Carburetion

[David Jackson]

Like a great number of Harley riders I find the carb sticks out where I want my right knee to be! I have a TSport with mid controls.

There is an outfit in Rhode Island which tells me they can make a forward mounting manifold set up for my bike.

I have been told that HD carbs are too close to the intake valve for the ideal. I don't really know what the relationship between intake tract length and power or torque is; someone told me that Jerry Branch had established that the ideal for HD is about 14" from venturi to intake valve. I have no idea if 1) Jerry Branch actually ever said such a thing or 2) if there is any validity to that idea regardless of who said it.

If there is some validity it might pay to have the carb moved out of the way.

Your thoughts Mike?

Thanks in advance.

David Jackson

[Mike]

Jerry is right in that the ideal intake track length, mathmatically, would be 14-16 inches. There are formulas to calculate this and vary depending on RPM, cam timing, harmonics (wave pulse) and exhaust. Typically, the higher the tuned operating RPM, the shorter the intack track. Another more common reason to change intack track length is to move the carb's emulsion tube out of sync with reversion waves to minimize signal problems. Spacers are placed between the manifold and carb as opposed to installing longer velocity stacks. In reality, it comes down to practicality (usually leg room).
The forward manifolds do seem to work OK but have an inherent flaw in that the length is unequal between the front and rear ports. This is less of a problem with those that have common runners or a plenum. Also the air has to make a tighter bend into the front port as opposed to the rear and this can make for some tuning issues and hp loss.
Regards, Mike

[David Jackson]

Hi Mike;

I understand that some sort of a plenum would be superior to two unequal length runners. I also understand that the sharp bend for air is not the most desireable situation there is.

What recommendations do you have for those who want to put their knee where the carb is?

Would a straight velocity stack be a good way to go with a CV carb?

Regards;

David Jackson

[Mike]

As far as I know no one has a good solution to your problem. It's just a realistate problem. Bikes with mid or rearset controls are not as much of problem. The velocity stack will work but does not offer protection for the motor (the small screens many use are ineffective).
Regards, Mike

[David Jackson]

Back in the old days I ran a velocity stack on my Tillitson on my CH and never had a problem that I know of ... but that was then. Actually I have not found anyone who even makes a stack for a 51mm CV so I guess I had better look to some sort of different seating arrangement!

Thanks Mike.

David Jackson