Well guys I took the easy way out.
I added a 3rd exhaust pipe and it made the difference.

The 1st 2 pipes went about 3/4 the length of the muffler and were 45ed and faced the back wall.
The new pipe is as flush to the bottom of the muffler as I could get it.

It may not be developing top power but watch me rock back when I rev it up.
The thing falling off the other side of the fence is a metal sign.
It was blown off a large head screw that barely fit through the hole.
This should make a 15 pound plane jump into the air.
My biggest concern now is ground clearance for the prop.
It is easily turning a 22x10w prop, probally a 24x10w would drop the rpm a little.
But I'm going to need a 3-blade prop for ground clearance.
Anyone have experence with a 70 something cc engine and a multi blade prop?

Compair this video to the 1st one.
2nd Video: http://rcuvideos.com/item/GYZZ4BDXYD2G4VVP

1st Video: http://www.rcuvideos.com/item/BMV2KV388GZSF0NZ

I think you should try the motor in the goped in the background!

Rich

If you want to slow it down with out going to a 24" prop, change to a Zoar 22x10. TheZoar has a much higher load factor than an APC

I need a 3 blade for the ground clearance.

3 bladed big props are big $$$$, care for bigger wheels???

Ralph that thing screams. Makes me happy to know the concrete saws do work and work well. What does it weigh as is? One of these days I will finish my DVIII I am building and then finish the 70cc Husqvarna I started and then get on the two saws I have left.

It weighs in at 4lbs, 4oz.

Your probally right about the bigger wheels.

I could always hand lanch it and land dead stick :-)