Notices
O.S. Engines Support Ask Bill Baxter your questions about O.S. Engines.

Os .91 Fx

Old 10-30-2002, 06:27 PM
  #1  
Senior Member
Thread Starter
 
Hircflyer's Avatar
 
Join Date: Dec 2001
Location: Kailua, HI
Posts: 956
Likes: 0
Received 3 Likes on 2 Posts
Default Os .91 Fx

I have right out of box......and the engine will not run.

I have 13x8 prop using Powermaster 10% nitro. OS # 8 plug

Engine pops, turns about six turns and stops.....

This has continued for many attemps by me and half the members of the club. Using both hand flips and starter.

Everyone agrees fuel system set-up is good, needle about two turns out, we tried 3 turns out and 1 1/2 turns out.

Should we try 15% fuel?

Thanks
Old 10-30-2002, 06:55 PM
  #2  
Senior Member
My Feedback: (2)
 
Join Date: Oct 2002
Location: League City, TX
Posts: 307
Likes: 0
Received 0 Likes on 0 Posts
Default Os .91 Fx

Where is the idle mixture screw on this engine?
Old 10-30-2002, 07:19 PM
  #3  
Bax
My Feedback: (11)
 
Join Date: Apr 2002
Location: Monticello, IL
Posts: 19,483
Likes: 0
Received 6 Likes on 5 Posts
Default Os .91 Fx

Hircflyer,

From your description, your engine's just not getting fuel. There could be many reasons for this, many of them are causes external to the engine.

Without seeing the engine, it would be hard to diagnose your difficulty. One thing to check though is fuel delivery. It's easy to get the idle needle set so lean that it interfered with high speed fuel flow. When the carb is at the full throttle position, you should see about a 4-5mm gap between the idle needle and the fuel nozzle. If it's closer than that, the idle needle may be blocking the fuel nozzle at reduced throttle.

You also may want to make sure that the carburetor's not gotten any trash that could block fuel flow. If you shoot some fuel into the carb opening to prime the engine, and it burns out the prime, fuel's not flowing and you'll have to check teh engine and fuel system to see why.
Old 11-01-2002, 07:06 PM
  #4  
Senior Member
Thread Starter
 
Hircflyer's Avatar
 
Join Date: Dec 2001
Location: Kailua, HI
Posts: 956
Likes: 0
Received 3 Likes on 2 Posts
Default Os .91 Fx

Thanks for the help guys. I removed the enging from the airplane and I'm going to mount it on a test stand.

Looking into carb inlet , with throttle full open I'm seeing about 3/32 " between the idle needle and the fuel nozzle, sorry I don't do metric(to old to change). I did notice as I reduce the throttle the gap gets quite small before the barrel closes over. I haven't touched the idle mixture screw can you tell a good starting point for that screw. OS muti-purpose manual says about 1/2 turn. Is that a good starting point?

I had to tighten the nut on the needle valve as it was leaking very badly, is there any other things I should check before I try to run it again?

Thanks again
Old 11-12-2002, 08:04 PM
  #5  
Senior Member
Thread Starter
 
Hircflyer's Avatar
 
Join Date: Dec 2001
Location: Kailua, HI
Posts: 956
Likes: 0
Received 3 Likes on 2 Posts
Default Os .91 Fx

After mounting on test stand, reseting mixture control to 1 1/4
turns out as per manual., needle valve out to 2 1/2 turns , opened the throttle to approx 1/4 open .....engine started on first flip.
Ran engine in mid range for several minutes......engine would not go to full throttle before it suddenly died.
No adjustment to the needle would allow the engine to reach 100%.
A club member came by and removed the needle valve and pronouced "this needle is bent".
After much discussion I removed the needle valve from my OS 61 SX which I have installed on another aircraft, installed it in the .91, opened it about 2 turns and engine started on first flip, and the ENGINE SANG !!~! WOW.
We had to adjust the idle mixture out a little to richen it a bit but thats all.
Engine now has 1/2 gallon of fuel through it and its going to get installed.
I'm going to leave that .61 needle valve installed.

The gap between the needle valve and the spray bar is approx 2MM, 4 to 5 is far to wide , engine will not fire, carb fills with fuel.

Who would have thought all that trouble because of a bent needle valve!!!

How about that?
Old 11-13-2002, 04:19 PM
  #6  
Bax
My Feedback: (11)
 
Join Date: Apr 2002
Location: Monticello, IL
Posts: 19,483
Likes: 0
Received 6 Likes on 5 Posts
Default Os .91 Fx

Hircflyer,

Well, a bad part wasn't considered. A bad needle can certainly drive you nuts! Glad to hear that you've located the problem.

We all assumed everything on the engine was correct.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Thread Tools
Search this Thread

Contact Us - Manage Preferences Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.