Clacking sound from Vac advance unit??

[bike punk]

So iv replaced the vac advance unit twice now and the loud ticking sound wont go away?? The diaphragm inside is ok, is there something else in the advance mechanism that could be causing this sound? It never used to be this loud.
Any ideas would be great, I haven't had a chance to pull the hole assembly of yet.

[natemoen]

Did you hook it up to the port on the #2 carb body or the intake boot? Should be on the carb, hooking it up to the intake causes a hammering of the advance.

[Eveready1100]

Are you still running those RS36's you mentioned in your previous thread?
If so, just wondering if you drilled and fitted a vacuum spigot in the same spot as the original carbs, as it's crucial to the operation on the vac advance.

[GLoweVA]

Are you still running those RS36's you mentioned in your previous thread?
If so, just wondering if you drilled and fitted a vacuum spigot in the same spot as the original carbs, as it's crucial to the operation on the vac advance.

Not only the location, but the size of the orfice too. Too big and it'll feel the pulsing of the motor, too small and it won't respond quickly enough to the changes in the vacuumn.

[bike punk]

Nope, im trying a set of mystery carbs at the moment of a XJ or FJ at the moment with limited success.
Iv tried running the vacuum of both the carb and manifold boot, it didn't seem to make any difference. I pulled the rest of the assembly of and it all works fine. I did spray a bit of lube in the diaphragm and that has seemed to quieten it down a bit. Ill give it a decent run and see how it goes.
Cheers!

[Eveready1100]

What you could do a an interim fix is to fit one of those little valves like on a fish tank air pump line into the vacuum line so you can open or restrict the flow to the diaphram. You should be able to get it to settle down with an adjustment either way.

[Eveready1100]

Just had another thought as to what could make it behave like that. How long has it been since you checked your valve clearances? Could be (possibly) that the inlet valve on that cylinder may not be closing completely and you'll be getting a bit of vac, then pressure, then vac, etc, which would make it behave in the way you describe. A compression check will show it up straightaway.

[bike punk]

The engine got rebuilt not long ago and the valves were set then but I guess it wouldnt hurt to re check em. Interesting idea on the fish tank valve sometimes you gota think outside the box

[motoman]

The engine got rebuilt not long ago and the valves were set then but I guess it wouldnt hurt to re check em. Interesting idea on the fish tank valve sometimes you gota think outside the box

If hooking up vacuum advance to both carb boot(non restricted) and ported vacuum resulted in same result, then ported vacuum isn't restricted. The stock Mikuni carb port has a built-in restrictor in the bottom of it, even though outwardly appearance doesn't give that away. As stated, you can restrict that hose, preferably on the carb end with the small overall diameter of a Kiehn jet.