Old O.S. .61 SF
 

I traded a guy for my .46 AX and I got his O.S. .61 SF. The problem is that now I dont have the instruction manuel, and O.S. dosn't have manuels for discontinued engines. So I just have some basic questions about getting this thing going. Which fuel I need(assuming a 15/20), which plugs I need, where to set the needle for start up, tuning instructions if any? The fuel I have now is powermaster 15/18 is that ok? The previous owner also notified me that the engine as a small air leak in the carb so that when the barrel is closed, the engine still runs for a bit. Is there any way to fix that? One other thing, the engine dosn't have the stock muffler, it has a brand new Mag pipe. Will that change anything?

Thanks,

LT-40

RE: Old O.S. .61 SF
 

If your an OS man ,the OS8 plug is fine. Your 15% fuel is fine. NO MORE THAN 15% That is a long stroke 61 so it will run 1 size up from normal 61's The perfect speed prop for a 61 is a
11x7.5 MAS so a 11x8 or 11x9 12x7 for speed IMO. Check the o ring under carb for cracks and gouges. That is an older model and may need replaced.

RE: Old O.S. .61 SF
 

You can contact hobby services for a manual for it .I have on several older engines and they have been more than helpfull.

RE: Old O.S. .61 SF
 

Does it have the 7L carb ?

RE: Old O.S. .61 SF
 

Thanks guys, I'm going to get this fired up and see how it runs. About the carb, I dont know what kind, but here are some pics.

RE: Old O.S. .61 SF
 

It's most likely a 7L carb. See the screw on top of the allen bolt ?
Set it straight up at first. That is the idle, or low speed screw. You
turn that screw "Out", to the left, or counter clockwise to richen
the idle. Turning it the other way will lean the mixture. Only move
that top screw a tiny bit at a time to make the adjustments.

It may idle ok set straight up at first, but you might have to make
small adjustments later. ;)

FBD. :D

RE: Old O.S. .61 SF
 

I have an OS .61 with the same carb that was given to me a year ago. After looking at the carb, I gave up evn trying to get the thing going. What are all those adjustments??!!

RE: Old O.S. .61 SF
 

These is the big main needle then the other three.

The top screw is the adjustment, just turn it either way. The middle allen
screw just holds the parts to the center portion of the carb, that rotates
back and forth as you make the adjustment. That is the part that changes
the idle mixture. The bottom bolt is slotted, and it holds the plate is place.
The plate moves back and forth when you turn the top screw.

The only other adjustment is the top screw with the lock nut on it. That is the
idle speed adjustment, but the carb is usually set so the barrel closes all
the way with the throttle trim adjustment on the radio, so the engine can
be shut off by the radio transmitter. ;)

Actually that carb is very east to set, once you figure out what the parts do.

FBD. :D

RE: Old O.S. .61 SF
 

The middle and bottom bolts don't do anything. The top screw adjusts the low
speed, and the main needle sets the high speed....just like any other carb.

It just looks complicated when you first look at the carb. ;)

FBD. :D

RE: Old O.S. .61 SF
 

Thanks. That sounds a lot easier than it looked. I thought these carbs had separate high, mid and idle mixture adjustment and could not figure out which was which. The idle seems like the Perry carbs (and a lot less confusing than the Merco!)

RE: Old O.S. .61 SF
 

Yep, it's easier to figure it out, once you know that the middle and bottom
bolts don't do anything.

Here is the scary one, the carb with the mid range adjustment. These are
pretty scarce, I have only see one. This I believe is really for heli's. I haven't
run this engine....it's a ringed .61 FSR.

FBD. ;)

RE: Old O.S. .61 SF
 

They're used on the heli and marine engines (7H and 7M). I was given a marine engine once to try to figure out why it couldn't be tuned and my first problem was working out what everything did. I figured out the main needle after a while :D and eventually worked out that the top one was idle and the lower one was mid range. But knowing what they were for didn't help because no way could I get the midrange set. After a lot of pulling things to pieces and thinking and thinking I finally realised the control plate had been put on upside down. There's a square drive hole in that plate which is machined off axis so when it's fitted upside down the spray bar has to be rotated about 90 degrees away from where it's supposed to be to get that plate on. After that, things went much easier :)

RE: Old O.S. .61 SF
 

Yes, it has the 7L carb. I got it started today and things went great. It started right up even though it hadn't been run for years. As far as the carb adjustment goes, I just set the screw in the middle and it ran fine. Here was my set up .61 SF, 13x6 apc prop, Mag pipe, O.S. A3 plug, and powermaster 15/18. And just incase you're interested, I'm going to mount this engine in my LT-40 that has been converted to a float plane.
Thanks for all the help
LT-40

RE: Old O.S. .61 SF
 

Never mind.

RE: Old O.S. .61 SF
 

I've got two of these that are pretty old and worn but reliable as heck. I've run as high as 30% in them (though mostly it's 15%) and I use the MACs muffler as well. They run great and really are a fantastic engine.

