Hello! So I am working on a 2004 TRX400 for a friend and the issue it is having when I got it was it sat awhile and ethanol fuel was put into it (I know that combination is bad). The carburetor was taken apart and cleaned and put back together by my friend and it still ran rough It would only run off the choke and it still ran bad. So when I got it I took the carb back off and figured out the pilot jet was clogged so I stuck a drillbit down it and unjammed it and put it back together. I sat there for probably 2 hours trying to adjust the air mixture screw and kept pulling out the spark plug and no matter what the spark plug was just black indicating it was rich. The screw currently is all the way in (from what I found this is the least amount of fuel) but it runs choppy it. My next thought is to either see if the fuel tank or a fuel line is clogged because the stream into the carb is slow but this wouldn't really make sense if it's running too rich. I've also heard of the choke plunger being stuck open or closed. Now I'm thinking to just completely rebuild the carb but I couldn't see how that would make much of a difference if everything is cleaned and unclogged. The ATV only has about 200 hours on it so I really don't know what I should do now or test. Any input is appreciated I'm just looking for what my next plan of action.

 

First change the plug, bad running doesn't have to be caused by the carb. If it is running rich, usual suspect is the choke not working properly. Most CD carbs use an excess fuel device for the choke and, if it doesn't close, you get excess fuel all the time. It is possible someone fitted a wrong jet or assembled the carb wrongly. I assume you have been messing with the idle mixture screw, the main jet makes more difference, and some have adjustable needles in the CD slide. If you are referring to the 400FA, that carb isn't a good one, why the bigger version used on the 400 and 500, should be more problematic than the small one used on 300 to 450 models I don't know, but worn CD slides and holed diaphragms are common on them.

 

Thanks for the response! So I changed the spark plug and it was no different between the new one and the old one I also check the diaphragm and the slide and the slide works fine and there are no holes in the diaphragm. I took the whole carb apart and cleaned it again today again. How do I check to see if the choke is the reason it’s getting too much fuel?

 

This is how it sounds.

 

nice

 

What

 

Difficult to tell if the excess fuel device is stuck. I can sort of tell from the exhaust smell and sound, but that sound recording is not a 400FA so I assume it is a 400EX and I don't work on them. If the choke feels stiff or doesn't seem to go right down, it is worth removing the plunger from the carb and checking it moves freely and the spring is OK, and that the cable runs free.