Topic: 69/70 carb boots vs 71 carb boots

[69cb750]

16211-300-020 Carb boot 1-4 (69-70) - (Yamiya insulator)
16211-300-030 Carb boot 1-4 (71-76)

What differs between boots ?

[Pbeattie89]

The cylinder heads from 60 to 70 had shorter intake spigots, so the boots would need to change to accommodate that. There may be other differences as well.

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[HondaMan]

I have a set of both: the early ones will fit onto the later heads, but there ends up being space between the engine end of the hose and the big nut of the spigot, and the angles are just different enough that then they won't fit onto the K1-K6 carbs in-rack, for reasons I didn't dig into (I used some K0 carbs instead). I've actually used them to test-fire an engine, but I had to support the carbs with a couple of slabs of wood because during the run they wanted to sag down and fall off the spigots with their short grip, once they got hot.

Naturally, the later hoses won't clamp onto the early heads' spigots very well, because the hose clamp groove is directly over the nub on the end of those early spigots, and the nubs don't reach far enough into the groove(s) in the hose(s).

[PeWe]

Here early short boots, K6 head and a modified VM29 rack.
I used later boots when mounted on bike.

[69cb750]

Thanks for the replies and photos.
I remember now.

[MauiK3]

Pretty subtle differences, I suppose they had their reasons but it seems so small.

[PeWe]

Maybe Honda found that a few mm longer spigots with wider area for clamps were an improvement?
I found that I got wrong boots over 20 years later. Ordered for K6 ca:1988, got the earliest to 69-70.

The earlier boots were made of a better material. Stiffer, not cracking.
Feels like a kind of fiber structure rubber.
Later softer.

I have found NOS K1-K6 boots in old Honda bags with paper labels inside. To be used when needed. The better model

My stock K6 carbs hanging in the stock boots 1985-1991.
Pods used so no support by an airbox. Did not crack.

[Don R]

 Now I'm wondering what I used on my diecast, it has a K3 engine with early carbs. I have to assume late model carb rubbers. I cooked a batch of carb rubbers in my ultrasonic cleaner with oil of wintergreen, then put them in a hermetically sealed mayonnaise jar and left it on funk and wagnels porch.