Hi,
I have a older ST S-29 that I'm having a few problems with, first off I've followed all the recomended spray bar/ high/low needle settings, tank/fuel lines are good,compression good etc. The eng. starts fine idles good, transition is fare, midrange is good, high end! here's where the problem occurs. At full throttle the eng. surges like it's not lean enough, 1 to 2 clicks to the lean side is to much, 1to 2 clicks to the rich side is to rich. Also upon a quick chop to idle the eng. will die, this happens at any throttle setting . Should I start looking for possible air leaks around o-rings and gaskets? It's driving me nuts!
Thanks in advance,
Robert

First thing to check is the carburetor. Is it the right one? A carb with a too-large opening will have fuel draw problems that will cause the engine to go too lean very easily. Adding more fuel pressure may help.

Another problem could be the fact that the engine's a bit worn. If the piston/liner fit is a bit loose, the engine will not have a good compression seal when it's at full throttle and fully warmed-up. This can lead to erratic running. When it cools down, the parts start to fit better again.

One other thing that could be a difficulty. Please check to see that the idle needle's not too lean. If it's too lean, it can interfere with high-speed fuel flow. Open the idle needle a LOT, start the engine at part throttle and see if you can then get the full-throttle mixture set. If it still misbehaves, then we'd strongly suspect the piston/cylinder fit.

Bax,
Thanks for the info, the carb is the one that came with the eng. when I bought it new in the early 90's, there's not any slop in the liner & piston,( maybe 1/2 of gal. of fuel ran through it) now that I remember I had similar problem's back then even sent it in thinking there was something wrong only to have it returned with them saying it was fine. The more I ran it the better it got with alot of tweaking. I'll keep at, just recently got back into the hobby, glad I didn't sell off the stuff. Are parts still available for this eng.? Also how does the new G34 stack up? If it screams anything like the S29 does when it's running properly, might be a good upgrade.
Thanks again,
Robert

The SuperTigre S-29 engine has been discontinued for quite a long time, and parts for it are no longer available. The G-34 is not a "replacement" for it, but was produced concurrently for a number of years.

Specs for the G-34 can be found at:

http://www.supertigre.com/engines/supg0105.html

Skyburner checkout my post at Super Tigre S29 -Sqilkey has given me some great tips for this engine--Wulf

Hi SkyBurner.

May be you not only burn sky - but maybe also engines ??

As a vital point i should mention your fuel for this ST - 29.

In those days ST liked a fairly " fat " fuel - i could recommend : 5 % ricinus oil + 15 % ML 70 oil + 80 % methanol.
You might try : 5 % ricinus + 15 % ML 70 + 70 % methanol + 10 % notromethane.

But the first mix should run !

Also ST - engines liked a hot plug.

Kind regards,

hld - OY-9901.

Robert, check if your fuel it´s no foaming due prop vibration, because this can cause this problem. Check the balance of your prop and the rigidity from the mount of your engine.
good luck