do all 2-strokes do this?

B

blckwlfny1

New Member
Hi Guys,

I am running a ktm -50 motor with a centrifugal clutch, it has no sprag catch so it should freewheel when the wheel rpm exceeds the motor drive.
THe clutch begins engaging @ 4k rpm. The motor redlines @10.5k
The carb designed specifically for this motor, is adjusted fine and jetted properly.
I am using the proper gas octane and oil ratio.
I have an expansion chamber and a muffler...motor seems to have no trouble getting "on the pipe"

The problem is this:
when the bike is not moving, the idle is fine...about 2k rpm
However, when i get up to speed and attempt to coast, backing off on the throttle, letting the clutch disengage and the letting motor idle, the motor dies.
To keep the motor running at 20 mph, I must keep the throttle revving. The clutch does not seem to have to be driving the wheels and is at least partially if not fully disengaged. When the motor dies, it does so all at once...no sputtering...just dies like the kill switch was hit (i checked the wires, theyre fine too)
When this happens, I can also confirm that the clutch freewheels because although the motor is not running, the tire keeps spinning without resistance.
I can restart it without a problem. Its not seized. It just dies.
:-||

This also used to happen to me with my china girl using a SBP kackshaft and freewheel if i disengaged the clutch at speed, it also died.

How do i solve this? I know that this cant happen on the ktm dirt bike that the motor is designed for.
 
Have you tried adjusting the resting height of the throttle slide? It sounds like something that some MZ250 riders used to do to get rid of the erratic overrun and poor idle, adjusting the slide to go all the way down so it had to be kept running manually.
 
The idle adjustment on the carbuetor does that and if I raise it any more its revving too high and ,the cluch begins to engage @ idle
 
I'd look at the idle circuit in the carb. Maybe a partially blocked passage or jet? (depending on your design) Maybe check the float level too, sometimes the fuel flowing in at full throttle can overwhelm the float and kill the motor like a choke when abruptly shut off.
 
The clutch on my Morini will drag a lot when first starting my motor cold the way I have it set up... Have to physically hold my bike still when feathering the throttle. A short time after when my clutch warms up that drag goes away and I can idle the engine with no drag to be physically holding back.
 
it runs fine at 20 mph with the throttle open,
it runs fine standing still at idle
it stalls when idling and coasting in neutral at 20 mph
:eek:

...air flow?
...carb angle?
....voodoo?
 
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Then mebbe your carb is too rich at idle and loading the motor up. Did you try intermittently blipping the throttle and it does OK?
 
Well If I idle my engine at a stop light for a long enough while I have to clear the throat out on my beast. Other wise I absolutely don't ''ever have to blip it at all'' even if I just came off of red line....
 
What I am suggesting/wondering is perhaps the progression of the carb circuit is off kelter just a tad? I found my engine was ''very finicky'' unless it was dead nuts on. If it was too lean or to rich t would do funny stuff for me in my Beginning impressions fine tuning stuff...
 
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