This is the carb I use on the ST .90 conversion. It is a .61 size carb with the thin spray bar. Maybe someone can enlighten me because it may be the stock carb. Thanks, Dave

It likely is the stock carb. It appears your carb is a later model carb as it has the idle needle recessed into the barrel and has a plastic throttle arm. The old ones have the idle needle external to the barrel that you can turn with your fingers or a screwdriver and has a metal throttle arm.

My G51 has the same carb your .90 has except the spraybar was round originally. The choke diameter should be about 8.9mm.

Thanks Q, I have a bunch of ST carbs and lose track of what is what. I was trying to answer a PM but couldn't send a picture so I posted the picture here.

No problem. I'm not particularly fond of the plastic throttle arms myself. Under the right circumstance, it could come off and then you're up s**t creek without a paddle.

If you (or anyone else) ever come up with some ST carbs you don't want or need, let me know. I wish they made one with a .627" neck.

Hi Hobbsy,

Please keep us posted on this one! I just got a Davis head for my S90K, and have to do all the setup work. I have a bunch of G60s, so may have my carb issue handled.

Jeff

So, it turns out that I wound up with 3 carbs when I got my 2 ST S90Ks. Two of them had throats that measured 8.8mm, and 1 measured 7.3mm, though it wouldn't fit the inlet on the engine. But, the throttle drums are all the same diameter, so I made a quick swap, and I should be all good to go now!