RCU Forums - YS .91 Supercharged mixture problems

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YS .91 Supercharged mixture problems

Hi all,
I have a YS .91 supercharged engine that I am having trouble with and hope someone can help me. I have a 14x6 prop on it, running 20/20 byron fuel and I have a fuel filter and pressure port check valve installed. I get the engine running, run about half throttle and adjust the fuel regulator until it runs stable, then I bring the throttle to full open postion and adjust the hi speed needle valve until just a touch rich and it runs stable, bring it back to idle and let it idle for a few seconds and get it stable. Then I roll the throttle to full throttle and it runs great for about 45 seconds then it sounds like someone is throttleing back and forth, down and up down and up, any hi speed mixture control adjustments seems useless, when I shut it down after that, it sits and pukes fuel from the carb..... Any thoughts??
Thanks
Dennis

RE: YS .91 Supercharged mixture problems

Quote:

ORIGINAL: Bipenut49

Hi all,
I have a YS .91 supercharged engine that I am having trouble with and hope someone can help me. I have a 14x6 prop on it, running 20/20 byron fuel and I have a fuel filter and pressure port check valve installed. I get the engine running, run about half throttle and adjust the fuel regulator until it runs stable, then I bring the throttle to full open postion and adjust the hi speed needle valve until just a touch rich and it runs stable, bring it back to idle and let it idle for a few seconds and get it stable. Then I roll the throttle to full throttle and it runs great for about 45 seconds then it sounds like someone is throttleing back and forth, down and up down and up, any hi speed mixture control adjustments seems useless, when I shut it down after that, it sits and pukes fuel from the carb..... Any thoughts??
Thanks
Dennis

I had a similar problem on a 2-stroke using those check valves. I dont know off hand which one I have but a lot of those checkvalves are too stiff and require too much pressure to open. In my situation, I could feel the valve opening and closing with the engine surging at WOT. It needs to open and close smoother. Perhaps someone else has input, but I think you might need to try a different brand check valve or take yours apart and modify it for less pressure.

I had surging with the check valve on the pressure line to the tank, and the engine would only run WOT with the check valve on the fuel feed line to the carb (because it would puke fuel out the carb if the barrel wasnt closed and wouldn't throttle worth snot without quitting.)

Just my 2 cents.

RE: YS .91 Supercharged mixture problems

Bipenut49,
Start with a fresh YS 4stroke or a OS type F glow plug, NOT! a brand X.
I've had this problem before.
Also be sure the check valve is genuine YS, none of the others will work right.
(theYS is the one with the little flapper not a ball and spring)
Be sure the regulator is absolutely clean.
If you have bottomed out the regulator screw then you have probably damaged something
in the regulator, replace the spring, plunger, and related pieces.

http://www.centralhobbies.com/

Talk to petec in the YS support forum here on RCU, he knows his stuff!

Happy flying, Oscar

Edit; Fuel pouring from the carb after shutdown usually means the regulator is not closing off the fuel.
I suspect you have a damaged plunger, spring, or diaphragm.
Or possibly some kind of crap in the regulator.
This website can help troubleshoot.
http://www.geistware.com/rcmodeling/index.htm
Go to the section on YS engines.

Good luck!