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Can defective Vacuum petcock cause this? [GS850G]

Redman

Redman

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Seemed to start and run fine, got about 4 miles and motor just slowly died off in a matter of a couple seconds. Would not restart, so I pushed off to side of road. Several minutes later it did start, so I headed back home. Died out again before I got home. After a few minutes I did get it restarted and got home.
When it dies out it seems like a fuel problem becuse of how it slowly dies out. Will try again and next time try putting petcock to prime when it starts to die out. BUt anyway, does this sound it could be a problem with the fuel petcock? I have all new intake rubbers so no vacuun leak there.
Do you think I should try a petcock rebuild kit?
As a test of any tank venting or blocked fuel screen: I pulled hose to carbs off the petcock and put on a hose to a gas can, put petcock on PRI, and gas ran out solid till my 2 gallon can was full without slowing down, so I dont suspect any problem with the tank venting or the fuel filter on the petcock.
 
Re: Can defective Vacuum petcock cause this? [GS850G]

The next time you go for a ride, switch the petcock to prime as soon as you have the engine running. If you can ride for ten minutes and the problem is gone, then it is the petcock diaphram or its vacuum line leaking. I would not mess with a rebuild kit. There are those that disagree with me, but I think they are a complete waste of money and time. I would rather spend the extra couple bucks, buy a new petcock and forget having to fight it. From the experiences related on the forum with problems in rebuilding and fighting with petcocks, it isnt worth it to me to spend two weeks pulling my hair out and walking home everytime I try to go for a ride to save $20.
Earl


REDMAN said:
Seemed to start and run fine, got about 4 miles and motor just slowly died off in a matter of a couple seconds. Would not restart, so I pushed off to side of road. Several minutes later it did start, so I headed back home. Died out again before I got home. After a few minutes I did get it restarted and got home.
When it dies out it seems like a fuel problem becuse of how it slowly dies out. Will try again and next time try putting petcock to prime when it starts to die out. BUt anyway, does this sound it could be a problem with the fuel petcock? I have all new intake rubbers so no vacuun leak there.
Do you think I should try a petcock rebuild kit?
As a test of any tank venting: I pulled hose to carbs off the petcock and put on a hose to a gas can, put petcock on PRI, and gas ran out solid till my 2 gallon can was full without slowing down, so I dont suspect any problem with the tank venting.
Click to expand...
 
Be sure you don't have a vacum leak, on the line from the #2 carb & the fuel valve. A small leak here can cause problems
 
your tank vent could also be blocked in some manner. OPEN THE GAS CAP WEHN IT HAPPENS AND TRY TO START THE BIKE.
 
sounds like mine sometimes, only it happens when I run it out for any real distance (i.e. 70-75 mph for a mile or so, still hard on the throttle) it'll start to just barely run, no gas to give it on the throttle, but if I wait it'll come back. I'm pretty sure it's just a fuel delivery problem, but I think I know mine's in the filter or petcock somewhere as I can see the plastic/paper filter trying to refill fast enough.

I would suggest it might be in your fuel lines after the tank/petcock/filter, maybe in the carbs or floats?

but then again, I'm a chemist, not a mechanic!! good luck!
 
UPDATE
- Tested gas tank vent by running out a lot of gas, it didnt even slow down, so no problem there.
- Inspected the vacuun line to #2 carb, inspected closely with a good light, looked at both sides, twisted back and forth and around, looks good.
- Went for ride today, took ignition tester and volt-ohm meter with me for a quick check of ignition if/when problem reoccured. Started out on PRI, no problem in 4-5 miles, switched to ON position and kept on going for for another 10 or so, including some stop-n-go like yesterday. No Problem. Is 48 degF today, not 72 like yesterday when it slowly died out after 4-5 miles, twice.
- - Did notice one thing though, when I got back and parked it, a few drops of oilly gas dripped down the front of air box from area of #2 intake boot. Not from others, just #2, and not out airbox drain (doesnt have a tube).
Seems like if petcock was defective such that it was letting gas run into that vacuum line and into #2 carb throat, that would cause more problems than what I am having.
- So, I quess I'll just keep those test instruments with the bike and see how it goes, unless anyone has any further insight. (suppose to be cold-wet and maybe snow again in few days, so I have time).
Idea of having another fuel filter that can be visually monitored sounds like good idea.
 
You may want to try this, and maybe not. get some hose, the same size as the fuel hose, and another, the same size as the vacum line. attach the hose to the outlet of the fuel valve and put the other end in a pan, bucket, or jug. Attach the vacom hose to the vacum outlet of the fuel valve. With the fuel valve in the pri. position, lightly suck on the vacum line, it takes little vacum to operate the fuel valve. If everything works properly, the fuel will flow, you won't get any gas in your mouth, and you won't feel any vacum leaks, while sucking on the line. I know it sounds terrible, but ti really isn't that big of a deal.
 
Okay, I see, test operate the petcock vacuum operation by producing the vacuum yourself.
Do we know how intake vacuum compares to what a person can produce? (oh, oh, possibility of some joking here)
Sounds like maybe you have done this, have you?
 
Required vacuum is a pound or two. If you can drink a milkshake through a straw, you may consider yourself to be excessively vacuum endowed. :-)

Earl

REDMAN said:
Okay, I see, test operate the petcock vacuum operation by producing the vacuum yourself.
Do we know how intake vacuum compares to what a person can produce? (oh, oh, possibility of some joking here)
Sounds like maybe you have done this, have you?
Click to expand...
 
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