Coffman Sizzler setup and tuning

[Req]

Im sure that it will rev higher with a taller port and/or shorter tuned length, my porting was 120/182. Once you get the pump load light enough for good response the pipe will go rich and wont rev much more. Small CC engines struggle getting on the pipe with much more than a 9-15. A programmable ignition and high compression will help a lot with that issue allowing a little steeper prop.

I will also be at 83mm bore, it will help a little but its still only a 736 ported and matched, epoxied cases and fingers with heavy porting.

Regarding the pipe going rich, I have never heard that term before.

 

[kevbo]

The mixture requirement is much richer whenever the pipe is working. Power falls off very rapidly when the RPM exceeds the pipes resonance mostly because of the air/fuel mixture becoming overly rich for the conditions. The slightest reduction in torque is where the RPM will stall since the pump load is highest at that point. You cant just flatten out the prop and get an extra 1000 rpm like you can an open exhaust outboard.

 

[Req]

The mixture requirement is much richer whenever the pipe is working. Power falls off very rapidly when the RPM exceeds the pipes resonance mostly because of the air/fuel mixture becoming overly rich for the conditions. The slightest reduction in torque is where the RPM will stall since the pump load is highest at that point. You cant just flatten out the prop and get an extra 1000 rpm like you can an open exhaust outboard.

If I am not mistaken you can get some more rpm by adding back a bit of timing at high rpm to push past the hump and light the rich mixture. I imagine its pretty dangerous and could turn into destructive testing if you were not careful.

 

[kawa js550]

What would you guys recommend for a starting point for my ski.

61x/61x 701
170psi ada head
Carbon tech reeds
Coffman sizzler
Atermarket f/a

Right now here are my specs:

145 main
120 pilot
2.0 n/s
28 psi pop off

 

[jpersons44]

Hey guys, been looking for a pipe for my 650 superjet and stumbled on this, guy says its for a kawi, but I've read a few things about people running kawi pipes or something on the superjet. Can anyone identify this? will it work or not?
Thanks!!

 

[blasterdude]

View attachment 393399

Hey guys, been looking for a pipe for my 650 superjet and stumbled on this, guy says its for a kawi, but I've read a few things about people running kawi pipes or something on the superjet. Can anyone identify this? will it work or not?
Thanks!!

That is for a Kawasaki 440/550 and will not work. You need a Kawasaki 650 pipe setup to run on your Yamaha 650 and still need the Coffman's or Factory pipe exhaust manifold to run it.

 

[jpersons44]

That’s what I thought. Thanks man.

 

[jpersons44]

Found this one from a 650sx. Guy wants 225. Paired with a superjet manifold it will work correct?

 

[kevbo]

The Kawasaki pipe mounts farther away from the engine than the Yamaha version.

 

[Dom650]

I made some diagrams showing some viable cooling setups for sizzler pipes.

View attachment 311047 View attachment 311048 View attachment 311049 View attachment 311050 View attachment 311051 View attachment 311052 View attachment 311053 View attachment 311054

Here is a link to a pdf with them all included.

Is the red a flow control valve ?

 

[King Kang]

Is the red a flow control valve ?

Yep!