I've fallen back to my number 3 airplane after engine problems in the number 2 plane. And have now have yet another engine issue. Just not my year, I guess. The plane is powered with a Saito 56. This setup ran pretty well previously, but has sat in the box (in a Ziploc bag, engine well oiled) for probably a year. I cleaned it up and put it in the plane along with a clunk tank of the same vent design used previous, though not the same tank. This is a new unit. All this worked fine previously.

So, I put 4.375oz in the fuel tank (previous amount needed to fly a pattern),  prime the engine and flip. What I got was what you get when you burp a pipe plane. A quick wow! Start and stop like it starved. I keep repeating this process, all the while opening the needle. Started at about where I ran it before; around 3 turns out. At about 6 turns out, it finally starts and stays started...for about 20 seconds. I diconnected the battery and picked the plane up. Seemed to be running OK, but as soon as I tip the nose up it quits. Hmmm.

So I continue to mess with it. Got it started again several times and tried various positions. Same thing. The last time I started it and just held the plane level. It ran for about 45 seconds, pretty steady, then sagged a little and quit.

If feels like a starvation problem. Perhaps just a bad NVA? The engine had been stored without the NVA in place. I put an ST unit in (this is what was in before). It could be an air leak or just a bad NVA, I suppose. Any ideas on this?

I also thought it could just be bad fuel, so I cracked open a brand new gallon and tried that, Same thing, so I'm thinking this is a fuel delivery problem.

Oh, probably should say the venturi setup is my own design. Worked fine previously. a .310 venturi with ST NVA through the middle. OS 4 stroke plug. First fuel was some Powermaster 20/20 that I used previously in this engine (not year old fuel, just the same type). The new fuel was Wildcat 10/23.

Thanks for any input.

I pulled the engine and tank out and put them on the test stand. The good news is, it does the same thing so it's something to do with the setup, not the plane. I suspect and airleak. Pressure checked the tank and no leaks. Also checked the fuel line and filter. Again, no leaks. I'm going to pull the needle valve assembly out and replace it with another unit and try it again. We'll see what we get.

Randy - My list would be - Make sure the crank case breather is not plugged, or partially plugged. Check your intake valve lash. Maybe you "adjusted" it before you bagged it, and set the lash too loose? Other than that, it would have to be a fuel draw issue somewhere between the spray bar to the tank and all plumbing/filters etc in should be flushed, replaced, checked over etc.
Let us know how it works out.

EricV

Out of curiosity, do you have any idea what caused the bent pushrod?

Sounds like a piston strike...

New valves should solve it, providing the stem bushings were not damaged. The lube on the valve stems might have gummed to the point that positive cam pressure would open them, yet the gumming might not have let spring pressure close them  far enough to clear the piston at TDC.

I 'happened into' a MAGNUM 52 4C that had severely gummed valves AND deposits on the valve seats that prevented full closing. Fortunately, tho not cheaply for what I'd paid for the engine, a fresh head - with valves installed - was available from the importer/primary USA agent. Cam, pushrods, etc., were in good shape, and it sounds like a runner. Weather and a few other things have delayed bench proofing of the rebuild, but it makes the 'right' click-click when the shaft is turned through. BTW, the head on the engine as received had the threads for the exhaust pipe broken away.

I'm looking forward to trying this one out, even in 'lashed full throttle' condition. From some experience with an OS 40 4C (the original, wimpy one) I expect that the massive exhaust pressure from 4C engines will help with most fuel delivery problems...

Bob,

Thanks for the info. I may just send it off the Horizon. Good Idea!

While I have your attention. The other Saito 56 has an interesting problem. It runs fine, but in level flight, I get some rpm fluctuation. The rpm wanders around (300-400 rpm) in level flight. You can hear it sort of going up and down without pattern. Seems to have plenty of power in the maneuvers and runs fine, but that seeming inability of the engine to hole a consistent rpm is troublesome. It does the same thing on the test stand. Plane uses a clunk tank and I tried the same tank on the test stand. Does the same thing. Also does it with the usually test stand tank.

I like this engine, but the floating rpm bothers me.

Thanks for your thoughts on this.

Bob,

That's what I thought and put in a new PA style NVA and resealed everything (soft silicon washers on the NVA where it contacts the venturi. Resealed the venturi to the intake tube, too. But it continues to wander.

Hi, Eric - with what model OS did you have that problem?

Bob Z.

Dick - that is why I addressed the question to Eric. On a 2S engine, any crankcase leak produces run problems in that the case is a conduit for the fuel/air mixture. Disturb it and the run quality suffers.

On a 4S engine, the crankcase is vented to atmosphere - an intentionally leak. In a 4S engine, crankcase pressure would reduce the amount of piston ring blow-by, thus inhibiting lubrication. Remember, our engines nave no lubrication sump per se. Instead, ALL lubrication is derived from the residual fluid (mostly oil) that passes the ring(s).

If you look at the older 4S engines, most of them had the breather nipple in the backplate. The newer and more powerful variants have the nipple in front of the rear bearing. This insures that any flow of lubricant exiting the case must first pass by the bearing. It will also get into the cam drive gears and be flung around to the remainder of the valve gear.

Here's a trick I use - whenever I buy a 4S engine, new or used, I remove the valve cover(s) and flood the valve gear with oil. I also squirt a teaspoonfull into the breather nipple and wrap a rag around it to catch the oil. Flipping the prop a few times insures that all is wet inside. When I start it, the excess just burbles out.

I forgot to mention - when I have the cover off, I check valve clearance. I have seen new ones with none. Better a bit on the loose side for run-in.

Bob Z.

I pulled it out last night and went over it pretty closely. No cracks (as far as I can tell). I am fitting up a new venturi with a better seal around the intake manifold. I think it may be leaking there.