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Discussion Starter · #1 ·
I'm guessing I need to clean out the carb, but here's the scenario:

Its a 1973 Olympique with a F/C 340 (339.2cc Rotax type 338), with a Tillotson HR131A carb. There's a single adjustment screw and an idle stop screw. Teshio's pages list the adjustment should be set at out .75 turns, but I've got it at an even 1 turn. The snowmobile runs great for the first few miles, then it begins to bog down at anything above 1/4 throttle. This happens slowly; I can run it wide open and once the process starts the engine will continually bog down until it just bogs to a stop. Let off the throttle and the engine will return to idle, but give it too much throttle without letting it sit a couple minutes and it just kills. I also can't use any choke when starting the snowmobile, and its spewing gas out the overflow/return on the carb. It seems to me that the engine is running as if it were at full choke full time, once it warms up it begins to flood when I crack open the throttle. I can still limp it home at about 15 mph (1/4 throttle), but that's about it. Today I limped it home and immediately threw it up on a jack stand and ran it a bit, it still bogs a bit but with the track spinning freely it will still work itself up to where I would guess redline would be (no tach). The fuel filter is new, the fuel lines are new, the tank is clean, good spark, and it runs like a raped ape for the first few minutes until it gets warm.
 

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You may be running out of fuel. Check the tank vent and make sure that it is clear.If no air can vent into the tank then no fuel can come out.Check the fuel pump condition. Another trick I've done is to put some fuel in a spray bottle and when it bogs give the carb a spray of fuel and see what the reaction is. All you need is a fine misty spray. Good luck
 

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Discussion Starter · #3 ·
dar.rox said:
You may be running out of fuel. Check the tank vent and make sure that it is clear.If no air can vent into the tank then no fuel can come out.Check the fuel pump condition. Another trick I've done is to put some fuel in a spray bottle and when it bogs give the carb a spray of fuel and see what the reaction is. All you need is a fine misty spray. Good luck
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Possible, I took it out again today and tried various thing with the fuel lines & tank... I'm pretty sure its the carb, which I'll take apart tomorrow. Will keep posted.
 

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to me it sounds like ur taking it out as sonn as it starts up and runs like crap but then when it gets warm runs fine so let it sit for a few minutes running then take it out, if that doesnt work it sounds like ur choke cable is seazed or or stuck in one possition .
 

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SPRAY SOME CARB CLEANER AROUND THE CRANK SEALS. IF IT BOGS DOWN IT IS YOUR CRANK SEALS. IT SOUNDS LIKE THAT TO ME
 

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Discussion Starter · #7 ·
Alright, I seem to be having the same problem as this thread:

http://www.dootalk.com/forums/index.php?showtopic=89505

Anyways, I've replaced the diaphragms, gaskets, needle, and needle seat in the carb. I haven't replaced the low-speed adjustment needle (looks fine) or the high speed fixed adjustment/jet. It seems to be sucking plenty of gas, at least it sends a good stream through the return line. Even with a steady flow through the return line it is running out of gas when I open the throttle. Once it starts to bog with the throttle open giving it a little choke will pep it up again. I'm wondering if the fixed high speed adjustment is the culprit. There's a little jet with "050" stamped into it. Also would the check valve (the little piece with the ball in it) have anything to do with this? I didn't replace either of those parts, and I'm not sure how the check valve is supposed to function. I'm also wondering if the 050 jet is too lean. I don't think it is crank seals, as it seems to run fine with a little bit of choke. Although it floods if you leave it choked at idle; it only needs the extra gas when the throttle has been cracked.
 
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