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Hesitation and stuttering at constant throttle

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Hi just joined thumper talk so I'm new to this post thing and stuff. I have a 2004 crf450r that is having problems. I have cleaned out the carb to try and solve the issue but didn't fix it. Here is a video that shows exactly what it's doing. Thanks!

 

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Thats not the carb. That's electrical. Id bet there's iron debris on the coil pick up contacts on the stator. Pull the stator, wipe the debris off the soldier points. It should run fine afterwards. But while youre in there, remove the timing chain tensioner and grab the crank and see if there's ANY play in it UP AND DOWN. In and out isnt a big deal, but up and down is. If there is, you can look at a new left side main bearing. The debris, I suspect is coming from the bearing cage on the left side of the engine.

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1 hour ago, Shawn_Mc said:

Thats not the carb. That's electrical. Id bet there's iron debris on the coil pick up contacts on the stator. Pull the stator, wipe the debris off the soldier points. It should run fine afterwards. But while youre in there, remove the timing chain tensioner and grab the crank and see if there's ANY play in it UP AND DOWN. In and out isnt a big deal, but up and down is. If there is, you can look at a new left side main bearing. The debris, I suspect is coming from the bearing cage on the left side of the engine.

Will I need to get a new case gasket?

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I was able to replace the crank bearing on my 1976 RM-125 with out splitting the case.  I don't know about doing it on a four stroke.

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1 minute ago, GlennRay said:

I was able to replace the crank bearing on my 1976 RM-125 with out splitting the case.  I don't know about doing it on a four stroke.

sorry I meant for the cover

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On the RM that cover gasket did not seal up internal oil, it only kept out dust and dirt.  I would think that you should be able to re-use your gasket as that stator assembly is not designed to operate in an oil bath.

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You have to split the cases to replace the bearing. You'll probably need a gasket. But every once in a while, ya get lucky.

Start with the stator cover, go from there.

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I had to do this on my 1979 349 Montesa Cota and one thing that I found very helpful was to put the engine cases in the oven and heat them up to 150 ~ 200 degrees.  This expanded the aluminum and allowed the bearings to be tapped out with a hammer and punch with ease.  When it came time to put the new bearings in I put them in the freezer over night and then warmed the engine cases back up again.  The bearings practically fell into place.  Make sure that the engine cases are clean of all oil and solvents before you put them in the oven!

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I just checked the stator and didn't see any debris. Wiped it down just to make sure. Tomorrow I'm gonna go get a new cover gasket and check over the stator a little more. Hope this works!

Edited by Brayd24

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22 hours ago, Lead Head said:

Does it only do it at that particular throttle position?

Yes mostly, but sometimes on slowly increasing speed.

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4 hours ago, Brayd24 said:

Yes mostly, but sometimes on slowly increasing speed.

I'd suspect a carb issue still then. Or possibly a TPS problem.

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Waiting far a gasket now because there is no shipping over the 4th:lame:  Will have to see if cleaning the stator works. If not I will look into the TPS.

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You can unplug the TPS and you wont notice anything.

Does it idle fine? Starts right up...like 1-2 kicks?

About the only thing that could make it run like that, if it was a carb issue, would be something floating around in the bowl that's getting sucked up into the main jet and plugging it. Not impossible, but unlikely. Could be a bad stator too.

A customer brought me a bike that had a Baja Designs lighting stator in it that was over driving the CDI box. Did that exact thing.

Some basics might be handy. Clean the spark plug boot etc. New plug, and if it does it again check the stator. You need to do this when the stator is warm. You could set the oven at 180F get it nice and warm and then check the resistance. 

 

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2 hours ago, Shawn_Mc said:

You can unplug the TPS and you wont notice anything.

Does it idle fine? Starts right up...like 1-2 kicks?

About the only thing that could make it run like that, if it was a carb issue, would be something floating around in the bowl that's getting sucked up into the main jet and plugging it. Not impossible, but unlikely. Could be a bad stator too.

A customer brought me a bike that had a Baja Designs lighting stator in it that was over driving the CDI box. Did that exact thing.

Some basics might be handy. Clean the spark plug boot etc. New plug, and if it does it again check the stator. You need to do this when the stator is warm. You could set the oven at 180F get it nice and warm and then check the resistance. 

 

It's starts amazing, pulls super hard, idls good. The only problem with it that I can see is the stuttering. I cleaned the carb already but that did nothing. Waiting for a gasket to see if cleaning the stator will fox it or not. Change spark plug couple weeks ago didn't help.

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Pull the slide on the carb and see if the needle clip is in position and secured in the slide. Running to rich will stutter like that. There is also a small leak jet in the bowl and if plugged will deliver too much fuel from the accelerator pump at low throttle position. Make sure it is not plugged. The video does not show if the stuttering quits after the pump duration is complete. So, steady state throttle where the issue is seen and wait to see if it clears.

Also, pull on the coil wire where it connects to the blue boot. It should be snug. Often times the wire inside gets corroded and needs to be cut off and re-inserted. I like to safety wire the blue boot to the inserted wire.

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On 7/4/2017 at 10:58 AM, Shawn_Mc said:

Did the bike ever have lights on it?

nope no light on it.

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On 7/4/2017 at 9:28 AM, Rocksalt said:

Pull the slide on the carb and see if the needle clip is in position and secured in the slide. Running to rich will stutter like that. There is also a small leak jet in the bowl and if plugged will deliver too much fuel from the accelerator pump at low throttle position. Make sure it is not plugged. The video does not show if the stuttering quits after the pump duration is complete. So, steady state throttle where the issue is seen and wait to see if it clears.

Also, pull on the coil wire where it connects to the blue boot. It should be snug. Often times the wire inside gets corroded and needs to be cut off and re-inserted. I like to safety wire the blue boot to the inserted wire.

All good ideas

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