It's pretty obvious that there are two problems:

1. The ST line of engines is *very* sensitive to changes in fuel mixture. I've seen this on just about every "overbored" engine I've ever used. When the transfer ports become too shallow (large bore in a small casting) then quite a bit of choking can occur and there may also be some aggregation of the fuel droplets into larger ones due to the fact they're forced so close together as they pass through the transfer ports without the aid of combustion chamber heat (but that bit's speculation on my part.)

2. The ST carbs are not very good at fuel regulation at different throttle settings or with different airflows at a fixed setting.

Either of these problems on their own isn't too bad.

I've seen bad carbs on good engines and they still perform adequately (some folks find that the ST carbs work just fine on their OS engines for example)

I've also seen good carbs fix many of the woes that occur on a stock ST engine. This can also be verified by fitting an OS, Magnum or other "good" carby to an ST. This often produces a far more reliable engine with vastly improved throttling.

But, put the less than optimum ST carb on the hyper-sensitive ST engine and you have a recipe for disaster.

Careful tuning, painstaking selection of glowplug, meticulous testing of various props and tuning the formula for the fuel being used can all help mitigate some of the symptoms of this situation, but the root cause remains.

The fact that the engine will run so much better with permanent plug heat shows not that the head design is wrong but that the carb can't meter fuel well enough for the transfer port design of the ST engines.

ST either has to change their porting or use a better carb.

In the meantime, a *small* percentage of ST users will luck out and get a combination of prop, plug, fuel, tuning that provides reliability and throttling that meets their needs -- but a whole lot more folks will have to cope with deadsticks, lousy mid-range and other woes that OS, Thunder Tiger, Magnum, and a raft of other engine manufacturers seem able to avoid with ease.

However, so long as they're the cheapest option on the block they'll continue to sell.

And, so long as there are people (like myself) who are prepared to "fix" them so that they run properly, and people who buy because they have a religous brand-dedication, some people will find them okay.

I bet there are a lot of broken models as a result of ST's poor matching of carb to engine and I bet there are also a lot of STs that sit in boxes under modellers benches after their owners give up on them.

And, as I've said before, I just can't understand why ST doesn't bite the bullet and switch to a more conventional twi-needle carb such as those used by OS, Magnum, GMS, Thunder Tiger etc. For the sake of a few bucks in re-engineering they'd have a whole new (far better) engine and the vast majority of those threads that ***** about STs would disappear overnight.

As a consumer, I get annoyed when a manufacturer blames *me* for a design deficiency in their product rather than simply going out and fixing the problem they've clearly got.