engine problem?

I am having problems with a used OS 35S I put on a Banshee. First day out 10-6 balanced zinger prop. Ablsulutely no needle valve response. The engine would only start and run at one very rich setting. Using 5% Nitro 25% castor. Steps I took:
1. inspected needle valve assembly nothing found but replaced it with a brand new ST assembly anyway
2. flushed out the gas tank with alcohol
3. replace fuel line and filter
4. put a new thunderbolt long glow plug in
Results
much easier to start and full throttle response
HOWEVER
No mater how rich I try to set the engine run, it flys 3 to 5 laps fine then begins to lean out and quits.
I raised the fuel tank height from 1/4 inch above venturi to 1/2 inch NO CHANGE
I have had one great run no problem plenty of pull but all others have quit on me. So what do I look at next?
John

Your problem is vibration but I don't have a simple fix. I fought the same problem with an OS 30 S on my Flight Streak and a 35S on the TwistMaster for the first several months after I returned to the hobby. My ultimate fix was to put a 25 FP on the Streak and a Saito 30 on the TwistMaster but that is probably not the solution you are looking for.

What I have determined is that it really doesn't matter how stiff or how well you build up the nose if the rigidly of the nose happens to be within the resonance of the engine it ain't gonna work. I have seen box stock Ringmasters with the little short motor mounts and crappy plywood doublers work great with older vibrating engines but darned if I could get one to work on the TwistMaster with long motor mounts and aircraft ply doublers.

LAST EDITED ON Aug-25-03 AT 11:41 AM (CDT)
 
>I am having problems with a used OS 35S I put on a Banshee.
>First day out 10-6 balanced zinger prop. Ablsulutely no
>needle valve response. The engine would only start and run
>at one very rich setting. Using 5% Nitro 25% castor. Steps
>I took:
>1. inspected needle valve assembly nothing found but
>replaced it with a brand new ST assembly anyway
>2. flushed out the gas tank with alcohol
>3. replace fuel line and filter
>4. put a new thunderbolt long glow plug in
>Results
>much easier to start and full throttle response
>HOWEVER
> No mater how rich I try to set the engine run, it flys 3 to
>5 laps fine then begins to lean out and quits.
> I raised the fuel tank height from 1/4 inch above venturi
>to 1/2 inch NO CHANGE
>I have had one great run no problem plenty of pull but all
>others have quit on me. So what do I look at next?
>John

John,
Try running the engine with pressure to the overflow if you are running a uniflow tank and plug the uniflow vent tube. If pressure is not available, still give it a shot to see what happens. I fought some erratic runs earlier this year and this helped a bunch (I tried a bunch of different tanks with similar results on the erratic run). At some point I would like to return to uniflow venting, but have not tried as of yet. Will have to move some tubes around so that the uniflow and pick up are not too close together. Good luck.

LAST EDITED ON Aug-25-03 AT 12:18 PM (CDT)
 
Besides a possible problem with foaming fuel, due to vibration, There may be another item to consider.

You didn't state if you were using muffler pressure. I personally prefer using pressure as it negates the tendency to richen up going into the wind. I had a similar problem with runs getting progressivly leaner, and the cure was to open up the small hole in the pressure nipple. These, if too small, or carboned over, can cause a similar problem to yours.

Still, The most likely suspect is foaming. one squirt of Armor coat in a gallon of fuel will cure this tendency. Some have reported that the formulation has recently been changed. I don't know, as I have a lifetime supply of the old stuff. Others have reported other problems, that may or may not be caused by using this product in our engines. Again, I don't know, as I only use a small squirt of the stuff. This may not be a case of, "if one is good, two are better".

There are archived threads which discuss this solution in detail.

I'm wondering why everything is spinning around?

LAST EDITED ON Aug-25-03 AT 01:46 PM (CDT)
 
If you have a test stand, put the engine in that & test for whether it is actually broken in, or was essentially still new inside when you got it. With a two sizes smaller, two pitches flatter prop, set the needle for a seriously leaned out run. A normal prop for your engine is not that Zinger 10-6, it's someone's 10-5, so cut a 9-4 down to an 8-4 for a test and breakin prop (the hub on most 8-4's is too small). If it heats up too hot to hold the cylinder in your hand in less than a minute of lean running, pinch off the fuel line (or if it quickly sags and wants to die lean). It's still "new".

"Too hot" doesn't mean you could continue to hold on, just that it won't BURN you from heat in a second's worth of gripping around that cylinder. If you cannot close your fingers around it without injury, in other words. That's the acid test with an Iron Piston motor. They almost all have to be heated "some", but not "too much" when breaking in, and allowed to cool completely between runs.

I've acquired a lot of older engines lately, many of which weren't described as new, but turned out to still need breaking in. I have a Torp GH 29-S that was slightly dirty, had some of the green worn off one side of the head, and had obvious marks on the lugs from having been bolted down and run in some plane. But it acts like a new engine; get it too hot, it leans out and dies.

.
Kiwi