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Hi everyone,
I'm hoping someone out there can get me pointed in the right direction! I acquired an '05 Foreman 500 (TRX500FE) that had been sitting for at least a year. Before running it I drained the gas and rebuilt the carb with a standard carb kit. I'm having a hell of a time getting it to run smoothly, though. The engine backfires/sputters and misses every few seconds. I replaced the pilot screw with the new one in the kit and started it at 1 1/4 turns out. For a while, it would do this crazy thing where in neutral, it would idle normally for a few seconds, but would then gradually start creeping up in RPM. It would get so high that I had to just kill the engine. I took the carb apart again, cleaned everything once more and got it back together. It doesn't seem to have that problem anymore, but is still backfiring and missing. Other details that may or may not be important:
1) I have done nothing to check or adjust valves - is it common for them to need adjustment?
2) Spark plug is the one it came with (age unknown) but looks fine
3) Sometimes I can't get the thing started at all - it will sputter a bit, then it appears to flood out and won't start again at all until it sits for a while.
4) The choke knob is pushed out a little bit (about 1/16" - 1/8"), but I think the needle is seated because when I hold the knob in it doesn't seem to have any effect.
5) The idle speed knob was completely loose when i got it, so i I don't know if I have that set right. In other words, I can get the idle speed correct by a combination of adjusting the idle knob and the pilot screw, but I have no idea if I have the idle knob at the correct starting point to begin with. I can't seem to find any information on how far open the throttle plate should be at idle.

Sorry for the long post, but Ii figured I'd try to anticipate as many questions as possible. So, any ideas?
 

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Yeah I got a few... firstly, if the carb kit you put in it was not a genuine OEM Honda carb kit, it is probably useless china junk and you'll need to take the carb back off and put all of the original parts back in it, except for rubber o-rings & gaskets ONLY, assuming those all fit correctly? I recommend thoroughly cleaning the carb again while you have it apart and blow all the passages clear. Assemble the carb by following the factory service manual word-for-word. Take no shortcuts and do your best on it and you'll be a winner!

1) Yes, after 12 years your motor probably needs a valve adjustment unless it has been regularly (& professionally) maintained throughout its past. If not it is long overdue... along with a gazillion other regular maintenance routines.

2) Replace the spark plug with a brand new NGK properly gapped. That is one less item you'll have to question, and its part of routine maintenance.

3, 4 & 5) See the comments above concerning your carb.

You can get a copy of the FSM for your Foreman HERE. If you have any questions please let us know.

Welcome to the forums!

Edit:
Thank you for your longish post! Please don't ever apologize for that! I for one, very much appreciate seeing all of the information you got... in one spot!
 

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I think backfire is a lean condition. I would check to see if your carb is fully seated in the intake boot and that the boot is tight on the head.
The rise in throttle suggests to me perhaps a fuel flow constraint, such as blocked or kinked line. So check float pin fully seated
 
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