250 trail boss carb upgrade - Polaris ATV Forum
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post #1 of 7 (permalink) Old 04-28-2019, 01:43 PM Thread Starter
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250 trail boss carb upgrade

Will a vm 34mm mikuni fit the stock vm30mm carb adapter on a 93 250 trail boss. I've read that it makes a good performance upgrade.
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post #2 of 7 (permalink) Old 04-28-2019, 05:12 PM
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Yes, I think it will fit. If not, then the port size on the cylinder is about the same for all the small singles so get an adapter for 325 engine. But I don't think just changing the carb will help performance. You will need to do porting and polishing along with exhaust to match and probably fiddle with the jetting to get it to run right. Don't get me wrong, there are a lot of things you can do to get more performance from your 250. But you have to address the whole system not just one part. An engine is just a big air pump. So if you increase the size of the inlet without doing something to get the air through and back out you won't gain anything.

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post #3 of 7 (permalink) Old 04-28-2019, 05:26 PM Thread Starter
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Ok,I've bought a DG pipe and new crank seals ,new piston ,rings ,bored so it should be in good shape ,I was wanting to know if the 34 carb would fit in the 30 adapter.
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post #4 of 7 (permalink) Old 04-29-2019, 06:44 AM
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According to the Mikuni manual - both carbs have a 40mm spigot - both are 93mm long - both are 137mm tall - both are 83mm wide but, the bell for the air filter connection is 59mm on the VM30 and 58mm on the VM34

Yes, the 34 will fit the holder on the engine

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post #5 of 7 (permalink) Old 04-29-2019, 10:20 AM
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Sounds like you are on the way then! Let us know how it goes please. I have a 250 Xplorer and my son in law has a 250 Trail Boss

Mine: 2018 Sportsman 850SP - 26" Bear Claw HTRs on OEM steel wheels(I really don't like the Aluminum ones)
Polaris Hand warmers, Mirrors.
Hers: 2019 Sportsman 450. 26" Bear Claw HTRs on Moose 427X Wheels.

2007 Sportsman 500 EFI, Polaris Winch, 25" Bear Claws QSC Clutch Kit, Hand Warmers
2001 Magnum 325 MOSE 12" rear wheel conversion. 25" Sedona Coyote tires
2017 Polaris Ranger 1000XP - Roof and front glass
2018 Kawasaki KLR650
2001 Magnum 325 Warn winch and Moose 60" plow-Sent to Daughter and Son-In-Law since his blew up
SOLD 2004 Sportsman 600 Twin
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post #6 of 7 (permalink) Old 05-01-2019, 05:46 AM Thread Starter
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Ok,thanks for the info ,I'll post the results when I get this thing running and jetted.
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post #7 of 7 (permalink) Old 05-01-2019, 09:46 AM
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I don't want to discourage you, however. Unless you are going to put a lot of time and a few bucks in for little return I would rebuild the old carb. I would rather ride than tune. let us know. Have fun

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