Frozen float bowl drain screw ?

As I'm cleaning and rebuilding Mikuni 28mm accelerator carbs., my #2 float bowl drain screw won't screw out or loosen ? These are used carbs. I'm rebuilding and the float bowl drain screw slot is a little buggered up but still able to get a large thick blade screwdriver between the screw head slot and hold well.

I've soaked both sides of the screw with Kroil oil for at least a day or so. Even tried running my Heat Gun over the outside of the float bowl body around the screw for a couple of minutes but still not budging ? Tried tapping the top of the drain screw with a hammer, still no luck ?

Any ideas on how to remove it or just leave it alone ?

Anyone, Anyone ???

Please take some pictures to get a better view of your problem

Sorry, I don't have anything to take a picture with. It's just that the big slotted drain screw on the bottom side of the float bowl doesn't loosen ?

If you are referring to the screw shown below be sure to use a screwdriver with a large blade that fits the screw. That should give sufficient bite to loosen it. Ed

Leave it as it is. If you use more force on it you will crack the bowel or snap off the screw head.
Rust or oxidation lock the threat very strong
Try to find a replacement on eBay.

Ed, That is the screw that I'm talking about . And I'm using a Large Blade screwdriver that fits the slot well ? Unfortunately, nothing is working yet and I didn't want to use an impact driver in fear of breaking something. I really wanted to remove them and even replace with new and o-ring. but maybe I should leave well enough alone ? Then it would prevent me from setting the float levels with the clear tube method.

You could try a torch to heat it. Heat the screw, not the float bowl, and get it HOT.

I had a drain screw on a CV34 Keihin recently that wouldn't come out. I wound up buggering up the the head of the screw big time but eventually got it out. Huge pain in the butt. Hope yours isn't as stubborn.

Maybe an idea, try to boil it for an half hour in water with citric acid and try it again

Hi kzdcw,
Been thinking about this. Apply too much torque to a slotted brass screw and half the head might break off at the slot.

If you're willing to sacrifice the screw, try to get a toothed tool to grab the edges of the screw head, something like the curved inner jaws of slip joint pliers. It should only require a few degrees of rotation to turn free. Hopefully a PO didn't apply thread locker for some reason. As previously mentioned, heat gun. And gloves. Good luck.

Good Ridin'
slmjim & Z1BEBE

Like Nessism say's use heat, but when I do it I heat the bowl to expanded it and soften the lacquer on the threads.
hot air or boiling will work, boiling may be better.
patents, it will come loose, use the biggest flat blade screwdriver that fits and clamp it down or hold it in a towel or a heavy leather glove

Do you heat the head of the drain screw or heat the area of the float bowl around it ?