Hello all,
I have a problem and I'm not sure what to do about it , so I guess I need some advice. Here is the story, I own a 1999 Scrambler 400 4x4. I bought it about 4 months ago and it ran great, it would start right up idle, everything seemed fine. One day I went to start it up and all it would do was crank and backfire, so I swapped out the plug. All of a sudden it seemed to want to crank over a few times more than normal before it would start. Well I took it out with a couple of friends on a short trail ride, approx 5 miles one way and it seemed to run fine. We even stopped a few times to B.S. and it would start right up and seem to run like it had no problems. Then we stopped at one of our friends house to take a break, and when I went to start it, it cranked for a long time before it would start and when it did it just didn't want to run for anything. It just didn't want to stay running for anything, If I hit the gas the only way it would even think about accellerating was if I gave it full choke, once I would get it going it would run fine as long as I didn't let off the throttle to slow down to much , then I would have to choke it again or it acted like it was going to stall. Well, it did get me back to my tow vehicle so I could trailer it home. After it sat for a day I noticed about a gallon of gas on my garage floor under the quad, of couse I forgot to shut the fuel off after I parked it. Either way I found that the fuel was leaking from under the carburator, possibly from around the drain bolt in the fuel bowl. When I removed the drain bolt it looked like it was ground down and even had small holes in. "BINGO" I believe I found my whole problem. So I temporarily patched the bolt with some J.B. WELD until I get a new one and put everything back together. We'll , something is still not right. It still seems to want to crank forever before it will even think about starting with the electric start, in fact I started pull starting it to help keep from draining the battery. It will start but it is idling rough enough that it seems to surge or something. It will idle for a bit then backfire and stall.
Now all of a sudden, I am starting to see oil dripping on the floor. This thing never dripped anything to my knowledge. I find that it appears that the oil is coming from the cylinder gasket where the cylinder is bolted to the crankcase. Looks like a blown gasket, took a compression reading, book calls for atleast 115psi, I appear to be getting 50psi. I assume all I need is a gasket.
Now, I have never tore into an engine like this before, So I figured it couldn't be to hard to install a gasket and put everything back together. I get down to where I pull the cylinder up and off the piston and I notice the piston doesn't look like how I would think a piston would look, It looks like it has chunks missing and I don't know whrere to go from here. I posted pics in my profile page so that you can see what I am talking about. Now I don't know how long it has looked like that or if there is some crazy reason that it should look that way but until my little trail this quad ran great with no known problems. Now I need some advice on what I should do, I have no experience at tearing down and building engines. I really don't have any idea how much it would cost to have someone rebuild this thing. I just need ideas on what I should do.

Thank's

 

yup you are definately missing chunks of your piston skirt. you will have to get a new one. me? i would rebuild the entire engine because you have no idea where the metal fragments got in to.

 

That is one crappy looking piston. You will have to rebuild that motor.

 

Welcome to the 2 stroke world. You need to get all the pieces out and then you can put on a new piston, bore the cylinder, and gaskets. Get a weisco piston. The piston is around $90, head gasket around , $15 and you should be all good.

 

This might be another option.
http://cgi.ebay.com/ebaymotors/ws/eB...category=43977

 

That sucks...total rebuild time for that motor. You have to pull it completely apart and rebuild due to all the parts that when in the lower crankcase....