Preliminary Settings on 250 2 stroke
#1
06-19-2018, 02:11 AM
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Preliminary Settings on 250 2 stroke
Hi guys, I just got a couple of 250 2 stroke trail bosses with unknown history.
There is only a 7 digit VIN so I can't even determine the year of these ATVs. I can only tell by the 7 digit vin that the are before 1996.
Neither were running when I got them and there were a lot of funky things done on these so I don't have a good starting point.
I can get both running. Have good spark, 120 PSI on each and think it's carb related in both cases.
One has what appears to be a stock Mikuni carb with a stock airbox and K&N filter. I've order a rebuild kit it seems to have clean passages. What is the main and pilot jets typically? What notch is the default clip setting? How many turns on the pilot and idle speed screws? How much will I need to compensate for the K&N filter
To complicate matters the second one has no airbox and doesn't seem to have a stock carb.
Does anyone have the 95 and older service manuals. I also can't find the owners manual.
Thanks,
Tim
There is only a 7 digit VIN so I can't even determine the year of these ATVs. I can only tell by the 7 digit vin that the are before 1996.
Neither were running when I got them and there were a lot of funky things done on these so I don't have a good starting point.
I can get both running. Have good spark, 120 PSI on each and think it's carb related in both cases.
One has what appears to be a stock Mikuni carb with a stock airbox and K&N filter. I've order a rebuild kit it seems to have clean passages. What is the main and pilot jets typically? What notch is the default clip setting? How many turns on the pilot and idle speed screws? How much will I need to compensate for the K&N filter
To complicate matters the second one has no airbox and doesn't seem to have a stock carb.
Does anyone have the 95 and older service manuals. I also can't find the owners manual.
Thanks,
Tim
#2
06-19-2018, 10:00 PM
I could take a wild guess on a couple of those things, but this place has PDFs of service manuals for Polaris ATVs for each year from 1985-2015 for $4.95 each. They have them for other brands and other types of vehicles too. Figuring out which year Trailbosses you have will be the hard part. A model number on the engine or something like that could possibly help. Polaris ATV Service Manuals PDF Download
#3
06-21-2018, 02:57 PM
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Uuummm, your guess is probably better than mine. But I did dig up a bunch of good info.
Some info I got on the web suggests it's a Mikuni VM30ss and needs a 140 or 145 main with 40 pilot jet. Air screw is 1 turn out. The slide is 2.0, but I'm not sure how to verify the slide visually. The Jet needle/eclip is 5DP7-3, so I'm assuming the carb rebuild kit will have the correct needle, but there is a way to verify using this document.
Mikuni-VM-Roundslide-Parts-Diagram.pdf
I think they count clip settings from the top position down, but 3 is in the middle so I can't get it wrong if I start counting in the wrong direction.
Here's the carb rebuild kit I got.
Ebay Rebuild Kit
Anyway the carb details are not changing a lot from year to year from 88-99. I think I'll get close enough with those settings.
Tim
Some info I got on the web suggests it's a Mikuni VM30ss and needs a 140 or 145 main with 40 pilot jet. Air screw is 1 turn out. The slide is 2.0, but I'm not sure how to verify the slide visually. The Jet needle/eclip is 5DP7-3, so I'm assuming the carb rebuild kit will have the correct needle, but there is a way to verify using this document.
Mikuni-VM-Roundslide-Parts-Diagram.pdf
I think they count clip settings from the top position down, but 3 is in the middle so I can't get it wrong if I start counting in the wrong direction.
Here's the carb rebuild kit I got.
Ebay Rebuild Kit
Anyway the carb details are not changing a lot from year to year from 88-99. I think I'll get close enough with those settings.
Tim
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