I've got several G90s and love them, but the mid-range on all of them is still a bit rich. When tuned for a nice reliable idle and a few hundred RPMs short of peak at full-throttle, they still 4-stroke from about 1/3 to 2/3 throttle.

After reading the FAQ about tuning ST engines I tried rotating the spraybar assembly as per the instructions but this has had absolutely *no* effect -- even after methodically moving it in about 2 degree increments through a total arc of about 40 degrees and re-tuning the idle/top-end needles each time.

Is rotating the spraybar supposed to richen or lean out the mid-range? The FAQ doesn't state this and the effects (at least on my 3 engines which vary from 1 hour to 30 hours running time) are not obvious at all.

Lots of people seem to complain about a fat mid-range with their STs and I notice it's quite hard to make precision throttle adjustments in that 1/3-2/3 throttle range when landing a fairly heavily loaded plane with a G90 up-front. The fat mid-range means that changes in throttle position (even quite large ones) involve significant lag -- producing a lot of smoke and burbling before any change in RPMs.

If the midrange is much too rich, then it's likely the idle's much too rich. Too many times, a very low idle is achieved, but the midrange is not right. You may have to give up some idle RPM to get a good midrange setting. Any idle below 2,500 RPM is considered good.

Rotating the spraybar actually tends to richen the midrange, but you then have to reset both the high-speed and idle needles. You want the idle needle as lean as possible, yet still giving you a good midrange. The mid will still be slightly rich, but that's OK, you won't have the severe hesitation.

The engine will take a set more easily once it's had 2+ gallons' worth of fuel run through it.

Even with the idle as lean as it can go without cutting when the throttle is advanced, the midrange remains fat (I'm talking about an idle speed of 2500 RPMs or so).

I've retuned the needles after rotating the spraybar each time but still notice no change in the mid-range mixture. At all rotational settings (with the idle and main needle tuned correctly) the engines 4-stroke and blow lots of smoke with very delayed response between 1/3 and 2/3 throttle.

In all other respects these engines are *perfect* and I'm about to buy another (call me a satisfied customer) -- but I sure couldn't use them for 3D stuff where that 1/3-2/3 throttle response has to be crisp and reliable -- which is a shame because I love flying my 3D ships even more than my warbirds.

If this fat mid-range is just a characteristic of the ST engines then I can live with that but I had hoped that following the FAQ instructions would eliminate the problem. Maybe it's just that we 3D fliers are used to using engines with a "perfect" transition and are too picky?

The main concern with the design of SuperTigre engines was good top-end, good idle, and a transition and midrange that works. It is very, very difficult to make a model carburetor act in a linear manner. To do so, usually costs more money. Also, it may help to get better fuel pressure. Higher pressure means you can lean the low-end needle more, and this helps. The 'Tigre engines really weren't designed with 3-D needs in mind.

Also, please be aware that your engine's performance will only improve as it's run. It usually takes 2-3 gallons' worth of running to get them to really come in.

That's fine -- I was wondering if I was doing something wrong because I couldn't get the kind of transition and mid-range performance I get from some of my other engines -- but then again, most of them cost at least twice the price of the SuperTigres!

In terms of value-for-money, the SuperTigres can't be beat and, as I've discovered recently, the after-sales service and warranty support you offer is second to none -- so I'll keep on buying STs for my sport planes and warbirds, while sticking to 4-strokes and far more expensive brands for my 3D ships.

Yes, I'm a satisfied customer :-)