My friends 400 sports quit running today and he thought he might have fouled a plug. So he got it home and before he tried the plug he was cranking on it and he said it sounded funny like it was turning over to free. He took the plug out and its crystal white. I told him he probably burnt a hole in the piston from it running to lean. Some one had built the engine right before he got it and he was wondering how he could tell what size piston they put in it? It has RCR stickers all over it so could it be built by Rick Ritter or maybe have some Rick Ritter parts in it? Thanks for the help.

 

Pulll the topend off the motor and look at the piston.It should be marked on top.Any of a number of things could have leaned it out.

 

sound like a lean over carbs conditions or a bad cylinder to piston walls
clearance (boring),again a lot of thing can influences the problems
right out from the shop.

 

How hard is it to put a piston in the 400 sport? Does he have to pull all the plastic and the engine off or just the plastic?

 

Just the front plastic,gas tank and airbox will get him to the motor.

 

Thanks I will let him know.

 

Certainly sounds blowed up to me, do a compression check, to confirm. You should be able to pull the exhaust and peek in the port and maybe get some visual evidence. The exhaust will have to come off anyway.

 

Well I tore down my freind 400 sport today and sure enough it has a hole in the piston. It has a wiseco piston sticker on the atv but I could not find any where it said wiseco on the piston. It has some numbers on the piston and half of them are gone from the hole. How do I know what size the piston is now? Also he has a 260mj in his carb is that to small?

 

Well I got a wiseco piston ordered and will be putting it back together as soon as it gets here. He was wanting to block off the oil injection what all is involved in doing this?

 

You will have to pull out the oil pump and put a block off plate in it's place. Be sure to use a real good sealant on the plate cause it will leak if you don't. It's really an easy project. I would put a bigger main jet in there for sure and raise the needle while breaking it in. Don't want that to happen again.