Suzuki 2 Strokes

this was on another forum any answers as to what the cause is??
I must admit I'm a bit baffled. I though it might be the small ends or worn out piston..hence piston slap?

(Hi there any ideas whats broken, I have a Suzuki T250 J I bought it as a nostalga ride and restore project it is in average condition and has done very little KM it starts first kick ticks over nice.
The problem is when it gets hot it starts to rattle and looses power and starts to missfire, the rattle I thought might have been the small ends so I have changed them also fitted new rings at the same time. I was thinking bottom end but it dosent sound like the noise is coming from there could it be the crankcase seals causing the problem?)

There are several tests to try, compression is one, when hot. Do it cold first so you can compare readings. Also swap condensers, then next ignition coils. It is unlikely that both coils are breaking down at the same time. I just thought of this, when it loses power and I presume dies at idle, quickly open the gas cap to see if it sucks in a lungful of air. It could be a plugged vent hole, causing a vacuum in the tank. It is slightly possible it is the crank seals, but I think it would affect one cylinder more than both at the same time. Also check your head light when the engine loses power, perhaps if the light goes real dim, your battery is going flat. Even on a simple bike, there are many thing to check.

Sounds like it's getting too lean when it's hot. A quick test is to give it a little bit of choke when it starts to rattle (just a little, not full choke). If it picks up and stops rattling, carburation's too weak, which could be incorrect jetting, an air leak, or crank seals.

Failed or failing crank seals often make for hard starting, especially when the engine's cold.

Could also be the ignition timing is incorrect (too advanced).

Blocked exhausts? My 350 had a wrong baffle in one of the exhausts before and started to knock/ping when it got hot. If it is a low milage bike it could maybe have been standing for some time and have a mouse nest or something inside the pipes.