Re-Attaching Vacuum Advance

[IanDMacDonald]

What a fun thread this has become! I'll send Andreas a question to see if he has a plate and advance unit.

[3Phase]

What a fun thread this has become! I'll send Andreas a question to see if he has a plate and advance unit.

Why? Just set the base timing to 10 degrees and make sure it's 36 degrees @ 5200 RPM and you're golden! The '78s were the best of the XS11s and with the ignition timing set, verified and out of the way you can move on to other things, like picking lint off the dog or figuring out why the gas mileage on your XS is down.

If you don't want the '78 mechanical advance send it to me (Please! Oh, please, please please!) and I'll try to figure out something to do with it.


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[IanDMacDonald]

Umm, I don't have the '78 advance yet. I have the '79 on it, and there is no way to know what this thing is at during idle.

[3Phase]

Oops....

Umm, I don't have the '78 advance yet. I have the '79 on it, and there is no way to know what this thing is at during idle.

Oh! Right!

Modifying the mechanical advance doesn't change anything on the Timing Plate. IF the Timing Pointer hasn't been messed up then you just shoot it with a timing light.

Whatever mark is lit up next to the Pointer, that's the where it's firing at idle and that's the base timing. It will work the same for the max advance @ RPM mark too. I think someone posted a picture somewhere that shows the timing marks on the '79 Timing plate and what they mean.

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[IanDMacDonald]

Okey dokey. So, I just went out there to see where exactly it is @ idle, and again @ 5k. With her warmed-up, the plate shows 19° @ idle, and 35° @ 5k.

Note: With my ear next to the plate, I just noticed the metallic pinging noise while idling and @ 5k.

Suggestions?

[MPittma100]

Advance

19 degrees at idle is a little much, but would give better throttle response "feel".
I'm wondering if the mechanical advance has been changed to advance at that low RPM or if it is static at 19 degrees. If timing is set to 19 degrees, it might make it a little hard to start when hot.

MP

[IanDMacDonald]

I should note, that timing was checked with the advance vacuum line attached. Does it make a difference?

[crazy steve]

The vacuum line should be disconnected. It may not make any difference, but that's the only way to get an accurate check.

And 19 degrees at idle is a lot of timing.......

[IanDMacDonald]

Yeah, I figured it was. so, for you timing gurus, does turning the plate alter initial timing or just the higher rpm timing? And, which way do I turn the plate to get closer to stock timing numbers?

[bikerphil]

CCW=advance, CW=retard

[IanDMacDonald]

Calling me a retard Phil? Lol, jk. So, I obviously want to retard the timing, correct? Another question: if I'm okay @ full advance, but not okay @ idle, wouldn't retarded timing affect both idle and full advance timing?

[bikerphil]

Lol, yes you want to turn CW for less timing and yes it will affect idle and full advance.

[3Phase]

Ian,

It depends. As Phil said, changing the base timing will change the max advance timing @ RPM. That's why you have to check the timing with the vacuum advance disconnected before you try to change anything.

The pinging noise you're hearing could be the vacuum advance assembly vibrating, light detonation in the cylinders, or both. I couldn't tell you from here.

There should be no vacuum advance at idle but if the carburetors are a little out of synch then the throttle plate on the #2 carb can be open too far at idle. That will partially uncover the vacuum advance port in the throttle body and send a small, pulsed, vacuum signal to the vacuum advance when there should be no signal at all.

Since there's no real intake manifold on an XS11 the vacuum advance signal behaves like it's coming from a thumper. There should be a very small restrictor pressed into the brass vacuum fitting on the #2 carburetor body to damp the pulses but it's not always in there.

I'm not sure if the restrictors "fall out" or people remove them "... to make the bike go faster" but if you see the vacuum advance assembly pulsing, or doing anything at all, really, except sitting there quietly and not moving until you crack the throttle open then the carbs are out of synch.

Carbs that are out of synch can put a serious dent in the gas mileage too.


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[IanDMacDonald]

Yeah, it's just sitting there, lol. I'll look at what's going on with it in the morning.

[IanDMacDonald]

Aha! I figured out what Scott did to the vacuum advance. He drilled into the pod arm to lock it out.

http://db.tt/Z34fyCRx