Topic: K7 throttle shaft seals

[starf]

Hi all, long time reader, first time poster.

I'm working through a set of carbs from my 1977 CB750 and have come to the dreaded throttle shaft seals. These disintegrated when I split the carbs with no hope of saving. I already have felt and a punch set to make some new seals for #1 and #4, and some o-rings to replace the seals on #2 and #3.

My question is why are there different types? As far as I understand it, the felt is to make a low-friction lubricated dust seal, and the rubber seals are also to keep dust out but with more friction(?). It seems as though there are steel(?) bushing inserts to provide bearing surface, so why use different types of seal?

My intention is to replace like-for-like, but it got me thinking. Could I replace them all with felt? Could I replace them all with o-rings? Hoping someone has an insight into the original design intent.

[HondaMan]

I've only seen felt in those, that I remember?
Maybe someone beat you in there, and replaced them with rubber ones when they broke? I would think rubber would add too much 'stiction' to the shaft's rotation.

[starf]

Just to follow up on this, I am experimenting with using o-rings instead of felt.

I have new nitrile o-rings for the throttle shaft seals (15mm OD x 11mm ID x 2mm), and for the choke shaft seals (9mm OD x 6mm ID x 1.5mm). So far there doesn't seem to be any extra stiction, or any perceivable difference at all.

I'll keep an eye on them, and I have felt seals to replace them if I ever need to.

[fizzlebottom]

contact Mike @ The Motorcycle Project: https://motorcycleproject.com/

For context, you do not want to use o-rings. They have a high potential to cause binding issues. The felt seals do not actually seal. They just keep dust out, but allow nothing but free movement.

I replaced mine years ago with some basic medium-weight felt from a craft store and making my own. They've held up for over 10 years. Don't use o-rings.

[madmtnmotors]

Don't use o-rings.

I concur. The choke plate shafts especially which are spring driven and have no direct linkage connection. This makes them very prone to stiction under the slightest resistance.

[starf]

Don't use o-rings.

Thanks for the advice. Next time the carbs are off I will replace with felt. O-rings were easier to find locally when I first started looking, but now have felt too.