I agree with Volfy, - can't be too expensive that way.

Car pumps ( too large for your purpose ) will have a relief valve built into them so that when the needle closes, the relief valve will open, the mechanical ones run constantly.
Tank in the centre section of the wing as in full size high wing types could be an answer.

Best solution? listen to Volfy! buy one from Ebay, maybe buy a kit for it too. but don't forget it won't just fit straight on as I said somewhere before.
Need to check your inlet tract size too!

Carb on the Stihl will be a Walbro, Tillotsen, Zama etc. the engine makers don't usually make their own carbs.