vacuum advance problem

[abetterday]

Does any one have a vacuum advance for a 81 xs1100, took bike to shop man said the advance was not working when you give it gas except only on slow accellaration. Do you have any suggestions.

[SanDiegoMike]

You can confirm this yourself by removing the left side cover of the engine, removing the vacuum line from the nipple on the carb, and applying your own vacuum and seeing whether or not your vacuum canister is indeed bad. You can do this without having the engine running. More often than not, the problem is in the vacuum line (split or cracked), not the canister. Movement of the advance plate under slow acceleration is also a function of the centrifugal advance mechanism that consists of little spring-loaded weights that move outward from their static resting spot as enginr rpm increases. This mechanism sits behind the vacuum advance/PUC assembly. Hope this helps!

[AlanB]

Hi abd,

Most bike shpos won't know anything about vac advance since the only bikes I have ever seen with it are the XS11..... and the RD200.

The vac unit adds extra advance when there is a lot of vacuum in the inlets; gentle acceleration, cruising, and on the over-run.

It gives smoothness and a little more economy on the cruise and should take out some of the popping and banging on a closed throttle.

There are NO benefits to power, or in economy when riding hard.... which is why most manufacturers didn't fit it to bikes, but ALL do to cars.

In short, it SHOULD add advance on closed throttle, or very low throttle opening..... It SHOULD NOT add advance on a wide throttle.

It does not sound like there is a problem with the bike; problem is probably the mechanic!

AlanB

[JACKHAMMER01]

Brion, depending on how the bike has been kept in the past, ie: stored inside or out, serviced on a regular basis, etc, the advance may become dirty/rusty. My last XS was also an 81, and I had to remove the advance, clean it, polish the center with a scotchbrite pad, and then spray the weights and springs with wd40. After that I had no more problems with that. Worth a try.

[abetterday]

Here is my problem, when I start off the bike spits and spuders like its not getting enough gas but after the rpm gets up it runs fine. This is what I have done
1. Replace the wire on the the advance mec..because it was broken.
2. Clean carbs and blowed air through jets
3. Sinked carbs
4. Changed fuel
5. Changed Plugs
6. Ran fuel line to a different rout

I would like to know the best way to run fuel lines

[TopCatGr58]

Hey Brion,

Just to add, the 81 doesn't have any Cent. Adv. mechanical parts, because the Cent. Adv. Timing curve is built into the 4RO TCI. So...even if the vacuum adv. wasn't working, you could essentially run without it without any harm or loss of power to the bike, just as Alan said, the civility and slight fuel economy would be sacrificed.

Tell the shop that's OKAY, tell them to leave it alone, and just make sure that they connect the vacuum hose to the #2 carb BODY port, not the INTAKE MANIFOLD ports!! Then get it home and to like Jim said, just clean, lube, and you can get and apply a vacuum to it...should contract/pull to full limit/range with about 5.9 In.Hg of vacuum! IF it doesn't hold the contraction/pull, then the diaphragm may have a pinhole leak in it, then you would be best to just plug it going to the carb, and then either look for a replacement, or just run without it!
T.C.