Take me to carb school
#1
10-21-2012, 10:12 PM
Take me to carb school
I recently rebuilt my 1995 Polaris Trail Boss 250 engine. Compression and everything is good. Ignition is good. Moving on to the carb. I have it torn apart and cleaned. Waiting on the rebuild kit.
Note: Oil pump has been deleted and I will be premixing.
My questions are as follows:
How do I adjust the carburetor??
I hear that once I go to premix, I should re-jet the carb. How do I do that? How much bigger do I re-jet to? What size and so on.
Lastly, How much oil should I pour into one gallon of fuel?
Please advise. Thank you in advance
Note: Oil pump has been deleted and I will be premixing.
My questions are as follows:
How do I adjust the carburetor??
I hear that once I go to premix, I should re-jet the carb. How do I do that? How much bigger do I re-jet to? What size and so on.
Lastly, How much oil should I pour into one gallon of fuel?
Please advise. Thank you in advance
#2
10-22-2012, 08:01 AM
Polaris ATV Expert
Retired and loving it!
Retired and loving it!
Just premix 40-1 with a good synthetic oil and it's not necessary to change jetting in most cases! This is a low compression engine! Get a ratio cup to accurately measure the oil OR just look at the back of the bottle, it will show how many ounces oil to 5 gallons of gas and use the wife's measuring cup 
For smaller batches (2 1/2 gals) just half the amount of oil. Just mix it up thoroughly in the gas can first.
The carb air/fuel screw is set between 1 1/2- 2 turns normally,not as sensitive as the fuel/air screw setting on the four stroke machines. Unless oil pump is definitely bad,most pumps are really dependable,but a lot of people discard em. I had em on several old 60's street bikes and the Mikuni pump never had any problems. OPT
For smaller batches (2 1/2 gals) just half the amount of oil. Just mix it up thoroughly in the gas can first.The carb air/fuel screw is set between 1 1/2- 2 turns normally,not as sensitive as the fuel/air screw setting on the four stroke machines. Unless oil pump is definitely bad,most pumps are really dependable,but a lot of people discard em. I had em on several old 60's street bikes and the Mikuni pump never had any problems. OPT
#4
10-22-2012, 08:19 PM
One last thing. There are various little vent tube plugs all around the carb. I do not remember where they go. I know about the big one where the fuel goes in. However, not the three little ones. There is one brass on under the float, one brass one on the top by the inlet, and one plastic one on the top by the motor side of the carb. Any advice?
#5
10-23-2012, 08:43 AM
Polaris ATV Expert
Retired and loving it!
Retired and loving it!
#6
10-23-2012, 09:00 AM
Extreme Pro Rider
God forbid he lets the polishing secret out!
God forbid he lets the polishing secret out!
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I like this link for Disassembly and Cleaning of a Mikuni Round slide Carburetor.
The only real trick they state is.
lots of youtube vids on it also.
The only real trick they state is.
4. Using a flathead screwdriver, screw the pilot air jet in until it is fully closed, while counting the number of turns. Now write this number down, and you can remove the pilot air jet by fully unscrewing it. You will need to make sure the air jet ends up the exact same amount of turns out as it was originally when you put it back together. Set this aside for cleaning also.
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