kitman09

hi, i have a os-91fx that will run all day long flat and level but when you go vertical it will die every time, changed planes and it still does the same thing, runs good on the ground when you hold it vertical, but will die in the air. please help.

David Bathe

Try richening it up some.

kitman09

i've richened it up on the ground, holding vertical, when wil run all day like this, but when i fly it and go vertical it will die everytime.

estradajae

The problem is not on the engine....take the fuel tank apart and check everything there...

mk1spitfire

Clunkline to long sticking to back of tank?
Pinhole in fuel tubing.
Cracked tank
blocked fuel tube
fuel tube too small

check plug and wether you have enough cooling for engine

Sounds like it isn't getting fuel

N429EM

Check your clunk, for any blockage.
Interesting that I just read this, as tonight one of our instructors was having problems with a club trainer.
It started when he tried to fuel the plane and the fuel blew off. To make a long story short, when he finally pulled the fuel tank out, he noticed some sediment in the tank. As best we could tell, some crud had become lodged in the end of the clunk. After all the jostling, the clunk must have become cleared of the blockage, because it worked fine after that. Flew well.

EJ

Mikecam

Does it die right away with a full tank or after the tank fuel level has dropped some?

kitman09

it will die with a full tank, half tank, quarter tank does'nt matter how much fuel is in the plane, when it turns vertical in the air it will die, but on the ground it will run all day long vertical, dont understand this.

TCraft Lover

My Feedback: (1)

Hi Kitman09,
You do have a maddening issue here. I wonder if it could be that the gavitational pull on the fuel caused when you pull vertical is starving the engine temporarily. I'm grasping at straws here but maybe just try richening up your LSN a touch. Theoretically this should have nothing to do with the problem but it is easy enough to try.
Good Luck,
Dave

blw

My Feedback: (3)

How old is your 91 FX?

kitman09

maybe 4 years old

estradajae

Maybe you have the a problem associated to the remote needle valve?? the overheating problem there that caused O.S to change the design of it?

Try fastening the needle assembly somewhere else in the firewall.

Saludos,

Jorge

boex

If the plane has a cowl maybe the engine overheats when at maximum stress and quits. Probably, you need to baffle the inlet to dissipate the heat.

TVL

My Feedback: (5)

I have a 61FX that's doing the same thing only mine does it as soon as you hold it vertical. Runs great as long as the plane is horizontal. If you figure out a way to stop this from happening please let us know. It does it even if I have it set so rich that it struggles to stay running on the table, it just seems to run out of fuel when you pick it up and point it vertical even thou you can see the fuel line never shows any sign of a lack of fuel' no air bubbles or nothing it stays solid pink but the engine seems to start running lean and quits. I'm going to try the large size fuel line and see if that makes any difference

estradajae

What kind of muffler are you using?

Cyberwolf

My Feedback: (4)

When a engine is pulling vertical, it makes the most demand for fuel. I would say you don't have enough tank pressure to keep fuel to the engine. Several things can cause this. Heres a few to check.

1.Tank to far back for the engine
2.Incowl muffler that makes to little tank pressure
3.Pressure line has a hole in it
4.Muffler is leaking between the block and flange
5.Plugged up nipple or pressure line.
6. HSN set to lean.

Theres a few things to check

Does your engine have the sheet metal mount for the needle or is it the cast one?
Its been asked but we need to know what muffler you are useing that will help out alot.

TVL

My Feedback: (5)

On my 61FX I'm using a Pitts style muffler I'm not sure what brand it is but I'll check the next time I stop in at the hobby shop. I'm using 3/32" fuel line for the fuel and pressure line. I'm going to switch it out this weekend with 1/8" line and see if that helps. I'll keep you all posted.

estradajae

Tue fuel tubing is not causing you the problem and changing it won't make any difference

You may not have sufficient mufler pressure....Restrict the outputs of the muffler by pinchin them or something similar. Some people just close one of the outputs.
That the pitts muffler don't provide enough back pressure seems that is a very well known problem in RCU.
Give it a try.

Saludos,

Jorge

TVL

My Feedback: (5)

Jorge you hit the nail right on the head, I blocked off one of the outlet holes and the engine ran great until the bolt that I screwed into it vibrated out in flight even then she still ran okay until I would start to climb, she then would almost clonked out by just raising the nose a little to much Now the big question is can you have to much back pressure, and how do you know if you have to much.