Bonneville America Forums Forums Technical Forums Performance Mods Dremel the carb manifolds?

When I took the carbs off initially to change the jets, I noticed the intake manifolds had casting marks on the inside. Also they are a little smaller diameter than the head ports.

Has anyone used their dremel or filed the manifolds to make smooth and match the ports? (remove from the head first of course) and will this help increase power or have a negative effect?

Just sounds like a cheap mod that most riders could do (the cost of gaskets only) easily....

Cheers,

Having the manifold slightly smaller than the port is not a problem. The ridge that's formed helps cut reversion into the carb (carbie?).

Ok then, so I guess it is no real benefit to open the manifold up any bigger.......thanks for clearing it up for me, I didn't want to try it before asking someone!

I asked about this same thing right after I rejetted my bike. My goal wasn't to enlarge the intakes but rather just smooth out the castings. The responses weren't too positive, IIRC, so I just left well enought alone- but I'm still thinking about it.

You can get the intake TOO smooth - you need a little turbulence to properly mix the fuel and air. As for opening up the manifolds unless they're throttling the engine you're better off working on the ports first. Might be of use with a big bore, but with the standard displacement it's probably not an issue.

Matt

I understand that- turbulance and velocity. My idea was just to remove the casting flash.

The surface of the metal shouldn't really create turbulance, just drag. The sharp edge coming in would creat the actual mixing turbulance I would think. Smoothing the surface would just make it flow faster.

Removing the casting flash and aligning the manifold ports with the head ports and carb outlets could give you a bit of a power increase. It's not likely to hurt anything as long as you don't get all crazy with it.