I have a ST 3250 and a Bison pitts muffler and would like to know if I will have to plug one of the stacks for proper pressure ?

Don't change the muffler, it's fine as is. Plugging off the muffler and using pumps are a less than ideal way to address the real issue, which is an easy fix anyway. If you look carefully at the fuel nipple on super tigre's carbs, it's VERY tiny. Measure it with drill bits and you'll find the fuel inlet area is less than half that on any other engine brand out there, even 40 in sized engines. Compare it to the volume in the needle valve assembly. It's simply too small to consistently supply the engine as the throttle setting changes without unnecessarily high pressures and too much back pressure can cause overheating. The needle should control the mixture, not the fuel nipple. Either drill the stock fuel nipple out to 1/16" or better yet, I just replace them with pressure nipples of large ID off ill fated mufflers. You should be using large fuel tubing to ease the fuel draw, especially if the tank is large and has 12+ inches from carb to clunk. Be sure to use a large ID clunk and brass tubing as well. Sullivan's "HD Klunk" works great. Do remember, if this is your first big tigre, don't expect it to be broken in until you have nearly 2 gallons or more through it. Bench run it and get it broken in and set and youll be very happy with the engine. Gobs of thrust and great throttle response. BTW, I have 5 big tigres and 4 ST90's. I find the 90's are also much easier to adjust, have excellent midrange now, and make more power by simply drilling the fuel nipple out to 1/16" and removing the muffler baffle. Best wishes.

Thank you very much for the info never thought about the nippel .

There are many factors involved when using different brands of mufflers, other than the stock muffler. Many mufflers just do not provide enough pressure to the fuel tank to give adequate fuel flow. Many fuel tanks have inadequately-sized fuel line plumbing to allow for good fuel flow. Many people believe that the fuel inlet nipple on an engine is a problem.

Usually, we've not found problems with the large SuperTigre engines once you've gotten fuel to them. The inlet nipple is large enough for the carburetor's needs. The orfice at the needle valve will actually be smaller than that when the engine's properly-tuned.

If your engine's not getting good fuel draw, then you'll have to see what the difficulty may be. Many times, it's inadequate pressure to the tank. If that's the case, you'll need to find a way to increase pressure. Reducing the area of the exhaust outlet of the muffler is one possible solution.