Brakes Right way to slow down and brake with these HT engines?

[motorpsycho]

The motor may not be trashed "right now" but the damage is done. Those big end connecting rod needle roller bearings have all got flat spots on them.

From this point onwards, it's just a matter of time before the case hardening breaks up and exposes the soft base material - i wouldn't give it more than 500 kilometers before the big end bearing fails, either locking up the motor, or spitting the needle rollers out the exhaust and bead blasting the cylinder head and piston face.

After such high revs, the motor is effectively trashed...

so, the times that I've held my throttle wide open while sitting still has trashed my engine? Wee eaters run at wide open throttle, as well as leaf blowers and chain saws. granted they probably have higher quality bearings,.but I doubt that his engine is trashed.
think of how many people have these engines and have air leaks, which rev uncontrollably until they can fix them.
they aren't trashed.
it is possible that he has an air leak, but based on his description of the problem, it doesn't sound like an air leak. but his description of the problem may not be exactly accurate.

another problem could be that the float bowl is running empty, causing it to lean out while riding. maybe he has bad fuel flow into the carb?

 

[Fabian]

If the carburettor slide has been stuck in the wide open position and the engine has been allowed to rev to the point where it wouldn't rev any more,,,, the connecting rod bearings are damaged. It's just pot luck as to how long the engine will last before the needle roller bearings fail.

As i've previously said:

The motor may not be trashed "right now" but the damage is done.

 

[Skyliner70cc]

There is a difference betweeen running an engine at WOT with a load on it and unloaded. Weedeaters load is the cutting string that limits rpm to safe levels.

With that said, the HT engine's quality is poor. Please consider using an oil that contains some castor, that should help prolong engine life a bit.

 

[motorpsycho]

ok, so we have different opinions, lets move on.
did the o.p. ever figure out his problem?
in his original description, (his second post about this) he says it idles fine, runs fine and accelerates fine.
the only time that it revs out of control is when he's riding and he pulls in the clutch to come to a stop.
personally, to me this is indicating a stuck throttle, binding throttle cable, float bowl running empty (leaning out, but the engine doesn't die), warped carb body (stuck throttle), carb cap on too tight, bent jet needle causing it to bind in the hole, making the throttle stick, or a possible air leak.
or maybe, he's forgetting to release the throttle with his right hand before pulling in the clutch even tho he says that he is...ANYTHING is possible.

 

[Fabian]

Looks like the OP will need a new throttle cable and crankshaft assembly and engine gaskets.
Might as well replace what's likely to have caused the problem and purchase parts for what is likely to "become" the problem...