Will the performance be affected by removing the muffler on my 4 stroke Saito 82 and replacing it with a long straight pipe?

If your straight pipe is not too long (say 4-6") and is nicely shaped internally, especially near the flange/exhaust port, it may even improve performance over the stock muffler.

I have an OS .91 Surpass that picked up 200 - 250 rpm with a 4.5" straight pipe over the stock setup.

You will love the sound too!

Thank you Harry

What do you mean by shaping the pipe internaly near the exhaust port? Please elaborate.

Thank you

It's not super-critical but make sure as much as is practicable that it's a smooth flow out of the exhaust port into the pipe, without any nasty kinks, sharp corners or sudden reductions in diameter

what about the pressure niple? you dodnt need the tank pressure?
achilles

I run my Saito 91 on homemade straight pipe about 5" long with one 90 degree bend about 1-1/2" from engine exhaust port, no muffler pressure, runs great and sounds good, but its not any louder than stock muffler. Just use the fitting that comes with engine for muffler and braze on a short piece of copper tubing (K & S brass tubing will crack under vibration). Try it, you will like the sound and how the engine runs.