The Tower gasket works. I use them. But they're thinner. Something like .007 instead of .0012. Half the price and a little more than half the thickness. Often I try a thin one first, if the engine is still breaking harsh, might flip a thick one in also or another thin one. The difference allows for finer tuning. Definitely a plus. I need to get into cutting up aluminum cans or legit metal gasket material. $8 or so for 2 OS gaskets way too much. There must be a cheaper source for these items. Maybe Randy or Richard? I find that as long as I have a hot plug (we've been using Enya #3s a lot) the engine will stay lit, even when compression is on the low side.
There are lots of factors. Often a click in either direction will tune the engine into a sweet spot. Eventually, you develop a feel for this. Problem is that the setting on the ground may not resemble the setting in the air. I had a twister that would take off on the lean side and settle back into a nice fat two stroke once the prop unloaded. My Primary Force stays pretty much as set when taking off. Just started working with an ARF Cardinal... Almost. Not quite right. But it leans out some in the air. The PF likes uniflo some planes do not. I think the problem is engine vibration that sets off bad harmonics in certain ranges causing foaming in the tank. Each plane is a law unto itself. Hit the bad spot and fuel foams big time, making for a run run runaway. Profiles are usually worse than full bodies. Also, it's important to have the engine warm to operating temperature before making a final needle setting. Usually when the setting is found the engine will stay in that zone and you're set. Maybe varying some for cold weather and hot weather. Probably barometric pressure is another factor. Part of getting to know the engine. True for serious big buck engines as well. A friend in our club, a top 20 flier, told me he turns the needle on his PA61 a full half turn between morning and late afternoon. Compensating for temperature. Then of course there are issues of props. His PA is one sweet engine by the way. Putting in four heavy duty stunt seasons. Very impressive.
My recent experience with an ARF Cardinal is I think revealing. This is the first time I've used a clunk tank on a profile. First couple of flights definitely bad runaway with the LA46. Now this is a reputed well behaved engine, nevertheless it exhibited the classic bad runaway syndrome. Fat and happy 2 stroke (may have even been a fourstroke- sure pumped lots of oil out) but as soon as it broke lean, jet power. Dan Banjok looked it over and said it's a vibration problem. Sure enough when the engine broke lean on the ground (when we pointed the nose up) the fuel in the tank went nuts, it looked like fast boiling water. We could see this through clear plastic tank. The engine went very lean. We put a bit of armoral in the fuel. We cinched up on the engine bolts up. Laid in row on row of rubber bands on the tank. All this helped some. Getting there. I'm going to grind into the balsa cheek cowl where the bolts exit soon as I get a chance. Make sure the washers and nuts are laying up against hardwood. Also I'll make a brass strap to further secure the tank. (This has worked on some of our ARFs, helping to eliminate vibration problems. We find that tanks like a very solid mounting.) I have some new metal uniflo tanks from RSM, will probably try one of these. Also have some vibration absorbing material to lay under the tank. Then there is the genuine 1/8" steel mounting pads, Dan used to tame the truly remarkable vibrations of his Foxberg Fox. It turns a genuine 14,000 rpm pushing a 9x6. Grab the wing on the Cosmic Wind, the vibes actually sting. But he's getting the plane to run consistent and fast.
In conclusion I think lots of runaway problems can be traced to bad harmonic vibrations set up as an interaction between plane, engine and tank. Bad vibes. We need to work on that. Often it's not the engine alone, it's the system.
Topic: FP40 $92 and (Read 1613 times)
