Well I had it souped up and burnt one piston so I tok it back stock and after only 66 miles it burnt another! Im staarting to wonder about the mechanic! Any ideas?

 

If you are burning holes in pistons then you are running it to lean. You probably have an air leak somewhere in your motor or in maybe in the intake boot. It apparently had nothing to do with your first engine mods. Unless for some reason you went to a smaller carb jets.

 

What kind of air leaks? Thru the head? Or maybe a hole in my block? I thought maybe my fuel line had blockage but throttle wasfine until aboiut 5minute prior. I noticed just a slight decrease, barely noticeable. So I stopped and let the fan run till it quit just a cou8ple minutes than ran it again and then it just stopped.

 

PaulC,

It could be any one of a number of things. You could have an air leak between the carb and cylinder, it could be that the cylinder base gasket is leaking or it could be that you got it ported and never changed the jets to richer ones. You did mentioned it being "souped-up. I'm guessing that's what you meant. You have to be more specific other than you burnt a hole in the piston. Did it have a high RPM idle after you had it rebuilt both times? Did it make a whistling sound while running? Did you spray WD-40 around the intake to see if the idle would slow down? There could be many possibilities that you aren't telling us. It's kind of hard to diagnose the problem with out specifics.

 

get rid of the thing and switch over to a d a m n yamaha[img]i/expressions/face-icon-small-happy.gif[/img]

 

Do you know if these were both stock Polaris pistons?

 

Ok, I bought the atv April of 2000. Totally stock brand nre from the dealer. Broke it nicely. In April of 2001 I the dealer to install an Aeon trail pipe, KN airfilter, Delta Reeds, and Clutch kit. I didnt touch the piston. They jetted it according to the prescribed size. No porting was suppost to be done I didnt want it. This wasnt suppose to max the thing out. Anyway, I put about 200 miles on it over the next few months and ws riding my wife on the back one and it just died. I took it in and they said I must have run it too low on gas and it leaned out and burnt a hole in the piston. So, I said I want it all back stock. 20/20 hind sight. I want it dependable again. They bored it 20 over and put in a wiseco piston and they left the reed valve kit on it...they said it wouldn't effect dependability at all. I had to ask about the break in period. He said just baby for the first tank of gas and you should be fine that it wasnt like the breakin for a new atv 500 miles etc. Anyway, I ran 2 tanks of gas thru it and was on my third just putting along about 30 mph and it just quit. The light came on after I stopped. I changed the plug and it didnt fix it. I pulled the manual start .. no compression that I can tell. Its been there a week and they havent even looked at it!

Thanks,

Paul

 

I bet a dollar to a doughnut your needle in the carb is too lean. I just bet on it.

Raise the needle until it blubbers slightly when doing approx 10-20 mph. Then slightly give it gas and it immediately should run good. If so, then you are set.

You see, these auto trannys run at a higher rpm when cruising then if you were shifting manually. If you were in control of the gear you would shift until the rpm is at a comfortable level. But the CVT is always ready to go; running at higher rpms. So you need to richen it while driving at 1/4 to 2/3 throttle.

You can have the right pilot jet (for idling and just taking off), and main jet (for wide open throttle), put the 1/4 to 2/3 throttles are controlled by the needle position.

It doesn't matter if it is stock, mildly modified or wildly ported, this condition is unique to Polaris. Call HPD (Darrell or Mike) or call Rick Ritter (my favorite). They will tell ya about this. There is another thread talking about a SP500 that burned a piston too just putting along. I am sure it is the same issue as this.

Simply, running at higher rpms (CVT's choice) on the mid-range of the carb (the needle) requires more fuel. So richen it (raising the needle) until you get a slight blubber putting at 20 mph. If you aren't too rich, the instant you give it a little more gas, it should pull good and clean.

That is the sweet spot of a 400 Polaris CVT.

Chunky

 

Well after 2 weeks the dealer finally looked at it. They didnt even work on it. Thery say its running great. It starts up fine now. It didnt the day I took it to him and he tried. He said sometimes the cylinder wall will gets scared and eventually it will seize up and I'll need it bored again. How do u stop the cylinder wall from scaring? I already use the best oil and baby the thing?


tx,

Paul

 

PaulC,

The next time you need to have the motor redone, get a Swaintech coated Wiseco piston in it. The "Poly-Moly" side coating will resist scuffing and the Ceramic coated top will prevent cold seizure by allowing the piston and the bore to come to the same temperature at the same time.

Which reminds me, are you letting the machine warm up before you ride it? The forged Wiseco pistons have a tendency to cold seize if the machine isn't warmed up properly before you rip and tear on it. Because the grain structure of the metal is aligned during the forging process, the pistons tend to expand more side to side than top to bottom. This isn't a problem with a stock cast piston as the grain structure of the metal is not aligned when the molten metal is poured into the mold.

Hope this helps!