Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: MyckMcClung on April 24, 2017, 11:57:42 AM
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2007 KX250, jetting is perfect, float level is perfect, stock carb is clean as it gets, ultrasonic and brushed. cleaner than from the factory.
All vent hoses are new no pinches, new fuel line, with inline filter, flowing fine, installed to hopefully eliminte the following issue, with no results.
V-force3 reed block, fmf gnarly, T2. no compression leaks.
Here's the situation, and I'm at my witts end trying to narrow it down.
Fast shallow whoop section, in the pipe 4th gear, second bump, goes lean, like I'm running out of gas, I chop the throttle, the slide closes, pull in the clutch, still screamin it's head off, feather the clutch and it drops back down to normal Idle. it only does this in this same condition, smooth straights no issue, only in the whoops, or in a heavy G-out and it is inconsitant, as in it doesn't do it every time, but those are the conditions where it occurs.
I have checked the float height, I have replaced the floats, and the fuel needle, cleaned the seat, all of the circuits in the carb are clean and smooth.
The only possible conclusion I can conjur is a cracked reed on the bottom of my reed block...I haven't pulled it yet to look.
Any experience with this issue on a 05-07 KX250 would be helpful. thanx in advance, I'll let you know about the reeds when my replacements arrive
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whoops you say? try a boyesen super bowl.
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if they made one for this carb I would already have it.... sadly the cut off is 94.. from what I can tell
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after comparing pics, it looks like it might fit, but man I hate to spend $100 on something that might fit....
but it's not bogging....it's acting like it's starving for fuel
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That is an interesting one.
At first you might suspect the floats but in a G-out situation the floats would be forced into the open position not the closed.
Stuck open reeds will actually create a rich condition because the air moves back and forth through the carb picking up an extra fuel load. Early bikes without reeds used to load up really badly at low rpms because the air would change directions 2 or 3 times.
Have you carefully inspected the carb boot for cracks? In a hard G-out the carb can move down a surprising amount and may open up a crack you can't readily see. Try pushing the carb down and see if something appears.
Also check your throttle cable for enough slack. If the carb moves down and the cable is too tight it can pull the slide up.
Some of the things you think are stationary really aren't when the bike is under a G load, I would be looking for things like that that would fit your issue.
--Ron.
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thanx Ron, it's coming apart next week, I think(hope) it's a bad reed valve/boot gasket, there arent any tears in the boot.
gonna do a leak down 1st in an attempt to eliminate the possibility of a stator crank seal
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Push on the carb when you are doing the leak check and see if it has any impact.
It seems like it has to be something that is moving under certain circumstances that normally sits still.
Let us know what you find, I'm very curious to know what it ends up being.
--Ron.
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Wow this is a tough one... I agree with Ron's assessment that something is moving causing the lean condition. It has to getting the additional air somewhere. I think a leak down test is a set in the right direction. I also agree that while doing the test, you'll need to really look at the carb boot for any issues.
Good luck and let us know what you find. :-\
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What did you find when you tore it down?