Can't figure this out

[2strokes4life]

I am trying to jet my 1991 RM 250. I have just finished restoring it. Here is the problem. When I start the bike I can start it cold with no choke. When it first starts it revs moderately high, but then will settle down. It doesn't really want to idle stable until I turn the airscrew counterclockwise like 3 turns out. I am wanting to put one smaller pilot jet in. I am currently jetted by the FMF specs. I realize these are not set in stone. The bikes runs really hard mid and top end. The plug is perfect on WOT plug chop. The bike is really boggy on the low end. Do I need a smaller pilot jet or do I need to raise the clip one notch. I have a FMF fatty pipe, flywheel weight, a new top end that's barely broke in. There is one other thing I have noticed lately. I thought I had the float height set correctly after I rebuilt the Carb, but when I went riding the other day I saw gas had leaked onto the bed of my truck. The float height could be too high. I'm kind of stumped. What do you all think? It smokes at idle pretty bad. I just replaced the wet side (clutch) crank seal and still does it.

 

[FNG]

Did you replace the float needle? It may "look" ok but if you are leaking fuel it is not stopping the flow. It will leak and cause a rich bottom end but clear out.

 

[2strokes4life]

The carb has all new internals including all jets, needle and clip, float valve assembly, orings, and the floats themselves. All indications indicate rich on the pilot, but I don't understand the high rev at starting. Is that because of excess fuel being delivered at the start (no choke)? The top end is new and I'm afraid of leaning out too much, but I know it shouldn't hurt much on the pilot side even if I do run it a little lean to troubleshoot.

 

[helio lucas]

high idle usually is related to air leak: exhaust, left crank seal or air boot...
eric gorr as a real good article about carb jetting on his book. if you don´t have it, the article is on his web site...

 

[whenfoxforks-ruled]

Give a spray of brake cleaner around the intake manifold, base gasket and left crank seal, listen if it idles up? Reeds are tight? If the bowl drain does not have a bleeder valve in it, put one so you can hold a clear hose along side the carb. You can see if its flooding the engine. A lot of the float heights are measured differently, the hose knows. Wrong part or installed wrong? Look at the plug, how is the timing?

 

[sr5bidder]

3 turns out on the air screw does not sound unreasonable.... how does it idle when you are fully heated up? (after about 10-15 min of riding)

I think if it where an air leak the engine would not settle back like you said.

did you do any heat cycles ( warm up then cool down) for breaking the new engine in?

I had an rm and it had nothing in the bottom for power.... RM's are made to be reved out at all times so I'm not certain you can tune it for bottom end power.

 

[2strokerfun]

Sounds like you might have a piece of dirt in your carb. It happens. If it did, it's a real easy fix. Try cleaning your needle and seat and recheck your float height while your at it.