Problem with Saito .91 in hover
 

I have been getting flameouts when I bring my Pizazz into a hover with my Saito .91. I noticed that when I hold the model's nose up at idle it slows down, and when I put the nose down the idle speeds up again. The 8oz tank is about 1.25" back from the firewall. The funny thing is it only happens on cold days, below 50 degrees. On warm days it's fine. I'm using a new OS F plug, 15% Red Max. The idle does not seem steady even on the ground.
Fortunately the Pizazz is strong enough in the nose area to take a drop from 20ft, but it's annoying to say the least.
I think I'm having two separate problems, the glow plug is cooling in the cold air, and my muffler pressure is too low at idle. I think a Perry 4-stroke fuel pump and maybe on-board glow for the cold days would help. Maybe I have an air leak at the header or carb?
-Tom Andersen
Greensboro NC

Richen her up!
 

IMHO, it sounds like you're running it too lean. When the nose is pointing up it has to strain to get fuel, so it goes lean. That's why it gets better when you lower the nose. As far as the temperature thing, that makes sense too: warm air is less dense than cold air. So for a given needle valve setting, flying in warmer weather (warmer air) means there's "less air" per a unit volume of air (less dense), making you're mixture more rich than in colder weather. All this plus the fact 4 strokes seem to like being run rich. I've got a Saito .91 on a Doghouse eXtreme, and it almost has to be gurgling to perform well vertically - what sounds about right for "normal" flying doesn't seem right for hovering. But it's got plenty of power so running rich doesn't affect normal flight, and when you point the nose up it leans just a little and runs perfectly. So just try running 1/8 to 1/4 turn richer next time, and see how the engine responds. BTW, what prop are you running? I've been using a APC 14x4W with good success.

Good luck!!!
-Matt

Problem with Saito .91 in hover
 

I too believe that you are lean on the low speed needle. You all should give the 15x4W APC a try. When I had this engine on a .60 Cap 232 I was getting 9200 rpm on a 15X6 APC using 30% heli. The 15x4W should be ballistic then. Also don't be afraid of the higher nitro fuels. Satios love nitro and anything up to 30% will not hurt them.

Thanks
 

I'll try richening the low end. Indeed it doesn't sound right when I richen the low end but I'll try it. I think it just isn't getting a constant fuel supply at idle. I'm running a MA 14x6 prop on it. I probably have clearance for a 15x4W but the blade seems wide enough on the MA. One time I ran a YS120 on just a Perry pump and it ran flawlessly, although I was not hovering with it. It's a bolt on affair, it can't hurt to try it. -Tom

Problem with Saito .91 in hover
 

I've got that 15/4 prop you can at least try on it next time we go out Tom. Thats an easier bolt on than the perry pump, right :)

Problem with Saito .91 in hover
 

Why would you use a perry pump on a YS 120. It already has a very good working pressure system design in place. Here is a ball park setting for the low speed needle on the satio 91S. Screw the low speed out until it is flush with the throttle arm.

had the same problem...
 

Wingspan,

I had the same issue with my Pizazz - but with a Saito 72. We went back and forth trying to figure it out, but the thing that solved the problem was moving the tank up higher - so that the middle of the tank was where the middle of the carb is...

The tank bulges out a bit, as the area behind the engine on this plane slopes up toward the canopy. But it solved my problem.

On my next plane (I built it instead of using an ARF), I paid particular attention to the tank-to-carb relationship, and have had no similar problems as I had with the Pizazz. By the way that plane is a Sig 4*60 with a Saito 91 on it.

T.