Any have an OS FS-56?

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Steve - 15 Feb 2010 06:03 GMT

I just installed one on a Pitts and I'm in the proccess of tuning it.
This being my first 4 stroke I have a couple questions...

The manual says to run it at full throttle and use the high speed
needle to lean it up to almost max speed for about 5 sec, then richen
it up and let it slow down to cool off. Do this over and over for a
full tank. The needle seems to have almost no effect on the prop
speed until it either leans all the way out or bogs down rich and
dies. Is this normal behavior for a 4 stroke? My two strokes would
notice even just a couple clicks of adjustment.

I'm getting a max prop speed (12x6 prop) of about 9,700 rpm and the
lowest I can get is about 3,400, and that's iffy. The manual says
"practical" is 2,400 to 13,000. How close should my "reality" be to
the manual's "practical"? Am I in the ballpark?

I'm about 2 tanks into it. During the second tank I started tweaking
the low speed needle and it's helped some, out of the box the lowest I
could go was 4,000+.

Am I on the right track?

Thanks,
Steve

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MJKolodziej - 15 Feb 2010 17:03 GMT

>I just installed one on a Pitts and I'm in the proccess of tuning it.
> This being my first 4 stroke I have a couple questions...
[quoted text clipped - 20 lines]
> Thanks,
> Steve

All I can mention is that you measure with a tach. Your not going to "hear"
the rpms to be able to do this. Do ax rpm with tach, then back off, oh maybe
500 rpms to cool.
mk

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Steve - 15 Feb 2010 20:39 GMT

> All I can mention is that you measure with a tach. Your not going to "hear"
> the rpms to be able to do this. Do ax rpm with tach, then back off, oh maybe
> 500 rpms to cool.
> mk- Hide quoted text -

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Six_O'Clock_High - 15 Feb 2010 21:03 GMT

> All I can mention is that you measure with a tach. Your not going to
> "hear"
> the rpms to be able to do this. Do ax rpm with tach, then back off, oh
> maybe
> 500 rpms to cool.
> mk- Hide quoted text -

I'vew been using a tach, that's where the numbers that I gave came
from. I'm just curious how close I should be able to get to the
"practical" max rpm (seems to me I shouldn't be coming up 3k short)
and if it's normal for the high speed needle on a 4 stroke to have
almost no effect on rpm's until it's either too lean or rich to run.

Thanks,
Steve

I would be astounded if any 4 stroke turns much over 11K. The valve trains
just aren't up to it. On my Saito's I generally richen them up to max out
around 10K

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Robert Scott - 15 Feb 2010 21:59 GMT

>> All I can mention is that you measure with a tach. Your not going to
>> "hear"
[quoted text clipped - 15 lines]
> trains just aren't up to it. On my Saito's I generally richen them up to
> max out around 10K

Your RPM figures sound pretty normal to me, but the lack of needle valve
response sounds a little extreme. The four-stroke Magnum, O.S., RCV and
Saito engines I have are definitely less sensitive to high speed needle
valve changes than the average two-stroke, but they still respond in a
similar manner.

Are you using muffler pressure, and are your tank fittings secure and fuel
tubing leak-free? Last fall I had trouble with a Saito .65 that had always
been rock-solid for many seasons. It wasn't running well and seemed almost
totally unresponsive to adjustment. Turns out the fuel tank neck had split
and I was losing the effect of tank pressurization from the muffler tap.
(Some of the inexpensive Chinese ARFs are decent models, but toss those
supplied fuel tanks in the trash!) When I have engine trouble I just can't
figure out, I don't hesitate to completely dismantle, check, and re-plumb
the fuel system with fresh tubing to eliminate that common cause of
mysterious engine problems.

Personally, I think listing 13K RPM as a "practical" operating speed for
this engine is a little much. I don't run any of my four-strokes (.52 to
1.50) at, or higher, than 10K. As for your comment on any four-stroke
turning more than 11K, I believe some of the YS engines can do this as a
matter of routine....

I brushed off some of the winter dust by doing some flying today. The snow
has melted off the runway at the club field, so I fired up a high-wing model
with a Magnum .52 four-stroke on the nose and had some fun in the 5-10 MPH
cross-runway wind. There is nothing more relaxing and satisfying than the
sound of a four-stroke putt-putting around the sky.

Good flying,
desmobob

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Steve - 15 Feb 2010 22:43 GMT

> Your RPM figures sound pretty normal to me, but the lack of needle valve
> response sounds a little extreme. The four-stroke Magnum, O.S., RCV and
> Saito engines I have are definitely less sensitive to high speed needle
> valve changes than the average two-stroke, but they still respond in a
> similar manner.

I guess I'm just used to my 2 strokes having a significant sound
change with each click or two of the needle. Since 4 strokes are new
to me I figured I'd put my situation out there for some feedback.

> Are you using muffler pressure, and are your tank fittings secure and fuel
> tubing leak-free? Last fall I had trouble with a Saito .65 that had always
[quoted text clipped - 6 lines]
> the fuel system with fresh tubing to eliminate that common cause of
> mysterious engine problems.

This wasn't the first factory supplied tank I ditched and I doubt
it'll be the last... I had almost the same thing happened before I
knew better to get rid of the hard, brittle "factory" tanks.

> Personally, I think listing 13K RPM as a "practical" operating speed for
> this engine is a little much. I don't run any of my four-strokes (.52 to
> 1.50) at, or higher, than 10K. As for your comment on any four-stroke
> turning more than 11K, I believe some of the YS engines can do this as a
> matter of routine....

I never expected to achieve the "posted" 13k max rpm, just wasn't
sure if a shade under 10k was where I should be.

> I brushed off some of the winter dust by doing some flying today. The snow
> has melted off the runway at the club field, so I fired up a high-wing model
> with a Magnum .52 four-stroke on the nose and had some fun in the 5-10 MPH
> cross-runway wind. There is nothing more relaxing and satisfying than the
> sound of a four-stroke putt-putting around the sky.

Hopefully next week I'll be in the air with this one. I figure
another couple tanks of fuel to let everything settle down and I
should be good to go.

As always, thanks for everyone's input..

Steve

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Six_O'Clock_High - 15 Feb 2010 21:01 GMT

>>I just installed one on a Pitts and I'm in the proccess of tuning it.
>> This being my first 4 stroke I have a couple questions...
[quoted text clipped - 25 lines]
> oh maybe 500 rpms to cool.
> mk

Let me add a couple of things. Use a tach, as was said for all the reasons
that were said plus a couple. The tach allows you to identify peak prior to
toasting the top end as that is the point you want to know. Do not run the
engine at peak rpm, but richen it up 200 or 300 RPM to keep it operating
during all attitudes. As for the 'break in' runs, run it as lean as
possible for 30 seconds then richen it up at least 500 RPM for 1 minute
periods until the tank is dry. For the second tank, lengthen the lean runs
to 1 minute and the rich times to 1 minute 30 seconds. After 2 tanks, begin
tweaking the low end and test the high end each time you change the low end.
Remember it takes 10 to 30 seconds for a change (however small it is) to
show up on the tach. Be careful not to get the low end too lean as you will
experience excessive deadsticks as the engine will flood the glow plug as
you go from idle to full throttle. Remember to NEVER try and set a 4 stroke
without a tach.

Good luck.

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Model Forum / Radio Controlled / Air Models / February 2010

Any have an OS FS-56?