Bad petcock?

[wilsonsandy07]

82 Gs1100ez

Long Time no post…

riding seasons back and so are my problems lol

just want to confirm with an issue, rebuilt/cleaned carbs over the winter and the bike ran fine with an aux gas tank gravity fed. Slapped the tank on, won’t run in ON. Runs in prime. Thing is I checked the petcock while it was off the bike with a hose and it pulled fuel when sucked.

anything else I could be overlooking? As far as I can tell there’s no other vacuum leaks of any kind on any of the boots, airbox, etc.

[1978GS750E]

Check the simple stuff first! Is it connected to the correct vacuum port on the carbs? Is there a hole in the hose? Do you have vacuum on the hose when it is not connected to the petcock with the bike running?

[rphillips]

A guy came by a few yrs back with the same problem as you. Told him only thing I could imagine was a vacuum leak. Quick look found his 40 yr. old vacuum hose had cracked right where it plugged onto the pet cock and fell off. trimmed and reinstalled and all was good. You already said you had sucked on the petcock vacuum inlet, and it was working. Like with him, first be very sure you have no kind of vacuum leak between carb and petcock. Other vacuum leaks on boots nor air box should have no effect on pet cock... of course my opinion. Yes, plus what he ^^^^^ said.

[wilsonsandy07]

I did put a brand new hose on, but looking at it now it’s slightly long and forms a bit of a horseshoe. I’ll trim it down a bit and see if that helps at all

[wilsonsandy07]

so took off the petcock, and tested it again, could pull any fuel with a hose. chalking it up as bad and ordered a new one.

[wilsonsandy07]

UPDATE

changed the petcock with a brand new OEM one, and seemed to work great. tested it and then installed and rode perfect for 30-40 mile commute. 12 hrs later (albeit in pretty cold temp about 35 degrees) started right up but about 5 miles down the road started starving. made sure i still had gas, ended up having to ride in PRIME all the way home. tried multiple times to switch back to ON but everytime it would start to starve.

potential for a bad oem out the box is there but it shouldnt have worked the first ride if so,

my tank is clean, i dont have an inline fuel filter, and i just thoroughly cleand and rebuilt my carbs. also the bike runs perfevtly in prime so that eliminates bad carbs.

going to change my vacuum line again just in case, but i dont have high hopes for it as nothing is wrong with the line itself.

[rphillips]

2 things... 1st. that seems really strange, both old and new with the same very unique problem, almost impossible...2nd. I have no clue.

[wilsonsandy07]

2 things... 1st. that seems really strange, both old and new with the same very unique problem, almost impossible...2nd. I have no clue.

were on the same page

[dgates1]

Maybe the nipple on the carb for the vacuum hose is leaking/loose??

Testing the petcock in the on position while you suck on the vacuum hose will tell you if the "new" petcock has failed... it either works, or it doesn't.

[rphillips]

Almost David, but you'll need to know and be sucking the same amount of vacuum as the carbs do, and I have no clue how much that is.

[wilsonsandy07]

Maybe the nipple on the carb for the vacuum hose is leaking/loose??

Testing the petcock in the on position while you suck on the vacuum hose will tell you if the "new" petcock has failed... it either works, or it doesn't.

Definitely not loose, but i suppose it coul possibly be leaking. still doesnt explain why it worked just fine for the first ride though and then stopped working. ill let yall know what happens with the new hose for now got no choice but to run it in prime. just gotta remember to switch it back when im off and gotta be a little more weary of my fuel level but besides that she runs pretty good

[wilsonsandy07]

Well i replaced the line with another brand new thicker walled line and still no luck. Im definitely running lean but since its running fine in prime i dont think that would change at all. Maybe its lean enough where the vacuum just isnt pulling quite enough to keep it alive?

besides that other than the OEM valve being bad out of the box im out of ideas

[rphillips]

Only 2 possibilities I can imagine. 2 faulty pet cocks and both doing the same thing, or insufficient constant vacuum. I can't imagine a lean carb lessening vacuum enough to affect pet cock, but not sure. Odd ball thought, disconnect vacuum hose from petcock, gently suck and blow on it, just to be sure something isn't restricting flow in either direction from the carb.