New GX40 Gasoline engine
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TOPIC: New GX40 Gasoline engine

Re: New GX40 Gasoline engine 4 years, 6 months ago #215

  • hllywdb
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It is a 2 needle carb so both needles affect the other. For staring settings, move the throttle to wide open. Your low speed needle should be just a smidge away from entering the fuel tube (high sped needle side) This way as you close the throttle it slowly slides into the tube and cuts the mixture back to meet the decreased air flow.

Then start the engine and adjust the high speed needle for 500 off of peak. Then see how your midrange is and if transition is improved. From there you can adjust the low speed needle in to get improved transition, but do this in very small steps. By doing this you may find you need to again adjust the high speed needle at wide open throttle again. Repeat this until you have found a good balance. Once you have found a good setting, set your linkage or trim on the transmitter to hold a reliable idle. Do not use the low speed needle to set the engine for best idle, it is not an air bleed carb, so you will simply lose your midrange and transitions by doing this.

Hope this helps :)

Re: New GX40 Gasoline engine 4 years, 6 months ago #216

  • j.j.rutter
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I had similar problems but think I might have found the answer. The O ring between the carb and crankcase on my engine was very thin. I replaced it with a fatter one, pushing the carb tight against the crankcase while tightening the pinch bolt and got a much more consistent engine run. Of course now the carb. settings are all to pot as they'd been adjusted while seemingly having an air leak around the bottom of the carb. I'm not 100% sure I've cured the problems but I've certainly improved things. My engine also seems happier on a 10" prop, just as well as I've run out of 11x6's with the number of "flame out" into long grass landings I've suffered.

Re: New GX40 Gasoline engine 4 years, 6 months ago #217

  • hllywdb
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When mounting the carb, you need to apply a firm downward pressure while tightening the pinch bolt to achieve a good seal, as well as making sure that the throttle barrel is aligned 90 degrees to the crankshaft. I haven't had any problems with any of the O rings as long as I do this.

Anothe trick that I have used on other airplane/motor combinations is to drill out the exhaust pressure nipple slightly to provide more flow. This has helped me in the past with some airplane/fuel system configurations. I had to do this on my OS 55AX when using a tower muffler on an inverted installation.

Re: New GX40 Gasoline engine 4 years, 5 months ago #218

  • j.j.rutter
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Got a slightly odd problem with my Gx-40 in a plane. Since putting a fatter O ring under the carb the engine's now starting and running beautifully, expecially on a 10x7 prop, idles slowly, picks up cleanly, plenty of power - for about 8, 1/2 minutes, then it stops. Very strange as there's enough fuel for 15 minutes in the tank and if I drain it through the fuel line there ar no air bubbles or any other problems. This is fine in a way as 8 minutes is enough for a lot of fun, I just changed my timer settings and land it after 8 minutes but why should it stop? The tank is new, flat rectangle shaped, 4oz capacity. The clunk reaches the bottom properly but doesn't meet the rear wall (which sometimes causes suction blockages), it doesn't leak, all the pipes inside and out are fine. The change in fuel head is ony about an inch from full to empty, much less than it seems happy to suck fuel through when the models nose is pointed to the vertical so surely a change of 1/2" (8 minutes of flying) can't be the problem can it? Yet it consistently cuts, even on tick over (which I left deliberately a little on the rich side) after no more than 9 minutes. Refilling the tank it'll start and run on exactly the same settings in exactly the same manner but still stop after about 8, 1/2 minutes. Good consistency but slightly frustrating. Anyone got any thoughts on this?

Re: New GX40 Gasoline engine 4 years, 5 months ago #219

  • hllywdb
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Check for a pinhole in the pickup line in the tank. It sure sounds like that.

Re: New GX40 Gasoline engine 4 years, 5 months ago #220

  • j.j.rutter
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I agree it sounds very like a pinhole problem but it isn't. I've replaced the pick up line twice - just in case - but on neither occasion has it made any difference as there was no fault with the line. It's got to be a tnak fault of some sort as the engine runs so well for the first 2oz or so of fuel and shows no sign of "stress" prior to stopping as if out of fuel. I'm looking into supporting the tank in foam to see if it's a vibration/foaming problem, about all I can think of as everything else seems fine.
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