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03 CRF 450 Basket case Please Help

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Posted by: PAB670---------------------

My buddies 450 stumbles and sputters at 1/4-1/2 throttle not sure why, We have taken parts off of my bike and tried them on his and still no change Here is a list of what we have done

changed CDI,TPS,COIL,STATOR, PICK UP COIL, SPARK PLUG, AIR FILTER ,FUEL
NEW INTAKE VALVES 2 WEEKS AGO and we did a leak down test. Als checked the head pipe for cracks its ok. I put his carb on my bike it ran fine we have checked all the wiring connections they look good. The bike runs ok when cold after doing 5 laps on the track it starts to act up and just gets to the point were you can't ride it safely. It runs fine wide open let off and try to accelerate and it stumbles mid range is awful tried riding it at half throttle and it skips badly. Any ideas?
Thanks for any help

The only thing's we have not done is change out the fly wheel and put my carb on his bike

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MOTOCROSS== No Time outs, No pit stops. That's what other sports are for




Posted by: Ol'89r---------------------

[QUOTE=PAB670]My buddies 450 stumbles and sputters at 1/4-1/2 throttle not sure why, We have taken parts off of my bike and tried them on his and still no change Here is a list of what we have done

changed CDI,TPS,COIL,STATOR, spark plug,filter,fuel
The bike runs ok when coldQUOTE]

PAB670.

Check your pick-up coil. It is the little coil near the flywheel. They are affected by heat and will act as you described when they go bad.

Just my $ .02


Posted by: PAB670---------------------

i tried the pick up coil when we did the stator. Thanks for the help


Posted by: turboandy---------------------

You are fat, the fact that your motor is only acting up at 1/4 -1/2 throttle openings tells you it is in the carb. Ignition is not going to act up only at specific carb openings but rpms. I agree about the ignition heating up but your problem is going to be in the carb. The other strong indication is when it is cold it is ok. A cold motor likes to be richer than a warm motor. Check the carb and clean it. If you are mistaken and the engine is not only acting up at 1/4-1/2 but only when hot check the valve and decompression clearance then ignition.


Posted by: Ol'89r---------------------

[QUOTE=turboandy]You are fat,


the fact that your motor is only acting up at 1/4 -1/2 throttle openings tells you it is in the carb. Ignition is not going to act up only at specific carb openings but rpms. QUOTE]


HEY! Don't get personal. (jk)

turboandy is correct. Although, I have seen the pick-up coils come loose in some of the XR motors and they will act very similar at low to midrange. Thought it was worth checking.

Check your hot-start system. If the hot-start valve is not closing all of the way it will make your engine stutter on bottom.

It should not change with a hot or cold engine but, a bent needle in the carb will cause a similar condition. When you changed the carb, did you also change the needle or use your existing slide and needle? If the needle is straight, check the needle jet/ emulsion tube. Make sure the jets are in place and tight.

Just my $ .04


Posted by: a454elk---------------------

I can attest to the hot start button problem, makes it extremely tough to keep at a decent idle as well.


Posted by: turboandy---------------------

hey Old89, I did not mean to insult you, if I did I am sorry we cool ?


Posted by: turboandy---------------------

http://www.thumpertalk.com/forum/sh...5/o/all/fpart/1


Posted by: Ol'89r---------------------

Quote:
Originally Posted by turboandy
hey Old89, I did not mean to insult you, if I did I am sorry we cool ?


Andy. Just foolin' with ya buddy.

It's pretty hard to insult me. Elk's been trying for years now and it just aint happening.


Posted by: PAB670---------------------

Ok case solved we replaced the the needle and nozzle and the floating side of the slide. BIKE RUNS GREAT I also found that the top cover was not sealing due to the locating tabs were to long so dirt was getting sucked into the carb. So I filed down the tabs and it seals mint.. Again Thanks For all the help....

--------------------
MOTOCROSS== No Time outs, No pit stops. That's what other sports are for



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