1970's arctic cat 500 hearth engine

**hotroddal** · 12-12-2005, 05:59 PM

i have a 500 hearth mounted in an arctic cat sled, and i am having trouble with the plug fouling out, its only fouling one plug, just yesterday i put two new plugs in it and i drove it 6 times for 10 minutes each time, and now i whent to start it this morning and the darn thing fouled just one plug again.so what could be the problem here, when i put new plugs in it it runs really really great, with plenty of power.

**hotroddal** · 12-12-2005, 06:02 PM

by the way its a twin cyclinder.

**MTS** · 12-12-2005, 08:10 PM

Is it the one closest to the fan? might try a grade hotter plug on the cool side.

**hotroddal** · 12-13-2005, 09:27 AM

my trike sucks, your correct, it was the plug closest to the fan, i whent and bought one new plug for the one that fouled out, and i installed it and im going to see if it foules this plug too, becuase maybee i just got a bad plug to start with, the coils are suppling sufficient spark also.

**Jason Hall** · 12-13-2005, 09:34 AM

Does it have dual carbs? If it does I would check the choke to see if it's hanging up in the fouling cylinder. Some carbs have a cable operated choke plunger, that can get stuck open. Or someone could have the wrong jets in one carb. If it has an old diaphram style tilltonson carb I would get rid of it. Some people like the diaphram style, but you can tune a slide style carb better in my opinion. I guess there is a slight posibility that a leaking crank seal could push air & fuel from the good cylinder into the bad cylinder also. If it has 2 pipes also make sure mickey mouse did'nt build a condo in the one pipe.

**hotroddal** · 12-13-2005, 06:09 PM

it doesnt have dual carbs,its got a 32mm mikuni carb,it has a header that goes to both cylinders and then joines into 1 muffler.

**Jason Hall** · 12-13-2005, 10:56 PM

I bet you need to set the points. If it's an old engine (I have no clue what year it is). That would be the first thing I would do. It will still have good spark, it will just be there at the wrong time.

**hotroddal** · 12-21-2005, 05:35 PM

well, i replaced the plug thats fowled out with agood one, i rid it about 100 times since then and its not fowling the plugs, maybee a just got a bad plug to start with.

**hrc85250r** · 12-23-2005, 12:11 AM

that might be right, with the hotter plug, but make sure you arent slowly melting a hole in the piston.....

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1970's arctic cat 500 hearth engine