I bought a pitts muffler last year for my zdz 80. This thing cut a LOT of power from the engine. Has anyone ever torn one apart to see what is so restrictive ? I'm thinking maybe the two outlet tubes are pushed all the way to the top of the can thus cutting off some flow.
Any ideas?

Probably a lack of volume in the can combined with small outlet tubes. Is it loud? If not, then it is simply corking the engine up to keep it quiet. To be quiet and make power takes significant muffler volume, something that pretty much no Pitts muffler has because of their design and application.

Edit - If you are worried about a fabrication error on the outlets, you can measure that with a probe and tape measure to see if they are cut off correctly or sunk too far into the can. I bet that's not the problem, though.


Mark

You didn't mention the brand but if you have the Bison Pitts style you can remove about 1/2" of the outlet tips to get rid of the swag. I did this on my ZDZ80RV and picked up 200 RPM.

It's a JMB silencer...The outlet tubes are pretty small.

Remove the outlet tubes. Get two 1/2" to 5/8" ID aluminum tubes. Fit them to the muffler. Find a custom welder willing to do the job and get er done.

Good enuff, thanks for the repies........

I just build a canister muffler for a 72cc engine.
I used 2-5/8 id tubes and the engine was choking out.
I installed the third pipe and now it runs pretty good.

2 hole muffler: http://www.rcuvideos.com/item/BMV2KV388GZSF0NZ

3 hole muffler: http://www.rcuvideos.com/item/GYZZ4BDXYD2G4VVP

If you only use 2 exhaust tubes they will have to be bigger than 5/8

Any way that is what I found.

By the way I just finnished a 61cc Echo Twin conversion
It does use 5/8 tubes and it does run good.
http://www.rcuvideos.com/item/8PXSLQ2FFLSVFK62

Look inside the muffler and see if there's an exhaust arrestor or baffle inside. If so you know what to do.