snowmobile runs only when choked

[mtmogs]

This is a question for the 2-cycle gurus out there, particularly the Alaskan guys who may run my model sled. I've got a '97 Yamaha VK540II snowmobile with a 535cc engine and mikuni B38 carb, has only 990 miles. I've not run it much at all since buying the Snow Trac a few years ago.

I ran it yesterday for the first time this year. It starts, idles, and runs well and clean after warmup. However, it dies if it's not choked, even after running it for a good 30 minutes or so. Any thoughts on what the problem might be? It seems like it may be a vacuum issue of some sort like it needs the choke plate at least partially in place to "pull" against. I'll tear down the carb and clean it good. I hope it's not the bottom end seals...

 

[Snowtrac Nome]

i think you will find water or sludge in the bottom of the carb the idle circut pulls fuel off the bottom as does the main jet circut the fuel enrichment circut what you call the choke pulls fuel off the top of the bowl so if you have heavys in the bottom it will displace fuel and lean out your carb so it won't run should be an easy fix if the crank seals are out the engine wont run at the topend because your crank case works like a blower and compersses the fuel air mix to force it accross the top of the pistion and if the rings leak it would be hard to start i would expect to find the problem to be at the carb

 

[Mtn-Track]

DON'T RUN IT UNTIL YOU CHECK THE MAIN JETS IN THE CARBS! It sounds like there is crap in the mains and if you keep running it the engine will be in a lean condition and burn up the pistons and seize.

If the carbs are clean and it's still an issue, then what Don said about the crank will be the next suspect. Again, running it with a bad crank seal or choked main jets will burn the engine up.

Been there, done that!

 

[mtmogs]

Thanks a bunch Don. I figured you would have some good ideas. That's interesting about the choke drawing off the top of the bowl and the main jet from the bottom. Makes perfect sense that gunk on the bottom would cause my problems. I'll let you know what I find. Thanks - Paul

 

[mtmogs]

Thanks for that info. It sound's like it was a painful experience!

DON'T RUN IT UNTIL YOU CHECK THE MAIN JETS IN THE CARBS! It sounds like there is crap in the mains and if you keep running it the engine will be in a lean condition and burn up the pistons and seize.

If the carbs are clean and it's still an issue, then what Don said about the crank will be the next suspect. Again, running it with a bad crank seal or choked main jets will burn the engine up.

Been there, done that!

 

[Mtn-Track]

Not really painful, but COSTLY.

...took a new block, crank, rods, pistons, rings, money, money, money....

 

[mtmogs]

Ouch. I always find a cashectomy rather painful.

Not really painful, but COSTLY.

...took a new block, crank, rods, pistons, rings, money, money, money....

 

[XeVfTEUtaAqJHTqq]

Sounds like what happens every other year with my Craftsman mower. I finally put a fuel cut-off on it to drain the fuel system before storage. The ethanol in the gas these days can really cause issues when you store a small engine and don't drain the fuel.

 

[300 H and H]

I leave two summer cars and a boat full, with ethanol in the tanks, in storage with out issue. Snowmobiles the same way, but with Sta Bil. Again no issues. It might be the gas but probably not an E10 issue. Unless your supplier has an issue.

I have to admitt 30 years ago when E10 was first marketed here there were issues with plugged fuel filters and such, for a while. But eventually the "system" that stores, and carries our fuel to the retailers tanks, were cleansed by the ethanol and the issues went away. For those of you with ethanol just now in your gasoline, and have issues, there is hope with time the situation will get better. Honestly in my neck of the woods if you asked about fuel issues with E10, you might get a collective yawn....

Please don't make this a ethanol haters thread, pretty please....

Best regards, Kirk

 

[Snowtrac Nome]

stop this stuff about gas again none of you guys work in the petrolium industryfirst off adding agents like alchol and mtbe to the gas does change some of it's propertys it's change we have to live with it's an easy fix with a card'd small engine up the jet's 2 sizes also old fuel is nt exactly better most of you are old enough to remember gas turning to varnish and screwing up your carbs and fuel systems that dosn't happen any more because of additives alchol will absorb moisture from the air that is why your brake fluid turn's black the best thing you can do is run the tanks dry and pill the bowl drains on the carburators before seasonal storage and also $hit happens not just because of fuel so don't blame it on the gas your suppliers spare no expence to provide you a quality product and i for one reutilize gas deamed not fit for moderen fuel injection systems and small engines in my old jeep it drinks it just fine so i hope this is the last i will here about the gas and government scamms if you want to know how to make it work i will offer you my advice your choice if you take it but this stuff isn't like health care the republicains e arn't going to get rid of it so we must learn to work around it

Don XXXXXXXX
Fleet manager Bonanza Fuel
Nome AK

 

[mtmogs]

I work in the petroleum industry, but only up to the point of getting the black gold out of the ground. Beautiful stuff to see and smell in that condition. Why you'd want to dilute it with corn juice is beyond me - just joking. I have visited several refineries however, and it was eye-opening to see tank trucks bearing the brand of many different major gasoline retailers filling up at the same place. The only difference in the different brands are additives, and our old petroleum chemists tell me the differences are minor at that.

stop this stuff about gas again none of you guys work in the petrolium industryf

 

[Bulldog1401]

stop this stuff about gas again none of you guys work in the petrolium industryfirst off adding agents like alchol and mtbe to the gas does change some of it's propertys it's change we have to live with it's an easy fix with a card'd small engine up the jet's 2 sizes also old fuel is nt exactly better most of you are old enough to remember gas turning to varnish and screwing up your carbs and fuel systems that dosn't happen any more because of additives alchol will absorb moisture from the air that is why your brake fluid turn's black the best thing you can do is run the tanks dry and pill the bowl drains on the carburators before seasonal storage and also happens not just because of fuel so don't blame it on the gas your suppliers spare no expence to provide you a quality product and i for one reutilize gas deamed not fit for moderen fuel injection systems and small engines in my old jeep it drinks it just fine so i hope this is the last i will here about the gas and government scamms if you want to know how to make it work i will offer you my advice your choice if you take it but this stuff isn't like health care the republicains e arn't going to get rid of it so we must learn to work around it

Don XXXXXXXX
Fleet manager Bonanza Fuel
Nome AK

Such a joker.......

 

[mtmogs]

Okay, pulled the carb, disassembled, cleaned with carb cleaner, blew ports out with compressed air, reassembled. The carb was very clean and looks near new. I didn't see any H2O globules when I drained the bowl. The jets didn't look fouled. I hand started it easily without the choke and it idled fine.

Took it for a quick spin and it didn't die per usual and ran smooth. I didn't get a chance to really whine it out of respect for the neighbors. So the problem seems solved but it was in the warm shop all day, I'll leave it out tonight and see how she goes tomorrow.

The one thing I spied out of place was that the hose clamp for the rubber boot on the intake side of the carb worried itself loose. It seemed like the boot was tight, but what I should have done is sprayed some carb cleaner around the boot while running to see if it was sucking air. Thanks for everyone's help!

 

[Snowtrac Nome]

i would bet there was a piece of dirt or sone snall flake stuck in a port somewhere if you look at some of the brass tubes you will see small holes in them as for suction side leaks try a light machine oil it will plug the leak momentaryly and speed up the motor with out having a flamibal liquid like starting fluid or carb cleaner

 

[mtmogs]

Thanks Don. Who knows, there could have been a small piece of crud in there. In any case, whatever i did with the cleaning, etc., worked. I just took the viking out for a good long run and it ran like new.