Honda trx400 ex

I know I could post this in the atv forum, but, I really don't want to  wait 3 months for a response. 

I got a real head scratcher. This quad starts and runs fine. If I rev it up without the airbox on it, it's fine. However, when I do that, there's what appears to be a fine mist/spray coming out of the carb. If I put the airbox on, no filter, and try to rev it out, it blubbers badly due to too much fuel, and  black smoke comes out the exhaust. Also, the choke flapper wont stay closed all the way. It closes partially. WHen I got it, it had a zip tie holding the choke open. I'm at the end of my rope. :(

The fine mist you see coming from the mouth of the carb is perfectly normal, it's called reversion and happens when the intake valve closes, forcing the moving fuel/air mixture to rebound back into and through the carb. It gets sucked into the engine as soon as the intake valve opens on the next cycle.

The choke butterfly (it actually has one instead of an enrichener knob?) not staying fully open is causing your rich jetting condition, or at least contributing. It sounds like it's time to fully service the carb.

Edited by The Spanky
3 minutes ago, The Spanky said:

The fine mist you see coming from the mouth of the carb is perfectly normal, it's called inversion and happens when the intake valve closes, forcing the moving fuel/air mixture to rebound back into and through the carb. It gets sucked into the engine as soon as the intake valve opens on the next cycle.

The choke butterfly (it actually has one instead of an enrichener knob?) not staying fully open is causing your rich jetting condition, or at least contributing. It sounds like it's time to fully service the carb.

The kid tried to explain to me what it was doing. I didn't run it first, either. But, I took the carb off and cleaned it thoroughly. And it wasn't really dirty to start with. I zip tied the choke like it was when I got it, so that's not it. Idk what the purpose of this little flapper is on the choke butterfly. This is where  the airbox connects. I'm thinking that maybe the thing is running right on the edge of too rich. Then any  restriction  in the airflow puts over the edge. I put a new plug in it, and hooked up an aftermarket coil, and those didn't help.

 

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