Topic: 77-78 CB750 F2-F3 Reproduction carb boots and other Honda rubber bits!

[kmb69]

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They seem to seal well but while I was synching the carbs I observed that the boots are so soft, that you could actually see them pulsating with each induction cycle.
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The very early 69 and 70 boots (short spigot heads) had a much thinner wall section and you could see them pulsating big time to the extent that the carbs would move. Never heard of any leaking though until they got hard and crusty. They were beefed up considerably with the -305 revision.

[MarshallCS]

Just curious, but why are these made out of rubber? Wouldn't a set of aluminum, or some type of metal work just as well without the deformation or the burning up the rubber ones have?

[Bailgang]

Just curious, but why are these made out of rubber? Wouldn't a set of aluminum, or some type of metal work just as well without the deformation or the burning up the rubber ones have?

Pure speculation but I would imagine the primary reason the boots are rubber rather than a direct metal to metal contact is because the rubber acts as a heat insulator, without some sort of heat insulating material between the cyl head and carbs then all the heat from the cyl head would transfer to the carbs. I'm just guessing though.