I have been flying glow models for about 40 yrs. Gas for about 20 with just a smidge of diesel time thrown in for good measure. Tuning my 51's glow carb on gas is not hard but I can't say for sure that it would be OK for everyone. Once I got the low end set I haven't moved it. The high end is sensitive but I can live with it. Since the carb on the 90 has the same thread pitch as the little motors I can't see why it would be any worse. I know that CH and others sell the adapter to put a walbro on your engine and they're not that expensive. If you already have the walbro maybe that would be the way to go although I would try the glow carb first and see how it works out for you. Some say the ST carbs are hard to adjust even on glow and I have never found that to be the case so that is why I hesitate to say it work well for you on gas. I have shown some of the people at our field my tricks on adjusting the mag carb (ST) and now they adjust them with no problems. Seems most people don't know about the ability to turn the spray bar to help the mid-range. I run my low end quite lean on gas in order to keep the mid-range in check but the only problem is it's a little cold natured that way. Once warmed up it runs very well. Most who see it run are quite fascinated that it runs that good on gasoline. Let us know if you decide to convert yours and how it turns out.