ms 260 pro/extremely lean?

dozerdan · Nov 9, 2002

bwalker
I am not really sure how you figured that I was running them with the low speed jet turned way out,I never stated that and would never let a saws out of here that way.
This is a prime example of why I read more then I post.
Why is it when you try to give someone good,free information,it always turns into an argument or a full scale debate?
Dan

jokers · Nov 9, 2002

Power Porting and the Fixed Jet

Hi Dan and Ben, and of course everyone else, from what I understand the fixed jet in one of those carbs would need to be changed after tuning if it wasn`t running lean in the first place. From what I have been told, you routinely need to lean the hi speed screw after tuning so a lean jet right from the start would be OK in this case. The lo speed screw is significantly richened and it supplies about 1/3 the hi speed fuel. Accordingly, the ms260 Pro that Dennis just built for me runs right on the top end with the stock jet. of course this means that all the stock 260Pros are running lean, LOL. Russ

dozerdan · Nov 9, 2002

jokers

After porting,I adjust the low speed jet the same way as you would any carb.After that I check the high end.If it does not 4 stroke,I will go with a larger main jet.Granted you can compensate somewhat by richening the low side but then you have an overly rich condition on the low end.
I am sure someone out there that never had a saw engine apart is going to tell me that I am doing it incorrectly.
Dan

jokers · Nov 9, 2002

Hi Dan, what I think you are saying, that sometimes you have to richen the hi speed after tuning, makes sense to me, but I don`t have any experience to back this up. I haven`t built any two strokes and the built saws that I have, I`ve never had any cause to see how far out the screws are, I`ve just made small tweaks as needed. So anyway, unless I misunderstood, which is possible, one of the recognized experts on this subject told me that from his experience the bottom is richened and the top end needs to be leaned out after changing the ports. I won`t divulge the name of this person in case I am mistaken, which sounds likely. I know that my tuned saws use substantially more fuel and they don`t idle much, so that supports what you are saying. Hope I`m making sense, my head`s a little punky after a few days of the flu. Russ

bwalker · Nov 9, 2002

I am not really sure how you figured that I was running them with the low speed jet turned way out,I never stated that and would never let a saws out of here that way.

Dozer,Relax, I assumed thats what you where doing to get the high end to run right. Mine was so lean it would bog in the cut and had no power to speak of. Its not hard to understand why I was a bit sceptical of a tuned saw running a stock jet. At least till I gave it a little though and realised improvments in scavangeing usually require leaner jetting.. I am going to tear the carb apart and see what jet is in it and go from there maybe the fcatory put the wrong jet in.

bwalker · Nov 18, 2002

Update: Stihl does make a 56 jet that is richer than the standard 54 and the 52 high altitude. I have seen the jet with my own eyes, but I do not have a part # and my dealer cannot find one for it. Maybe stihltech can shed some light on this.