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OMP 81" Profile & 160fx: Lean midrange

Old 08-06-2003, 11:05 AM
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Default OMP 81" Profile & 160fx: Lean midrange

I have a new 160 FX mounted horizionally in a OMP profile edge. It has almost 1 gal. of 18% Wilcat fuel through it.

My problem arises when I try to lean out my low & high needles. I get a terrible midrange detonation before I reach a satisfactory mixture on either needle. To get rid of this lean detonition at midrange I have to adjust the high & low needled very fat (rich), real fat.
I am running an untuned Mac's header with a mousse can pipe (I was waiting on a good breakin to tune the header). 18-6 MAC prop. A 14 oz. tank is mounted with the centerline of the tank in line to the aluminum joint on the remote needle valve. I can't get the tank any higher.

My question(s) to the wizards are:

1) Is there such a thing as a 3 needle carb for the 160fx? That would be the berries!

2) Would tank placement give this lean midrange condition? If so what way do I need to go.

3) Any other suggestions?

I have posted this to the os max engine forum. I have included 2 pics, in case i missed something.


Thanks in advance!!!


Stan
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Old 08-06-2003, 11:06 AM
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Default OMP 81" Profile & 160fx: Lean midrange

pic # 2
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Old 08-06-2003, 01:08 PM
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Default OMP 81" Profile & 160fx: Lean midrange

I'm no engine guru, but I'm wondering if running that pipe is part of your problem.....I have about 8flts on an FX160, running stock muff, got it mounted the same way yours is mounted. I have an 18x8 APC prop. The plane is a 13.6lbs GIANT SUDOKHOI. Starts pretty easy, we did have to tune the low end a little, but its pretty good right now. Maybe you should try it with the stockmuff, just to see if its tuneable.Maybe if its a new eng, that also may be causeing you grief.....Good Luck with it...GATor
Old 08-06-2003, 01:32 PM
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Default OMP 81" Profile & 160fx: Lean midrange

How long is the header? how big is the pipe? don't have the measuresment here but can give you a email to talk to some one about it. He is running either a 20x6 or 20x8 prop on his with mcp turning around 8400 rpms'
Old 08-06-2003, 02:22 PM
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Default OMP 81" Profile & 160fx: Lean midrange

Thanks for the quick replys.....

My Macs header (#4311)is stock length, 9"x 3/4". The mousse can is 1 3/4" x 14".

I was wondering if the exhaust was part of my problem. I think I have a friend who has a stock OS exhaust for this motor. I will see if I can procure it for a test. As I stated in my original post, I would rather not tune the exhaust until the motor is broken in fully. I hate to run a new motor many times at peak rpm to tune the header length.


termagator: how high is the center of your tank mounted in relation to the needle valve? Eyeball measurement would be nice....


The saga continues!!!

Stan
Old 08-06-2003, 02:37 PM
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Default OMP 81" Profile & 160fx: Lean midrange

from the pic the can looks a little small, how big is the outlet
Old 08-06-2003, 02:41 PM
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Default OMP 81" Profile & 160fx: Lean midrange

heres a pic of my tank mount
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Old 08-06-2003, 02:45 PM
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Default OMP 81" Profile & 160fx: Lean midrange

Originally posted by termagator
another
you can see its right underneath the bottom of the engine
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Old 08-06-2003, 03:11 PM
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Default OMP 81" Profile & 160fx: Lean midrange

I've heard people with this plane mention a rattling noise. I have the GS540 and mine does the same thing. It's supposedly the wing dowels rattling and there's a fix for it. Do a search for it or email OMP. The fix isn't hard to do. I could have easily mistaken the rattling for engine detonation but it wasn't that. Just a possiblility that yours is doing the same.

John Wells
Old 08-06-2003, 03:52 PM
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Default OMP 81" Profile & 160fx: Lean midrange

Originally posted by propnut1
from the pic the can looks a little small, how big is the outlet
I am guessing it is in the 1/4 / 3/8" range.

This pipe setup was bought from OMP for this motor. I believe the can is made by Jerry smith (working from memory here).

I am going to try to get a stock muffler & see if that cures my problem.

As for the wing dowels vibrating, mine does not have any. It has a wing tube, & 2 bolts that pass thru the fuse and the root rib on the wings.

I originally thought that I had a vibration in the plane due to the vibes given off by the motor. This is not the case. The sound I am hearing is coming from the motor & I can make it go away by fattening up both the needles.

Sounds like a midrange lean condition to me!!!

Keep the ideas coming, will post an update Thursday evening (next flying day).

Stan

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