vacuum advance

[oldnortonrider]

(?) Anybody out there ever had a vacuum advance quit/fail?
........not a hose leak; the vacuum advance unit itself.

[79XS11F]

I myself haven't but the diaphragm in it could develop leaks. If you have a vac gauge you can test it to see that it goes to full advance at the right vac level
Rob

[petejw]

My 82 xs parts bike and on Stralyas 78 standard,
both vac adv units wouldnt hold vaccuum.

to check remove the hose from No:2 carb port
and then suck on the hose, the vac adv unit should raise, hold ur tongue ovr the hose and the vac unit should hold vaccuum if not
itll require replacement.

[Stralya]

Hey old

I got a replacement unit from Andreas Wiess. That man loves us XSives and is a fair and square dealer. Drop him a line.

Dan
Fan of Andreas

[grovesy]

Hi chaps, greetings fom England.
Having the same problem checking my vacuum advance. Should I be able to move the advance through its whole arc just by sucking on it? I can only get it to move a fraction (about 5 degrees) which is all that it moves when i rev the engine. With my fingers i can rotate it through its full arc easily.

[79XS11F]

The unit should move through its full range with ease. It should move to full advance at a predetermined vac level. I don't have my manual handy but the specs are in the manual in the section on ignition. This spec is not printed in the spec overview of that section. If you can't move it through its full range it is hanging up somehow or the vac line is leaking or the carb nipple is partly blocked. Check it, clean and lube as needed.
Rob

[grovesy]

I haven't got access to a pump so I can only really test it using lung power. This might be a stupid question but should I remove the unit from the bike to test it? If not then I'm sucking against the return springs of the automatic timing unit.

[79XS11F]

I doubt you'll get enough draw with you lungs. I would just take the unit off and clean it and lube it and put it back and then test it again. that unit should go to full advance at 5.9 in. Hg. with a vac pump hooked up.
In use the mechanical part of the auto advance should be at full advance at 5200 RPM with the vac line disconnected and plugged. cap off the cab input vent as well when testing

Rob