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Have a 1990 trail boss 250. Recently rebuilt top end. I'm trying to tune the carb now to get it to idle and run properly. First off it requires being pulled over about 7 times with the choke on full and the throttle wide open when it's cold. Then when it's running it will idle fine but I just reved it a bit and the rpm went up but didn't come back down. The throttle body went back down but the rpm didn't. I have tried messing with the air screw and idle screw but just can't seem to get it to run properly. When I did the rebuild the carb came off to be cleaned. I notice it was in bad shape so I replaced it with a 88 carb from a cycle salvage. I am using the original throttle, and I put a new stock main jet and pilot jet. I also swapped out the needle jet for the stock one too. Am I missing something? Cause its becoming very frustrating. About to set this thing on fire and call it a day... Any advise would be greatly appreciated.
 

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by needle jet, do you mean needle and seat? sorry I'm not big on jets,...or carbs....anyway my trail boss starts the same way, but it runs and idles fine, my 350L however has the same prob. but worse it won't start at all unless you blow in a tube on the carb or use starter fluid. then it will rev all the way up then die, then rev etc. its rideable but it keeps backiring and sometimes revs and won't come back down. I yhink its the needle and seat so I'm replaceing that, I'll post again hopefully later this week if it works or not.
 

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Have a 1990 trail boss 250. Recently rebuilt top end. I'm trying to tune the carb now to get it to idle and run properly. First off it requires being pulled over about 7 times with the choke on full and the throttle wide open when it's cold. Then when it's running it will idle fine but I just reved it a bit and the rpm went up but didn't come back down. The throttle body went back down but the rpm didn't. I have tried messing with the air screw and idle screw but just can't seem to get it to run properly. When I did the rebuild the carb came off to be cleaned. I notice it was in bad shape so I replaced it with a 88 carb from a cycle salvage. I am using the original throttle, and I put a new stock main jet and pilot jet. I also swapped out the needle jet for the stock one too. Am I missing something? Cause its becoming very frustrating. About to set this thing on fire and call it a day... Any advise would be greatly appreciated.
crank seals?
 

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A possible soultion

Hi Morrison, I have a 1989 trailboss, so I speak from experience. I suggest you put the original carb back in the the machine. Did you rebuild the carb? If not you should put new needles and gaskets in it, you can get them here for under $25.00. http:Polaris Trail Boss 250, 1989 1990 1991 1992 1993, Carb Kit | eBay When you install the main needle put the clip on the top or second to top adjustment setting.
Another thing to check; the throttle cable going to the oil control could be pinched, it could be holding the fuel cable up since they are attached.

ps: If you decide to "set this thing on fire and call it a day" please take the time to drive down to Vernon CT USA and I'll pay you $100.00 for your trouble.
 

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Check your choke adjustment. There should not be more than an 1/8th of an inch play on the choke lever. Also check the condition of the choke plunger. I have a 90 trailboss and have had good times and bad times with it. They are temperamental in their old age!
 

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Sounds more like an air leak to me, either the gasket on the throttle cap isn't seated properly or the cap isn't tight enough or the base plate gasket is not set correctly. Fire it up and spray carb cleaner in those two areas and see if the idle craps out when it reving high if it does you found your leak.
 

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Could be the butterfly in the carb is sticking open, I had this happen once when I changed the carb to manifold gasket on a car, the gasket had a burr that hit the butterfly and held it wide open.
 

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Sounds more like vacuum leaks, crank seals or intake boot leaks, but I would go back to your carb and take it apart and see if you can fix that one rather then trying to fix a used one.
 

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If you think it a cracked or
leaking boot, you can spray carb cleaner on the outside of the boot and if there a leak you will hear a change in the RPM's, might even stall if it a bad leak. I'd go back to the original carb and work on it.
 
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