EDIT---------- save yourself some time and skip to the last post in this thread.

I've used OS engines since back when the first 35S hit the hobby shop counters. That's 50 years???? I've made engine parts and tried to hop 'em up with some success. I been there and done that a lot. And can usually solve about any engine problem at the field.

But I never bothered with 4cycles for myself. Got a bunch running for other guys, but never bought one for an airplane of mine.

So I figured it was time. I got a 46size Clipped Wing Cub that just cried out for a 4cycle. So I bought an OS70FL. I figured it'd be like the 6-7 OS46AXs I've broken in in the last 6-8 months (5 of 'em are mine). After all, the advertising said it had the same ABN and breakin proceedures.

Well, the instructions say to open the HS needle 2.5 turns etc etc. This one didn't and won't run unless that needle is about three quarters open from closed. The instructions say that you won't have to touch the settings. I assume they're talking about the airbleed. After believing what they said about that, I simply started trying to break the sucker in. When I finally got it to where I was trying to get it to idle, it stumbled every time the throttle was opened. So I did what everyone does. I did the pinch test and when it showed rich, I started opening up the airbleed screw. But before I did, I thought I'd turn it in to see where it was factory set. I didn't turn it in because when I looked, the tension screw was compressed. So I didn't bother. I figured it wouldn't turn in and if it did it'd just run into the spring. So I started turning the screw out a quarter turn at a time. It never changed the way it stumbled on throttle up. Yesterday, I figured all my turning would have finally opened the hole completely and decided I had to pull the engine out of the airplane so I could check some things.

I'd put the engine in the airplane like I've done with my last few 46AXs. Those suckers really are good enough to bypass bench breakin. But with the engine on the plane I couldn't check the airbleed to see if it was plugged.

With the engine out, I discovered the hole was as I suspected. wide open.... And I pressed fuel hose to it and blew and it sounded completely clear. I also did the blow test on the highspeed needle body. I pulled the hs-needle and blew again and no trash or anything came out. I'd replaced all the hoses at least twice. The two pressure fittings from the muffler had open holes that appeared to be flash free (no flash plugging the diameter holes that were drilled in them). The fittings were tight. The hoses from those fittings went to the right places, the small fitting to the backplate, the large to the tank.

My fuel tank will hold pressure overnight. No leaks. My fill/pressure pipe goes to the top of the tank. The pickup pipe has the clunk still connected and it's far enough away from the back so that it won't suck itself closed on the back wall. The clunk will move completely around in there. I've even swapped the lines and the engine won't pull from the vent, so it is working as a vent, and the muffler will blow bubbles out of the clunk so it's a working pickup. Got no reason to suspect the fuel system isn't perfect.

I checked the backplate for cracks and its screws. They're tight. The headbolts are good and tight. I don't have feeler gauges in the right sizes to check the valves, but they have paperthin at least gaps. The rocker cover was tight when I looked at the valve settings.

The thrust washer (prop hub) has freedom from the front bearing. However, there appears to be no windage in the crank. There is no forward-back "loosness" in the crank. But it's as free to rotate as any of the tightest 46AXs. Even if the crank was being slowed by the bearing fit, I can't see that as causing the engine to run the way it runs. The way it runs......

At about 3/4 opening on the hsneedle and any setting at all on the airbleed...... It will turn 9,200 on the ground and sound solid. A couple clicks toward lean on the needle and it stops dead. No backfiring, just stops. About 5-6 clicks out (richer) on the needle and it does what it's supposed to do, slows some. It'll take about a half turn in on the needle before it goes rough-rich. It is always weeping out of the venturi, no matter the needle setting, but not anything like excessively. There are always very small droplets of fuel spitting out of the venturi when it's running, but very very small ones and not many. I've not seen that with my couple of hundred 2cycles in the past, so assume that is simply what a 4cycle does between intake sucks. When the engine is tuned to turn 9200, that spitting is at it's least.

I'm flying the sucker on a Cub. I can't get a needle setting where the engine runs smoothly in the air. I fly a couple of laps and land and try another setting. It either runs with power and missing or it runs rich and missing. It will fly inverted the same. The max opening on the ground seems to be the same needle setting it'll take in the air. I expected it to take a couple clicks richer in the air than it'd do on the ground.

