700 mm needs choke but floods

T

tosten

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Dec 23, 2015
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Montana
I've just bought a 700 mm, 2000 model. It has been piped and has aftermarket reed valves and I have a strong suspicion that it has had the ports polished. The work was done when it was new by a reputable tuner. It has 1900 miles on it and wasn't used much for the last few years. The owner is a friend of mine and he treated the fuel and started it regularly while in storage. I checked the carbs and they are clean as new. I checked the main and pilot jets and they are fine. It ran fine when I first got it running and it suddenly began to foul plugs and not rev at all. It pops loudly in the exhaust on occasion. It now sounds like it is running on 2 cylinders and won't rev enough to kick in the clutch. The previous owner was very easy on it and it ran very strong when he put it away. It seems like the problem started suddenly. I have changed the gas. Could it be a fuel pump problem or something with the tors? I'm kind of stuck. I have never really driven the thing hard. Just up and down the drive in early snow. It seemed to work better for awhile when I changed the plugs and then it began to flood again. I have to watch the choke system so it completely releases but I can push it in now that I know that it is doing that. I have dried the plugs with a torch a couple of times. Is there a chance that they are not recovering from that? I can hardly see a spark when I pull it over with the plugs out. I'm stuck. Anyone have any ideas?
Thanks!
 
I would
1: get rid of the old gas
2: clean carbs, change fuel filter
3: make sure tors is adjusted and possibly clean switch contacts

If that doesn't work start looking at things like plug caps or wires

Personally I think the guy couldn't have been worse in taking care of the engine. "Starting occasionally" is the worst thing you can do to an engine in storage. You warm it up just enough to create condensation on everything when the engine cools off. I've seen it first hand pulling spark plugs in the early fall when temps are moderate and the humidity keeps passing the dew point. The plugs have frost all over them.

As far as the gas goes I think it's toast. I don't care how much stabilizer is in the but "a couple of years" is well beyond the life of gasoline even with additive. With the best stabilizer you might get a year, max. The stabilizer is there to prevent phase separation not maintain octane indefinitely. Empty the tank and start with some fresh and I bet you'll be surprised that your problems go away.

I use a shaker siphon to drain all my sleds for the off season. I fog them and then drain the gas and pull the carbs and put them away with dry carbs and tank. It's not worth rolling the dice on that first tank of bad gas and if I don't pull a sled out one year it's ready to go for the next.
 
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you say you changed the gas. Completely drained and filled with fresh?
You need to get those carbs sorted out first. If you need to push on the enrichener to get it to close then it's not right. You will just chase your tail until you get that sorted. Once the carbs are right you can systematically address any other issues if they exist
 
Thanks for the ideas. First chance I get i'll check out the carbs again. Sounds like the pilot jets may be the problem. If I change to dry plugs it will work well for a short run but the next time I run it the plugs foul. Are the plug caps that big of a problem? I've never seen this problem being common on cars and motorcycles. The sled worked fine for awhile. It seemed to show up when I put fresh gas on top of the old, now that I think of it. I haven't found a fuel filter yet, not even in the repair manual that came with the sled. The saga continues..I'll let ya'll know what I figure out.
 
The fuel filter is in the tank. It's on the end of the hose and acts as the clunk for the fuel tank so the hose is always in the low spot.

The plug caps make up half the resistor that the ignition uses. The cap has a 5k ohm resistor and the plug is 5k ohm to make up a total 10k ohm resistance in the ignition system.
 
Fixed. i checked the carbs again and put it together Started it with the old plugs. Put in new ones and it lit up just fine. The old gas had ruined the plugs. No way to recover them. Except for a brief foray with a well worn Phazer my main snowmobile experience was in 1971 riding a brand new 18 hp Olympic. That thing would carbon the gap shut and we'd chip it open with a jack knife and burn the things out on the stove when my mother went to the store. Times have changed. The Yamaha runs great now. It has an unreasonable amount of power. I'll get it onto some trails
tomorrow and see how it works out. There's some deep stuff about 5 miles away above 5000 feet. What I learned. Just put in fresh gas. Don't mess with anything more than one summer old, even if it has been treated. I also learned how to clean the carburetors. Not a tough job. These were clean but now I don't have to think about it. Onward and upward. Thanks for the help!
 
Glad you got it figured out. I never risk old gas. It's too easy to empty the tanks and put it away dry in the spring. I get my monies worth out of the gas. It's amazing how well my small engines run on winter blend gas in the summer. It's crazy what the difference in vapor pressure does.
 
If you have ever run aftermarket egts , you will see that a fouled plug never seems to allow a cylinder to gain temps again as quick. They are never the same.
 
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