OT : scorpion snowmobile

I've asked this on a few snowmobile forums but thought someone on here may know. I have a '81 scorpion 440 tk. Rebuilt the engine, just can't get it to suck fuel from the tank. It runs good when primed but when pull throttle it seems to bog down, then cut out. Any ideas?

Check for a colapsed fuel line or one that is deteriorating.With the new fuel gas line don't have a chance. I've replaced mine on my log splitter 5 times,looks good from the outside but the inside is swelled shut.

did you replace the crankshaft seals? there should be a fuel pump somewhere in the fuel line , just a small black box with a vacuum line from the crankcase going to it, then the fuel line to motor, and line to tank. there is a rubber diagphram in the box that uses vacuum pulses from the crankcase to pump fuel. check the vacuum lines, then check the box also, could be the diaghram has deteriorated too. bad crankshaft seals would give low vacuum causing fuel delivery problems.

You might want to check carb.They used a Walbro float type carb on the 440 Cuyuna engines.

I would bet that the crankshaft seals are leaking. I had a Bolens snowmobile. It was a hard starter until I replaced the crankshaft seals. If you have a low PSI gauge you can check the crankcase for leaks. Leaks can also be caused by bad lines or air boots.

Also some of the older carburetors had the fuel pump built into them. They don't like the alcohol in the newer gas. It drys the gaskets out.

First, make sure the fuel can get out of the tank. An '81 Anything will have crud in the tank. Check for an in-tank filter. If you have fuel flow from the tank, check the fuel pump if it's a float-type carb, or the carb filter if it's a diaphragm carb. For the float carb, the fuel pump will be in a remote location with a air line attached to the crankcase, to make it operate. Get a new piece of fuel line long enough to reach from the pump to your mouth, and alternately suck and blow into this tube, and it will pump fuel if the pump is operational. (Disconnect hose from carb first). If it does not work, disconnect the test hose from the atmospheric side of the pump and attach it to the pump inlet. You should be able to blow through the pump but not suck backwards. If you can go both ways the check valves are dirty or defective. If you can't go either way, it's plugged up. Find out what kind of pump it is and order a kit. You might consider a new Mikuni pump, a reliable unit and parts are readily available. Diaphragm carburetorpumps built in) Old round body Tillotson will have a screen under a plastic cover to which the fuel line attaches. Remove center screw to remove cover, and pull the screen out. Some large square bodied Walbro carbs had no internal filter, but an in-line type. For maximum reliability, I recommend you completely dismantle any diaphragm carb for inspection, and they work so much better when no shortcuts are taken. Replace all fuel lines in system, including air line if you have a remote fuel pump. Take your fuel tank off and make sure it's spotless. Make there is no blockage in the nipple for the air line (remote pump).you should feel the air rush out when the engine is cranked. Regarding crankshaft seals, they have nothing to do with pumping the fuel. However, they should be replaced if defective because they'll suck air from the outside, leaning the mixture and eventually smoking the engine. If, when you get it running, you can adjust it for a smooth idle, they're probably okay. Inspect the plugs, they say a lot about the mixture. A NGK B9HS is a good plug to run, pre-mix Bel-Ray MC-1+ @ 50:1, from there on you can read the plug colors for carb adjustments.

Did not replace crankshaft seal. I have one but hate to tear apart again. I think some carb adjustments needed, fuel pump rebuilt. Full lines tested, stumped. We don't get a lot of snow in il, especially this year but I want to be ready!

Some of those engines had a crankshaft seal inside between the cylinders too. Had a 340 John Deere that gave me fits and it was that inside seal.