Calling on all electrical expertise!

[JTP obsession]

Hey fellas,

Over the winter I rebuilt the engine on my 81 xs1100 H. Since then I've been experiencing problems with my vacuum advance (I believe). When I have it plugged into the #2 carb, the bike idles rough and eventually begins to race, at operating temp, once I give it a bit of gas. It'll either sit at 3000 and slowly crawl back down or slowing rev up to 4000. If I unplug the advance, bike runs beautifully. I stupidly got another advance diaphragm, figuring later on that the one I had was in good condition. When I add suction to my advance hose both units are advancing. I also tested my coils, all 4 are within spec.

Any thoughts? What are the consequences of riding without the advance?

PS: I will do better at letting folks know the end results, haven't been too good at that in the past.

Thanks

J

[speedlimit85]

I was riding with the vacuum advance pinched off for awhile. Ran fine...less mpg. Make sure there are no vacuum leaks.

[Radioguylogs]

Vacuum Leak?

It seems like you have a vacuum leak.

Climbing idle speed when hot is a classic symptom.

Do you have the vacuum advance hose on the correct nipple? There are two of them on the #2 carb. The correct nipple is on the carb body, not the intake boot.

The unused vacuum port on #2 boot is plugged?

The vacuum hose has no leaks?

[motoman]

Hey fellas,

Over the winter I rebuilt the engine on my 81 xs1100 H. Since then I've been experiencing problems with my vacuum advance (I believe). When I have it plugged into the #2 carb, the bike idles rough and eventually begins to race, at operating temp, once I give it a bit of gas. It'll either sit at 3000 and slowly crawl back down or slowing rev up to 4000. If I unplug the advance, bike runs beautifully. I stupidly got another advance diaphragm, figuring later on that the one I had was in good condition. When I add suction to my advance hose both units are advancing. I also tested my coils, all 4 are within spec.

Any thoughts? What are the consequences of riding without the advance?

PS: I will do better at letting folks know the end results, haven't been too good at that in the past.

Thanks

J

Have seen this exact scenario happen when vacuum inches are weak at all four carb vacuum ports. Found that it was due to coils low voltage output. Both my original 3.0ohm coils were at 2.4ohms. Replaced coils, in my case using used Honda VFR 3ohm coils. Vacuum came back up to the normal 18ins. here at 5,000ft.elev. Before condemming coils, unless ohm check across both poles of coil comdems them, check voltage at battery with key on. Then, with key on, that voltage should be the same going to coils. If it is lower, then you have either cruddy connections or grounds, which there are many on these bikes. Other low input voltage is normally due to cruddy connections inside RUN/STOP switch. This switch completes the running circuit. Remove, take apart and soak pieces including switch itself in a cup of Evapor-Rust for a few hours. Remove, wash with water, dry, re-assemble and install on bars.