Idle chatter MKII

[uk1.1s]

Sorry guys - this one again.

New member to the XS forum - and I see one or two threads on this one already. Ken seems to have suggested in one thread that idle 'chattering' could be coming from the vacuum advance unit a while back - and Yep - I definitely have that.

The old XS has been off the road more than it's been on in recent years and the one that is making me pull my hair out at the moment is the Vac. advance unit behaviour. It is undulating violently at tick-over and 'clacking' away.

Any advice on the way to go to fix it - have a new vac. advance hose now, have new carb diaphragms (blind ally maybe - but needed doing when I looked. My next guess is that the No. 2 carb stub connecting it to the head needs replacing as the connection for the vac. advance hose is holed, cracked or something.

Any ideas much appreciated - one of these days the beastie could be out on the road again!

[xssiveone]

Did you reconnect the vacuum hose to the mainfold, or to the carb? Connecting it to the manifold will be too much vacuum and might cause the symptoms you describe. And is the advance unit clean and free.. not sticking at all when you move it by hand? It's a fairly simple device, the vacuum pulls it one way, the springs pull it another. You've replaced the vacuum hose, if everything above is OK, then perhaps either the vacuum diaphram has a hole in it or the mechanism is just worn out.

[uk1.1s]

Brian,

Am I being a complete idiot here - not unlikely!

Been a while since I messed about with this - but connection is directly to the carb - I think - will check tonight when I get back.

Advance unit seems OK and I picked up a second hand replacement which I tried with the same result. If I put the original unit under a steady vacuum it moves cleanly and sits still - so hoping that the diaphragm isn't holed.

It's starting to sound like I've been fixing it up to the manifold directly maybe - doh!

I'll slink away and try not to feel too stupid if that's the case!

Thanks for the reply

Let you how embarrassed I feel

[xssiveone]

Am I being a complete idiot here - not unlikely!

No, not trying to imply that... just been there before. Not with this particular item, but have missed the obvous many, many times before and know the feeling well. Hopefully it will turn out to be just this simple for you.

[uk1.1s]

Brian,

No worries - I - like you - have been here before and missed the obvious. Had a lot of research material in this case, but my XS manuals (Clymer, Haynes, Yamaha) all are pretty sketchy in this area and trouble shooting my XS problems have been a pain in between moving house and getting married this year!

In answer to the problem - I just had a look on how I've got the hoses hooked up and find that the vacuum advance unit IS connected directly to the manifold and the strange vacuum tap junction (4-legged thing) above the carbs is connected to the carb off-take.

I guess there's my answer, if I understood you right - when I switch them around all should be well.

Thanks a lot for you help - will have another play at the weekend as work tends to get in the way of a good few hours in the garage these days - especially as the light is gone at this time of year.

Now all I've got to figure out is why cylinders 1 and 2 don't seem to be firing - that should keep me occupied too!

[Mike Hart]

Switching the hoses around might cure the other problem too. You have too much vacuum (and pulsing) to the vacuum advance, maybe not enought to the octopus giving fuel delivery problems...hope it's that easy!