I've run through 3 glowplugs. Using OS-FS plugs. They all glow GOOD and have straight coils. I'd use every one of them again.

I'm using a balanced 13-6. I'm using good fuel and have tried a different fuel. I use 10% with 18% oil. It works great in another guys Magnum FS. There ain't no magic fuels. I use a filter on the fueling system and in the airplane between the tank and NV. It's tightly closed and has never had a speck in it yet, and you can believe me, I've checked that sucker more than once.

After discovering that I'd had the airbleed set every setting from closed to open I reset it last night to be 50% blocked by the screw. No change in the idle/throttle characteristics.

The engine will now idle slowly. It wouldn't until after about 10 tanks. After I discovered that it'd hold an idle, I decided to try and set the throttle-up because it would stumble rich on throttle-up. No matter the setting, the pinch test causes the engine to lean out when the tubing is pinched. Like I've mentioned, the last runs in the last few days had the airbleed screw set the full range at one time or another, either completely unblocked by the screw to 100% open.

The muffler is tight. The engine is tight on the mount and the mount is tight on the airplane.

It would seem that the factory suggested setting of 2.5 turns versus the actual setting of 3/4 should suggest something to an experienced engine guy. I'm experienced, but not with 4cycles. And truth is, this one isn't going to influence me into buying any more. Matter of fact, so far, this one sucks. I've suggested to the guys I'm always telling to buy OS, that this one must be a counterfeit.

Can't think of anything else to check or try................ any suggestions?

I think I ought to sum up what I find wrong......

It wouldn't care if the airbleed screw fell out. It doesn't seem to respond to it at all.
The transition from idle to full throttle stumbles every time unless the throttle is gently advanced.
The engine runs ragged with just about any needle setting except a window of 4-5 clicks that work on the ground. Take the airplane off with that setting and the following describes how it reacts.

The optimum "high speed" needle setting is almost impossible to find. There are about 4 or 5 clicks where the engine will tach 9,200-9,400 rpm. It doesn't seem to care which of those clicks you're in and moving around in them does little to the tach reading. If I click out of those 4-5 on the lean side the engine instantly quits. If I take off on the lean side of those 4-5, the engine will quit in the air. If I take off on the rich side of those 4-5 the engine runs ragged and anyone with experience would say it's too rich. I've landed it and gone one click leaner on the runway, taken right off and seen no change , landed and clicked leaner, still rich, landed and clicked leaner, taken off and engine runs smooth and sometime in that flight gone deadstick. Check the fuel level and it's almost full. Done that a number of times.

I'm not running with the cowl on the airplane. It hasn't been on yet.

BTW, I forgot to mention....

The needle threads in and out easily. The rachet is tight. The threads look perfectly cut. The O-ring is very slightly larger than the barrel and there are no symptoms of blow-by, it's sealing. The needle taper looks good and no burrs on the end. Looking down into the female structure shows no burrs. I originally had a needle extension, but pulled it in case it was causing some jiggling. No change.

I will be glad to post any closeup pictures if you wish.

Thanks for "listening". I hope you can help.

daRock

OK, last night the lack of fore-aft freedom of the crank caused me to inspect the prop drive washer. I wanted to make sure that locating pin was still in place and that it's groove in the washer wasn't too deep.

When I pulled the prop and spinner I noticed that the back of the spinner was worn from the backfiring. So I pulled out a new spinner.

Then I pulled the drive washer and noticed something. There was a black residue on the back of the washer. It looked like the aluminum was either scuffed (which it couldn't be unless the front ball bearing was seizing) or had something like plastic baked to it. The stuff wouldn't wipe off with denatured, so I rubbed it off with emery cloth. The pin was where it was supposed to be. (of course, it fell out and I had to find it)

The washer went back on and maybe, just maybe the crank turned over a bit free'er. That and the newly indexed airbleed screw caused me to want to give it a run to see if there was any improvement.

