hsanchez

My Feedback: (46)

Good Morning. I have an O.S. .61 SF with the O.S. 7L carburetor. I've been having a hard time properly tuning the engine. When I get the carb tuned to what I think are proper settings, and then "cycle" the throttle, I find the engine doesn't transition from idle to full throttle too well. It often hesitates, then I have to fiddle with the throttle before it runs steady. Sometimes, if I have it at an idle and then give it full throttle, the engine will stop. I have the engine mounted sideways in my current plane.

Two questions:
1. What could be causing this rough transition problem?
2. Does this carburetor have three needle valves, or just two adjustment points next to each other?

I need to have a consistently running engine before I can fly this plane.
Any advice here would be appreciated.

Thanks,
Harry Sanchez
[email protected]

speedster 1919

My Feedback: (3)

Your problem os in your LS needle setting. But that is a 3 needle carb with a mid range needle too that has to be set special.

rainedave

My Feedback: (1)

Actually, the 7L only has one needle - the high-speed needle. The low speed adjustment is made by turning the slotted screw at the top in front of the needle valve. It works sort of like a Perry carb: Turn the screw to the right leans the low speed setting; turning to the left will richen it.

Look at my photo. Make sure your assembly looks exactly like mine with the screw slot directly in line with the centerline of the carb throat.

It should run pretty good with the screw slot in that position. Like a Perry, it only takes a very tiny turn either way to change the setting. If it coughs and sputters going from idle to WOT turn the screw about 1° to the right. If it sounds too lean on transition, turn about the same to the left. It only takes a very tiny turn to make a big difference. But, start out with the screw slot in line with the carb throat centerline.

David

Quikturn

My Feedback: (12)

If I could throw my 2 cents in, I would recommend looking at the condition of the o-rings in your carb including the carb to engine o-ring. I have seen many older engines with cracked or hard o-rings which can allow small air leaks. This could explain inconsistent engine performance.

rainedave

My Feedback: (1)

Excellent point Quikturn. I did the same for my 7L's a while back. In fact, Tower still has the 7L O-rings in stock:

http://www3.towerhobbies.com/cgi-bin...H=7l&search=Go

David

Quikturn

My Feedback: (12)

Hi Rainedave, You are correct. Tower does have them in stock. In the past I was able to locate o-rings for an OS 40 FSR, and now I am rebuilding a 61 SF-P w/#86 carb. which is almost identical to the 7L carb and have found what I need on Tower. I also use a light coating of silicon grease when putting parts together with new o-rings as the fit can be tight. I have used after run oil in the past during assembly but I found that it doesn't lubricate the o-rings as well.

To try and answer Harry's question, if the engine hesitates during transition (idle to full RPM)- the low speed adjustment is too rich. If the engine suddenly quits during transition - the low speed adjustment is too lean. If your results are inconsistent, I would look for air bubbles in the fuel line or leaks around the carb. Hope this helps.

turnbub

This is a very old thread, so I can only hope.....
I just acquired an old OS .61 SF, old but looks like it never ran.
A friend gave it to me, having acquired it on auction a few year back.
I THINK it was sold because someone messed up the carb???
In trying to start it, it kept flooding, jamming, I would actually turn the spinner and mess up the prop/spinner ass'y.

More to the point, I put a piece of tubing on the usual fuel thingy and blew thu it and it is obviously way to far open.
The low speed adjustment is supposed to be the top slotted screw, but it seems to be jammed, i.e. I can turn it slightly
with difficulty, but it is still to far open.

Any thoughts??

GREG DOE

The screw isn't jammed. It's what the screw is trying to turn that is jammed. The screw is an eccentric cam that moves the idle adjustment, and that is what is jammed. Also note that there is a hex head screw on the bottom of the idle assembly. Interestingly on my engine it is a slotted screw. It might be that that screw is too tight. I suspect that the lower screw is just supposed to put a drag on the assembly, and not be tightened solid, but that just a guess? Remove the carburetor, and soak it in any solvent that will loosen it up. If that doesn't work try a film covering heat gun. If more heat is needed remove the O rings, and plastic throttle arm.

turnbub

Greg, much appreciated!
In fact, what I just did was to remove the bolt on the bottom, and (dangerously?) remove the bolt holding in the actual mixtore thingy./
Then I could turn the adjustment screw (and then put back in the 2 bolts, of course).
So what your saying, and what I observed seem to match.
The bottom bolt on mine has a hex head and needs a wrench as a socket can't get in there,
and it looks as tho I'll have to loosen it a little to make the adjustments.
The way I did it, I could see what was happening better.

Going to try again to run it.

turnbub

So, more fool me - I thought the OS .61SF was way too rich, but I was not assessing it correctly.
The main problem was having the fuel tank way too high on my test stand!!

I lowered that and was actually able to hand-prop the engine.

On the other hand, as the weather around here changes so much I will have to adjust the carb from time to time,
and now i know how - on this one I need to slack off the bottom bolt a little, then it turns easily.

2W0EPI

Just thought I'd bring this second hand thread back to life. I decided today I'm going to get my plane out of the shed and have a go at running it, i.e., try and start it up and see what happens. My plane is a boomerang 2 and the engine is a Force 46. I used a hangar 9 starter.

Well, I got it running okay but I had that common problem of the engine cutting out once the glow starter was removed. I remember from last year that I had read about this problem but couldn't remember what the solution was, I tried a leaner mix but the problem still persisted. I then started reading this here thread and consequently changed the glo plug with a brand new OS plug, straight away the problem was gone.

I find this rather strange because the two older used plugs that I was using glowed bright orange when energized which I wrongly thought were therefore good to go, so now I have 2 faulty plugs which is shame as they are quite expensive.

2W0EPI

Oops, I screwed up, I selected the wrong thread, my apologies!

Here is the correct thread,

engine stops when glow stick is removed