Vacuum adv hangs up

[hondakid11]

my adv is hanging up and not coming down unless i release the clutch at a standstill and force the idle to drop. it will idle fine, but once you rev to about 2500 rpm, it "sticks" (ive watched it with the timing cover off)

things ive done:
cleaned carbs thoroughly
snyced
colortuned
timed
double checked sync
double checked timing (mach adv works fine)
checked for vacuum leak with carb cleaner spray.
ripped out my hair
tried to run without vac adv (runs rough)
tried to use motion pro syncpro resticter (made the adv not move)

if i rev it up it will hang at like 3000 rpm until i either put it in gear and release the clutch, or take my finger and push the vacuum advance down...

any ideas?

[jetmechmarty]

I believe the vacuum advance is supposed to come in at engine start. The mechanical advance comes in at 5000 rpm. Are you saying your idle won't come down? Your carburetors probably need to be bench synced properly. Your description leads me to believe they're way out of sync. There must be an error somewhere.

Ignition timing set with vacuum advance hose capped, correct? Mechanical advance comes in at 5000 rpm, correct?

[hondakid11]

yea the carbs were vacuumed synced multiple times during all the processes. mechanical adv was set and checked with vac hose off and plugged. comes in at 5000 rpm at 31 degrees. but the idle doesnt hang with the vacuum hose disconected. so i know this is a vacuum adv issue.


ive been all up and down this forum for the last 3 months. but just now was able to join.

[jetmechmarty]

The vacuum advance is connected to the port in the #2 carburetor, correct? Did you check the vacuum diaphragm for a leak? The hose as well?

What you describe sounds like a bad sync. Before you hooked up a manometer or gauges, did you bench sync the carburetors? That's actually very important.

http://www.xs11.com/forum/showthread.php?t=88

Set the butterflies to this position, where you have half a hole showing.


This thread may be helpful to you, until someone responds who knows more than I do.

http://www.xs11.com/forum/showthread.php?t=42569

[SFerinTEXAS]

Where are you connecting the vac hose? int boot or #2 carb?

[donebysunday]

If I may, the hose goes to the carb not the boot.

[hondakid11]

Connected to #2 carb body brass nipple. Sync was done properly. Carbs do not have vac leaks nor tears in cv diaphram. I didnt pull the vac canister off the pick up assy. If it were leaking there it wouldnt pull the adv.

Im thinking this may be worn springs inside the vac adv mechanism.

**sorry for all caps, im at work and have to use caps, not going to re type lol**

[TADracer]

If it is sticking or if it has a leak they both should be easy to determine. With engine off, rotate the pickup coils by hand. They should turn easily and snap back to the base position under spring pressure on the centrifugal advance mech. If not then remove, clean and lube the centrifugal advance. Then disconnect the hose from the #2 carb (the carb, not the #2 boot is where it is connected) and pull about 5-6 in. vacuum on it and the vacuum mech should pull in and move the timing plate with the pickup coils. You can do it with your mouth if you don't have a hand vacuum pump. Hold the vacuum and the plate should stay put. if it does not then the diaphragm is faulty (very rare).

Everything should be clean and move freely otherwise it will not work.

FYI, the vacuum mechanism is on metered vacuum from the carb. At high vacuum conditions like cruising (throttle open and not closed) is the only time the vacuum mechanism is in play. All other times like idle or acceleration it will retard back to its idle position.

[hondakid11]

everything moves freely as far as i can tell. ill have to pull it all off and give it a good cleaning.

[motoman]

Connected to #2 carb body brass nipple. Sync was done properly. Carbs do not have vac leaks nor tears in cv diaphram. I didnt pull the vac canister off the pick up assy. If it were leaking there it wouldnt pull the adv.

Im thinking this may be worn springs inside the vac adv mechanism.

**sorry for all caps, im at work and have to use caps, not going to re type lol**

Remove the vacuum assembly, and THEN check that rotation of the advance assembly rotates freely, as in floppy free. If it's not, then that mechanical assembly and its little bearing need cleaned up first, THEN lubricated. Worn springs is NOT the issue.

[trdriver71]

If I were you I would check your valve clearances I had the same thing on my bike turned out that almost all of my valve were tight.

[alaskey2]

If I may, the hose goes to the carb not the boot.

Wait what? From my petcock I have a thick tube (fuel line) that goes to my carbs and then a skinny tube that goes to an intake boot. Is this wrong?

[jetmechmarty]

Barb on carb #2 goes to vacuum advance (left engine cover). Barb on manifold #1 goes to vacuum shutoff (octy) on a Special, or the left petcock on a standard. Barbs on #2&3 are capped. #4 is capped on a Special and goes to the right petcock on a standard.

[Prisoner6]

... Barb on manifold #1 goes to vacuum shutoff (octy) on a Special, or the left petcock on a standard.

Marty,

On my SF, the #1 manifold barb is capped, and the vacuum line from the Octy is connected to the barb on the #2 boot ... does it make a difference?

[jetmechmarty]

Marty,

On my SF, the #1 manifold barb is capped, and the vacuum line from the Octy is connected to the barb on the #2 boot ... does it make a difference?

No. You may run the vacuum shutoff (octy, octopus, spidervalve, POS) from any manifold you choose.