Quick question about vacuum advance

[Douglas Money]

Is there a restrictor that keeps the vacuum advance from bouncing at idle?

[TopCatGr58]

Sort of,

It's the smaller sized metal tube on the #2 carb body that provides that restriction. You do have the hose connected to that, and NOT to the synch port on the #2 Intake Boot??

If it's properly attached to the #2 carb body, then there may be something wrong with your vacuum module, but sounds more like you've got it on the wrong vacuum port!?
T.C.

[Douglas Money]

I checked it before and its on the right port, but you can hear it bounce at idle. It runs fine, just noisy at idle. Causes no problems, I was just checking. I am reinstalling the carbs today. Hopefully!

[John]

The bouncing could be a weak spring in the vacuum pot assembly. The vacuum may be able to overcome the spring tension easily, and cause the rattle.

[80mdnt11]

dreded left side noise

Doug, I too have the same issue. Think it may be deeper in my case, as in primary drive chain, hope not but???????? Have checked timing & vac. advance on revs with timing light. All good, look over seems OK. Haven't went any deeper as she runs fine, may later on. More of a nuisance than anything else as these bikes are prone to this. (vac. adv. noise) Although a little investigation isn't always such a bad thing? Good luck & post if you go further.

[Douglas Money]

Yes, I just checked the hose one more time and it is connected to the correct port. There is no orifice in the metal tube. Maybe the problem. I have had the cover off and seen the vacuum adv pulsate at idle. Thanks.

[John]

There won't be an orifice in the tube. It is actually a small hole drilled into the carb body, that the tube connects to. Could it be that a PO had opened the hole up for some reason?

[Douglas Money]

Never can tell what this PO did. I can look right through the tube. It is basically just a nipple now.

[John]

There is your problem. Is there any way you can make the hole smaller? I have a junk #2 carb...I'll go look at it and see how big/small it should be.

[John]

The smallest drill I have is a #60, which is .040 inch, and that is too big. You will need to find some way to restrict the orifice for the vac advance tube. You may be able to fill the tube with some JB Weld, or similiar substance, and before it sets up, poke a hole through it with a single strand of copper wire from a small gauge wire, like a 18 or 20 gauge. If the hole that is in the carb body seems as big as the nipple itself, then that is your problem.

[Ken Talbot]

Like the restrictor in the tubes of a set of mercury sticks, you could stuff a small plug into the hose, with a small hole drilled through the plug to give you the dampened vacuum signal you are looking for.

[Douglas Money]

Thanks, I will try that out.

[80mdnt11]

wooooooops!

Sounds like Yours is/was a pulsating issue! John, Ken & TC have pointed you in the right direction. Aren't these Gurus great!
Get it fixed and come to Moonshine, IL. for a burger @ the 14th!
Not to take anything away from you John, but I like Ken's idea. Small plastic rod/ like dowl rod should do the trick.

[Ken Talbot]

I just fished a piece of 0.021" stainless steel wire through the orifice on a #2 carb. That is equivalent to a #75 numbered drill.

[Douglas Money]

Thanks guys. Where is Moonshine, IL?