Hi everybody, I have a 2001 Honda 400EX. When it comes to the motor etc. everything is stock. I’ve been having issues with the way it runs lately. Seemingly carburetor issues. I removed the carburetor, disassembled it, thoroughly cleaned it, and installed a new carburetor rebuild kit that I purchased from Dennis Kirk. I put the needle “E” clip in the center position. I started with the Air / Fuel screw lightly seated and I backed it out 2.25 turns. The ATV starts right up and idles nicely, the engine revs just fine when I’m in neutral. Then I shift into 1st gear and start to ride, if I accelerate slowly things are okay. (The choke is off and the wheeler is warm.) (The gas is new / good, and my air cleaner is clean.) If I accelerate even semi-fast the motor bogs down. I’ve tried adjusting the Air / Fuel screw in and out by quarter turns, with no luck. I believe the furthest out that I turned the screw was 3.5 turns; I also turned it in as far as 1.25 turns from seated. I’ve also tried to turn the choke on to different degrees while I was riding to see if it would affect the bogging down. When I turned the choke on it would bog the motor down even worse, so I assumed that it was getting too much gas.

So I decided to try moving the “E” clip down one notch, raising up the needle as a test. I had the Air / Fuel screw backed out 2.25 turns for this test, and the wheeler barely ran.

I guess I’m not sure where to go from here. If anybody has any suggestions on what to try I'd greatly appreciate it! To be honest I’m getting fairly frustrated with this.

Thanks,

Dan

 

Have you pulled the plug, to see what color it is? No exhaust/filter/etc? or...? I had similier problems with a foreman 450 but I increased the main jet a size or two, then played with the air/fuel screw and finally got it to run just fine. If you can't get it running right with raising or lowering the needle mixed with the air/fuel screw, I'd up the main jet. Then repeat the raising and lowering of the needle, while playing with the air/fuel mixture. Cover half the stock airbox snorkel up and see how it runs. If you cover half the airbox snorkel up (tape or something), then the bike is running to lean and by cutting off half the air the bike is running fine. So then you'll have to take that into consideration and make those changes in the carb to fix that problem.

Anyways, rambling really. But take a look at the plug and see what color it is and we'll go from there.

 

if you think you are to rich a way to check is to take off your airbox lid if the problem gets better I would say you are to rich. I don't understand why a totally stock 400ex would start running rich.They are notorious for being lean from the factory. I agree with the above poster. If you want to know what your situation is you should pull the plug.

 

http://www.bikebandit.com/oem-parts/...14553#sch98409

 

Hi, I have had this same exact issue with my '03 400ex. I am assuming the rebuild kit included the jets. I would change the main jet back to the original and reset the clip. You can get to the main through the float chamber cap, but if not then you will have to remove the float chamber... My reasoning: If it started fine before you moved the clip then it was probably good there. As far as I know the high RPMs rely on the main jet, if it is too rich at high RPMs then the main jet needs to be smaller in my opinion... And I would assume the new main jet is too large. I used a rebuild kit and the numbers on them matched the original, but when put next to each other they were clearly not the same. I went through the same problems you are having, and after about 6 months of it sitting in the garage I swapped in the old jets one at a time just as a last effort to get it running, and the main jet fixed the problem. This is my first post, I just joined the forum 10 min ago, hope this helps, good luck.