Vacuum advancer

[Andries]

Greetings,
My mechanic (whom I have my doubts about) has told me that I need a new vacuum advancer for my xs1100SH. Can anyone tell me what it is, what it's function is and most importantly, where I can get one.
Thanks guys.
New Guy.

[Jerry]

Under the left-side engine cover (as you sit on the bike) is the vacuum advance. The device changes the timing of the engine at low (below 3,000) RPMs. This makes the bike start and run better at low speeds. later model XS and XJ 1100s have an all-electronic system where a 'black box' calculates the advance rather than depending on a mechanical system.

The vacuum advance requires maintenance, but rarely has to be replaced. The 2 most common problems are sticking mechanical parts and broken wires. Many owners have reported that cleaning and lightly re-lubing the moving mechanical parts has cured many ills, and many others have reported broken wires (due to flexing in normal operation) that cause intermittent problems. If you pull *gently* on the wires and get an 'hourglass' shape, the wires need to be replaced. Do a search on "vacuum advance", "pickup wires", or "pickup coil" and you will get several threads on testing and replacing these items.

It could be your advance needs to be replaced, but in the majority of cases a good cleaning/lube job and replacing the wires will fix you up as good as new.

[John]

Vacuum advance

It is located on the left side of the engine, under the cover that says Yamaha. It advances the engine timing, making the plugs fire sooner, when the RPMs increase, preventing the spark from being deliverd to the plugs too late in the compression stroke. The spark is normally delivered a few degrees before top dead center of crankshaft rotation, allowing the fuel to begin burning before the piston reaches the top of it's travel. This way the fuel burn is at it's optimum when the piston is beginning, or slightly into the power stroke. The fuel air charge takes a while to fully combust, so if it was fired when the piston is at the top of it's travel, by the time the fuel is burned, the piston would be so far down the cylinder that it would have too much room to expand and therefore not deliver much power. Are you really good and confused now?
Try advertising in the parts wanted classifieds here and ask if anybody has one for sale, or check the parts for sale ads here. In fact there are a few guys advertising parts for sale that have some engine parts for sale. Sorry I don't have one, or I'd offer it to you.

[pgg]

If your dubious mechanic is talking about the small metal vacuum 'pump' - take it off and suck on its hose connection to test it for smoothness and a good seal. The chances are there's nothing wrong with it at all. If he's talking about the centrifugal unit, (actually- he probably doesn't know WHAT he's talking about,) then strip that, clean it, lube it and check those wires.

[Andries]

Thanks for the advice

Thanks for the advice guys. It is appreciated more than you know. The dubious mechanic has actually drilled a hole in the advance unit to be able to set it a few more degrees forward.
How that would make my bike ride better is a subject only he would understand.