I have a customers Honda 500 Foreman here.... Didn't run, wouldn't start when they brought it to me. Starts instantly, idles perfectly, runs very well until until mid range but then starts missing. If I go into the throttle gradually, runs better, but still misses...no popping, and actually sounds like an electrical issue.
Here's what I have done to it.
- Rebuilt the carb, all new parts/kit, and verified the jets were the same
as the ones removed. Cleaned it in an ultra-sonic washer, as I do all my
carbs.
- Pulled and went thru the carb again, verified no holes/tears in the
diaphragm....carb is spotless, inside and out
- New IR spark plug
- New battery, verified charging, 14.3 VDC at idle...slightly more when
revved
- Drained old fuel, added fresh, new fuel.
- Super clean air filter
- Inspected spark plug boot...looks good ( little wire in boot is there and
looks good).
Seems like a fuel issue, but I don't think it is as I have built literally hundreds of carbs. Any ideas on this? I know that these 500's have a TPS....but never had one fail and as of yet, I have not purchased a manual. I will if needed and the $5 is insignificant.....just have so many on my PC...and may never need it again...

 

"Old timers" way of checking if it is an electrical problem is to hook up a timing light to the plug wire. When you rev it up and it misses,if the light flickers in unison with the miss it's an electrical problem. If the light is continuous then still probably carb or fuel related or some other problem area.

 

There was a recall on the 500 TPS. Honda had routed the wires so water could get in and run down into the TPS. No idea if this has anything to do with your problem as, on the only one we had, a new TPS didn't cure it, though we thought it had. The owner found the fault after we had given the bike back (embarrassing), it was a wire chafing on the frame somewhere, giving an intermittent misfire.

 

Thanks OPT, I have actually done this before for idle and low RPM missing, and it works! May try it on this machine as well but it's missing in the mid to upper RPM range and not sure I will be able to see it. If it is the carb....then I'm at a loss....
Thanks merryman, I may have to inspect the wiring...it's seems to be electrical but at times I can get fooled.

 

Tried a few more things on this Honda.
- Removed and cleaned petcock....it was fairly clean
- Checked the coil connections, all good.
Still does not want to take throttle unless it's "eased" into, then still misses a bit. The problem it has would seem typical of a hole in the carb diaphram, but I could not find a hole. Also typical of a bad spark plug...but replaced with a new one...same thing. Owner is going to take it as is for now, and bring back to me in a couple of weeks. When I get it figured out, I will post the results.