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Any have an OS FS-56?

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

Reply to
Steve
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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
Reply to
MJKolodziej

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

Reply to
Steve

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.

Reply to
Six_O'Clock_High

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

Reply to
Six_O'Clock_High

"Six_O'Clock_High" "practical" max rpm (seems to me I shouldn't be coming up 3k short)

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

Reply to
Robert Scott

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.

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.

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

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

Reply to
Steve

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