BuddChiari

Does anybody know a good starting point for the TT .91FS idle mixture screw?
The manual makes no mention of that adjustment and mine is out of whack (I moved it thinking it was the speed screw--DOH!!!)
Help appreciated

w8ye

My Feedback: (16)

Set and maintain the throttle position at what would be the normal idle position. (Barely open).

Connect a piece of fuel line to the fuel inlet. Adjust the idle mixture needle to where you can determine there is a small amount of airflow while blowing into the tube. This will be your initial setting.

Sport_Pilot

How could you mistake the mixture for the idle speed screw? The idle mixture is in the center of the barrel in a sunken hole in the middle of the throttle arm.

BuddChiari

I mistook it because this is my first four-stroke engine and I just assumed that the screw with the spring on it was the idle mixture, since that's how they look on my 2-stroke engines.



Thanks for the advice w8ye. Do you have a rough idea of how many turns out that would be? Like, should the screw be about flush with the carb side, a little sunken, or a lot sunken?

Anyone?

Sport_Pilot

Just wanted to be sure you had the correct screw. The manual has a few holes in its description.

joesabido

BuddChiari:

Just screw it in untill it gets hard to turn (but don't get it tight!!) and unscrew it 4 full turns.

Now the idle mixture will be very rich, but here's what I did (i have a TT91 FS too, 1st 4 stroke too )

1.- Screw it in all the way
2.- Unscrew 4 full turns
3.- Screw the high speed needle all the way in (don't get it tight or you'll ruin the needle, don't ask how I know )
4.- Unscrew high speed needle 5 full turns
5.- Place the throttle around 50%
6.- Have someone hold the plane and start the engine, leave the glow driver attached
7.- Lean the HSN (high speed needle) untill it's about to peak, remove glow driver, peak it then go back 800RPMs

Now to tune the LSN (low speed needle)

8.- Pull back the throttle slowly and see where it starts to cough (maybe it will halt), probably around 30% throttle because LSN too rich
9.- Lean (screw in) the LSN half turn
10.- Start the engine, go full throttle and pull back slowly untill it iddle reliably

11.- Is it sputtering and throwing a lot of smoke on iddle? YES:Go to step 9 / NO:Continue to 12

12.- Is the iddle smoth and around 2500RPMs? YES:Continue / NO: Go to 11

13.- Wait 10 seconds on idle and punch the throttle, does it speed up right away, hesitates and dies, hesitates and speeds up or dies right away?
a) Speeds up right away: You're done
b) Hesitates and dies: Still too rich, close LSN 1/4 of turn
c) Hesitates and speeds up: Slightly rich, close LSN 1/8
d) Dies right away: Too lean, unscrew LSN 1/4 and go to Step 12

When you are done:

1.- Start your engine
2.- Throttle 100% for 10 seconds
3.- Back to iddle, wait 5 seconds
4.- Point nose 60ΒΊ up, if it stops it's too lean, open LSN 1/8 of turn.
5.- Point nose down 45ΒΊ, if it stops it's too rich, close LSN 1/8 of turn.

Hope this helps