has it ever happened before to any of us? LOL Yes like a hundred times! My motor (Top end ) has let go so many times I cant or dont want to remember. From lean conditions,Overheating,etc,etc. One time while racing on track during main event my counter balance bearing let go (sheared the balancer shaft in half) which then let the gear disloge like everything in my tranny and blew right out of the top of the case and clutch sidecover that was polished to chrome and hit me in the leg while I was going down the track. Needless to say I didnt finish the race and one of the other riders that was right behind me said all kinds of stuff was flying out on the track.LOLso many things to break and could get into cylnder its not even funny. I would pull all the way apart if you dont know exactly what happened and inspect it all! rings could have cought a port because some backyard idiot did your porting?you still havent said who did porting?could be bearing coming apart,chipped trans gear,piece of spark plug electrode,its all happend to me before with the extreme racing I have put mine through. better safe then sorry. Or you could always part it out, I see some stuff I wouldnt mind having for extras.LOL just kidding bro. If you want to play, sooner or later your gonna pay. Ive got like 8k in my quad and would be lucky to get 3k back as everyone is so darn cheap and cant understand all the time and money that goes into old Quads when they could go buy brand new one for like 7k if you want a good one.
just my 02 cents.
K-dog

 

It sounds like lean fuel mixture to me. Good luck and let us know what it was when you figure it out.

 

The cylinder is back at another cycle shop so it can be bored again. Everything should be back together in about a week. I guess there is no damn way to tell for certain just exactly what happened. I guess all you can do is put it back together and try again.

I plan on running things a bit richer for the first couple of rides just as a precaution. I've been using Klotz R50 Super techniplate oil. I like the stuff but always have to mix around 40:1 to keep from fouling plugs when trail riding. I have been told to switch Golden Spectro or Power Mist. Are either of these any better?

 

I think you had better stick with 32:1 on the gas[img]i/expressions/face-icon-small-blush.gif[/img]il mix. If you are fouling plugs, check your jetting. I fouled a lot of plugs when trail riding also before. I took the airbox lid off and that helped. Then I repaired a float valve and havent had any problems with fowling.

 

adding more oil will actually lean out your motor more, it only gets so much fuel and if more is oil less is gas so it will run leaner and it is the gas that cools the top of the piston, and what you are describing i would definately say you are lean.

 

Lean and rich conditions describe your fuel to air mixture. You need to have enough oil for lube.

 

R50 is a full synthetic oil and will lubricate well at 40:1 for our application. I bought a gallon of the stuff and I called klotz and they recommended 40:1 for my lt, 32:1 for the banshees I ride with. I'm not too crazy about this stuff, but the only thing bad I've heard is that it tends to leave alot of goo - not the worst thing for a fresh rebuild. I used to run 927 and liked that better. I've heard good stuff about Amsoil and will probably try that next.

Wildcard is absolutely right about more oil leaning out your mixture. I would stay at 40:1 and richen the carb on all fuel circuits so that you know it's defitely rich and then work your way down.

 

When I installed the Boyesen Rad Valve I kept having to go down with the main jet to get this thing to run right. I went from a 250 main to a 210 main in order clean up the throttle response.

I kept the jetting the same after the rebuild. My cylinder is still at the shop but I have decided to go up to a 220 main to start with.

I never messed with the pilot jet. Should I go larger on both the pilot and up another size on the main to a 230 just to be safe?

I also plain on switching to Golden Spectro and a 32:1 mixture.

 

A 210 main jet is definitely too small and I beleive this is your problem. I would start with at least a 250 main and also rebuild your carb before you even start it. If the jet is too big, you will just foul plugs, but there could be other reasons you are fouling plugs. Make sure your filter is seated properly and is clean also. If your jet is too small, you will blow the engine again.

Are you still using the stock airbox? If so it the lid still on it?

 

yep, stock airbox with lid.