hillclimber

Member
Aug 16, 2001
46
0
I have two CR500's that have been ported each time I had to go smaller on the main jet. Is this because of an increase in flow creating more vacume on the main jet?
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,838
16,902
Chicago
It's probably a result of improved exhaust scavenging due to changes in the transfer ports. Generally when the scavenging is poor the percentage of residual (burned) exhaust is high in the combustion chamber so additional fuel is needed to get a mixture that will consistently burn. Improving the scavenging makes it easier for the oxygen molecules to find a fuel partner so less fuel is needed.
 

hillclimber

Member
Aug 16, 2001
46
0
So would that mean that on top end the cylinder scavaging is improved and making more power?
If so why does everyone claim that a rad valve is'nt any good for top end becuase when you install one you also have to go leaner on the main.
The reason for my curiosity is that on my 86 CR500 I had Erric Gore port work and a rad valve, bored carb, K&N air filter and PC pipe and I went from a 172 main to a 162 and probably could get by with a 160 main.

Thanks for any more info.




:) :) :)
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,838
16,902
Chicago
Originally posted by hillclimber
So would that mean that on top end the cylinder scavaging is improved and making more power?

Old exhaust products just cool the combustion chamber and take up space, so the lower the perscentage that get left behind the greater the potential power. A reed valve's effect on jetting is caused by a different set of conditions within the engine.
 
Top Bottom