While you're waiting, do the bypass. It's a 5 minute job with the plastic off and 5 minutes to un-bypass it. Don't forget to plug the vac. hose.
After hour ride, bike starts stuttering or missing.
- Thread starter Winfried
- Start date
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- Mar 18, 2006
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- Ilkley, W Yorkshire, UK
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- 2013 ST1300 A9
- 2024 Miles
- 000679
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Check the 4 vacuum tubes that are used for balancing the carbs. If they are leaking air, that can cause stuttering behaviour, and the tubes themselves have been known to split after many years (Or so I have read on these forums). Behaviour has been reported to change as the engine heats up and the tubes become more flexible. 3 tubes are capped, the 4th is the rear right which is connected to the fuel shut-off valve instead.
I am having the same issue with my '01 with 33k on it. I fueled up but didn't get the gas cap on right initially. I smelled gas after two miles and discovered the cap issue and fixed it. Later rode about 70 miles and she starved for fuel and died. After sitting a while I managed to get her to start again, a cylinder at a time as described above. Had two more instances on the way home where she nearly died but managed to idle okay on the shoulder and then would run good. I have a new fuel filter and petcock rebuild kit. I'm not clear from the discussions above if I should test by riding until she falters, then loosen the gas cap and see if anything changes?
Slydynbye
Will ride for Pie
Loosening the cap will test for a clogged cap or vent hose.
If it's the vacuum fuel cut-off then a bypass will quickly solve it.
Many including me have bypassed the fuel cut-off permanently. The rebuild kits are often unsuccessful.
Thanks for the info! So get this--Before I tore into the bike I thought I would ride it and try to duplicate the problem so I could do the gas cap test. I had the gas cap on tight but the "gas" label on the cap was upside down in the 6 o'clock position. I switched the cap 180 degrees, aired up the tires, and then drove it like I stole it for nearly two hours and no issues. Needless to say, I'm going to hold off until something happens down the road.
Slydynbye
Will ride for Pie
Sounds good but..
Familiarize your self with the vacuum fuel cut-off bypass procedure and make sure you have the tools with you or bypass now and never look back. One less thing to go wrong in my Book.
I did mine in the middle of Death Valley. Just Sayin.
Ok, will do the fuel bypass, run it without for a while and see if the problem repeats before I fix the old one. I assume it's for safety/not flooding the carbs with the bike on but not running (I can hear it come on with the key to on)?
It cut out a couple times last night again, this time with the tank nearly empty, so it doesn't seem to be a vacuum in the tank issue. It doesn't happen with sustained highway speed during the day (it's been about 80 degrees pretty consistently), but it does happen when it's cooler at night. I'm able to start it with choke on after about 10 sec (even before stopping, just pull in the clutch, thumb the choke, and start it), and after the second time it happened, I reduced speed and limped home without incident, so flow does seem to be a factor, as does ambient temp. If the bypass doesn't work, I guess it's on to the fuel pump.
It cut out a couple times last night again, this time with the tank nearly empty, so it doesn't seem to be a vacuum in the tank issue. It doesn't happen with sustained highway speed during the day (it's been about 80 degrees pretty consistently), but it does happen when it's cooler at night. I'm able to start it with choke on after about 10 sec (even before stopping, just pull in the clutch, thumb the choke, and start it), and after the second time it happened, I reduced speed and limped home without incident, so flow does seem to be a factor, as does ambient temp. If the bypass doesn't work, I guess it's on to the fuel pump.
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the bypass is there to shut fuel off from the gas tank in a tip over. I had a tip over and no fuel escaped with cut valve removed. Many carb bikes don't have one.
Andrew Shadow
Site Supporter
I don't think that it has anything to do with that. From what I recall, it was in response to the EPA mandated sealed fuel systems and the new problems that that created.
ST1100Y
Site Supporter
I'd start with a visual of the cap vent line, folks manage to unintentionally flip the cap around during refills and twist/kink the hose in the process...
Probably EPA chicanery.
Anyway, pulled the petcock, waited for it to cool off out there, and went for a spirited ride. 30 min and no hiccups, despite continuous high rpm cruising (finally dropped to 4th just to see if I could increase the fuel flow enough to get it to starve itself out).
On a side note, I applied some dynamat extreme to the plastic handlebar cover today as well, and I think I solved the resonance problem there at mid to high rpm. There's a ton of room under the cover, and the dynamat is only a couple mm thick. Works way better than the foam I originally stuffed under it.
Took apart the valve today, the air side diaphragm is clearly torn, not surprising it was failing, I'm actually surprised it worked at all.
Got a better cap for the vacuum line, when I removed the makeshift one, there was some fuel in it--is that normal, or a sign of another failure to come soon?
Got a better cap for the vacuum line, when I removed the makeshift one, there was some fuel in it--is that normal, or a sign of another failure to come soon?
The vacuum hose is the one going to the carb (#3) and that's the one that should be plugged/capped after removing the shutoff valve.
get all the fuel out and monitor it. Since its a vacuum line it shouldn't have any fuel in it, but because it was previously attached to the valve with a split in the diaphragm fuel would be able to enter the vacuum line because of that. It may have been there before and you just didn't notice it.
BTW, when the diaphragm tears and allows fuel to enter the vacuum line, it sometimes flows into the #3 cylinder through the carb as raw fuel and can foul the plug over time. Pull the plug and take a look at it.
Plugs are new, I replaced them recently, and the old ones looked fine. The torn side was the vacuum side, not the fuel side, looks like both sides seal in their respective chambers. There is a small pressure equalizer in the middle chamber that vents to atmosphere, so it doesn't surprise me that a leak on the fuel side can be smelled.
Regardless, replaced both sides, and reinstalled the valve. I tried turning the bike on with only the vacuum line connected, to see if the valve opens (it does, although not very much), then put the whole thing back in and went for a ride. Seems to function, although there's little enough time/miles on it to yet claim success. I will say that the old one was obviously broken, and the new pieces seemed to go together without the misshapen business talked about in the write up, so we'll see how it goes.
Regardless, replaced both sides, and reinstalled the valve. I tried turning the bike on with only the vacuum line connected, to see if the valve opens (it does, although not very much), then put the whole thing back in and went for a ride. Seems to function, although there's little enough time/miles on it to yet claim success. I will say that the old one was obviously broken, and the new pieces seemed to go together without the misshapen business talked about in the write up, so we'll see how it goes.
