Idle stays high after rev'd

[Extremerider]

I have an 04/05 TRX450R with an 04 CRF250R carb bored to 42.5 mm's. I am running a 162 main jet, 45 pilot jet, HRC needle with the clip in the 4th position, and a 55 leak jet. My head is ported, I have an HRC cam, CP 13:1 piston, and a pro design pro flow kit with a Uni air filter. I run VP110 fuel straight.

I have 14 hours on this setup, and the quad runs amazing, except the idle stays high for a little bit after I rev it. This has been going on since April.

Tonight I decided to diagnose the problem. There are no air leaks, I installed a brand new throttle cable, and made sure the cable was adjusted properly. Still my idle stays high after I rev it.

Logic would say I'm running lean. Here's where things get interesting, when I closed my air fuel screw my quad stayed running and didn't miss a beat. When I pressed in my hot start lever the quad rev'd up slightly. This led me to believe I'm running rich. Dropped my pilot to a 42 and a 40, still rich and I can still close the air fuel screw without stalling the quad. Dropped my main jet to a 158 and then a 152 still rich (closed a/f screw still runs) and the quad still runs fine, and the idle still stays high after I rev it. Leaned out my HRC needle, no change.

Tomorrow I am pulling my carb apart and cleaning everything. Can anyone think of anything that could cause my idle to stay high after I rev it, and also make it seem like I'm rich? I'm guessing there's a clog somewhere maybe.

And yes the plate on my slide is facing the right direction.

Any help would be great. Thanks

[blacknblue#2]

Be sure you have a full air fuel screw assembly. Spring, washer and a good undamaged o-ring. Can you change the idle of the quad at all woth the a/f screw. Obviously cranking it in has no effect but what does it do if you start cranking it out?

[fastredrider44]

Are you running a stock carb spring? Still have the spring in your throttle housing? Make sure your cable is routed correctly.

[Extremerider]

My timing was off by one tooth. Straightened that out, but still have a hanging idle. It helped with the air fuel screw, and now when I close it the quad dies. Still running the stock carb spring. Something is definitely off with the throttle though because after I pressure washed the quad my throttle was getting stuck. It cleared up at the end of practice yesterday before my race, but something is definitely off. I am going to take the carb apart again this week. I have a feeling the o-ring on the slide is shot, but I'm sure there's something else going on.

I also figured out after the weekend that the idle does not get hung up when its cold. Only when things are up to temperature does the idle stay high for little bit after I rev it. It does eventually fall back to the normal idle, but it takes a minute.

[blacknblue#2]

My timing was off by one tooth. Straightened that out, but still have a hanging idle. It helped with the air fuel screw, and now when I close it the quad dies. Still running the stock carb spring. Something is definitely off with the throttle though because after I pressure washed the quad my throttle was getting stuck. It cleared up at the end of practice yesterday before my race, but something is definitely off. I am going to take the carb apart again this week. I have a feeling the o-ring on the slide is shot, but I'm sure there's something else going on.

I also figured out after the weekend that the idle does not get hung up when its cold. Only when things are up to temperature does the idle stay high for little bit after I rev it. It does eventually fall back to the normal idle, but it takes a minute.

I wouldn't lay a tire on an mx track with a sticky throttle. I once rode a wheelie with a sticky throttle and it cost me every square inch of skin on my back haha

[Extremerider]

Been almost a year since I posted this, but have some updates in case anyone else experiences this.I replaced the oring on the slide, as well as the fuel inlet, and fuel inlet orings. Problem solved! Only took me a year or so!