SOHC.co.uk Forums > CB750

One for the Engine Tunners to ponder

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neilg:
In a moment of madness I have created a monster using an F2 motor with a K7 exhaust. So I ask myself, where should I start with the carbs. Should I start with F2 jetting due to the combustion chamber design. Or K7 due to the 4 into 4 exhaust design. I have to use PD carbs to keep in with the theme of the build so swapping for earlier types is not an option.
I need to rest now cos my headaches are starting again 🤔

Neilg

hairygit:
Go with whatever the K7 uses as stock.

Sent from my X6pro using Tapatalk

K2-K6:
I'd go the opposite as it's the F2 cam, valves,  combustion chamber shape,  compression and rpm ceiling that hold much more relevance to carb setup.

In addition,  the F2 carb's are PD42A with the K7 using PD42B spec which looks like a different throttle slide geometry to match the engine spec and lower rpm expectations of the K.

neilg:
Mmmmm now you see why my head hurts 😢

SumpMagnet:
I'd go with the F2 setup as a start point.

My thinking would be the F2 would need bigger jets and draw more fuel. If you start at the richer settings, it's safer and you can work down to optimise running. The opposite could be running lean which is far less desirable.

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