400ex bogs on acceleration.. Too lean?

[troutman561]

Today I was out riding and my friends new to him 02' 400ex would bog down on the trails when giving it gas in 2nd and 3rd. We took it out to an open area where we could open it up and it would bog hard if you got on it. If you took it easy it would get up to almost WOT sometimes bogging, sometimes not. We stopped and looked over everything and the air filter had actually fallen off.. I figured that was the problem and we put it back on but it still happened.. Any ideas?? My friend is at least the 3rd owner of the bike and the previous owner did not know if it had any motor work.. It has the stock pipe with the silencer part removed. From riding it it did not seem any faster than my 400 so I doubt it had any motor work.. Thanks in advance for the info!

[JOHNDOE83]

I had a similar problem once and it turned out that the screws that held the needle in place came loose.

I also had a similar problem on a xr dirtbike, the carb was gummed up from sitting before I bought it.

Id check the carb out, clean every jet with a toothbrush, soak the carb and blow it all out with a air compressor.

Check for air leaks, try again.

Check out the jet sizes while your in there, where in palm beach county troutman?

[trxPOWER]

when i had a bogging problem on hard accel, i found that the need jet was in the wrong postition, try moving it up a notch, and if it gets worse, move it down a notch from where you started. thats what i did and it worked amazingly for me.

[troutman561]

Thanks for the info guys.. Im going to check it out next time I get a chance...




Originally posted by JOHNDOE83


Check out the jet sizes while your in there, where in palm beach county troutman?

And I was in the North Palm area but now am up in the Daytona Beach area at the Chiropractic college up here... I will be done in a year and am planning on practicing in the Jupiter/Tequesta area.

[evan402]

not sure how common my problem was, but when i got my 01 400ex it did the same thing, i cleaned the carb and jets out really well and it still did it. I ended up buying stage 2 kit from dynojet and replaced all my jets with the same size and it fixed the problem. Apparently my jets were plugged and i didnt clean them out good enough.

Hope you figure it out tho.

[troutman561]

Well, I opened up the carb tonight and the main jet was set at 170! I have no idea if this engine has work done but this seems way to rich.. Any suggestions?

[JOHNDOE83]

get me video of the bogging so I can see what its doing?

[JOHNDOE83]

usually, bogging is a lean condition.

[troutman561]

Just pulled the plug.. It is brown, not very black so if anything it is rich. But, the main jet is appears to be a 170 dynojet due to the fact the number is written on the bottom and it takes a flat head to remove. If this is the case that means its at a 190 Keihin equivalent which means it is jetted for a 440 kit???!!! It is definitely no 440... I have a few dynojets left over from my 400ex and I have a 150 Dynojet which is a 165 Keihin. Perhaps I should start there? What about throwing my stock 148 Keihin in there and see what happens? This sucks not knowing what has been done to the machine...

[troutman561]

Well, I put everything back together with a 142 dynojet main ( 155 Keihin eqiv) and now she wont start. Could a main jet that is too small be the cause? I put everything back together as it was but no dice...

Oh yea, I also checked the valves while I had everything off and they were good to go so I did not touch them..