add a modest intake extension between carb and head. Longer runners improve low speed torque and our machines engine fits the bill. These are available from at least one supplier of flatsides whose name escapes me right now.
About how long would you suggest? I am going to put a 32mm flatside carb on and all I can find so far is a short rubber mikuni manifold. Everything I find seems to be 2" center-to-center and the bullet seems to be 60mm center-to-center.
For me, I have decided not to port it or do the valve job yet, I want a reason to take the head off. Like maybe to celebrate 3,000 miles.
Thanks,
-Rick
Rick,
There's very little room to extend the intake manifold length, before you can't fit the carburetor under the tank anymore. Very little room to extend.
I tried it with a longer rubber hose, and I forget the exact amount, but I think it could only get about 3/8" to 1/2" longer, before the throttle cable adjuster was hitting the tank. Unfortunately, that small of a change isn't going to do anything noticeable.
If you try to extend it way out past the end of the tank, and use a long cable, such as 72westie's race bike has, then the carb is hanging out where your knee normally is, and you have to sit back further and use rear-sets, because the carb is in your way.
The next best option is to do the stack.
The max stack length that can easily fit where the airbox was, is about 6" long. And that's an unusually long-looking stack from an appearance viewpoint, but it is still visually acceptable. Anything longer than that starts to look pretty odd.
Chumma7 is getting very good results from his 6" stack on his Amal 32mm. In fact, he had a similar issue with it getting lean and "hitting a wall" in revs, and is having to go alot richer.
I pulled my plug after running that really long extension, and it looked quite lean.
You will have to keep an eye on your plug when you do this stuff, to make sure you aren't leaning out from the mods. Re-jet as needed.
It will get more air in, and if it's working as intended, it will need more fuel.
I've already got to the point where my clutch is slipping from the additional torque in the midrange, and I need to do something to beef up my clutch. If I give it a twist at 3500 rpms, the clutch starts to slip.
Regarding manifolds, you can go to the Sudco website and look over their selection of Mikuni manifolds. They should have something there.
I just bored my stock manifold out to 32mm. This leaves a very thin manifold wall left for supporting the rubber hose and carb. So, I epoxied a metal sleeve over it, using hi-temp epoxy, so it would strengthen it back up. Then your rubber hose will have less difference to account for on each end, because your 32mm Mikuni has a 40mm connection stub leading to the manifold, and your stock manifold is smaller. Enlarging the outer diameter of the manifold stub helps when using a straight hose. I tried to find a sleeve diameter which had a close sleeve-fit onto the manifold stub, so that I didn't rely totally on the epoxy for strength and integrity. It's just a bonding agent if you get the right size sleeve fit.