vacuum advance

[motoman]

If pinching off the vacuum advance stopped the backfire it's not the issue.


Sounds like you have some bad pickup coil wires and are losing contact intermittently when the pod moves the breaker plate..

A good suggestion!.........gotta' hate it when carbs are having electrical issues.

[BA80]

A good suggestion!.........gotta' hate it when carbs are having electrical issues.

You disappoint me Brant. Usually the first thing you say is "check your voltage" or "clean the contacts in the right handlebar switch"

[motoman]

You disappoint me Brant. Usually the first thing you say is "check your voltage" or "clean the contacts in the right handlebar switch"

Sorry Greg, amazing at times what 'old age and treachery' brings to mind....sometimes nothing.........or, better yet, just let you cover the possible issue. Least that way, I can be the one to dispute it instead of other way around...for a change.

[speedlimit85]

If pinching off the vacuum advance stopped the backfire it's not the issue.


Sounds like you have some bad pickup coil wires and are losing contact intermittently when the pod moves the breaker plate..

Yea that's what I fixed. I soldered a wire. But I didn't know that last year when the Yamaha shop fixed it by pinching off the vacuum advance.

So now the pick up wires are good, the vacuum advance is not pinched off and it's running right.

Can I just ride for a while? Or is it urgent to adjust timing, idle mixture, or synchronize carbs right away? Since the Yamaha shop must have adjusted something last year so the bike would run well with the vacuum advance pinched off? Do I need to put stuff back the way it was?

[bikerphil]

Yes you can ride it that way. Listen for any detonation regarding the timing. Check the plug color after some miles. Report back.

[speedlimit85]

Awesome. Thank you.

[3Phase]

Ride it for a while!

You really should synch the carburetors and set the idle with the vacuum advance disabled so you should be alright for a while.

If you want to make a really quick check: Disconnect the vacuum advance hose or pinch it closed and the idle speed shouldn't change at all.

If the engine idle speed drops, then goes up when you uncrimp the hose or put it back on the carburetor then the carburetors are out of synch and at least the #2 carburetor throttle plate is open too much.


The vacuum advance on the XS11 uses ported vacuum from the airbox side of the throttle plate, not the engine/manifold side. It's normally supposed to be completely off at idle -- zero vacuum signal and no ignition vacuum advance. Vacuum advance starts to come on during throttle transition at ~2 inHg and max advance is at ~6 inHg.

Basically any time the throttle is not closed and there's more than 2inHg at the vacuum port you'll have some advance.

[speedlimit85]

Ride it for a while!

You really should synch the carburetors and set the idle with the vacuum advance disabled so you should be alright for a while.

If you want to make a really quick check: Disconnect the vacuum advance hose or pinch it closed and the idle speed shouldn't change at all.

If the engine idle speed drops, then goes up when you uncrimp the hose or put it back on the carburetor then the carburetors are out of synch and at least the #2 carburetor throttle plate is open too much.


The vacuum advance on the XS11 uses ported vacuum from the airbox side of the throttle plate, not the engine/manifold side. It's normally supposed to be completely off at idle -- zero vacuum signal and no ignition vacuum advance. Vacuum advance starts to come on during throttle transition at ~2 inHg and max advance is at ~6 inHg.

Basically any time the throttle is not closed and there's more than 2inHg at the vacuum port you'll have some advance.

Now that's an answer I can follow. Thank you. I will do that test in the morning before riding.

[motoman]

Yea that's what I fixed. I soldered a wire. But I didn't know that last year when the Yamaha shop fixed it by pinching off the vacuum advance.

So now the pick up wires are good, the vacuum advance is not pinched off and it's running right.

Can I just ride for a while? Or is it urgent to adjust timing, idle mixture, or synchronize carbs right away? Since the Yamaha shop must have adjusted something last year so the bike would run well with the vacuum advance pinched off? Do I need to put stuff back the way it was?

Well, since shop personnel was obviously clueless with the bikes running issue, definitely re-adjust mixture settings and then a carb sync. Be sure to have a cooling fan in front of engine while doing this procedure, as it does take a bit.......no such thing as a ten-minute tune.

[BA80]

Yea that's what I fixed. I soldered a wire. But I didn't know that last year when the Yamaha shop fixed it by pinching off the vacuum advance.

So now the pick up wires are good, the vacuum advance is not pinched off and it's running right.

Can I just ride for a while? Or is it urgent to adjust timing, idle mixture, or synchronize carbs right away? Since the Yamaha shop must have adjusted something last year so the bike would run well with the vacuum advance pinched off? Do I need to put stuff back the way it was?

Like I said, if the vacuum is pinched off and the backfire stopped it's because the pod is NO LONGER working as it should and moving the breaker plate/pickup wires.

They may have adjusted the base timing up to compensate for the Vacuum pod not working. Your base timing should be 5 degrees before TDC with the vacuum disconnected to the advance pod.

[speedlimit85]

So, I rode 100 mi today after doing that test (pinching the vacuum advance hose at idle...no change in idle).

I hear a fffttt sound at a stop. One of the rubber plugs on the intake cracked and was leaking air. I replaced the plug and now this bike is a pleasure to ride.

When I do a full tune up it could be even better!

[3Phase]

Yay!

When you check the ignition timing, beware of bent timing pointers! The timing pointer is easy to bend or snag on a rag while you're wiping stuff down, then you'll have to whip out ye olde degree wheel or a reasonable facsimile thereof and find TDC again to reset the pointer. Don't do that.

The stock timing plate on the '80G is locked down with special break-away anti-tamper bolts from the factory to keep people from messing with the static ignition timing.

The special bolts have to be drilled to remove them and adjust the timing, then by Federal smog law they're supposed to be replaced with new break-away anti-tamper bolts but shucky-darn there are no more available from Yamaha so that's the end of that tune.

If there are regular bolts holding the timing plate on your '80G then someone's been into it, if not then it's totally unlikely that anyone did anything to the static timing since it was set to 5 degrees BTDC at the factory almost four decades ago.

Have fun!

[speedlimit85]

Yay!

When you check the ignition timing, beware of bent timing pointers! The timing pointer is easy to bend or snag on a rag while you're wiping stuff down, then you'll have to whip out ye olde degree wheel or a reasonable facsimile thereof and find TDC again to reset the pointer. Don't do that.

The stock timing plate on the '80G is locked down with special break-away anti-tamper bolts from the factory to keep people from messing with the static ignition timing.

The special bolts have to be drilled to remove them and adjust the timing, then by Federal smog law they're supposed to be replaced with new break-away anti-tamper bolts but shucky-darn there are no more available from Yamaha so that's the end of that tune.

If there are regular bolts holding the timing plate on your '80G then someone's been into it, if not then it's totally unlikely that anyone did anything to the static timing since it was set to 5 degrees BTDC at the factory almost four decades ago.

Have fun!

Cool. my timing could have been set in 1980.

[3Phase]

Cool. my timing could have been set in 1980.

It most likely was. Go out and look at your roof and see if it needs to be adjusted. It's probably set right where it was when the house was built but you never know.

The rotor and mechanical advance are bolted directly to the end of the crankshaft, not a shaft run by a series of gears or chains. There is no way the static timing can change unless the crank or the case move or twist and if that happens you probably have other things to worry about besides static timing.