Idle adjustment doesn't work

[JCW]

I've got a 250 MC 2 stroke that runs great but the idle adjustment on the side of the carb doesn't seem to work. The idle is so low that I have to adjust it at the throttle and that's not a good thing. The bike cranks easy and has great power everywhere, especially off idle. What would keep the idle screw from making any difference from half out to full in?

Thanks,
JCW

 

[RBD]

Maybe the tip of the plastic idle screw broke off (I have seen this once before).

Ron

 

[rpduc]

Is it possible to wear a divot in the bottom of the slide where it contacts the screw? I imagine the plastic tip Ron mentions is to prevent that?

The idle screw on my '05 MC 250 is just about all the way in to get a proper idle. The tension spring appears to be fully compressed. I didn't notice that there was a plastic tip on the screw, but I wasn't looking for one when I cleaned the carb.

Could it also be incorrect idle jetting? Ron would be the guy who knows.

 

[eff]

Is it possible to wear a divot in the bottom of the slide where it contacts the screw? I imagine the plastic tip Ron mentions is to prevent that?

The idle screw on my '05 MC 250 is just about all the way in to get a proper idle. The tension spring appears to be fully compressed. I didn't notice that there was a plastic tip on the screw, but I wasn't looking for one when I cleaned the carb.

Could it also be incorrect idle jetting? Ron would be the guy who knows.

This could be an indication that you are running a PJ that is too lean.

 

[widebear]

If your pilot jet and corresponding air screw adjustment is out of wack you'll have a hard time setting a proper idle speed

 

[rpduc]

This could be an indication that you are running a PJ that is too lean.

Thanks eff,
I'll have to pull the jets out of my carb and see where I'm at. The bike seems to run fine, but then again it's been YEARS (30+) since I was last on a 2T dirt bike so my frame of reference is quite cloudy...

 

[GMP]

If the slide and/or needle straight diameter is wrong (rich) you will also over compensate with the idle screw. In my experience with three different GG 250s, its much eaiser to jet around a #7 slide than a #6, and thats at sea level to 1000'. I recenty had a similar experience doing a Keihin PWK conversion to a Husky WR250. Going to the #7 made the bike much more responsive to other changes. Ross, post your jetting and we will see.

 

[JCW]

Thanks everyone for the replies and I will check all of the above issues. The idle screw does absolutely NOTHING from half way out to full closed (in). Oddly, the bike runs great. I'm fairly comfortable with jetting but this is a new issue. I'll check the slide # on the bike, the idle jet, and the tip of the screw. Hopefully I can report the "fix" shortly.

Thanks again everyone!

 

[rpduc]

O.K.,
WAY too much going on around here to get in much riding so I just got around to checking the jetting on my '05 MC 250. (thanks to the spammer for reviving this thread ha-ha)

'05 MC 250, FMF Fatty with TCII, no dual map CDI that I can find...

38 pilot
N1EF needle #3 position
178 main

Didn't bother checking the air screw

I guess the lean pilot jet theory is looking plausible...

As a side note this thing seems to suck a lot of fuel. Almost double the consumption of my buddy's '04 DE 250.

Based on pobit's excellent post in one of the needle threads and my propensity to loop this thing I'm thinking I should try his "tame" reccomendation for the 250 i.e. 42pilot, CCK#3, 178 main for a while...

What considerations do I need to make WRT the MC ignition, compression, etc. Are there significant differences there that would affect these jetting decisions?

 

[Eric K]

Overall, that setup works quite well across a range of conditions.

You may have to do some slight tuning. If you run the engine at race pace, you may want to up the pilot. Also at higher elevations you will need to tune accordingly.

 

[rpduc]

Thanks for the quick reply Eric,

By "that setup" I assume you mean what's in there now...

I'm reasonably happy with the way the thing runs, but I really have NO basis for comparison so I wonder. The fuel consumption is one thing.

Others are:
- It seems to "sputter" a lot at smaller throttle openings
-The "beast" within comes on with a vengeance at times too. That's why I was intrigued by Pobit's comments on the CCK needle. At 55 yrs. I don't need to loop that thing again...
- It kills very easily if I get clumsy about braking into corners.

 

[Eric K]

Ross,

I spent a lot of time trying to tune the setup you currently have and was never pleased with it. I had the same issues you have.

The set up starting point I was referring to and recommend is #7 slide, 42pilot, CCK#3, 178 for sea level, 60F. (A #8 slide works a bit better on some engines.) With fine tuning, this set up will address the issues you are having. Further, you will get better part throttle controllability and better fuel mileage.

 

[rpduc]

Thanks Eric,
GOOD! I'm glad you weren't referring to my current setup...

I'm anxious to see how this beast behaves with the CCK. I'd characterize the power delivery right now as "angry" or "violent." I'm not into angry or violent any more...