Why haven't I seen an inline twinn with one carb and one pipe yet? Any reasons for not doing this? Tuning would be alot easier and you could still split exaust for the whole twinn appearance.Would be a lighter set up--a little anyways.

Chris...I split this post for the Tuned pipe topic. Marc.

Biggest trouble spot would be using our PUMPER type carbs. Unless engines are timed to run with the intake and exhaust cycles in sync, The fuel pump/metering timing would be off and carb would not work right.
If a Float bowl carb was fitted that is not crankcase impulse controlled, it could be made to work.

Another thing in doing that is being able to maintain VERY CONSISTENT operating temperature between both engines.
If one carb is delivering a fixed quantity of Air/Fuel at a known engine temp and it is right on, if one engine for some reason starts running hotter its air/fuel ratio will go lean. If one engine starts running cooler it will go rich.

Along with that is "Piston Port" induction engines have cyclic intake pulses, going from a strong draw on carb to a spitback phase.
2 engines timed 180* from each other using a common carb with split intake tracts would be real sketchy getting engines to have good intake cycles. REED VALVE engines however do this all the time in smaller outboard type applications.

Hope this helps :