Ihave a new YS F-91 AC.I followed the starting directions that have been posted on the YS board here and I've gotten the engine started.

But two things are happening. With the throttle stationary on my transmitter the engine will slowly run up and then back down then up and then back down. Sort of like it is pulsating up and down without me touching a thing. As it starts falling down I'll have to bump the transmitter throttle control to keep it going even though it is within idle range. If Ididn't bump it, it would just go dead.

Also, if Iremove the glow plug starter it dies, and the plug is new. I am trying to err on the "rich" side and Imay have it too rich. It is about 2.5 turns out and it blows some smoke and the wing has oil on it. I noticed though that if I turn it in to 1.5 turns out, it won't even start.

Pete is this normal for the initial break in? Do Ijust need to keep doing this until it starts running smoother and smoother, or is there something else going on?

Thanks.</p>

Also, I am using 30% cool power in it for break in. Is the oil content too high in that fuel and making this happen? If so, Ican get YS 20 at my LHS.

Thanks again for any help.

30% Cool Power is fine, in fact the higher nitro will make tuning easier. What you are describing is far from normal and given the age of the engine (I know you said its new but it has not been produced in while) you may have to clean out the regulator if it was stored with any oil or fuel in it.

BUT...Let us start at the beginning and work our way through this.

1) You are using a YS check valve and it is installed properly correct?
2) The tank is holding pressure correct?
3) You put a new YS #4 or OS Type F plug in the engine.
4) Flush the regulator
5) Take the HS needle out and crank the engine over at full throttle WITHOUT the glow driver to flush out the needle passage.

The LS needle is just an air bleed and further CCW you turn it the leaner you are making the idle.

GIve the above a try and report back. That surging is typical of a lean condition and I suspect there is just something that just needs flushed out of the passages in the engine.

Pete

Ok - Thx Pete - Why does it die when I take the glow starter off?

Could be a bad plug. I had a 1.40L that drove me nuts and it turned out I replaced a bad plug with a another bad plug. I actually sent it to Richard for repair and he called me and asked where I got the plug that as in it. I told him it was in my field box and he said it wasn't a YS or OS plug. It was another brand from when I was playing with other four strokes years ago and my YS did not like it. He did nothing more than put a new YS #4 in it and send it back. Ran great until I sold the plane it was in. I still have that engine and it still has the plug Richard put in it.

Run down the list of usual suspect above....unless you have a servo oscillating at idle or a REALLY soft mount allowing the engine to move a lot what is listed usually clears things up.

Pete - You said something about a soft mount. I bought this plane used, but it had never been flown and it had this engine in it and the guy Ibought it from said he only ran it a few times to taxi around his driveway. I took the cowl off just to inspect things and Inoticed that I could move the engine if Iheld thespinner in my hand and shifted it up and down with my hand. Upon furthur inspection I noticed that the two engine mount bolts closest to the firewall had a small gap, meaning they had worked loose, or hell they may have been that way when I bought it. I'm going to try to tighten them back down, but Imay just have to redo the engine mount. Would that cause the condition I am experiencing?

Thanks again.

If the engine is moving at idle and the servo is not you are in effect moving your throttle linkage.

I guess I'll take that as a "Yes". I'll get everything tightened down and see what happens.

Thanks!

Yes.

Pete - I changed out the glow plug to a new OS and reset the low end to factory settings (it was actually unscrewed by 4 turns and Ibelieve he thought he was richening it by unscrewing it) and it cranked up and ran perfectly. A lot of smoke on idle so should I lean out the low end a bit?

Also, this thing is turning 10,000 RPMs at half my transmitter throttle.

One other thing. The muffler tube will not stay tightened to the engine. What is the best way to address that? Should I use a threadlocker on it, or is there some type of lock washer that should be put on that tube?

Thanks!

What prop are you running? 10k at half throttle? What is your RPM at WOT?

I've never used thread locker on the muffler, the AC has a straight muffler that is threads directly into the head and I just tighten it. The 91FZ has a pipe that goes from the head to the muffler and it has lock nuts on either end..again never needed thread locker so I can't in good conscience make a suggestion.