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dirt bike bogging? Answered

i have this crf150rb and i will let it idle for about ten minutes to warm it up then try to give it a fast throttle wile its in nutrule but it will bog out and sometimes kill the bike but if i rev it slow then i stop reving it it will idle really high like it is still being reved. so me and my dad took out the carboratour and cleaned the jets and the jets were clean so we replaced the lean and ritch screw because we relized the top was broken on it so wee adjusted the leann/rich screw and we put the carb back on and nothing changed so we have no idea what is going on can anybody please help im desperate!!!!!


Quercus austrina

2 years ago

As I'm sure you know, the purpose of the carburetor is to provide the correct air to fuel mixture for the required rpm, all the while maintaining that mixture ratio at or very near the optimum of 14.7 to 1 (14.7:1) , air to fuel. This means that when you open the throttle, the butterfly valve, or in your case of the Keihin carb, the slide valve, allows more air through and then needs to add more fuel to keep the mixture right. When you "whack open" the throttle, it needs to have a shot of fuel added immediately until the feed circuit can catch up. This is done by a mechanism normally called an Accelerator Pump, which gives a measured shot of fuel into the airstream of the carb, the amount which is dependant on how far and how hard you open the throttle.

1. Now, since you can slowly open the throttle and the engine runs okay, it sounds as if your accelerator pump is stuck or dirty, preventing it from responding as needed. I'd take the carb apart again and thoroughly clean it and make sure all deposits are removed before further inspection. Look at the accelerator pump (it may be called something else, but still does the same thing) and make sure it moves easily, but does not have excessive play in its stroke, otherwise, it may bind, preventing it from moving. Once you have everything working as it should, reassemble the carb and try it.

2. You say that when you slowly run it up and then let off, it sounds as if it is still running at a fast / high idle. Is your slide valve or throttle cable sticking? Once you let off, the slide valve should return to its resting position and drop the airflow to the minimum needed to idle the engine.

3. This is the, ahem, fun part. According to the factory website for your bike, the current model comes with a TPS, or Throttle Position Sensor. Is the connected and working properly, are the wires in good shape all the way to whatever controls it? Is that module / computer functioning properly? For the answer to that, you'll need to speak to someone who has experience with them, most likely a factory authorized technician. I will defer to that person.

All that being said, here is a link you should peruse:


Good luck!



3 years ago

Check the air filter. If the carb has been serviced, then it's possible that you simply overlooked the next issue... air intake.


3 years ago

It's quite difficult to parse your spelling and grammar - can you give a more "technical" definition of "bog out"?