CN250 clone air cut-off valve By gdoug12 (Read 1,086 times)

[gdoug12]

Hi There, I have a YY250T-2 that I have been trying to resurrect for quite some time. Keep in mind this puppy only has 120 mile on it. The original owner had no idea of what he was doing and never performed the checks recommended by JR, i.e. coolant flush, oil change, vacuum lines. Anyway this resulted in clogged coolant hose, burned rings, damaged head, severe blow-by, you name it. Tore it down and replaced the rings, head, piston, long story short after getting it back together, confirming timing is correct, it has always started right up and idled. Also runs while the enricher is working, but once it would really warm up and the enricher circuit closed it would become a real dog and eventually stall. Replaced the intake boot, no change. After playing around with it for a long time, today I had it out, let it warm up and when it started getting bad I happened to squeeze the u-shaped vacuum line going from the air cut-off valve to the side of the carb. When I did this the idle came right back and again it had throttle response. Let it go and it would die. I cut the line and installed golf tees and now it runs much better but more importantly it isn't trying to die. Does anyone know how that valve works, and why the drastic change in behavior when I close it off?

Also noticed that the helix CN250 connects the ACV to the manifold. Mine has it connected to a "T" which goes to the manifold and the fuel pump. Did the Helix have an electric fuel pump?

Thanks

[alleyoop]

Hi there,
The ACV valve works like this:
By DEFAULT is allows air to pass through and when a strong suction is applied LIKE WHEN LETTING off the throttle is closes the air and allows EXTRA FUEL to be sucked out so it does not run LEAN when a quick close of the butterfly happens.

That is why when you pinch it, what you just did is allow more fuel to the motor.

But what your problem really is you need to ADJUST your CARBS FUEL RATIO MIXTURE and reconnect the ACV valve as it was.

So the problem your having is it needs more fuel so re-connect the ACV valve and TURN your FUEL RATIO MIXTURE COUNTER CLOCKWISE to feed it more fuel. You want to turn it COUNTER CLOCKWISE and get the HIGHEST IDLE with the mixture.

Now if turning it Counter Clockwise does NOT RAISE the IDLE and it appears to do nothing THEN what that points to your PILOT JET is clogged and you will have to take the carb off and Clean out the PILOT JET and its PASSAGE to the tiny PILOT FUEL OUTLETS by the Butterfly.
Alleyoop