function properly. They're VERY picky and just a few inches of stinger length can change the torque curve by a thousand RPM. (Or so said my buddy whose Kaw 100 froze up on the freeway at 75mph and gave him a plastic knee. His next bike was a Husky 400 which could dig trenches faster than any known size or horsepower Ditch Witch. That was one scary bike with what felt like a toggle-switch throttle; OFF or WOT. ;)
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On Thu, 30 Mar 2006 05:29:30 -0800, Larry Jaques

Removing the exhaust would tell if the muffler etc was plugged with spooge. Thats all. If it then revs up..you know what the issue is. All one needs do is loosen and let hang the connectore between the head and the down pipe.
Gunner
"The importance of morality is that people behave themselves even if nobody's watching. There are not enough cops and laws to replace personal morality as a means to produce a civilized society. Indeed, the police and criminal justice system are the last desperate line of defense for a civilized society. Unfortunately, too many of us see police, laws and the criminal justice system as society's first line of defense." --Walter Williams
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...... and doncha just luv it when they come here, post a question about a problem, then just "go away" - never letting you know if a solution has been found or not.... damn.... Ken
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"..... and doncha just luv it when they come here, post a question about a problem, then just "go away" - never letting you know if a solution has been found or not.... damn.... "
He didn't go to rec.motorcycles.dirt, either.
dave
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On 29 Mar 2006 08:57:13 -0800, snipped-for-privacy@yahoo.co.uk wrote:

Reed valves are bad? And have you checked the compression?
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3
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snipped-for-privacy@yahoo.co.uk wrote:

Sounds like it might be a plugged exhaust system. I see you've "decoked the exhaust", but have you looked for dirt dauber nests in the expansion chamber or muffler, etc.?
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Gary Brady
Austin, TX
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Look at the gas cap, gas cutoff, filter. The carb may be pulling a vacuum on the tank.
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Clif Holland KA5IPF
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"decoked

expansion

From whats described it could be any of; carb jet blockage, wrong slide setting, slide needle position, choke blockage, airfilter clogged, exhaust blockage, and depending on the year the exhaust powervalve might be seized closed or the operating cable broken or disconnected.
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The one thing I've not seen suggested yet is to check the magneto. I've had the same symptoms from a bad magneto. It would run fine till I tried to push it and then it would start missing till I eased off. I tried everything and finally took it to a dealer who found the bad magneto.
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Try also to reset timing! It may help!
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On 29 Mar 2006 23:18:32 -0800, with neither quill nor qualm,

Yeah, just refile those I/O ports. <bseg>
I'm wondering if the carbs are jetted for that exhaust setup, or if the pipes are plugged. Some friends of mine got into that eons ago and I recall their buying a new exhaust system and having to play with stinger length (and/or size) and carb jetting to tune the bike to top performance. Changes in exhaust scavenging can greatly affect carb jetting.
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Worn crankshaft seal/shaft can lead to loss of crankcase compression. I've heard it's sometimes possible to slap some grease around the outside of seal, restoring compression temporarily for diagnosis.
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