Quote:
Originally Posted by BadMouth
I haven't determined anything yet. I was just asking if anyone else had needed to make that type of modification. If the general consensus was that it has been an issue on other bikes with similar mods, I'd like to address it now, before I start the rejet shuffle.
|
Gotcha...
I checked the fuel flow one time and if I remember correctly it looked like about 1/4 gallon per minute -- way over what you'd need for sustained high-rpm operation.
I've run up to 150 main jets with no fuel starvation problems on the CVK's and the only thing that
looks like an insufficient fuel supply is related to the carburetor airflow velocity, not the real fuel supply capacity of the system.
What can happen to drive the top end lean is insufficient
air flow. With the stock exhaust system he instantaneous velocity with respect to rpm through the carb venturi actually decreases as rpm increases. That reduces the fuel 'draw' through the main jet and causes leaning.
The condition is due to a combination of back pressure (muffler, pipes, valves, cams, porting) and that the stock downpipes are not designed for efficient scavenging.
The stock 'green' cams are a low-overlap design and can't produce much scavenging effect so Triumph didn't need to put higher-perfomance pipes on the Clasics. If you look at dyno runs for these bikes you'll see that they have an air:fuel mixture transition at about 6000 - 6500 rpm where the restrictions of the exhaust system start to drive the mixture lean.
With the 'blue' cams installed you'll see the same effect with stock pipes -- a 'leaning' of the mixture at around 6000 - 6500 rpm but of a higher magnitude than with the 'green' cams. In this case the 'blue' cams have a good overlap but can't make use of it due to the restrictive exhaust system.
Make sense?
Jim