redball8

My Feedback: (128)

Every third or fourth flight the ST3000 on my 38.5% Corby Starlet will "flame-out" - taxies out to the runway just fine, throttles up well and then maybe 10 seconds after full throttle she dies. The OS 7D carb seems to be set just fine, great transition & steady idle at ~1700 rpm. Engine runs wide-open throttle at about 300 rpm off peak (7400 rpm), running a fairly high-oil fuel for break-in (~7% nitro, 16% oil with 50/50 castor/synthetic). 18x8 prop, Hangar 9 3011 (four-stroke) plug, all large size fuel tubing, clunk drilled out, large filter, Bisson pitts muffler. I can have 2-3 flights and she runs strong, then a flameout and things get exciting.

I'm wondering if perhaps I'm setting the high-speed needle a bit too lean? Something new for me is how the larger engines react once airborne and unloaded; I really notice too rich a HS needle setting as a lack of power, and think perhaps the flameouts tell me she's too lean?

Thanks,
RB8

mike31

My Feedback: (67)

Maybe there is not enough back pressure. Try making one of the exhaust tubes smaller. Drive a wooden dowel in one of the outlet tubes. See how it runs then. If ok you know what is going on. You can always drill a small hole thru the dowel if need be, or just remove it. Tigres like back pessure! I have a 3K and a 2K and use a pitts muffler. No issues with back pressure.

Bax

My Feedback: (11)

Well, with the non-SuperTigre carb, we'd not really be able to comment much, even if it's an O.S. carb. It's just not one that's made for the engine. That aside, if the engine cuts clean, it's just too lean. The engine's not getting fuel. You should check to make sure you have large-size fuel tubing running from the clunk to the carburetor. Many fuel tanks have regular-size tubing inside, and the large glow engines need bigger tubing. Even on a 20-ounce tank, we re-plumb the tank to large brass tubing, larger silicone tubing, and we drill-out the clunk. You also need to make sure your muffler is giving good pressure to the tank. Many after-market mufflers just don't have much pressure to deliver to the tank.

You may also want to increase the idle RPM a bit. A too-low idle RPM will result in the carburetor getting unbalanced regarding the high-speed and low-speed mixtures. A too-low idle will likely mean that the idle mixture's too lean. This will cause fuel flow problems at full throttle.

redball8

My Feedback: (128)

I think you hit the nail on the head, Bax! I had become enamoured with low idle, put an onboard glow unit on the motor and had been running as low as 1400 rpm. There is definitely an interaction. Should I try the idle at say 2000 rpm?

Thanks very much,
RB8

Bax

My Feedback: (11)

2000 RPM is a good number. We consider anything under 2,500 as "good". You may also need to check to be sure the clunk isn't too close to the back of the tank. Under acceleration, the fuel is forced to the back. If the clunk is too close, it actually "sees" higher fuel pressure and can flood-out the engine, but only during the initial acceleration of the takeoff roll.