[electricpaps]

	Quote: Originally Posted by mfuess
	Thanks Kent. Nothing sounds better than a well tuned engine.

Hi everyone.
I’ve read just about all of this thread and have learned a great deal. Many thanks to all contributors.
I’m a newbie to gassers but have been messing around with model aircraft, on and off, since 5 years old (so that’s almost 50 years). I’ve pretty good knowledge of model diesel and glow engines and for the past couple of years I’ve been building electric powered aircraft.

Then I decided to build a glider tug. A 2.5m wingspan pushed me to purchase my first gas engine. Mark will be hopping mad I’m afraid : I got it from United Hobbies, a FTL 45cc with CDI electronic ignition. Nicely finished engine for only $200.
The apparent weak points are minor, the worst as far as I can see could be the Teflon adapter between the carb and the engine ( may leak a little under small deformations, I don’t know).

I’m getting to the point and my question. In all of the thread here just about everything has come onto the table except the problem I’m experiencing : How do I get a steady idle at around 1500 rpm ?

I can olny get the engine to idle at an acceptably low rpm if I enrich the low end excessively (3 or 4 turns out from closed). Then the engine runs very rich in flight from mid rpm down. When I lean out the low end, rpm increases and then it dies, before rpm drops back down to an acceptable idle.

Here is some basic info about my setup.
- engine mounted inverted
- Carb : walbro WT 717
- carb sticking out of cowl with static pressure vent forwards in airflow from prop.
- Bottom half of cowl cut away (excellent airflow around cylinder head
- timing advance (measured using a graduated disc and plug removed) exactly 30°
- runs fine at top end, 6400rpm with wooden 22 x 10” prop. I haven’t tuned it to MAX rpm yet with rev counter due to “pressure” from guys at the field. From what Mark says, I should.
- I plan to solder a brass tube to the static vent and lead back to the fuselage, maybe this will help.
- I lifted the metering lever about 1mm in an attempt to help, but it just made the engine flood during starting, so I’ll bend it back to the original position (which I carefully noted beforehand).
- Fuel : run in on about 5 litres of mineral oil at 3% with 20x10” wood prop. Now using 3% synthetic. Sure is sticky stuff this synthetic oil!
- Once the tug has flown, the idle is sometimes faster. Even with the butterfly valve completely closed the engine sometimes idles (fast). Imagine the landings with a friend running behind to catch it by the tail!!

So I still have the following things to try:

- Solder brass tube to static vent
- Tune rigorously according to Mark’s method, but normally the high end needle doesn’t affect idle does it?
- Bend metering lever back down.

I like these gassers, they smell good and sound good. I’m pretty impatient to get my FTL 45 tuned properly.
Well that’s it for now, any suggestions or comments will be greatly appreciated.

Happy flying,
Paul