djlyon

Oops
Didn't see the other posts and that Chuck had already responded. Didn't mean to confuse.

Denis

steveg_oz

Don't assume that you're new engine will be clean inside. I had a new YS110 that was pre-detonating. I disassembled the whole fuel system, and found an insect in the regulator with a further bit in the high speed needle. It could only have gotten in during manufacture. No amount of richening the mixture stopped the detonation, as fuel was just not able to get through.

Also, when you dissassemble the carb, you'll note a groove in the middle of the barrel that distributes fuel. Often , there is swarf still in this groove, that's been anodized in place. There was a little lip on mine where the two grooves intersect. I cleaned this out with a #11 blade. Hey presto, the engine runs fine.

I was queasy at first to disassemble such a complex engine, but not only did I fix the problem, but I now understand the fuel regulation, carburation and supercharging system, which was well worth the time invested.

Steve

Sport_Pilot

I don't know what the humidity in Enterprise, Ala has to do with this. He lives in Tennessee. But in any event water in the fuel will not cause detonation and pre ignition, in fact it will eliminate detonation. Water in the fuel will cause a poor idle, transition and lower power. In fact speed C/L racers have been known to add a bit of water in their fuel to eliminate detonation.

Waco Driver

When Clarence Lee tested the YS 63 engine as detailed in the April 2001 issue of RCM, he found that once maximum rpm was reached, leaning the high speed mixture even 1 or 2 more clicks resulted in detonation. He found that the lighter the prop load, the more pronounced the detonation became. This is opposite to the effect found in normally aspirated engines where the greater the prop load, the earlier the onset of detonation becomes, and the more severe the detonation. He surmised that in the case of the YS, the higher the rpm, the greater the supercharging effect became, thus the more severe the detonation.

He also speculated that a decrease in the 9.5 to 1 compression ratio would help this situation, especially if high nitro fuel were used. His tests were carried out using Omega 10% nitro fuel with additional Castor oil added to bring the total oil content to 20%.

My testing of fuel with Acetone reveals no adverse effect on silicone fuel tubing. This is not to say it will not effect the flapper valves in the YS engine.

Sprink

Check valve may need to be opened up. When I first got my 120fz I could not get it to run right, and found that there was no pressure building up in the tank.

I had thought I had put the check valve in the right way, but assumed I was wrong so turned it round. Still didn't work.

So I took it out to try it by blowing through it. It didn't work either way!!! I blew really hard down it and suddenly it released. Works fine now.

Richard L.

My Feedback: (24)

I used to get the same knocking sound with one of my YS .63's on a Graupner 12x7 prop. I switched to an APC 13x7 prop and richened up the high speed needle valve two clicks, which seemed to solve the problem.