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OS Max .61 SF-H, #6B Carb settings - Help

Oneyeflyr

Senior Heliman

Enid, Oklahoma - USA

Just bought an old Heli on eBay and wanna fly it, but I have run into one problem. Can't keep the engine running long enough to spin the blades. Anyone know how many turns I should set the carb at, in order for it to idle normally?

When it does start, I frequently get an intermittent rpm acceleration. Up then down. Can't seem to get it stopped. I've even changed out the O-ring and tried adjusting both needles, getting little to no acceptable idle. It's an OS Max .61 SF helicopter engine with a #6B Carburator. It's a discontinued model, so it does not have a manual to download. Nor does the carb.

What do I do? Buy new? I was hoping that I would have something to salvage off this old heli after I'm done training. The simulator's a big help, with the little red button and all, but I'd like to do the real thing for a change.

Only thing that seems to be keeping me from it, is the blasted engine. I've been told that the engine has had little to no use, this may be the reason. I'd be able to provide pictures if need be.

He who lands hard, makes brown skid marks

01-21-2008 02:59 AM
RAK402

Key Veteran

Alhambra, CA

I am trying to remember the carb you are speaking about.

If it is the older style carb, where the idle adustment is a very small sleeve/tube which can be screwed in and out (as opposed to the more modern carburators, which have a cam-screw that can only be moved back and forth), there is an O ring about the sleeve.

Once the o ring cracks, the motor will fire a bit, but will not continue to run.

Check this o ring (I saw you already changed the o ring on the main needle)-you will, due to the age of the engine, almost certainly have to replace it. Then try the following:

1) make sure the carb is completely clean
2) then turn the main needle in gently to where it stops.
3) Back it out two and one half turns.
4) Attache a fuel line to the nipple on the carb.
5) open the throttle and blow through the fuel line-there should be little resistance.
6) Close the throttle to where it is only a small amount open (approximately idle)
7) gently screw the idle tube in to where it stops
8) blow through the fuel line-no air should pass through
9) While blowing through the fuel line, slowly unscrew the idle tube until you just start to feel the air pass through (throttle is still at idle.

The engine will now run, assuming there are no air leaks, the ring is good, etc. It will be quite rich. The main needle will affect the idle and transition, the low speed adjustment will not affect the high speed, but will affect transition.

Tune it as you normally would.

01-21-2008 06:27 PM
f penfold

Key Veteran

uk

you have to set up the high speed needle before u adjust the low speed one just to add no to what you have already been told

01-21-2008 08:00 PM
HOMEPAGE  
Oneyeflyr

Senior Heliman

Enid, Oklahoma - USA

okay, thanks for the tips... I will give it a try after I check /replace that other O-ring. That seems quite simple.

01-22-2008 05:01 AM
Oneyeflyr

Senior Heliman

Enid, Oklahoma - USA

Still cannot get this thing to run...

Here's what I've found...
I checked the low end o-ring. It looks brand new and has no wear, or cracks of any kind. Cleaned the thing top to bottom of the carb, and with everything seated, I begin to adjust it just as explained. No start. I even removed the pipe, and added an adhesive gasket to it thinking maybe I was loosing my back pressure on an exhaust leak.

My back pressure is coming from the crankcase and not the exhaust.

It takes about 3 to 4 turns out on the low end and 2 turns on the high end to get it idling... anything else kills the engine at idle speed. (approx 10%)

At 20%, engine hesitates for a full second before rev'ing up to clutch engaging speed and back down to almost the death.

If I pinch the fuel supply line at the carb, the engine does not increase rpm, just decreases.

He who lands hard, makes brown skid marks

01-25-2008 08:47 PM
Oneyeflyr

Senior Heliman

Enid, Oklahoma - USA

FIXED the problem!

OKheli2 noticed that my fuel supply line could not keep up with the consumption.

OKheli decided that the tank backpressure line that went to the crankcase didn't have enough backpressure.

So I moved the backpressure line to the exhaust manifold and now it is up and flying. Got two good flights out of it so far.

lock out happend on the third flight while on the ground... still determining the problem. Using DX7 and 6100 with 1.2, battery was at 5.7v to 4.7v moving all the servos.

He who lands hard, makes brown skid marks

01-28-2008 02:33 PM
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OS Max .61 SF-H, #6B Carb settings - Help

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