1995 RM250 Bogs Down and won't idle

[buck_y_lee]

Hi there. I'm new here, so firstly hello (from Sydney) and well done on the quality of this forum. I'm new to trail bikes and have spent the last few days reading back over the wealth of information contained in your discussions, trying to learn as much as I can.

My RM has just received a top end rebuild and a new needle and seat in the carby. On picking the bike up from the mechanic it would not idle (wanted to stall), so I adjusted the idle (choke) screw and it idled well. I have since run it in with a few gentle heating/cooling cycles and two half hour rides. During the second ride the engine began to 'bog down' and would not idle again. I had to keep on the throttle to prevent it from stalling. Inevitabley, I stalled the engine and was only able to start it with a clutch start.

I rode for a further 5 minutes back to base and inspected the spark plug. It was quite black. I installed a new plug (iridum) and attempted to adjust the idle screw to get a decent idle, but it just died on me still. The brass screw is turned outward one and a half turns and the spark plug now burns quite cleanly, if a little dark in colour. But it will still not idle and under throttle it will not rev out. In other words, it still bogs down.

I suspect the problem is to do with the adjustment of these two screws, as I am a novice and have probably mucked up these settings. But I would expect that adjustment of the idle screw would at least make the engine either idle too high or too low, but it seems to not have any effect. The only effect I am getting is that the bike will not start unless the idle screw is adjusted fully upward ie no brass showing on the choke button. It seems (from experience with chain saws!) that the engine is running too richly.

Please help. This is very, very frustrating.

Thanks in advance,
Buck.

 

[sick 96 250]

check you jetting on the bike, is could be jetted to richly causing the bog. what jetting are you running. This is fmf's jetting specs for that bike so i would try matchin it up with this.
Main Jet: 172
Pilot jet: 52
needle position: 2nd clip
air screw 1 1/2 turns out.

Make sure you use a good synthetic 2 stroke oil when mixing your premix and try it at 32:1 or 40:1

 

[snb73]

buck_y_lee,

Here are a few good articles to help you tune your carb. Hope this helps, Steve.

http://www.ericgorr.com/techarticles/carbtuning.html#e

http://www.ericgorr.com/techarticles/sparkplugs.html

 

[buck_y_lee]

Thanks for the replies guys.

It turned out to be quite a drama.

It seems the mechanic did not re-jet the carby or hone the powervalve properly after the top end rebuild (twice!), causing damage to the new piston, ring and to the bore. *******. The idle circuit was also loose. Needless to say, I have found another mechanic.

Thanks a lot,
Buck.