motor blown

[LONG-ROD]

I just bought a 250r from a guy and had it less than 10 min rideing time and it blew. Was running fat at 1/4 throttle with lots of smoke then it blew when it got ran wide open for a while. the front right side of the piston rubbed the cylinder. I was told it was an 87 with a trinity 285 kit. It actually is an 87 with the stock cylinder ported alot with a wisco 66.50 piston 39mm keihin carb, it has a paul turner by Ducan raceing head, with metal gasket, the reed cage appeared to be stock but turns out it is kinda dimond shaped with 4 triange reeds, I have no idea what it is, It also has a bills pipe. the holes in the head gasket where not near as big as the water holes on the cylinder, and appears to have oil in the water, quit a bit. So I think it had to small of a main jet and thats why she popped. If anyone can help me figure out just what I have and what jets, and needle and position I should run whould be great, I am in kansas, I can send pics if needed.

[All250R]

Unfortunetely no one can give you 100% advice on jetting, but a safe main might be 180-185 and a D series needle like a DGH on a rich clip setting. HOWEVER, you need to have crank case system gaskets and seals all sealed correctly. That means from the reed cage to the head and back down to the cyl and main seals. An easy way to test the integrity of this seal is use a leak down tester you can buy or make pretty cheaply. That should get you "ok" with with jetting.

The holes cut in a CR or TRX head gasket are smaller on the back of the cylinder by design. Honda at the time wanted more volume of fluid to pass by the exhaust port so clamped down on the ports leading to the back of the head. If that's what you're seeing, it's designed that way on purpose. Oil in the coolant and vice versa is usually a sign of a bad head gasket. Worst case scenario it's a cracked cylinder or head. I like the metal gaskets as opposed to the Cometic fiber ones. Here again the mating surfaces need to be flat for a good seal. Copper gasket spray will help "heal" fine scratches, but if you want a good runing, reliable engine, you need to get these surfaces treated with quality in mind.

Smoke by the way out the rear end is not a sign of jetting in the usual sense. Usually people see a lot of smoke out the rear and it means one of two things (remember this is not a valved 4stroke):
* The engine is cool and the gasoline in the crank has evaporated leaving a large deposit of oil. Upon startup this oil needs to agitate and burn out, in other words, it's normal and will occur regardless of yoru jetting.
* Coolant is in the combustion chamber. If I remember correctly it blows a white smoke. It's a bad sign indicating oil is washing off the cylinder walls and piston rings. It usually indicates you'll find accelerated wear since you may not have stopped the engine as soon as the coolant system was compromised. In your case though, you're looking at a new top end anyway.

That should get you going hopefully. By the way the cage you are describing might be a Duncan Pyramid cage. I've never run or tested one, but I don't hear much about it. I'm sure it's a fine cage. http://www.duncanracing.com/ctgy/28