Hi, I have an Lanier Explorer 40 trainer with a new just run in SC 46 glow engine driving an 11x6 prop.(SC are Chinese engines available in New Zealand, club guys here have been having a good run from them) The engine starts very easily and the plane flies very well. My instructor is very impressed. However when moving the throttle from half power (a setting the planes flies very well at) to full power, or from idle to full power the engine will just stop. The engine tuning appears correct, flying around very happily on half to full throttle the engine just purrs, making all the right sounds

We have tried different needle valve settings, but with no success, different brand of fuel, current using brand new Sig Championship 2 stroke glow fuel, 10% nitro. The previous fuel was club mix and had no nitro, removed and checked the fuel tank and lines in case a line had moved and was causing foaming in the tank and hence fuel starvation, everything fine and no change to the engine behaviour. Tried 3 different glow plugs, and A3 which came with the engine, a Tower plug(don't know much about that one heat range and so on) and a genuine OS#8. The tank and carb have been checked for air leaks, but all is fine. Shortened the fuel line so it was not waving in the air stream and may be getting excessively cold.

It is summer here so the air temp is warm in the mid to high 20degree range(today is 26 -30 degrees) so I don't think believe air temp is a problem. The tank and set up is a as supplied by Lanier and looks very ordinary and normal. My very experienced instructor can not find any fault or problem here.

Running out of ideas of where to go next to solve the problem. Wondering if the glow plug may be getting cooled by the incoming fuel and air when the throttle is opened and no glow = no go. However I believe that the OS#8 is a hot plug. I believe idle bars were added to some plugs but I can't locate any glow plugs with an idle bar, are these a thing of the past, would it helpanyway?

My instructor says I am ready to land, but is not letting me until this engine problem is corrected as if I mess up the landing I can't put on some power and go round again, as the engine will stop.

Thanks for any suggestions, I a have an older OS 46 engine and are just about ready to put this in the plane!!

Cheers

David

The A3 is hotter than the 8. I would put a new A3 back in the engine and retune it. 5% nitro *may* be the lowest percentage for the engine to transition smoothly.

Does the engine seem to gurgle when you shove the throttle wide open? Low speed setting too rich. Or, does it seem to wheeze and die? Too lean.

You may have tuned yourself right past the lean point. A rich low end and overly lean high end will still produce good results at mid throttle.

Bring the engine up to where it runs well, then richen the high end slightly. Advance the throttle a little more and see how far you can take it. Then repeat the process. Richen, then advance the throttle again.

You want to find the point at which you can run wide open throttle, with slightly less then maximum rpm.

Now that the high end is set, start to work the throttle closed a little at a time. At some point of closing the throttle you may hear the engine gurgle. Continue to lean out the low end needle till you obtain a good idle with the carb open about 1/8".

Now check the high end again. You should be very close to perfect, but you may have to adjust with a click or two richer on the high end after adjusting the low end.

Always adjust high end first. Then move to low end.

I agree with blw, use the A3 plug, and use 10% nitro.

SC is the same as Magnum and ASP, they have a very sensitive low end needle and it is usually too rich. A rich low end needle will make that engine behave like yours. A friend of mine had the exact same problems on his Magnum XLS 52 and after I tuned the low end needle on his engine it ran fine and never stops. Gently turn in your low end needle (with the carb closed) and count the revolutions to see how far out it has been, on the 52 engines it needs to be at only 0.5-0.75 turns open from fully closed and I guess the 46 is very similar since it is basically the same engine, just a tad smaller. Use the pinch test to fine tune, it is a great engine once tuned right

If it is the same as a Magnum, mine has to be quite lean on the low end in order to transition good. If it is just a tad too rich on the low it will do exactly what you are describing. Mine also likes an A3 plug.

Thanks guys I will tune the engine to your instructions. We spent time this morning pulling the carb to bits again and this time washed it out with fuel, rather than just compressed air. Lot of small pieces of gunk came out, I expect pieces of grass and seeds (high summer here). The engine transitions OK now but does still hesitate a little, but does not stop. I am sure this hesitation will be eliminated following your tuning suggestions. I am also getting a carb filter to keep the little bits of gunk out. The engine just purrs when it running correctly.

Thanks for your help.

Cheers

David

The hotter plug may help that too. It would be interesting to see your tach reading with the OS 8, and then with the A3.

I will try that. The engine was producing exactly 10000 rpm with the OS#8 plug and happily idling at 2300rpm. (of course that is assuming the electronic rev counter is correct, although I guess all the readings will able to be compared if the same the same rev counter is used.)

David

10000 RPM shows your prop is wrong.I think those engines should like about 13000 RPM s.Try to use lesser prop.

I completely agree with turk. 10,000 is low, maybe more like 11,500 should be considered minimum. These small carbs do not have any type of accelerator pump so they depend on the engines ability to accelerate quickly so their is no bog. IMHO something on the order of 12,500 to 13,000 like turk1 said would be more appropriate. Sounds over-proped to me.

Hi Dave, try to open the idle nidle some 1/4 of a turn at each try, it should help. seems to be a lack of fuel trasitioning from midrange to full power. please inform on tour progress.
cheers

Hi!
If you run no nitro fuel you should also remove one or two of the 0,1mm head shims for best throttle response and power.

Problems solved. Thank you all for your help. I adjusted the low speed needle valve slightly, richening the engine by about 1/10 of a turn. Problems gone. Now idling @ about 2300rpm and toping out @ 12500 rpm. No hesitation in moving from idle to full power, mid throttle to full power, full or mid power down to idle with the engines continuing to idle and not dieing(stopping). Engine just purrs, doing all the things a glow engine should.

Just need the rain to clear away and flying again. (tomorrow???)

Cheers

David


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