Re-Attaching Vacuum Advance

[IanDMacDonald]

So, I learned not to do anything without asking questions when in-doubt, lol. So, I want to re-attach my vacuum advance to achieve better fuel mileage. I have a few questions concerning it.

1. Is it standard vacuum line I use to attach it to the #2 carb body?
2. should I re-time the bike according to factory spec of F @ idle, and 35° @ 5k?
3. do I re-tune and re-syn the carbs after re-timing?

thanks fellas.

-Mac

[jjz28]

Man, if you have been riding that unhooked, just wait till you hook it up. It will run much better. My bike struggled taking off until I found out I didn't hook the hose back up.

[IanDMacDonald]

Ehh, there's more to it than that. The PO modified the bike to run well without it. I just have it out of tune compared to where he had it.

[crazy steve]

So, I learned not to do anything without asking questions when in-doubt, lol. So, I want to re-attach my vacuum advance to achieve better fuel mileage. I have a few questions concerning it.

1. Is it standard vacuum line I use to attach it to the #2 carb body?
2. should I re-time the bike according to factory spec of F @ idle, and 35° @ 5k?
3. do I re-tune and re-syn the carbs after re-timing?

thanks fellas.

-Mac

Yes, yes, and yes.....

Note that the 35 degrees at 5k is with the vacuum advance disconnected....

[IanDMacDonald]

Okay, great Steve. Thanks for pointing that out regarding the 5k mark. One more question:

when I first undertook (is that a word?) this intetest in the vacuum advance, I tried to re-time the bike to spec (F @ idle), and found that no-matter how far I turned the plate one direction or the other, it was not resting on F. I think I remember if I turned it one way, it got closer, but there was not enough room to keep turning it. I think Scott said he altered tge vacuum advance slot, but I'm not knowledgeable about anything to do with that.

I don't want to time the bike wrong and cause damage. The bike runs well right now, but fuel mileage is horrible. I'll check plugs today, and maybe check valve clearance, etc. tomorrow. I will also pull the carbs off tomorrow and check float height and get the air filter changed, as its dirty. I'll also check to make sure I do not have brake drag. I'm not going to touch anything till I get more guidance here.

[crazy steve]

... he altered tge vacuum advance slot, but I'm not knowledgeable about anything to do with that.

He probably altered the mechanical advance. Not knowing what's been done, you really need to take all the ignition bits off and find out what you have.

Look here: http://www.xs11.com/forum/showthread.php?t=37189

If the mechanical advance has been altered, you may need to replace it if the change isn't reversible.

[jjz28]

Yeah, I remember reading that now. Still it will run better than it did then. I didn't understand that putting a bolt in there anyway.

[IanDMacDonald]

I didn't understand that putting a bolt in there anyway.

Scott cleared that up. The bolt was in the hole where the vacuum line feeds through the side case. I think he said that he adjusted the vacuum advance, as well as advancing the timing. I'll wait on more people to comment before I venture into this.

[crazy steve]

If the mechanical advance is unaltered, you'll find that out when you check the timing. The 36 degree figure is initial timing plus full mechanical advance.

The vacuum advance isn't 'adjustable' (well, not easily) but if it's not hooked up, what are you adjusting?

[IanDMacDonald]

This is Scott's reply:

The bolt is not placed in the advance slot, it's just in the hole in the cover where the vacuum hose used to be. The centrifigul advance slot was resricted by me to have more initial advance. The compression was up a bit also with 171# compression test average. With the vacuum attached there was too much advance. When I sold it it got 44 mpg without vac adv.

[DGXSER]

OK, so this may be why you can not get it to the F spot on the timing plate.

The centrifigul advance slot was resricted by me to have more initial advance.

So it sounds like he restricted the mech advance from coming all the way back to stock starting point, look at the slots in the mech advance. It sits behind the timing plate, so you need to pull the 6mm allen bolt out to remove the plate, then see if you can tell what was modified. Honestly 171 psi compression on a warm motor is not crazy high. Some folks have reported their stock engines getting that high.

So he then removed the vac advance to adjust for the mod to the mach advance. SO if you have the vac advance unit, you should be able to install it, then correct the adjustment to the mach advance.

Then you will want to adjust the timing, tune and synch.

[IanDMacDonald]

Perfect, thanks for clearing that up for me Don. I may not have time tomorrow, but I plan on removing stuff and taking pics and figuring out what is going on.

[IanDMacDonald]

Okay, so I took the bike apart today and found out a few things. One: float height level was spot-on. Two: spark plugs looked okay, if not a little lean. Three: the advance was altered, but not in the way I assumed. Scott elongated the advance slots making them longer. Also, unless it was from the factory, it looked like the metal behind it (weights?) were ground down a little. I'm thinking about ordering another advance unit and starting over.

I ended-up hookimg a piece of vacuum lime from the vacuum advance to the #2 carb body, and retimed the bike @ 3k= 35°. Not sure the advance is even working. The plunger does not even seem to move, it's very stiff. Does that blue allen bolt in the advance do anything?

[IanDMacDonald]

http://db.tt/tC4SP9TZ
http://db.tt/c9Hd1MNQ

[Rasputin]

Ian, when I look at the pic you posted it kind of looks like Scott may have ground down a few bits to get the weight he needed for them to work. If you look at the pics steve has posted in his interchange guide you will see a different looking pic.

http://www.xs11.com/forum/showthread.php?t=37189