Vacuum advance reving idle way high?

[vcgodinich]

I am new to motorcycles, and am trying to fix up a 79 xs1100 regular (non-special) that a friend gave me.

It starts fine, but as soon as it warms up (5-10 secs) it starts to rev up and up and up. I have to kill it before it red lines. I found that if i disconnect that vacuum advance hose that goes into carb 2 it idles fine. . . as soon as i plug it in, the rpms shoot up. I am plugging it into the right nipple, not on the boot. the one on the carb that is brass.

I had thought i solved this a few months ago. . . i thought it was because i had overfilled the oil, that seemed to fix it then, and now that i have some time to work on it again, it seems the problem is back. Any ideas?

[dbeardslee]

Sometimes out-of-sync carbs will do that. I'd check first to make sure they're set properly. Some members have put small restrictors inside the vacuum advance hose as too big an ID there can cause a similar problem. Still, I'd check the sync first.

[TopCatGr58]

Another thought,

TEST The vacuum advance POT to make sure it's not leaking. IF it's worn and leaking, then you get a vacuum leak and that throws the carbs out of balance, and can also cause it to run the idle up.

IF the vac. pot is holding vacuum properly, then you might also want to check to make sure that the vacuum coming from the #2 carb isn't excessive....a few folks have reported that someone took a drill to the port and reamed it out too big, causing way too much vacuum even from the carb port. vs. the incorrect intake boot port.
T.C.

[XSokieSPECIAL]

I know I'm just a lowly XSive, but if it's revving up to the point of reaching red line, there would have to be enough fuel as well as air to get it there.

Sounds like something in the carbs to me.

[XSokieSPECIAL]

Another thought,

TEST The vacuum advance POT to make sure it's not leaking. IF it's worn and leaking, then you get a vacuum leak and that throws the carbs out of balance, and can also cause it to run the idle up.

IF the vac. pot is holding vacuum properly, then you might also want to check to make sure that the vacuum coming from the #2 carb isn't excessive....a few folks have reported that someone took a drill to the port and reamed it out too big, causing way too much vacuum even from the carb port. vs. the incorrect intake boot port.
T.C.

The port for the vac advance is ported and has NO vacuum at idle unless the carb is jacked.

[xssiveone]

The port for the vac advance is ported and has NO vacuum at idle unless the carb is jacked.

In light of this, maybe it's connected to the wrong spot. Check to be sure it's connected to the carburetor, and not the rubber manifold.

[XSokieSPECIAL]

[QUOTE=vcgodinich;237010] I am plugging it into the right nipple, not on the boot. the one on the carb that is brass.

The first post.

[MrOzz]

I had a very similar problem when I first picked up my XS. Cleaning the carbs worked. I would also make sure that you throttle cable is not caught up on anything.

Ozz

[xssiveone]

[QUOTE=XSokieSPECIAL;237040]

I am plugging it into the right nipple, not on the boot. the one on the carb that is brass.

The first post.

Ooops....

[vcgodinich]

Solved

The problem actually turned out to be simple.


MrOzz was right, thank you!

I had routed the throttle cable incorrectly, so on the center stand if you threw the handle bars to the right, it would bind the cable, allowing it to just pull in, not out. hence the up and up and up.

Messing with the hose for the advance, i would move the bars back to center, fixing the bind. I never thought that moving the handlebars would cause the engine to rev!

Thanks everyone for the tips though!

[XSokieSPECIAL]

The problem actually turned out to be simple.


MrOzz was right, thank you!

I had routed the throttle cable incorrectly, so on the center stand if you threw the handle bars to the right, it would bind the cable, allowing it to just pull in, not out. hence the up and up and up.

Messing with the hose for the advance, i would move the bars back to center, fixing the bind. I never thought that moving the handlebars would cause the engine to rev!

Thanks everyone for the tips though!

Follow the yellow brick road.

[dbeardslee]

Good catch, Ozz.

[MrOzz]

Glad I could help.


Ozz