top speed on 244 robin

[mb523]

On the muffler bit... It acts as an expansion chamber to create a back-pressure into the cylinder while the piston is still in the exhaust stroke. During the exhaust stage there is a bit of air/fuel mixture that escapes out the exhaust port since the intake and exhaust stages overlap. The back-pressure forces the unburnt fuel mixture back into the combustion chamber in time for the combustion stroke.

By using any muffler except the stock one you will be releasing unburnt fuel into your muffler and eventually out the tailpipe, posing a fire hazard if the engine happens to backfire. Also, you are losing valuable power because there is a smaller amount of fuel and thus a smaller explosion in the combustion chamber. The expansion chamber essentially acts like a turbo charger, stuffing the combustion chamber with as much combustible mixture as possible before the combustion stroke. I have also heard of overheating the piston and burning/scarring the piston and breaking the rings. You can find some more info and a really cool animation on this phenomenon HERE.

Just a bit of advice here. The smaller diameter outlet pipe on the bottom of my muffler rusted off and left a fairly large hole. When this hole is fitted with a piece of 3/4" black pipe, not only does it run quieter, but it has a bit more power as well. Removing the governor is a good way to increase speed, just make sure to not hold the throttle at WOT for too long as these engines like to rattle themselves apart. I have a makeshift throttle limiter that can be adjusted on my carb butterfly. Acts as a fail-safe if the pedal is floored.

Hope this helped someone, and as always, happy carting!

[madoc1]

523 good info there. did you just weld a length of black plumbing pipe to the original hole? love the quiet idea with no loss in power. also thanks for your old post on the absence of preload on a 2 cycle. jim

[mb523]

Originally Posted by madoc1

523 good info there. did you just weld a length of black plumbing pipe to the original hole? love the quiet idea with no loss in power. also thanks for your old post on the absence of preload on a 2 cycle. jim

Yep, I did just weld the pipe on. One suggestion, clean the muffler sheet metal VERY well and use a good welder, mine ended up falling off after some time. I don't quite follow what you mean by a post on the absence of preload...