I was out ice fishing in some pretty heavy snow yesterday. At the end of the day while driving back to my trailer through he snow the engine suddenly lost power, put out a lot of black smoke and then stopped running. I let it sit a while and tried to restart. It would start but only run for a few seconds while putting out a lot of black smoke and then backfiring. I tried this a few times and then gave up and got towed in. Today I tried to start it again. It starts, runs for a few seconds then dies. No backfire today but still some black smoke. Can anyone give me some advice on what might be wrong before I make the dreaded trip to the dealer? Thanks much.

 

how old is the gas? carb leaking out the bottom?may be has the worn out cam lobe, some of the older machines would wear out the lobe on exhaust side of cam, causing these symtems, remove gas tank and valve cover, inpect cam shaft ,there will be a very noticable difference between the two lobes if thats the problem

 

Gas is fresh. Update: I took a look at the air filter and found that it looked pretty dirty. I removed it and the engine started fine and idled, but not as smoothly as normal. I'm wondering if a new air filter might fix my problem. Could a dirty air filter combined with riding in a lot of powder snow cause the engine to die so quickly?

 

I would change the air filter first if it's that dirty (why wasn't changed before this point),Lack of normal maintenance? Second I would change the spark plug, The Black Smoke did not help the plug in any way now.
third and most important I would get in into a heated garage and let it thaw out....Snow dust is know to cause many problems with Snowmobiles ...That's why they have had heated carbs, Foam on air-intakes to the carbs and air opening on the cowling that can be closed off due to deep snow conditions......Get it melted and get back to us..........Good luck.......Caper.....

 

Thanks. I'm going to install a new air filter tomorrow. Also, the Atv is in the garage now which will dry things out. I'll post results of new air filter installation.

 

Those older Magnums would sometimes get ice freezing on the body of the carb which would cause it to crack. I've seen that happen a couple of times and it would have the same symptoms your does -black smoke, backfiring etc.

Check the carb body really close for cracks.

 

I installed a new air filter and the engine starts fine and runs good. However it is loud. I think that there is exhaust escaping from the front of the engine where the exhaust manifold bolts to the engine. I can feel exhaust gas escaping there if I put my hand near the manifold. I'm wondering if an engine backfire may have blown out the exhaust gasket between the exhaust manifold and the engine. Is this possible?