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.

head on over to rec.motorcycles.dirt- lots of very helpful 2strokers
over there.

Dave

wrote:

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.

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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

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.

Leave the muffler off and try it...
Ken.

wrote:

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.

Clean the carb, change the gas _and_ the news group.

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO // Eigenbau-Digitalanzeige
http://www.yadro.de

On 29 Mar 2006 08:57:13 -0800, wrote:

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.

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

wrote:
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.

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.?

--
Gary Brady
Austin, TX
www.powdercoatoven.4t.com

Look at the gas cap, gas cutoff, filter. The carb may be pulling a vacuum on
the tank.

--

Clif Holland KA5IPF
www.avvid.com


"Gary Brady" wrote in message
ink.net...
wrote:
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.

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.?

--
Gary Brady
Austin, TX
www.powdercoatoven.4t.com

Try also to reset timing! It may help!

On Wed, 29 Mar 2006 18:08:07 GMT, Ken Sterling (Ken Sterling) wrote:

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.

Leave the muffler off and try it...
Ken.


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

On 29 Mar 2006 23:18:32 -0800, with neither quill nor qualm,
"Trident.darkstar" quickly quoth:

Try also to reset timing! It may help!

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.


---=====---
After all else fails, read the instructions.
---=====---
Website Design and Update http://www.diversify.com

On Thu, 30 Mar 2006 08:54:12 GMT, with neither quill nor qualm, Gunner
quickly quoth:

On Wed, 29 Mar 2006 18:08:07 GMT, Ken Sterling (Ken Sterling) wrote:

Leave the muffler off and try it...

Excellent idea!!

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.


---=====---
After all else fails, read the instructions.
---=====---
Website Design and Update http://www.diversify.com

Gary Brady wrote in news:BQHWf.9275
:

wrote:
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.

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.?


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.

On Thu, 30 Mar 2006 15:21:18 GMT, mike wrote:

Gary Brady wrote in news:BQHWf.9275
:

wrote:
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.

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.?


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.

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.

On Thu, 30 Mar 2006 05:29:30 -0800, Larry Jaques
wrote:

On Thu, 30 Mar 2006 08:54:12 GMT, with neither quill nor qualm, Gunner
quickly quoth:

On Wed, 29 Mar 2006 18:08:07 GMT, Ken Sterling (Ken Sterling) wrote:

Leave the muffler off and try it...

Excellent idea!!

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.


---=====---
After all else fails, read the instructions.
---=====---
Website Design and Update http://www.diversify.com

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

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.

On Thu, 30 Mar 2006 05:29:30 -0800, Larry Jaques
wrote:

On Thu, 30 Mar 2006 08:54:12 GMT, with neither quill nor qualm, Gunner
quickly quoth:

On Wed, 29 Mar 2006 18:08:07 GMT, Ken Sterling (Ken Sterling) wrote:

Leave the muffler off and try it...

Excellent idea!!

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.


---=====---
After all else fails, read the instructions.
---=====---
Website Design and Update http://www.diversify.com

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

....... 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

"..... 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