Hi,
I usually add about 4oz. of castor to my all my fuel for my 2 strokes. I have a YS 91 and use 15% wildcat fuel, is it recommened to add castor . I heard that it can gum up a 4 stroke?
Regards,
Frank

The only problem with using castor is that it builds up on the exhaust valve. Synthetics do it too, but not as fast. Castor becomes a thick goo after leaving the engine set for the off-season, so prepare to be gooey come Springtime.

You really ought to use the recommended fuel, 20 synthetic, 20 nitro. Lots of mfg's make it under the YS 20/20 name.

Thanks for the quick response Dave. I just started adding the castor to all my fuel this spring and noticed that I have been having trouble tuning my YS engine , (low and mid range). I`ll try some 20% and not add any castor and see what happens.
Frank

Let me know. The poor idle and transition is likely the low nitro fuel, and not the oil. If you add oil, you also cut nitro percentage unless you add nitro to compensate.

Hi Dave,
I used the 20/20 YS fuel and had better results (idle and mid) but still have a re-acuring problem. In the pits the engine idles great , mid good, lots of power at full 9300 with 14-10 prop. I taxie to the runway and the engine keeps quiting ! I tried every LSN setting with the same problem. If I keep the idle way up I was able to take off and fly with no problems, the engine ran good. Is it possible the plug is fouled and needs to be changed? If so what is the best plug for a YS 91AC?
Regards,
Frank

Could be the plug. Either OS type F or YS #4. They are both the same.

Hi Dave,
Changed the plug and all my problems stopped! Had three flights, engine ran flawless.
Regards,
Frank

See how easy that was?

Good Flying!