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Running lean(?) while doing wheelie

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Hi! I am struggling with this. I have got my keihin fcr 41 mx tuned in really good. It runs great across whole register. Super easy to start. (its a crf450x btw) 

Problem is, while doing wheelie, it always bogs out. I believe it runs lean, but not sure. Short wheelie is fine, but longer, it always start bogging. 

My question is, how the heck do I make it run clean even when doing wheelie? Or do I need fuel injection in order to make it work properly? 

Higher float level? 

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Ridding a wheelie is going to make it richer. The problem is, a carb float is designed to be mostly level-ish. Any extreme positions for extended periods are a problem. MX bikes do not run in street wheelie style for long enough to be a issue. To fully resolve, you need FI. You will also need to ensure oil pick in the engine is continuous. Extended wheelies can oil starve the engine.

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52 minutes ago, William1 said:

Ridding a wheelie is going to make it richer. The problem is, a carb float is designed to be mostly level-ish. Any extreme positions for extended periods are a problem. MX bikes do not run in street wheelie style for long enough to be a issue. To fully resolve, you need FI. You will also need to ensure oil pick in the engine is continuous. Extended wheelies can oil starve the engine.

Ok, thanks for your input! What can I do to make this less of an issue then? Smaller hole where float needle sits? Lower float? 

Over fill oil a bit? 

 

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47 minutes ago, Stefan.mx said:

Ok, thanks for your input! What can I do to make this less of an issue then? Smaller hole where float needle sits? Lower float? 

Over fill oil a bit? 

 

Not a lot can be done without extensive rework. If you lower the float, it will run leaner all the time forcing you to install rich jets for the times you wheel stand and then you are back where you started. You are trying to make a machine do things it is not designed to do. You can confirm, the float height is right (8mm) but otherwise, you are fighting gravity. You need EFI. You could try and set the carb at an angle using a different intake manifold to make it more level during wheel stands but not so steep as to make running on flat ground a issue.

Adding oil will simply get blown out the beather. Adding a external sump and a reflowing catch can can work, as can relocating the oil pickup, but that is a lot of work.

Stunters build a bike for vertical work, if that is your goal, TT is not going to be the best source of information.

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“Spitfires Fatal Flaw” is what ya have there.

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25 minutes ago, William1 said:

Not a lot can be done without extensive rework. If you lower the float, it will run leaner all the time forcing you to install rich jets for the times you wheel stand and then you are back where you started. You are trying to make a machine do things it is not designed to do. You can confirm, the float height is right (8mm) but otherwise, you are fighting gravity. You need EFI. You could try and set the carb at an angle using a different intake manifold to make it more level during wheel stands but not so steep as to make running on flat ground a issue.

Adding oil will simply get blown out the beather. Adding a external sump and a reflowing catch can can work, as can relocating the oil pickup, but that is a lot of work.

Stunters build a bike for vertical work, if that is your goal, TT is not going to be the best source of information.

Got it. I will then simply try my best to appreciate what I got and see it for what it is. Thanks again for your information.

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25 minutes ago, Chisler said:

“Spitfires Fatal Flaw” is what ya have there.

Had to watch Youtube for that one. Interesting piece of history 👌👍

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10 minutes ago, Stefan.mx said:

Got it. I will then simply try my best to appreciate what I got and see it for what it is. Thanks again for your information.

Don't blow off Williams suggestion of checking for proper float height. If it's off by a mm or even less, it could make a difference.

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4 minutes ago, Trailryder42 said:

Don't blow off Williams suggestion of checking for proper float height. If it's off by a mm or even less, it could make a difference.

2X - Always ensure adjustments are correct. Follow the manual precisely when setting the float. Sometimes,. perceived issues are just something that needs adjusting and is the source of the problem.

LOL - Float bowls should be on gimbals.

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4 minutes ago, Trailryder42 said:

Don't blow off Williams suggestion of checking for proper float height. If it's off by a mm or even less, it could make a difference.

Sure, but I did a complete rebuild of the carb just a couple of days ago, including lowered the float. What I did to measure the level was that I made sure it was perfectly parallell with the lower part of the carb, just where the float bowl meets the carb. That should be fine, right..? 

And as I said, it runs very clean now. Only issue is when doing long wheelie close to balance point. 

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13 minutes ago, Stefan.mx said:

Sure, but I did a complete rebuild of the carb just a couple of days ago, including lowered the float. What I did to measure the level was that I made sure it was perfectly parallell with the lower part of the carb, just where the float bowl meets the carb. That should be fine, right..? 

And as I said, it runs very clean now. Only issue is when doing long wheelie close to balance point. 

You are supposed to hold the carb at a 45 degree angle so the tang on the float is just touching the pin on the float needle and not depressing it. The float is to be 8mm from the gasket surface.

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3 minutes ago, William1 said:

You are supposed to hold the carb at a 45 degree angle so the tang on the float is just touching the pin on the float needle and not depressing it. The float is to be 8mm from the gasket surface.

Thats exactly what I did, but instead of measuring 8mm,i just made it parallell. Anyway, thanks.

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OP. Try playing with the float level, it wont hurt.

Tilt your bike up to balance point and make sure gas flows out your petcock properly.

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