Hi,
My TT .15 has 4 "needles". Needle valve, screw holding throttle arm on, vertical screw that seems to set low idle throttle barrel end stop (?) and a vertical "needle" screw that ??????????

Can someone explain these two "needles" or screws?

Engine is fairly new. Runs OK but won't idle down for landing. Full off throttle still pulls A/C along at landing speeds. Right after landing the engine quits. I'm afraid to idle it down anymore. Afraid it will quit in the air and land short. Just seems like low idle throttle setting needs fuel/air adjustment. But how?

Bill

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Let me ask a stupid question - do you have the instructions? The reason I ask is that I just bought two new TT .15's and I have the instructions for them. I haven't looked at it yet, but if you need a copy, we can work something out - like I'll send you a copy via email or whatever. How's that?

This engine has a high speed needle and an airbleed screw. The first needle you should set is the high speed needle. Once you get this set so the engine is on the rich side of peak, you can begin adjusting the low speed airbleed screw. To confirm the high speed needle is correct, I always run my engine up to full throttle and then point the nose up in the air for about 10 seconds. If the engine slows, it's too lean. If it stays about the same, it's still too lean. If it picks up a little speed and holds it, the needle is just about right. If it speeds up considerably, it may be too rich.

Once the high speed needle is set right, it's time to adjust the airbleed screw. The key thing to remember is this screw is basically just opening and closing the little air hole that's on the front of the carb. When you screw it in, you are closing the hole, which richens the idle. When you unscrew it, you are opening the hole, and leaning the idle. A good starting point is to look at the hole and have the end of the screw covering about half of it. Then adjust as necessary. Something that's always worked well for me is to start the engine and leave the glow ignitor attached. Run it up to clear out the carb and then bring it back to idle. Let it idle for a few seconds and see what happens. If it gradually slows down, but doesn't seem to get hot, it's probably a bit rich. At this point also see how it transitions from idle to full. If it stumbles and sputters, it's rich. Turn the engine off (you DON'T want to adjust the screw while it's running) and open the screw a little and then test again. When you think it's fairly close, see what happens when you remove the glow ignitor while it's idling. If it slows considerably, it's too rich. If it slows a very small amount and then holds this speed, it's pretty close to right.

Hope this helps, my GP-15 runs very well. It's yet to stall while idling, and shuts off when I want it to.

Thanks Chuck,

Only question, which is the low speed needle? Is it the vertical one at the rear of the carb or the horizontal one by the throttle arm? I know which is the high speed needle.

Bill

The vertical one should be the idle stop screw. Airbleed screws are almost always horizontal and they'll be near the front of the carb, in line with the air hole that you should be able to see in the middle of the front face of the carb. And yes, it will probably be on the same side as the carb arm. I'd have to go out to the garage (shop) to be 100% certain, but since it's New Years eve, I'm not risking the wrath of my wife by going to the shop tonight.

Thanks again Chuck. You are correct. I just didn't think a carb that small would have a low idle adjustment.

Your decision not to look puts you far ahead of most of us! I'm not that smart.

Bill