RE: Old O.S. .61 SF
 

The O.S. Max #7M carb was included with the original .61 FSR engines (airplane engines, too). With the high-speed, midrange, and idle mixture adjustments, you could get an almost linear response ouf of the enigne. O.S. dropped it, though, because too many users (notably in North America) complained that it was "too difficult" to get set properly, even though full instructions were included with every engine sold. They went to the #7L carb as a replacement.

Intitial 'ball park' setting on the midrange adjustment is to turn it clockwise until it stops, and then back it 2 full revolutions. You'd adjust from there as needed.

RE: Old O.S. .61 SF
 

Hey there LT-40


The 61SF is a great little engine .. However looking at your set up.. loose the mac pipe.. They work well on the 46 but they are really restrictive on the 61.

Long story short we had one as a replacement and it really took away from the performance.. The new OS 91Fx muffler works really well, better than the stock one.:0) (61fx too small) (if memory serves me, just under 11000 on an APC 13 x 6 / 15% nitro) I tried an ultrathrust muffler (tuned for a 91) and it works really well also.

PS: We are running a 91Fx on 20% nitro and the ultrathrust muffler and turning up about 10500 with a 16 x 6 (Not recomended by the folks at performance specialties but working really well non the less) This is insane performance on a 6lb profile.

Good luck. I havn't tried the higher nitro on the 61 but I'm sure it would be fine with the right plug.. I am going to experiment later this summer.

Enjoy whats left of the summer..

I just read that you are using it on an LT-40.. you will probably be happy with the mac muffler :D My son and I like a bit more power so we have opted for the 91 on the pipe.

Riverdancer

RE: Old O.S. .61 SF
 

Good thread to find. I am going to go look at a new in box .61 SF a club member has for sale. He said it is a Ball Bearing motor that they discontinued when the FX series came out.
Was the 7L carb standard on the SF? The motor is New in Box, he is a real horse trader that gets stuff all the time.

RE: Old O.S. .61 SF
 

See if it is the ringed version, if it is ....good. If it is the non-ringed type
it might blow the nickel plated liner, and the engine will be ruined. [:o]

FBD.

RE: Old O.S. .61 SF
 

Hi!
I hope you don't intend to replace your .46 engine with the .61 engine in your LT-40, despite the change to a float plane.
A .46 is perfect for such plane provided you run the correct prop! Try a 11x6 APC or a 12x4 APC.
Regards!
Jan K

RE: Old O.S. .61 SF
 

Yup, wouldn't you know it! That's the carb on the one I have. I just dug it out of my engine box and there it was in all its glory. I see there is another screw on the back beside the fuel inlet nipple. It is essentially inaccessible with the carb on the engine so it must be a critical adjustment! [:o]. The engine is definitely ringed.

So, now my curiosity is getting the better of me. What were these engines best for, and what are good props for it? Is it a slow speed torquer or?? And most important, what is the best way to get this carb adjusted? The engine looks like it has been run somewhat and part of one muffler mount hole is broken off. Time to get out the JB Weld! [:'(]

RE: Old O.S. .61 SF
 

I just bought two nearly NIB .61SFs (ringed) via a popular auction site.

These engines have unreal pulling power with large props. Nope, they are not revvers, but who cares? They get the job done without breaking into a sweat. That is what counts with me. Plus, they are easy on fuel and they are quiet while doing it.

I have a .90 size Mac's pipe I'm going to use with one of mine. The other will be sporting a PSP Ultrathrust G90 muffler with a home made adapter.

RE: Old O.S. .61 SF
 

Bax,

I was going to say the 7M wasn't a marine engine carb but came on the 61 FSR but figured I would be told I was wrong again. The heli carb was a 6H which was a ball bearing carb that was spring loaded to close. It had a long shaft that the arm was mounted on. Seems like there are a few guys here that tell me I'm always wrong. By the way, the 7M wasn't all that hard to set. It was a great carb.

RE: Old O.S. .61 SF
 

Funny seeing an engine/muffler combination identical to the one I purchased at a swap a few months ago. When O S started stroking their engines(hence the sf series) I cursed that I would never buy one. The price was right ,sitting in a Super Hots no less, and he had been sitting for years. He fired on the third flip and I must say I was impressed. I think the plane will get something else for an engine, The sf will go into a vintage pattern ship.

RE: Old O.S. .61 SF
 

The ringed .61SF is one of the best OS engines. The ABC versions are not ABC,
rather they are nickel cylinders that can self destruct. The ringed version will run
a very long time until the ring wears out. The SF and the RF are basically the same
port timing wise, the position of the exhaust being the only real difference. The 7L
carb is one of the best carbs ever made, and that it one reason the engine is so
desirable.

The best prop I have found for this engine is the Zinger 12-8. I have been running
this old Super Kaos about every weekend for way over 10 years. I have had a
lot of different props on it. It turns 11,400 RPM and runs 105 mph clocked. ;)

I wish the RF (rear pipe) engines were ringed, I blew up a nickel liner, and the liners
are out of production, and Performance Services doesn't make them anymore
due to lack of demand.

Hang on to those .61SF ringed engines, and get a spare ring for them while they
are still available. I use 15% PowerMaster in mine, and a K&B 1L plug. ;)

FBD. :D