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Revolution Models . CarbonXtreme . Midland Helicopters

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Engines Plugs Mufflers Fuel > Need help with O.S.-MAX .61 FSR-H carb setup
 
 
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Hello Heli Gurus,

I recently bought a GMP Competitor Pro that has an O.S.-MAX .61 FSR-H installed in it.Both the heli and engine are in new condition but about 10 years old. I ran the engine for the first time today and am having some trouble keeping it running at idle. (It's still installed in the heli. Lots of work to remove it.)The carb is not the 7B-H as the engine instructions say. The 7B-H pictured in the engine manual looks like any other O.S. two-needle carb. The one mounted on this engine appears to be machined from a solid piece of bar stock. It has a normal appearing high speed needle on one side and three other screws there as well. There’s a slotted screw, a phillips and a hex head. The other side of the carb has a snap ring that appears to hold in the barrel. The throttle arm is attached to the barrel on that side as well.

So, the big questions are:

Which carb is this?

How do I adjust the low end mixture?

Any other tricks I need to know?

I anxiously await your response.

Thanks in advance.

Bob Scott
09-28-2001 Over year old.
  WV   EDIT
 
 
Maxx
Key Veteran
Location: Shreveport Louisana

The best and most common mod for the SFN was a Supertigre .60 carb. Does yours have a Brass barrel that the high speed needle screws into? If so; the motor should run great IF the bearings, ring, etc. are OK. If you can E-mail me a pic off list I'll try to help. I love this motor and still have one myself along with parts. Helimaxx@sport.rr.com
09-29-2001 Over year old.
 
 
Steve Campbell
Elite Veteran
Location: Baton Rouge, LA

NWFlyer,

That is a 7L carburetor; great on a plank (it was designed especially for Pattern flying), pretty much useless on a helicopter.

You could probably make it work, after a fashion, but where it will give you fits is coming down out of forward flight. The cat-eye in the spray bar is too narrow (aside from being in the wrong orientation) and will not allow the mixture to richen up quickly enough during quick throttle changes in the mid-range. Your engine will sputter and complain all the way down, possibly flaming out when you put the power back on.

The 6B carb does this to a lesser extent, but you can make it better by aligning the cat-eye so it is pointing straight down into the engine- IOW, at ninety degrees to an imaginary line drawn through the needle valves.

I fly a 6B on my SFN. For the type of flying I do (mostly what 3F folks would call "scale") it works fine. But it just doesn't have what it takes for the rapid throttle changes necessary for flipping and flopping, or HARD aerobatics; and a 7L would be totally hopeless here as well.

I would seriously consider getting a better carburetor. Like Maxx said, the ST was the carb of choice at one time. But it has it's own set of problems; like a throttle stop screw that is not properly hardened and will break at the worst possible time. The carb barrel, when new, also has a tendency to freeze up- until it gets worked a bit and smoothed up. Still, it is leagues ahead of what you have now.

The slotted screw is your low-end needle. If all you intend to do is hover and minimum forward flight, the carb should do you fine. Just be prepared to do some serious adjusting.

Another thing; the FSR and SFN are totally different engines. The SFN is a classic that was a real jewel in helos, mine is not for sale at any price. The FSR was one of the best airplane motors of it's day (still is), but it has a longer stroke than the SFN, which can cause vibration in a helicopter under certain conditions. I'm pretty sure the 7L carb never came on the SFN; the 6B was designed for it to be used on helos. The FSR-H is a plank engine that they slapped a large heli heat-sink head on.

Something to consider; if that engine is indeed new, you might could get some serious cash for it from a collector or someone seriously into nostalgia. Certainly, you could get enough to buy a SX-WC. You might want to look into that option.

Any other good news I can give you???

Steve
09-29-2001 Over year old.
 
 
GMPheli
Veteran
Location: W. Bridgewater, MA USA

.

Hey Steve, are you sure that all FSR's are long strokes? I have had 2 that are not. I did have an SF that was a long stroke though. Interestingly enough, I made an SFN (kinda) out of an FSR and my Long stroke SF. I used the one piece crankcase and bearings from the SF (The SF has a larger rear bearing than the FSR), with the crank, con rod, piston, cylinder liner and head from the FSR. I did not actually compare these parts side by side with SFN parts to see if they where exactly the same, but all the parts fit just fine. And I ended up with a 22mm stroke instead of 24mm. The hardest part was getting the piston ring started in the cylinder liner. The FSR has a 2 piece crankcase, so you are supposed to put the piston in the cylinder liner before you put the liner in the crankcase. With a one piece crankcase, you must first fit the piston/rod to the crankshaft/crankcase without the cylinder liner in place, then slide the liner over the piston while it is inside the crankcase. One piece crankcase cylinder liners have a chamfer on the bottom to make this task easier. The FSR liner did not. To get around this, I compressed the ring, (while on the piston) and stretched a small o-ring over it. This held the ring quite nicely and was easily cut off the bottom of the rod after the liner pushed it down there. The motor ran fine, but it wasn't a powerhouse. The liner had a small score in it, so I did not expect a lot out of it. The easiest way to tell if you have a long stroke or not is to measure the stroke, 24 long, 22 short. Actually, in this situation, a long stroke could be advantageous considering the gear ratio of the GMP Competitor is 8.6 to 1. Long strokes make more power than short strokes at lower rpm's. With an 8.6 to 1 ratio, at a rotor speed of 1500, the motor is only turning 12.9K. Vibration would not be a problem @ this speed. It was the guys who let them spin up that had vibration problems. If you use a short stroke that likes to rev. with this gear ratio, you will have to run a real high head speed in order to get power. Well, I guess I've rambled on enough for now.

Alan Angus
10-02-2001 Over year old.
 
 
Steve Campbell
Elite Veteran
Location: Baton Rouge, LA

Now that you mention it, Alan; no, I'm NOT sure all FSRs were long strokes. And I do indeed now recall that some SFs were long strokes to placate the Pattern crowd. They hammered airframes too, as I recall.

Good call on the Competitor's gear ratio; I was thinking it was 9:1 like a stock X-Cell. At 8.6:1 that engine would do okay vibration-wise. But he'd still have the mixture problem to contend with. Trust me, the 7L carb is absolute zilch on a helicopter. Sure is nice on a plank, though. I'm gonna try to fit mine onto a 60 FP I picked up to go on a priceless 70s-vintage original Bridi Super Kaos 60 kit I have. The model wants a lightweight engine; these "modern" fully bearinged marvels weigh a ton compared to the bushed engines of the 70s, and I HATE adding tail weight...

Steve
10-02-2001 Over year old.
 
 
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Engines Plugs Mufflers Fuel > Need help with O.S.-MAX .61 FSR-H carb setup
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