Dave,

I have two questions about my 91FZ.
1st one: Since having it in a different plane last year, I have not been able to get it to come up to full power; it seems to be running very rich all the time when I open up the throttle. It's smoking a ton (way more than it ever used to), but if I try to lean it out, it will keep on running the same, then all of the sudden start detonating like it is really lean, but the thick exhaust is still there. It idles alright, with a little "coughing" sometimes. Transition is good. I have messed with the regulator screw some, and it doesn't seem to do much for top end. I have replaced the diaphram and gaskets. What should I be checking, adjusting? I'm running a Zinger 15x6-10 and YS 20/20 fuel.

2nd: I messed up my threads on the prop nut (the 1st one to go on) again today. This is my 2nd one I have gone through. What am I doing wrong in tightening it? Am I putting on the jam nut too tight, or isn't that possible? Or is it just a bit too soft of a metal? Looks like I'm going to order another new one...

Thanks in advance!

Carl

How fresh is the fuel? It could be the whole problem. It also could be that leaving the engine sit for a year caused problems with the diaphragm and plunger.

Can't comment on the nuts other than I think you may just be cross threading them. Tru-turn makes a proplock setup, I believe. You need one with 8x1mm thread.

The fuel is old enough that I don't remember exactly when I bought it.:stupid: It's at least a year old, but not more than two. I've kept it well sealed during storage. When fuel gets old, what deteriorates? The nitro? I ask that because that fuel runs my Rossi perfectly, and usually it hates 20%. The diaphram was replaced, and the plunger seems to be just fine.

As far as the prop nuts: They went on perfectly smooth and easy. It's when I went to take them off yesterday to replace the prop that the prop nut's threads were messed up. I had to put string into the combustion chamber to lock up the piston to get the darn thing off. The jam nut was fine. Could it be that I'm tightening the jam nut too much, and warping the prop nut threads?

Thanks for the quick response!

Carl

Valves set right? How's the compression?

The valves were kind of loose, but I reset them to the right clearances, and that had helped some. It has good compression. I'm thinking it could be the fuel...

Carl

I am having a nearly identicle problem with my new 120AC. I am about to try a new batch of fuel to see if that is my problem. I'll keep you posted.

I went out today with a new brand of fuel with 20% nitro and 20% pure synthetic oil. (wildcat YS 4stroke fuel). The engine ran flawlessly. The fuel seems to have been the problem this time. I had changed gallons before, but all were from the same batch I think.

Dave, you hit it on the head. I got new YS 20/20 today, and bam, instantly running 100% better than it was! The old stuff I had must have lost some of it's punch, and that's probably why my Rossi likes it so well!!

It still wasn't always solid, but found out why later on; I took the plane apart to move the CG back a little, and what do I find, but some fuel-soaked balsa!! The tank was a GP tank with the screw-on cap that didn't screw on very well. It leaked fuel all over inside! Looks like I've got some work ahead of me to get it flying again. And of course it happens when the engine is running so much better than it was! That's how it always works, doesn't it? Oh well, part of our great hobby...

Thanks again everybody!!

Carl

I LOST THE NUTS OF MY YS 120, I need exactly the characteristics as the step and Diameter to obtain the same nuts

Thanks for help.

The thread size is 8x1mm