Sled won't stay running? Any idea why?

[Sideshowrob]

First off I have to say, the sled in question is NOT a Yamaha. I picked up an 87 Ski Doo 250 Tundra at a yard sale for cheap, for my father in law. I would have preferred a Bravo or Enticer, but this was a good deal.
Now the story; I changed all the fuel lines, removed and cleaned the gas tank, put on a new primer, rebuild kit for the fuel pump, and cleaned the carb a few times, and a new plug. So it fires up on the 3rd or 4th pull, runs great for about 30- 40 seconds, then just dies. If I give it gas it will stay running, but I can feel it wanting to stall. To me it feels like a fuel issue, but I've gone over the fuel system and everything seems good. There are only 2 adjustment screws on the carb, and regardless of where they are set the result is the same. So, is it electrical and if so, what should I check first? Or am I missing something simple? The carb is a Mikuni, as well as the fuel pump. I'm just hoping this is a problem someone recognizes and can offer some suggestions.
Thank you.

Rob M.

 

[rx1jim]

I am not familiar with the sled you are working on but will try to help. Did you check the float height in the carb? You could also hook up a temporary gas tank above the carb so the gas will be delivered by gravity to the carb. Of course this is just for testing the sled while stationary. This will allow you to rule out the fule pump, while it is running, take the fuel line from the pump and put into a container. If the fuel pump is bad, the gravity feed from an overhead gas tank will allow the sled to keep running. While the sled is running, there should be no gas flowing from the line connected to the fuel pump. It is possible the pickup ine in the sled's gas tank is plugged or disconnected inside the tank. To check if it is an electrical problem, when the engine quits, connect up another spark plug, pull the engine over and see if there is a spark. I had an engine which would run for 10 min. until it warmed up then it quit. It was an electrical problem, there was problem in the ignition coil, it would have an open circuit once it got warm.

Try these tests and let us know what you find.

Jim

 

[Maim]

how long did it sit before you bought it?

what is the compression #'s?

could have stuck rings whitch will not create enough pulse for the fuel pump to keep it idling. uncle has a vk540 that is doing this but it has 18000 miles on it without a re-ring. might be your problem.

 

[Sxr700Bandit]

You may also have a problem with the crank seals while you have it running have someone spray either WD40 or carb cleaner at the crankshaft seals and see if it wants to run better or to see if the engine tune/pitch changes.

 

[Sideshowrob]

Thanks for the responses everybody. Now I have some more things to try. It really feels like a fuel problem, just because of how well it runs (before it stalls) but I will check everything. It may take a while to post my findings as this is not a top priority project. I will let you all know what I find though.