Outdoor Power Equipment and Small Engines - artic cat snowmobile

My friend just got an 1970 artic cat snowsled. We got it for free from his uncle and it ran when it was put in the garage. When we got it was taken apart and we have put flywheel back on and gapped the points as close as we could get them. Then we put the recoil on and got fire. Then we put a new diphram in the carb and all new fuel line. When we tried to start it we used the primer to shoot some gas in and then tried to start it without much sucess. It will start and then die instantly if you use a dry plug then you have to take it out the plugs and crank it oveer several times and sometimes it will go again put quickly soaks the plug. Once in a while it will backfire through the carb. Does this sound like we havent got the points right or the carb is messed up or something else. Any help would be great so thanks and Merry Christmas eneryone.

Hello Butterfingers!

You have a carburetor problem. It is allowing too much fuel to enter the cylinder. If it is just a diaphragm carb, with no float, you may need to double check the installation of the diaphragm and make sure it doesn't have a pinhole in it, and make sure the needle is seating against the seat when the diaphragm presses it.

thnaks cheese
Where is the needle the diaphram pushes? The only needle i knew about was the high and low speed adjustments. To check this needle do i take the diaphram off? Also is there gas know sitting in the crankcase and if yes how do i get rid of it? Thanks

I am not familiar with the specifics of the carburetor you have, but I would guess that there is a needle either clipped to the diaphragm, or at least in contact with the diaphragm on that sort of carb. Partial disassembly of the carb would be necessary to view it. I don't know if there is fuel in the crankcase now or not, but it is probable. Remove the spark plug and let the cylinder dry out, and reinstall it when the carb gets fixed and you'll probably be ok.

If the engine has a Mikuni or twin Mikunis, then you will have an external fuel pump..in which case just replace the pump for about, well, 30 bucks cdn...there could be old fuel in there clogging up the holes...If it is a Tillotsen it will have an internal fuel pump and you will want to make sure that all passageways are clear of old (chances are, rotten) fuel. The needle is under the diaphragm as cheese has said. If for some reason you have a float carb, which is highly unlikely, but possibly the float is not functioning properly. Oh yeah...the points setting is 12-16 thou...so .014 is a happy medium...Good Luck and have fun riding!!!

thanks for the great advice guys. I havent got a chance to work on this yet but i will definatly take the carb apart and clean it out. Also when i put a new diaphram in the carb i sort of forgot how it came apart. I know that there was a gasket that went on first. Then i was unsure weather the ligter colored piece with the small tabs that cover the passages went on or the actual pum part. I called the repair shop and they werent really sure since the only see one of these Tillotsen carbs once a year. Thanks again for all the great advice.

Butterfingers....is that an HD or an HR carb??