Engine idle and hesitation improves by lifting the tank?

Okay, I bought my [new to me] 2003 ST three weeks ago. After riding for a few days, I thought, "idling too high" (1500 rpms).
So, I grab a screwdriver and drag it back to ~1100rpm.

Erratic idle ... a time or two she dies when left to idle. Pulling away from a stop, it hesitates badly (is that a word?).
Note to self: "No wonder they set it to 1500rpm".

So the other night, I pull the plugs - gorgeous color! (though there's this weird 'drop of oil' on the portion of each plug 'above' the threads - I chalk it up to anti-seize being used).
Okay, plugs are fine.

Last night, I lift the tank to check the air filter. "Looks new" i think to myself. However, as I look at the bottom-side of the tank, i see the tab-retainer (which would retain one or more vacuum hoses and such) empty and I see a couple of hoses from the tank 'on their own'. Looking at an ST1300 microfiche, i see the 'drain tube' and 'breather tube' are the two hoses I [then] secured into the tab-retainer. After replacing the 'looks like new' air filter and securing the top of the air-box, I finagle the tank back into its position and tighten down the 2 retaining bolts.

A couple of hours later, I fire her up to go the the grocery store (and fill her up, as i have Kroger 10c\gallon discount) and notice that, suddenly, she's purring at idle and there is *no* hesitation pulling away from a stop.

(I researched 'erratic idle' and hesitation issues ... i've read there are vacuum lines around the throttle-body area that will affect this, but i did not see any vacuum lines with the tank lifted).

Question to the group:
Is there a vacuum line that was pinched which became "un-pinched" as a result of my raising and lowering of the tank, which would have improved low-rpm running?
.

The routing of the tank lines are specific locations. You could get them pinched if routed in a improper location.

It is possible that the tank vent line was pinched giving you vacum in the tank. This would cause fuel problems. But this would take time to build up the vacum and would be evident when you open the gas cap after riding a bit.
There is also a fuel return line from the pump that could have been pinched.
You have to remove the air box to get at any vacum line on the throttle body.

Basically, yes, it's possible the improper routing and possible pinched lines could cause a problem. Improper venting could be causing fuel starvation.

Place and route lines as appropriate, then re-assess the situation and go from there.

Thanks to both for the quick replies.

Now I'm hesitant to raise the tank in the future for fear I'll pinch a hose

caldercay said:

Thanks to both for the quick replies.

Now I'm hesitant to raise the tank in the future for fear I'll pinch a hose

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If you do it enough times, you'll get it figured out and won't be a problem in the future!

I'm going out on a limb here pitching in, but (insert IMHO and all that) the symptoms you describe are more likely a vacuum leak- not a pinched vacuum hose. I'm betting that you re-seated a hose (perhaps without realizing it) and stopped a leak. Starvation because of a vent hose would be more noticeable when the engine was under demand (the fuel draw becomes more significant). Vacuum leaks are more of a problem at low stress situations where the air entering the vacuum hose is a more significant portion of the air entering the system.

I have had vacuum leak (that I caused) and the bike behaved to the Tee like you describe.

PopJack said:

I'm going out on a limb here pitching in, but (insert IMHO and all that) the symptoms you describe are more likely a vacuum leak- not a pinched vacuum hose. I'm betting that you re-seated a hose (perhaps without realizing it) and stopped a leak. Starvation because of a vent hose would be more noticeable when the engine was under demand (the fuel draw becomes more significant). Vacuum leaks are more of a problem at low stress situations where the air entering the vacuum hose is a more significant portion of the air entering the system.

I have had vacuum leak (that I caused) and the bike behaved to the Tee like you describe.

Click to expand...

Makes sense. I've had similar issues with my cages. Problem is, i didnt mess with any vacuum lines (only the tank's breather and drain tubes).
However, as you stated, I might have, as a side-effect of lifting\dropping the tank, somehow re-seated a vacuum line.