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HelicopterOff Topics › FOX Planker engine help
04-26-2004 05:25 PM  13 years agoPost 1
Bubzilla420

rrNovice

Central Illinois

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Anyone mess with Fox engines... I have a 15 BBRC and need a little help with base settings.. I have never tuned one in before and dont know about the air bleed screw.
Any info would be great .
Thanks,
Brett

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04-27-2004 02:30 AM  13 years agoPost 2
dkshema

rrMaster

Cedar Rapids, IA

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Set the top end by starting the engine and adjusting the high speed needle first. After you get the high speed adjusted, go for the idle.

I've never had much luck with air bleed type idle settings.

As you screw the screw in, you're richening the idle mixture, as you screw it out, you'll be leaning out the idle mixture.

You're going to want to try to get the idle needle adjusted so that:

A. the engine will idle at a reliable low rpm (a lot of people try to just idle the engine way too slow).

B. Transition from idle to full bore smoothly.

For the idle, if you let the engine sit at idle and it slowly slows down and dies, the idle is too rich, and you need to open up the idle screw. If, on the other hand, the engine at idle slowly increases in speed, and dies, the idle is too lean, you have to turn the screw in a bit.

If, after the engine sits at idle for a while, and you suddenly open the throttle -- the transition to full power should be smooth, and nearly instantaneous.

If the engine spits, sputters, and then dies, the idle is too rich, and you need to lean it out some. If, on the other hand, the engine just plain stops, without spitting and blubbering all over, the idle is too lean, you need to richen it up.

I've found that the air bleed hole is generally too small to do any good. I have a fairly new OS 46LA that until last spring, I was willing to give it to anyone who asked -- simply because it ran like crap. I finally used a 3/32 inch drill to open up the bleed hole in the carb, and now the engine runs exceptionally well for a cheap bronze bushed, lapped piston engine.

You may have to resort to drilling out the bleed hole in your carb for the idle setting to really have any effect. If the screw is backed out all the way so the bleed hole is open, and you're still too rich on idle, you'll need to drill out the hole a bit. Be careful doing this.

I assume you've got a muffler on this engine, and that its pressure fitting is connected to the vent line of your tank so that you are using muffler pressure to insure a positive fuel flow. Your tank centerline is also going to want to be about the centerline of your needle valve too. If the tank is too high above the needle valve, you'll be rich a lot, if the tank is too low, you'll run lean a lot (and if you're doing rolls or loops, the engine will go from lean to rich or rich to lean as you change tank positions).

Dave

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04-27-2004 03:56 AM  13 years agoPost 3
Hoosier_Flyer

rrApprentice

Terre Haute, Indiana

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I'm not sure if this holds true with the Fox carb but on the air bleed carbs I've used, the base setting for the airbleed was with the screw half covering the hole.

I usually set the airbleed as such and set the main needle about 2 - 2 1/2 turns out and work it from there.

Just adding to what Dave said.

Brian

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04-27-2004 04:03 AM  13 years agoPost 4
Inspector Fuzz

rrKey Veteran

NLA

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Sweet motor...

Hey Bublzilla,
That lil' Fox is one of the sweetest running, slowest idling, best transitioning small motors I have ever had the pleasure of running. You shouldn't need to do and I recomend that you don't, do any special mods..
I fired one up once that was in a Clancy Aviation Speedy Bee plane.. The 12 year old kid who built the model was at my field and quite upset because none of the club "experts" would help him with it since it Fox motors "sucked" and the little plane he built was just too weird for them to attempt to fly..
The little motor started, first try, and a little twisting of the main needle and she was ready to go.. Sweet plane too.. On the first flight with it I was doing very slow rolling circles about 15 feet off the ground.. It was easy to land, too.
JEFF

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04-27-2004 04:44 AM  13 years agoPost 5
fritch1969

rrNovice

PA

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04-27-2004 12:46 PM  13 years agoPost 6
dkshema

rrMaster

Cedar Rapids, IA

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Your original description of "the airbleed screw" led me to believe this carb indeed had the basic airbleed hole and screw that opens or closes off that hole.

Looking at the Fox site, it appears that your carb actually is a two-needle carb. There should be no mods or drilling required.

The setup is basically the same as described. Get the engine running well at a wide open setting using the high speed needle.

Then adjust the idle needle while looking for the signs of being rich, or lean as I described above.

This carb should be a snap to adjust.

Dave

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HelicopterOff Topics › FOX Planker engine help
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