Hi All, Please need help . YS-63FZ. Idle 2000rpm perfect, Full Throttle 10,800Rpm-Perfect. At Quarter throttle runs rough after 5-10 secs and then cuts out. have set regulator both dirrections to no avail. Set valve clearance 0.0015inch (cold). I have also read most of your posts. Also very difficult to restart when warm in fact I have to wait for it to cool. Using fresh 15% Nitro 18% Synthetic 2% Castor. Operating altitude Johannesburg South Africa 5,500 Feet Above see level. Checked all fuel lines, filters, check valve,tank does hold pressure,using OS type F plug,swinging 12/7 APC prop. Its in a Super Stearman Done 3 flights with 2 Dead Sticks. Not flying until this engine is right. YS experts please help..

Regards
Dave Black
[email protected]
South Africa

Mine runs better on YS 20\20 fuel, 13X6 MA prop with an enya #3 plug. I also usw Fox Miricle plugs. The setting on mine were really touchy until I went with the YS 20\20 fuel. Now the needles do not need to be exact. If they are off a notch or four it still runs very well. How many runs have you done on this engine? I spent about half a gallon breaking it in. Now it scream and runs any where I put the throttle.

Dru.

Hi Dru,
Thanks for yr info . My ys 63 has run about 6 times when I can get it to run. I think I must at least up the nitro from 15%-20% for a start. I just cannot understand its refusal to start after it has run for about 2Mins.
Regards
Dave

In the hi desert of southern california the guys back off of the nitro! Its one of the few areas you will ever see 12 1/2% nitro. Because of the altitude and the heat. You did not mention the temp but the hotter it gets the more sluggish the engine is. It's not like some more modern engines where a computer adjusts the mixture. Put the regulator screw back to flush or about 1/4 in at the most and richen up you low end. Stay with the OS F plug. I dont think higher nitro will cure the problem.
Be sure your fuel and pressure lines are coming out of the correct nipple.( sounds like they are but double check!) Otherwise contact the YS guru in the maufacturer section(Mr Shadel).
Good Luck!

Thanks Deputy,
The temp here in Pretoria is in the early 70s at the moment. the engine was not worked hard and did not seem to run hot at all. I could still touch the valve cover after the 3Min run. What I find weird is that it runs fine at full throtle and at idle but likes nothing in between. I checked nipples -Facing the engine The right line goes to the tank via the check valve for press and the left one from the tank to the engine via fuel filter. I have also just released the press now which has held for two hours.

It really sounds like the midrange is rich and the regulator controls that! How much did you turn it in? When you do, you should richen up the low and hi needles and then retune. On past YS's I've had 1 or 2 that needed to be in almost 2 turns but 90% of the time I only turned it in 1/4 to 3/4 turn. At normal altitude (0-2000ft) and the newer YS (63/91..) only the low and hi needle usually needs to be adjusted. Also if its inverted! What size prop? Use a 12x8 for now. The 63 does have a hesitant midrange. A little more than other YS's. It may be accentuated by your altitude but you should still be able to get it to run at mid throttle.

Hi Deputy,
12-7 APC prop OSF plug. Taking the 747 to London tonight hopefully those 4 Rolls Royces will be set right-back on Sunday to continue the struggle.
Dave