The engine usually won't start unless the throttle is more than half open. It'll now start dependably if that's done. I finger choke it to fill the delivery line, and apply the starter. It usually runs after the fuel moves the last little bit and gets to the carb. It cranked good and I started around the airplane to pull the igniter. It was running like it does. Steady with a stumble. I was reaching for the igniter when it turned into a machine gun. It always had been prone to pop a backfire now and then, but not when running above 1/3 throttle, and only one at a time at low motor. This time it cut loose. I got no idea why it kept running but it just about beat the airplane to death. The impacts appear to have damaged the leading edge of the stab where the hold down was holding. The hold down has thick foam around 1" dowels but the LE looks less than pretty now.

I got to the TX and cut the throttle and it quit. It was blazing hot and had destroyed the backplate of the new spinner.

It's time I found out from Tower if they'll take it back. It's either going to Tower or better yet, to OS so they can do some R&D on it. I'd love to find out why it's so "user unfriendly". Unfriendly it is. It's wasted I'm guessing about a gallon of fuel, turned two brand new OS FS plugs into "used but probably good" (I seldom reuse plugs. Life is short and plugs are usually cheaper than what my flight time is worth to me.), chewed up one spinner backplate (and wore another one to marginally useful), and got me questioning my engine debugging talent. I wish it'd done this right away.

Looking the engine over now, about the only odd thing I can see is some kind of black gunk that appears to be forced out at the base of the pushrod shrouds. Those covers fit so well, I can't believe the stuff could be from inside, but there is no reason I can think of that anything like that would just happed to deposit itself in that fairly inaccessable place. It looks like it could be the same stuff that was sticking to the back of the drive washer.

Sorry to have taken so much of your time. I would have deleted this whole thread if the forum permitted since I'm no longer interested in trying to solve an "engine doesn't run smoothly" problem. It's more than that. It's going back to somebody. Hope I can get my money back.

damn..... you got a bad one. i thank you for the thread i now know to stay away from FL70.

I've bought OS engines since back when model airplane engines were chipped out of quartz with a harder rock. This is the very first one I've ever had any problem with. It is obviously a good design, but one single engine that had something wrong inside. I would have no problem buying another FL70 tomorrow. I would bet that if this thread were on the general engine forum, there would be a lot of guys there who'd post that they had no problems at all with theirs.

I've not heard anyone else have problems with the FL70. But then, I did a scan of all the forums and didn't hear ANYTHING about it either.

A few things...if you post on a weekend, don't expect a reply until at least Monday. We're not here to answer questions over the weekend.

"Factory" settings are only starting points. You'll NEVER have them as the settings you'll wind up running with.

The O.S. FL-70 does take a bit of running to 'come in'. We'll usually run it with a 12 x 8 APC prop for the first few runs. We'll use a 10% fuel with about 18% oil content that has a synthetic/castor blend. We'll not run it too rich, but we won't run it too lean.

There should be no wear between the drive washer and the case. If there is, then the crank's not fully-seated against the rear bearing, and needs to be driven forward a bit. Black from there does mean something's rubbing that should not.

When we prime the engine, we'll open the throttle to full, choke the carb, and turn the engine by hand in the forward direction. We'll do this until we actually see/hear fuel spitting out the exhaust (on upright or side-mounted engines). Turn it slowly backwards one or two full revolutions. Retard the throttle to about 1/4, add the glow plug battery, and flip hard backwards through compression. This will usually cause it to fire and start running forwards. We'll advance the throttle to full before removing the plug battery. We'll start adjusting from there, as the engine can handle or needs it.

We won't try to adjust the idle mixture (air bleed) until we have reliable full-throttle running.

Thanks for the answer. I'm retired and completely forgot that it was the weekend when I started the thread. I started the thread when I'd finally run out of things to try and didn't notice it was Saturday.

I mentioned the factory setting really just for info. I figured the factory suggestion of 2.5 turns must have meant that this engine's run setting of 3/4 of a turn might mean something to someone familiar with that engine. That's a heck of a difference. And once I got the hang of it, the engine was no problem to start. The technique suggested in the manual that came with the engine works great. And that's great because when it's cowled, it'll be really difficult to choke or prime as you suggest. Starting it now isn't a big deal, it is the way it runs that is the problem.

