Check your diaphragm

[E.Marquez]

No lady's not THAT diaphragm ...the carb vacuum piston diaphragm.
A fellow SH owner was in need of a new one due to his having a hole.... I had a bunch of spares so sent him one........he found a crack in the rubber...so I said Id send him another....... I went though 5 sets of spare carbs to find ONE diaphragm without cracks or holes rubbed in them. so from 10 vacuum pistons I had, 9 were bad with holes and cracks in the rubber diaphragm.
Of course I had to check the set on my bike now......and sure enough even though I felt no runability issues, the front one had a small crack in the rubber..likely not leaking much if at all, but it would have soon.

So two new ones ordered up at $62 a piece .. Surprising, that's cheaper then the smaller one I replace all the time on our training bikes..that little mikuni 28mm carb piston is $78.. But a whole new carb is only $198....wish the carbs on our bike were that cheap to replace. ($400 a piece)

So get busy, and check those rubbers for holes boys...lol

[jchesshyre]

Of the three sets of carbs I have, two have the problems you describe with their diaphragms. I hadn't noticed at first as the cracks are pretty hard to see.

Do we blame age, or ethanol, both, something else?

It's annoying that new pistons aren't cheaper, or that good pattern ones aren't available.

[sirch345]

You certainly don't want a hole in your rubber

Thanks Eric for pointing this out, it could I'm sure help save any of us sometime,

Chris.