Put a YS .63FZ into a Matt Chapman CAP. The engine starts and runs fine. Transition is great but towards the end of a flight if you go down to idle the engine will not run back up. It's not getting overly hot. Any suggestions??

Can you fly it without the cowl? I suspect it really is running hotter than you think.

What prop?

What fuel?

Lou55, I had a problem similar to yours with a 91fz....it would run fine full throttle, fine at idle, but if you cut back to maybe 1/4 throttle, as when setting up to land for example, it would go rich and not want to clean up again. I fiddled with the idle setting, I fiddled with the regulator, I fiddled with the high speed needle, all to no avail.
I was running my regular 15% sport fuel and somebody suggested trying 20% nitro, 20% oil. It didn't make any sense to me that this would solve the problem, but it did. You might try borrowing a tank of the stuff from somebody to see if it works for you.

I'm running the engine on PowerMaster YS 20/20 with a 13x4W APC Prop. I've opened up the cowl significantly since this photo was taken, at the build, to insure good airflow over the engine with a 4X exit opening in the bottom of the cowl for good flow. The top of the valve cover is now exposed and there is a large opening below the one in the picture to get airflow to the case and muffler. I'm only flying this plane in normal patterns at just over half throttle with no aerobatics or 3D so stresses are at a minimum. I can hold my finger on the valve cover after landing so I doubt it's getting overly hot. I just got this engine back from YS prior to installation in this plane and had the cylinder replaced due to a dropped exhaust valve seat. I'm running it in as if it were new so it's as rich as I dare run it and set per YS instructions. The regulator is clean and set level with the top of the housing as suggested and the tank is holding good pressure. After the last flight we started the engine on the stand to try and figure it out and it had a fuel leak from the carb barrel which went away about a minute later. Everything is tight and I've never put any type of after run oil in either of my two YS .63s. I read the thread titled "ys63 inconsistant" and it sounds as though I might be having the same problem although mine is an S.

Al Lewis

How flexible is your fuel tank? Lots of ARF's have fuel tanks which will hold pressure but lack the strength to keep from flexing. If you suspect that the tank may be on the wimpy side, try wrapping it with filiment tape and see what happens.

Your first post indicates that the engine runs fine until close to the end of the tank. That tells me that maybe it's not the engine but a tank problem. Are you running a fueling valve? If so, take it out of the system. Fuel dot and T fittings are much better.

The tank was wrapped in filiment tape prior to installation. I wrap all of my YS tanks. I'm also using a fuel dot with a T fitting.

Well , I'm just fishing, then.

It makes little sense that the engine will run most of the tank out and be fine, then go sour. That points to a tank problem or an overheating problem in my mind.

Do you know anyone who has some Cool Power 30% heli fuel? If so, give it a try and let me know the result. Don't forget to reset the needles when you make the change. If it works, it won't be the first time I was right!

Like I said, I'm fishing at this point.

Solved my problem. I put in a Super Tigre .61 tonight. May put the YS in another plane latter if I can get it to bench test. Thanks

So sorry I couldn't help. Good Luck!

you say that the valv cover doesnt get hot, the problem is that that isnt the part that get hot its the crankcase and the piston shroud
im using the same setup as you but in a different plane maybe a different sizqe tank, i belive mine has had some troubla along the same lines as yours as well have you adjusted the tappets and made sure that the valves are at near perfuect tdc as thay can

plane kissa. Once again you are on threads you should not be posting on. Read the rules for posting that are stickied at the top of the page.