Hello Dave
I'm looking for a diagram or the complete manual for the fuel line hookup for this engine 120 AC i have spent some time on the net to no avail finding one ,Whats throwing me a loop is the fact that this engine has the check valve going from the backplate to the air box and not the tank ,can this be correct????Oh and BTW I have enough of these YS engines now and I would like to show folks what I am useing for power any chance of getting some YS stickers to proudly display .
Thanks once again .

PM your address and I'll send a copy of the manual.

Dave: Can U help? I have a used YS 120 F that I recieved from an associate. He stated that it has been run maybe 1 hour flight time. It does sound good, "However" upon trying to fine tune it, I can shut off the mixture control completely and it will still run at full rpm and on high idle. When I go to idle at approx 4500 RPMs, it slowly comes to a stop. if I increase the throttle, it dies immediately. I have tried to adjust the idle adjusting screw and find that it will operate at 1/4 open from the closed position. As long as I leave it on high idle approx 5500 RPMs it runs good with no ill effects. I don't know too much about YS but it seems strange that given the cituations, I would think that the low and High mixture controls are not right. This is a closed system with new lines and no leaks. I am useing Excalaber 25%. I have also removed the Idle adjustment screw and the nipple looks good and the aera clean. I am running a 16 X 6 prop and the bird flys great as long as I am on high idle. I sure would appreciate some help. Thanks.

Ron

This engine has some issues which MIGHT be correctable by rebuilding the regulator, and installing all new gaskets and o-rings. Beyond that it is very hard to tell since I'm not there to see it.

By the way, the 120F has no idle adjustment screw. The regulator and HS needle were the only adjustments on the F. It must be the later version, an FZ.

Dave: My bad. I am calling the screw to the regulator an idle adjustment screw. I stand corrected. It is the regulator screw. As of yesterday I did install new gaskets and O rings. The regulator plunger is ok. looks new. Unfortunatly, I am still getting the same results. It must be something simple that I am missing. It usually is. I still haven't figured out why the engine will run full bore with the mixture control closed !!!!!!!!!!!!!!!!!!!!!!

Mixture control? You mean high speed NV? The seat in the spray bar may be worn out. Does the NV body bottom out on the hex of the spray bar? If it does, the NV assembly is shot and needs replacement. If this is what you find, the engine will never run correctly with a worn out NV assembly.

Thanks Dave. Yes I mean the high speed needle valve. I will check that out and let you know tomorrow.

Ron

OK.