OK, here's my nagging problem. I own a 94 Polaris 400 4x4, I guess you could call it a sport, but it doesn't have a name on it. Since day 1 it has been fouling plugs like mad. Sometimes it will run for a month and not foul a plug, and other times it will run for 2 hours and foul the plug. I have had it in the shop, ummmm 10 times or so, and they can't find anything wrong with it, I have also had it innumerous other shops, and still they can't find the problem. I am to the point where I am frustrated with dealing with it. Should I just start to use pre-mix or what? I have tried to jet down but I didn't jet down to far in fear of running it to lean, which would be no big loss, I have also noticed some gas residue on the airbox plastic, right before the carb, kind of like carb backwash. I always thought of this as normal for 2 strokes though.

Any suggestions?

Thanks

John

p.s

Also, I warmed up the Quad, ran it at full throttle for about 100 yards, shut off the ignition and checked the plug, the insulator was light grey, when using it at slower speeds, the insulator is black and fouled.

thanks
again

John


[This message has been edited by 91_350 (edited 12-29-1999).]

 

try running premix I removed the oil injector on a blaster i had just because i didnt trust the pump. i was running 34 to 1 in that bike. Or you can always try a hotter spark plug
Alex

 

Has anyone ever replaced the needle and needle jet or the float valve? Very common repair items on Polaris engines with Mikuni carbs. I run a 190 main jet in the early 400s I have worked on and no problem although in very cold weather a bigger jet might be wise.
Make sure the grey foam is not restricting the air flow at the intake. Only the yellow foam is breathable the grey is an air dam to keep warm air out of the intake. Seen that mistake many times, it can move up and you dont relize it till the plug fouls.Charlie

 

91,
I would buy a block off plate for the oil injector and just start running pre-mix... I think 40:1 ratio is what most Polaris seem to run good at.. Just remember that if you leave it sitting with alot of fuel in the tank, shake the machine pretty good before you fire up and go riding again. Not an everyday thing.. just if you let it set for several days without riding it...

 

I believe your machine is called a Trailboss 400 4x4? Not sure, but they upped the displacement of the earlier 350's to 400 like yours, then in '95 the Xplorer 400 replaced it. It sounds like a jetting or an oil injection problem. Does the oil in the injection tank go down fast? It sounds like the injection pump could be set wrong and giving it too much oil, or by the colors of the spark plug, the jetting is wrong. Let me know if the oil injection tank goes down faster than normal, because you can adjust that.

 

It sounds to me as if your main jet is correct because at full throttle the sparkplug is a good color but at smaller throttle opening you are running rich. try dropping the neddle (raise the clip) and see how it runs. also check the air screw to lean out the idle circuit

 

have a dealer or mechanic check the timing marks on the oil pump. it might be getting too much oil. use a good tcw3 oil. or synthetic oil.

 

"Also, I warmed up the Quad, ran it at full throttle for about 100 yards, shut off the ignition and checked the plug, the insulator was light grey, when using it at slower speeds, the insulator is black and fouled."

There is your problem right now..You can't run 2 strokes at a low RPMs..it's not hot enough to keep the oil burned out of the cylinder!

When running at lower RPMs the oil starts to builds up in the cylinder!

Same thing happens to my TB when i puttt around on it