1981 atc 200 not running right

[Savage99]

Well I put the new plug, wire and overhauled the carb on my 1981 ATC200 and it runs a little better. Problem I am having though is it doesn't idle that great and when I rev it up or ride it at higher throttle it pops alot, almost like mini backfires. When I rev it in neutral the rpms stay high for quit some time after I have let off the gas....I am at a total lose. Oh yeah when I did the carb I used a carb kit so it's got brand new jets, needle and everything looks clean. Thanks.

Mark. :wondering

[Huffa]

You must have an air leak or a bad head gasket. What an air leak does is causes a lean condition which causes the high idle like that.

Could be at your carb intake boot that is ahead of the carb. Loose, ripped or a small hole on the boot will cause this condition.

Spray wd-40 or carb cleaner all around the boot & motor (head & base gasket) with it running and idling high. If it does have a leak the second the liquid hits it the idle will drop just for the time that the liquid seals it, then it will go back up.

Also could be your header pipe is loose where it attaches to your exhaust port or you have a crack in the pipe somewhere.

[Savage99]

Would a header pipe leak cause this...it does leak there a little but I didn't think it would matter on that end as much. Meant to pick up a new gasket but havn't got around to it.

Mark.

[84250r]

Check the intake manifold,boot to carb from airbox. Adjust your idling screw 1 1/4-1/2 turns out. Reving high like that sounds like an air leak. Do a plug check.

[MTS]

if you used the slide needl in the rebuild kit, take it out and put the original one back in, the new one if MUCH slimer than the old one, also in the kit what did you put in for a main jet a 95 or 98?, air screw should be at 2-2 1/2 turns out is i belive what i got on mine, needle clip on the slide needle is the middle notch or 2nd from the top, ...cant quite remember....lol

[Savage99]

What about this header pipe where it attaches to the exhaust port, could a leak there really cause these problems????? I have checked fro leaks on the intake side and everything seems OK there. The stuff I used in the carb had the same numbers stamped on it as the old stuff, I just don't remember the numbers off hand. I believe the main jet was a 98 and I put clip on the second from the top and adjusted the float height to manual specs.

I am going to get a new exhaust gasket from Honda (if they have one) tommorow and try that anyway...I know there is a problem there...might as well eliminat that as the cause.

Mark.

[3 weelin geezer]

No, it wouldn't cause the high idle because the gas is already burned. just will let hot exhaust out onto your leg maybe.

[Savage99]

Forgot to mention that after one ride up and down the block my spark plug has a really black sooty look to it.

Thanks for all the input so far.

Mark,

[toyota200x]

I have a friend that has a 1982 atc 200 and it does that same thing as yours. We cleaned the air filter and that is about it. I couldn't figure out what was wrong with it. He has ripped air boot so I guess that is the problem. His spark plug is the same way. Thank you for posting this thread.
DREW

[HaggLE]

OK people, the boot between the carb and the airbox DOESNT affect the running of the engine to any great extent. It means that the engine will be sucking in unfiltered air (or potentially dirt) and can affect the mixture at high revs (makes it leaner). This will not AT ALL affect the idle.

Make sure that it isnt leaking air between the carb and the head. THIS IS CRITICAL. Spray it with WD40 or what ever as previously described and fix as necessary.

Make sure that your air filter isnt dirty or more restrictive then normal. This will make it run like the choke is on.

An exhaust leak close to the head will cause it to pop when deaccelerating but will not affect the idle.

Attached is a picture from a workshop manual. Make these adjustments and see how it goes. This is for a 185s but the principal is the same.

Another thing to check is the ignition timing. Make sure that the CDI pickup lines up (inside the cover on the head) when the flywheel has the "F" mark lined up.

Let us know what you find after these adjustments.