'87 250sx Runs Rich, Won't Idle

[Supraman0614]

I have completed a refresh on my machine (teardown, sand blast and paint parts, replace worn stuff, etc.). I disassembled and cleaned the carb per Flying W.'s tutorial (excellent info!). I also adjusted the intake and exhaust valves per the service manual. Machine is completely stock. I fired it up for the first time since it was reassembled yesterday and it will not idle.Once I got it warmed up, I ran it around the yard for a while to get it completely up to operating temp. It runs great, but still wouldn't idle. I played with the air screw; did not affect it at all. I pulled the spark plug and it is really black (rich). Installed a new plug and fired it back up. If I hold the throttle open a little, I can keep it running, but I noticed it was smoking a little and smelled very rich (black smoke, not blue). I don't believe there is anything wrong in the carb, but I may have missed something. It is also possible that I adjusted the valves too tightly. Any thoughts on a cause?

[MrConcdid]

I sympathize, I have the same symptoms/problem, I am waiting to see what the pro's have to say.

MrC.

[Atc 200x 1985]

I've seen this problem before this is what is happened on my 85 atc 200s. First, check your needle clip position in the carburetor I believe it is the second grove from the bottom but if it is running fine not breaking up at high speeds then you don't need to mess with that. Next check your jets the pilot jet aka the little one is a 38 you should probably change it to a 35 and if you have a manual or just go online and check all your other jets to make sure they are the correct sizes that should fix your problem. Don't go in huge increments don't go down or up more than 5 sizes

[Supraman0614]

Thanks for the reply. All of the jets are factory sizes. I know there are differences in each engine that make jetting very machine specific, but even if the pilot was off by a size or two, I should be able to get it "close" with the air screw. In this case, having the air screw completely closed or open 4 turns made no difference. I've never seen a machine run this rich with factory jetting.

[Atc 200x 1985]

Ok. then check your needle clip position try right in the middle that is a good all-around area. and yes you are right if it was off by one or two settings you should be able to get it close I tried to do that with mine but it never worked I changed the pilot jet and that has almost cleared the problem up. these motors are very picky about what it will run and idle correctly with. up on the needle will lean it out down on the needle will richen it. It is sounding like your needle is in the wrong place cause you said you can hold the throttle open and it will idle.