Stupid snowmobile. Tech advice?

Kamakiri

Kamakiri

The New Dynamic
Okay, working on a '72 Ski Doo Olympique 340. Won't start.

Looks like this one, but not as nice....

http://www.snowmobilelinks.com/72 ski doo Olympique.jpg

Both cylinders have excellent spark. On cylinder #1, it reads about 110 psi compression, and ~90 psi on #2. With the #2 plug out, #1 still reads around 90 psi, meaning that if there's any internal crank seal leakage, it's minimal.

Cranks seals do not appear to be blown out as there is no oil whatsoever in the engine compartment.

Plugs are getting gas, no I have no idea exactly how old it is, but gas is also leaking out the back air intake of the carb. I assume this is a ported engine, and does not have reed valves.

It fired up for about 3 seconds just once on ether, and wouldn't fire again even if I waited and allowed the plugs to dry. Heck, the spark was so good that it even ignited the little bit of fuel on the plugs when I had them out to check for spark again, so in that event I assume the gas is ignitable.

Ideas? :dunno:
 
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How's the timing? Does it have some kind of mechanical spark advance that is stuck?

- Pete
 
I've always said 3 esses: spin, stink and spark...

It cranks, and you found the spark adequate. That leaves fuel.(stink)

Have you cleaned out the carb passages, the last owner that ran it could have let the gas evaporate out of it, leaving deposits in the metered passages.

It happened on my car, getting progressively worse until in Feb I had the carb professionally "boiled(??)" out. When the emissions test was done after that, the numbers were so low I almost got dirt on my chin...

Rich or lean, there's only a narrow range that will work.

I'm working on something similar on a 25cc leaf blower, I'm waiting for an ignition "module" and the carb gaskets. After that, then it's the snowblower's turn.
 
markthefixer said:
After that, then it's the snowblower's turn.
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Gotta work on mine this weekend... here's hoping it's while before we need them! :yes:

Course, it would kinda suck for Tim when he gets the snowmobile running if it didn't! :D

Scott
 
Best suggestion I have is to live someplace where people would laugh at you for owning such an unnecessary machine.

But good luck getting her going, anyway, Yank.
 
Okay, but I'm thinking that the ether would have bypassed whatever is/was in the carb, allowing it to start, no?

I even shot a little down the plug holes when they were out. Bah.

Well, good ideas all. Time to yank the carb.
 
This is a 2 stroke right? I've run into problems with chainsaws, weed whackers, etc. where the carb uses some of the exhaust impulse to drive a plunger which activates a small diaphragm or "pump" inside the carb. These engines had the same kind of problem: prime it, runs for 3 seconds, dies, prime it, runs for 3 seconds, dies. It turned out that one had a plugged intake screen where the "pump" picked up gas, the other engine had a ruptured diaphragm.

If your carb uses a similar setup, check those diaphragms and soak the carb in laquer thinner overnight and clean with compressed air. Good luck.:yes:
 
1st rule of thumb on any gas engine -

Start with fresh gas!

2nd would be to follow technut's advice.

3rd would be to find a forum for snowmobiles of which there are likely several hundred.
 
The new gas formulas raise hell with spark plugs. They'll fire when pulled, but fail with fuel and compression. Marginal gas makes it worse. I'd try new plugs if the others are old.
 
tentoze said:
Best suggestion I have is to live someplace where people would laugh at you for owning such an unnecessary machine.

But good luck getting her going, anyway, Yank.
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toze,
Since you live in Jax, do you have a Jet Ski? ;-)

Doug
 
Old gas will get you nowhere and does nothing but make your carb a varnished mess. Start with fresh gas (make sure you get all that old junk out of the lines) and new plugs... If your carb is getting gas into the engine then it could just be the stale gas...but if it isnt

Two-strokes don't run well on ether in my experience. Take the carb off and get a kit for it, clean everything really well (get the big can of carb cleaner and use it liberally) and try it again.

If you think what you have is bad... stuff with gas in it for 20+ years that has turned to powder...neighbor's 1970 sears riding mower that was sitting outside for 10+ years...carb kit, new tank (old one rusted out) and 1 and 1/2 cans of carb cleaner fired up on 2nd pull

Attached pic of said tractor (after i mowed the guy's lawn with it)
 

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Sometimes with those old Ski-Doo's the needle valve in the float chamber would stick.We would run it on a stand, providing fuel into the carb with an oilcan.Generally after a few minutes of running it would free itself.If that fails you'll have to go into the carb....David
 
New plugs, shot of ether as they went in, and zip. Bah. I think somebody else is gonna figure out this mess for me, as soon as I get some spare cash.

I myself am a pretty damn good mechanic, but when you've got spark, fuel (of some sort) and compression in a two stroke and it STILL won't fire up?

:dunno:
 
Don't know what the compression is supposed to be for that engine, but try squirting some ATF in the cylinders to seal the rings and jack the compression up.

Just a thought.
 
Is it just a recoil starter? How's your arm and shoulder holding up?

I HATE 2 cycle engines.

I had a 2 cylinder 4 cycle briggs engine in an Onan 5 KW generator with only recoil start, and it took a year AFTER I got rid of it for my arm and shoulder to finally settle down...

I had an electric start single cylinder 4 cycle snowblower that was as nasty to start, but the 120v electric starter could crank while I made running adjustments to hit the "sweet spot".

But my 1993 craftsman 5 hp lawnmower wasn't too bad....
 
Some motors just do not want to run off of either. Clean the carb add fresh fuel and if you still have trouble it could be crank seals or a broken flywheel key thats letting the motor fire out of time. My bro had a polaris 4wheeler (2stroke) that had compresson fire but wouldn't wet the plug it just spit the gas out the carb.No reed valves on it either so I think it was a crank seal problem.
 
Kamakiri said:
New plugs, shot of ether as they went in, and zip. Bah. I think somebody else is gonna figure out this mess for me, as soon as I get some spare cash.

I myself am a pretty damn good mechanic, but when you've got spark, fuel (of some sort) and compression in a two stroke and it STILL won't fire up?

:dunno:
Click to expand...

The only things left are ignition; timing and HT leak. A good fat spark in air can fail in the cylinder because the higher electrical resistance of compressed vapor causes the HT to rise enough to track to earth via faulty insulation or damp anywhere in the HT section. A quick check could be to try closing the plug gaps. This won't work long term but if it starts like this, you'll need to fit new plug leads and plug caps................. Jim.
 
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