How to tune the OS.61 FSR?

[Greg Lee]

Bought a great engine for my winter project (SIG's Astro Hog).

Everything looks great and the engine should be a real powerhouse on a
pitts style muffler.

But, I do need some help tuning this (three screw?) O.S. FSR .61 short
stroke engine which was cleaned and reassembled by a hobby shop prior
to my taking it home.

Does anyone have the proceedure for tuning after reassembly.
(settings for initial positions after re-assembly)

I asked this question several weeks ago and received two good answers.
Figured I'd try one more time before the weather warms up.

Thanks.

Greg

[SKYLANE42]

Greg, mine only has two needle valves. One for high and one for low. There is
a screw for the idle stop. ??? I usually open the throttle up all the way and
hook a fuel tube to the carb and blow gently while adjusting the high needle
until it starts to restrict. This usually ends in a rich setting.

[Lenny Nipper]

I responded before with no good information and i will respond again
with a request for help. I also have a NIB 61FSR that has a type 7M
carb. This version of the engine is an ABC non-ringed engine and has
a cool gold sticker on the box advertising the 7M carb as if it were
important somehow. This carb has three adjustments on the fuel nipple
side of the carb and zero adjustments on the throttle lever side.
There is a cam-type screw for the low end, a shouldered screw that
moves the entire barrel in and out for mid-range, and a standard high
speed needle. At least that is the way it appears to me. Also, it is
unusual in that the low speed adjustment will not totally shut off the
fuel flow as long as there is even the smallest opening in the carb
throat. The throat opening looks huge for a 61 when the barrel is
fully open. I took the carb apart to understand a little about the
way it works and I can see that a small amount of dumby screw turning
will mess up the mid-range to such an extent that it is very difficult
to make it right again. This is because the shouldered screw can come
off the barrel and hold the mid-range fully rich. I have not started
the engine but have it mounted in an Extra waiting for warm weather.
I have no idea how it is going to run but could use some advice on
this wacky carb. I have a feeling that the original poster has the
same carb and no amount of type 7D advice will help us. Thanks in
advance for any help from the newsgroup croud.

Lenny Nipper

[JP1]

len...@spam.integrityonline.com (Lenny Nipper) writes, in part:

>>"I also have a NIB 61FSR that has a type 7M carb. This version of the engine
is an ABC non-ringed engine and has a cool gold sticker on the box advertising
the 7M carb as if it were important somehow. This carb has three adjustments
on the fuel nipple side of the carb and zero adjustments on the throttle lever
side. There is a cam-type screw for the low end, a shouldered screw that moves
the entire barrel in and out for mid-range, and a standard high speed
needle."<<

>>" Also, it is unusual in that the low speed adjustment will not totally shut

off the fuel flow as long as there is even the smallest opening in the carb
throat."<<

>>"I have no idea how it is going to run but could use some advice on
this wacky carb."<<

From a vantage point of having used the O.S 7M carb on a 61 FSR and also in a
60 FSR (a retrofit, because the carb works _so_ well) for the last 15+ years, I
offer advice that you not take such a negative attitude toward the carb until
you _have_ tried it.

You've got the mixture-related adjustments ID-ed correctly. Both the idle
mixture and mid-range mixture controls don't need much tweaking (travel range)
to cover conditions of very rich to too lean...as long as the main needle is
set correctly.

In addition, there is a throttle stop screw. Back that one off, and you can
close the card down so far that the engine will stop immediately.

Here are the ballpark control settings, from the 7M carb instruction sheet:

1. Main needle 3 turns if _not_ using muffler pressure or 1-1/2to 2 turns if
using muffler pressure.

2. Mid-range two turns open.

3. Idle mixture at mid-travel.

O.S. recommends that the mixture controls be adjusted in this order: idle
first, then mid-range, then main needle. (FWIW, I've never had a problem if I
set the main needle first, then idle, then tweak the mid-range after hearing
the engine response in-flight.)

If you can't cotton on to this "wacky" carb design, Lenny, I will be _glad_ to
take it off your hands for a nominal amount, plus shipping.

John Pothier
Anaheim Hills, CA

[Lenny Nipper]

On 25 Feb 1999 00:18:50 GMT, j...@aol.com (JP1) wrote:

>From a vantage point of having used the O.S 7M carb on a 61 FSR and also in a
>60 FSR (a retrofit, because the carb works _so_ well) for the last 15+ years, I
>offer advice that you not take such a negative attitude toward the carb until
>you _have_ tried it.
>>

>If you can't cotton on to this "wacky" carb design, Lenny, I will be _glad_ to
>take it off your hands for a nominal amount, plus shipping.
>
>John Pothier
>Anaheim Hills, CA

John,

Did not intend to use the word 'wacky' to imply a negative attitude
about the carb, only that I was not familiar with it's workings and
found it strange complared with all the carbon copy carbs on the
engines I usually use. All my friends will put the 'wacky' part on my
side of the equation.

The information you provided is exactly what I needed to know, but I
have one other question. The idle adjustment is very very difficult
to turn. Is this normal or is there something I should look into?

Thanks for you offer to purchase but now that you have told me how to
adjust, and how good the carb is, I think I might keep it. Thanks
again for the information.

Lenny Nipper

[JP1]

len...@spam.integrityonline.com (Lenny Nipper) writes, in part:

>>"The information you provided is exactly what I needed to know, but I have

one other question. The idle adjustment is very very difficult to turn. Is
this normal or is there something I should look into?"<<

Glad to be of help, Lenny. My tongue was definitely well-in-cheek when I
offered to take the O.S. 7M carburetor off your hands. I am confident that as
soon as you put the carb into operation, you will like it _very_ much.

About the idle adustment: yes and no. The mechanical advantage afforded by the
eccentric screw arrangement is less than would be afforded by a threaded
device, so it would be expected that the eccentric screw be harder to turn.
OTOH, the eccentric screw should loosen up when the engine is running and also
over time, with use. Of course, one wouldn't want the screw to be especially
easy to turn, else it wouldn't hold a setting. (If the carb were mine, I'd
chech the eccentric screw mechanism for any obvious interference and apply a
drop or two of after-run lube to see if that frees it up.)

John P.