TT 4 stroke inverted won't idle

[expo]

Hello,

I have 2 Saito 100 4 strokes that run beautiful inverted but my Thunder Tiger .91 turns fussy when inverted. No matter where my low speed is set, it's either too lean and stalls when I accelerate or too rich and flames out when idled down. I use an F plug in all my 4 strokes.

I've tried an on board glow starter on the TT and kept it on for the entire flight and it runs strong and idles well.

What could be wrong that makes it so sensitive to low speed needle settings?

[expo]

Hellooooooooo?

[tandemairbike]

Clarence has alot on his plate and it keeps him very busy.

While I don't even dream of having a fraction of his knowledge,
I will try to help you with your problem.

Assuming you are using fresh fuel, have you tried another plug?

The plug you are using may be a new F plug but it could be faulty even though new.

You might try a "Fireball" brand long hot plug. A hotter plug might be needed to burn off the higher oil content in some 4 stroke fuels.

Also make sure that all the nuts and screws on the carburetor are tight, lock nuts on spraybar, fuel nipple etc.

You did not mention if you ran your other 4 strokes in the same airplane as the TT .91. It might be a fuel tank issue that is peculiar to the installation.
Check your tank level. The centerline of the tank should be about level with the spraybar on the engine with the clunk about 1/2 to 3/4 inch below. If you are running muffler pressure this is in the ballpark and a good starting place.

Try these and let us know how you make out.

Tandy

[adamjedgar]

Hi, i have had a similar problem with my OS 52 four stroke engines. I have an engine that is mounted almost sideways (slightly inverted in a giles 202) and it starts easily and runs perfectly. I then used 4 more of the exact same engine inverted in an ASM C130 Hercules and to be honest they are hard to start and run like s#%t!!! I can only remember an ASP 61 two stroke i had 10 years ago in a piper cub, and it was such an ass of a thing to get going i used to turn the cub on its back to start the bloody thing.

I have a couple of solutions to your problem that were recommended to me by some senior club members where i fly.

1. Don't run any exhaust pressure into your fuel tank when engines are mounted inverted. A lot say you shouldn't bother using pressure in tank at all in four strokes as this type of engine configuration tends to develop better suction than a 2 stroke engine anyway.

2. Use an onboard glow system that is set to come on at low rpm. I think you will find this solves most of your problems provided you have tank level set correctly and no air leaks in your fuel lines etc.

Im no expert in these things but i hope that perhaps my comments help.

Oh by the way, you may actually have a problem with the engine itself. does it run ok when mounted upright??? I had to replace the first asp engine i had shortly after purchase as a front seal started leaking. Cheaper engines obviously are not as good in these circumstances, hence your 2 saito's are performing flawlessly... thats to be expected (although i personally prefer OS engines myself)

Cheers
Adam

[expo]

Yes that TT 4 stroke runs like a bear upright; sometimes I think it's stronger than the Saito 100. a 15-4 prop goes supersonic. I've got the Saito mounted inverted in my UCANDO and that plane has the bad reputation of being high tanked--where the tank is mounted about 1 1/2 inches higher than it should be and it would be a bear to move. The Saito just loves it no matter what the hs needle setting is. I've tried many different plugs in the TT without any different results. I've checked the obvious air/fuel leak points in the lines, tanks and carb and they are all good.

I haven't tried running the TT on it's side yet. That's next in my Edge.

[tandemairbike]

For what it's worth, although it sounds like tank position is your culprit, I would try one of the Saitos in the U Can DO and see if it acts similar to the TT. That way you have pinpointed the problem. If the Saito runs OK at all throttle settings then it's not the fault of the tank position but a problem with the engine. It's a god idea to try this before altering your tank position.

Tandy