17 replies to this topic

[timmy850]

I was talking to a mini guru yesterday about the balance pipe and he gave me this explanation.

- A series engine firing order is 1342, which is the same as 3421. This means you get one port (3&4) getting two intake events in a row, followed by the other port (2&1).
- SU carbs work on the vacuum between the carb and valves to raise the piston and increase the fuel.

If you blocked the balance pipe you'd have moment of intake vacuum followed by no vacuum, which would cause the pistons to move up and down and not maintain constant fuelling. So the balance pipe is there to provide a constant vacuum reading to both carbs

[grizzler73]

Ah, good explanation! So in theory you could put a smaller diameter pipe in there and fill the rest in, that way still having the balance effect but reducing the flow disruption.

[tiger99]

That is a good point. It is the fundamental limitation of siamesed port engines. So a larger balance pipe might be better?