atc high idle problem

[hondamanshawn]

Hi guys I could really use some help on my 81 atc 200. It starts right up on first or second pull but idles very high, it revs up when the throttle is hit without cutting out. let me give a run down on it, i hooked a mini tach up and it says its idles around 3000 rpm! I try to adjust the idle and fuel mixture screw but doesnt even act like im touching them, if i put the choke on it idles a hair higher but nothing changes, I have a sigma 6 jet kit but right now the jets are in that came with the carb (pilot-45 and main-95) I have tried diffrent jets and the needle clip at every possition without any change in idle what so ever. . The motor was rebuilt and has some new parts on it here is the list-it has new piston, rings, valves, valve seats cut, valve seals, ignition coil, magneto (used), pull start (used), plastic gas tank and petcock, knock off ebay "Keihin" carb, cone style filter, aftermarket exhaust, stator exciter coil, spark plug. It has other new parts but most likely not relevant to the idle problem. The motor has all new gaskets and o-rings. The valves are adjusted to spec (.002 in), the valve timing is set correctly, the ignition timing is set correctly and cdi air gap is set correct (.3 in), the cdi ohms out with in spec (50 ohms), the stator exciter coil ohms out with in spec (243 ohms). I looked around for air leaks but couldnt find none I sprayed starter fluid around the intake with no diffrence to the idle. The air filter is right on the carb witn no air box. I checked to make sure all wire connections are tight. I get good blue spark when starter is pulled. The plug looks a little wet with oil but cleans right off I figured it is normal intill the motor is broke in. it smokes a little puff when started but then thats it. Any suggestions and help would be greatly appreciated and sorry about the long post.

[Liquid-Darkness]

Sounds like maybe a real bad air leak from the intake. That or your throttle cable is kinked somewhere and causing it to get stuck opend. Probably near the thumb lever area. Thats all I can think of. :beer

[jb2wheels]

First, verify the slide and throttle cable are OK.

I think you're super lean with a 95 main jet along with an open air filter and pipe.

The 45 pilot ought to be close but I'd put a 110 or so main in there and see if it helps. Might need even bigger.

[AbnMike]

Yes, check that the slide isn't binding - reach in there and lift it up and down with your finger. Move the throttle by hand and see that it goes up and down easily, no matter the position of the bars (that is important). Right, left, center, etc. Make sure in every position the slide goes up and down. Also make sure that the slide does NOT go up and down when you move the bars.

If that's not the case your idle jet is likely blocked.

Also, very important, you need to wait 20-30 seconds everytime you make an adjustment to your idle or your a/f mixture. The biggest most common mistake I see when people try to adjust is that they adjust, listen, then move the screw again. You have to wait for the change to take effect, it's not like you're adjusting the timing. You're adjusting a mixture that has to still be mixed, then burned. 1/4 turn. Wait 30 seconds, listen, then 1/4 turn. Repeat. It takes a while to do.

here's what I'd do if I were you:

1: Check the operation of the slide like above. In every position. If it is good then remove the carb. Soak it in carb cleaner after you take it apart. Let it sit in that stuff for a day (not spraying it, the stuff you buy in the gallon can at an Auto parts store).

Blow it out with compressed air (if you don't have a compressor, then buy some cans of air. Don't huff them, you don't want to become retarded).

Check your jets, especially your idle jet. Tiny pieces of grit can get stuck in them and it will screw up everything. Make sure if it has a hole, that hole is clear.

Reassemble everything. Make sure that all your rubber is good, etc.

Now see what happens.

[hondamanshawn]

ok I will double check everything but Im sure the throttle cable and slide work fine I put the slide on the carb without it being on the motor to look in and make sure it slides easy when the throttle is hit. The carb, jets, fuel tank, petcock and fuel filter are new so I didnt think the jets would be clogged. All the o-rings are new also. I did wait at least 30 seconds when I adjusted the a/f mixture screw like the manual said. Could it just be running that lean? would that cause the idle and a/f mixture screw to have no effect and idle that high? I thought maybe it was the knock off "Keihin" carb that could have it out of whack I have a old stock carb laying around but the pilot jet is pressed in and your not able to change it so I didnt use it.

[AbnMike]

"Could it just be running that lean? would that cause the idle and a/f mixture screw to have no effect and idle that high?"

Very possible indeed though usually it's some kind of air leak you are missing, or perhaps a bad head gasket.

Some good info in this thread: www dot 3wheelerworld.com/archive/index.php/t-30857.html

[hondamanshawn]

Thank you I read the thread and im thinking it has to be an air leak im missing. the o-rings are new and every gasket on the motor are new so I dont think it is the head gasket. I did spray starter fluid around the boot between the motor and carb and it didnt change the idle at all. I will do some more tinkering with it this weekend and see if I can figure it out.

[hondamanshawn]

I just wanted to update on this post I decided to take the knock off carb off and just get a rebuild kit for my stock carb and after I did that it ran better then I just had to tinker with jets and the idle and a/f screws to get it dialed in and now it idles nice and runs good, for some reason with that eBay knock off carb it just idled high and would do nothing if I tried to adjust it... Thank you guys for all your help

[DohcBikes]

missed this post. 45 pilot is way too big.