bought a used 2000 400 2x4 scrambler and after about 400 miles the piston burned up. Took it in and had the top end re done and ran a mix of oil and gas in the gas tank along with the normal injection of oil. After about 300 miles, you guessed it, fried. Rather then doing top end again and dumping this junk on someone else I had the top and bottom done including gaskets and bearings. 300 miles later, yup, toasted piston. This new shop says they suggest doing the entire engine again.

My question for this knowledge base; top end and dump and run on some other fool or do you have something I should look at? FYI; all mechanics looking at the thing said it appears to be running lean yet getting plenty of oil which confuses them.

Note; this machine is near Cadillac MI now and if someone would like to purchase, ha ha, I have the shop leave it torn down and will sell for a very reasonable price.

 

Running lean and burning holes in pistons is not an oil issue. It's a lean air/fuel ratio issue. Put a bigger main jet in it. Go through the carb and make sure everything is correct and clean(no varnish) Look at the plug color after you ride it and determine if you need more fuel.

 

Whats the price tag ?

 

Hello, I have found the problem with the scrambler 400 engine that likes to melt pistons. after melting a couple myself, i discovered the only way to correct this problem is to install a fuel pump. if a 2 stroke engine melts a piston no matter what jetts your running it is still a leaning out problem, the gravity feed fuel system cannot maintain a full float bowl at higher rpms. HPD sells a fuel pump for this engine. I used a fuel pump off of a 1992 440 snowmobile. works awsome.

 

Is it burning holes in the piston or just seizing?
I have the same atv. Bought it used and seized twice on me. Asked my local Polaris dealer and they said it looked like a lack of oil but the pump was working. I also found out that there were previous warranty issues with this same atv. Polaris wouldn't do a goodwill for me because of the age.
Anyway, we finally found the problem and cut the banjo bolt in half. It's the last part that puts oil into the carb. There was a tiny piece of metal the size of a grain of salt that looks like it was there from the factory. It would float around in there and finally block the small port and cut off the oil supply to the motor and it was enough to seize the piston but the lower end was fine.
New banjo bolt and piston and never another problem.
FYI, pipe, clutch kit,k&n, .020 over and 270 main jet, needle on 3rd clip

 

Hey birda, what did you find out?

 

Hey, I'm building a 400 Scrambler that will need to be fed by means of a fuel pump. I know that I can buy a fuel pump through HPD for $65.00, but I can also buy a pump from Ebay for $15-$20 that will do the same thing, but I need to know how to install it using a pulse line. Where does a pulse line connect?
Thanks in advance!!!