Looking for help with OS Max .61FSR-H or a 7H carb

[ticedoff8]

I am trying to get an older GMP Cobra flying.

I have an O.S. Max .61FSR-H with the 7H carb. I got this motor in a big box of parts, and it looks like it is in pretty good shape.
I have no history on it and I never tried to run it. It was "gummy" when I got it, so I didn't want to chance ruining it before I cleaned it up a little.

Now, I am having a terrible time trying to get the engine to run smoothly or at full power.

I've torn pulled the engine completely apart and cleaned everything.
The piston ring and sleeve look good - the end-gap on the ring is un-detectable when it is in the sleeve.
When I reassemble the engine, it seems to have ok compression and everything is nice and smooth.

But, I think I screwed up the carb.
I flushed out the carb with kerosene and ruined all of the o-rings. I wasn't thinking.
So, I completely disassembled the carb, ordered new o-rings from Tower, and reassembled everything.
There are three o-rings on the idle jet sleeve and one o-ring on the main needle.

Now, it isn't running too well at all.
I may have reassembled it wrong, but I have nothing to check it against. The exploded view of the carb doesn't have that kind of detail.

I am using a 13-6 prop to to test, and the best it can do (open exhaust) is 12,200 RPM.
It is hard to start (I am flipping by hand), and doesn't idle very long before loading up and dieing.

The 7H has the 3 adjustments - idle, mid-range and high speed:
The idle adjustment is a simple off-center screw that turns +/- 45-degrees and "rocks" the "jet" sleeve +/- about 3-degrees.
The mid-range turns +/- 4 turns and slides the "jet" sleeve in or out of the carb barrel about 1/8".
The high-speed is the typicial needle valve for high speed mixture.

It all looks very cool and precise. And right now, it isn't working for crap.

Right now, the idle screw and the mid-rage adjustments have no effect on the idle or mid-range. They are always too rich. I've moved them to the complete CCW position (full lean) to no effect.
The high speed adjustment adjusts the mixture from too lean to too rich, but even at peak, it never gets more than 12,200 RPM.

The GMP Cobra has an 8.7:1 main gear ratio - and to get 1700 RPM main rotor speed, I need at least 14,500 RPM.

Tower has a complete 7H - but they want $95 for it! I could buy a new O.S. 50SX-H Hyper for $100 more. For all I know, it would have just as much (maybe more) power than a well tuned .61FSR-H.

Does anyone have a 7H carb they want to sell?
Or, a blown-up .61FSR-H with 7H?
Or, does anyone have detailed PIX they could share with the alignment of the carb jet sleeve inside the barrel?

Thanks.

[schluterdude]

is it possible that the needle is bent? take it out and roll it on a piece of glass... if it's bent, u r up the estuary without a formal means of propulsion, time for a new needle if you can find one, or a new carb. also, did the o-rings rip when you installed them? i don't know what the needle settings should be exactly, but, you can try starting the low end at around1.25 turns, mid range somewhere in the middle of its adjustment, and the high end around 2.5 turns out. it may not run well, but it should run. also, why are you running an open exhaust?? try putting a muffler on it and run the pressure to the tank, running engines with no pressure is a joke, unless the tank sits higher than the carb and it can draw enough fuel. how does you glow plug look? is it new or old? how 'bout the fuel?

[WiscHeli]

i would say replace the carb o rings the age it is ,, and yes add a muffler with tank pressure line ,,, you will find then were a problem is if any

go to your local ace hardwear ,,, cheap place to get o-rings

do not change the carb setting untill you have it set up to run as it would be in your Cobra

[ticedoff8]

Hi guys,

As I said in the original post:
I replaced all of the o-rings (4 total) with new OS Max factory o-rings. These were ordered from Tower Hobbies based on the OS Max part numbers.
I am 99% sure I didn't damage the o-rings when I installed them.

BTW - I did check at Ace HW for replacements - they don't have any 6mm dia x 1mm thick silicon-rubber o-rings. Kind'a a specialized part.

The initial adjustment settings are documented in the 7H Carb manual - I found it online (that's how I knew what o-rings to order). 2 1/2 turns for the high speed needle, 2 turns for the mid-range and the middle setting for the idle.
Pretty typical.
As I said in the orginal post: Adjusting the idle or the mid-range has no effect on the engine. Really: No effect. It still idles for a few seconds then dies on throttle up.

I think the key is the orientation of the idle bar and the main jet inside the barrel of the carb. There are cuts in these tubes (each with an odd shape), and I assume they must line up with each other in some way to allow me to set the idle and the mid-range.

I would love to buy a new carb - but Hobby Lobby wants $96USD for a new 7H carb - JUST THE CARB!!

[cbflys]

Have you seen this? The expoded view show the jet positions ...

http://www.rchelibase.com/engines/os7h.pdf

[ticedoff8]

Have you seen this? The expoded view show the jet positions ...

http://www.rchelibase.com/engines/os7h.pdf

Thanks, that's the same picture (although bigger) as the one printed on the 7H "Operating Instructions for the O.S. Type 7H Carburettor".

Because of the extra size, it does seem to show a little more detail about the alignment of the cuts (jets?) on the tubes.
In relationship to the carb body, it looks like the idle jet faces forward (with the "H" fork facing up) and the main jet faces back (in the WFO position).

I'll check to see if I am out of alignment (between the two tubes) based on this bigger picture.

Thanks.