I was not expecting that as the advertising says the design is similar to the 46AX so I expected it to break in like all the 46AXs I've bought or set for others. The manual that came with the engine describes almost exactly the same process as I've used with the 46AXs, and says after two tanks of that process to fly the engine rich and expect on each of the next 10 flights to go one click leaner each flight. Since this engine has way more than two tanks through it and it's needle settings from blubbery-rich to so-lean-it-stops cover only about 1/4 turn or about 6 clicks, I figured there might be something wrong with this engine. It's gotten enough runs on the ground to have "come in". And has probably had 10 flights and it's not changed one bit. It's got about 5-6 clicks adjustment. And they're right where they were on about the 3-4 run.

Set it lean enough that it runs smoothly in flight and it'll stop in flight. Set it any other of the 4-5 clicks left and it runs rough.

BTW, I didn't mess with the airbleed at all until I'd established the needle position. The reason is that the engine wouldn't idle at all below 3/4 throttle for a long time. I never had a chance to try and tune the throttle transition because it wouldn't throttle down in the first place. I guess it had 6 or 7 runs on it until it would actually throttle below half throttle. And it was a day later that I discovered that it would keep running at idle. Whatever the time line..... It really wasn't until I risked flying the new Cub that I started trying to tune the airbleed for throttle up, because I didn't want to risk that new airplane. A stumbling on throttle up wasn't what I wanted. Whatever the time line.... Last time I ran it, the idlescrew didn't do a thing. And I didn't start out messing with it at all.

But now that it's gone bad, it's time to send it in. Thanks for your interest.

And we'll be glad to check it out and see what's wrong with it. It'll either be repaired or replaced, per the warranty.

Thanks BAX, I knew that was how it worked. I appreciate your wading through most of what I wrote. Pretty longwinded, but I was hoping to give "enough" info to debug the thing over the internet.

LANNYBOB, to show you what I think about this OS Max FL70 and it's problems and OSMax in general, after I drop this sucker off at UPS, I plan to swing by the LHS to see if they'll match TOWER'S price on one, so I can get the new Cub into the air. It's motor mounts are already drilled for it, and after owning maybe a thousand OSMax's over the last 30-35 years (OK, maybe only a couple of hundred), I know there is simply either something I didn't do right, or something in the engine that was just enough out of spec that it was a lemon. I wish the cars I've bought in that time had as good a record.

Sent the engine back to service. They sent me a new one almost right away.

Used the same setup for the new one. It runs with none of the original's problems. Not surprised. Only negative was that I didn't learn a thing from the ordeal.

Hey guys..
I have bought my first 4 stroke O.S FS 70II. I had about 3-4 full tanks of fuel on it only. Each time I start it it sounds better and seems to be more solid.. I start the engine by choke and its no problem it starts straight away by first turn. Today I went to my garden to start the engine again to adjust it or lets say, try to adjust it. I need to start the engine at 1/4 throttle becouse if lower the engine dies after 2/3 seconds. It seems to be unstoppable when the engine is 1/4 power or more. but 1/4 is not the idleing point. The engine seems to eat a hell lot of fuel as I ran the first few tanks at 3 turns approximately.. Why is the engine seem to run richer when I turn the needle right(when i close it) and runs leaner when I turn it left(when I open it)?? This is a bit confusing becouse I want to know what is the approximate amount of turns on the needle you have to make so the engine runs perfect when idleing.

Thanks Patryk.

Hi Da Rock,

Did you ever find anything out about why they replaced your first 70FL?

I bought one last year about the same time as your posting. I've only just got around to running it and your posting describes it perfectly. I had additional niggles like the backplate leaking all over the place (cured with PTFE tape) and the needle being a "jiggler" (touching it with a finger whilst running would change the mixture, even whilst clamped to my very solid test stand), but the 4 -5 clicks of running OK on the ground transposing to stop or running rich in the air is exactly the same. No sign of fuel frothing, and now on second set of pipework just to remove usual causes of crappy running.

Its funny, I've always bought cheapy Chinese ASP or SC engines and have had great engine after great engine. This is my first OS...

Arnie