Fuel petcock questions
06-08-2020, 06:29 AM
#1
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Fuel petcock questions
Hello,
I'm trying to tell if everything is working properly. Could you please tell me:
1- if you take the vacuum tube out of the petcock and push/pull air into the carb, should there be any resistance?
2- if you take out one of the fuel lines out of the petcock and apply vacuum to the petcock, how long should the fuel be flowing until stopping? Is it normal for the fuel to flow for 30-60 seconds?
thanks!
I'm trying to tell if everything is working properly. Could you please tell me:
1- if you take the vacuum tube out of the petcock and push/pull air into the carb, should there be any resistance?
2- if you take out one of the fuel lines out of the petcock and apply vacuum to the petcock, how long should the fuel be flowing until stopping? Is it normal for the fuel to flow for 30-60 seconds?
thanks!
06-08-2020, 12:08 PM
#2
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Location: Bisbee, AZ
Posts: 1,874
Hello,
I'm trying to tell if everything is working properly. Could you please tell me:
1- if you take the vacuum tube out of the petcock and push/pull air into the carb, should there be any resistance? No
2- if you take out one of the fuel lines out of the petcock and apply vacuum to the petcock, how long should the fuel be flowing until stopping? Is it normal for the fuel to flow for 30-60 seconds? I would think that as soon as vacuum has ceased the valve would close.
thanks!
I'm trying to tell if everything is working properly. Could you please tell me:
1- if you take the vacuum tube out of the petcock and push/pull air into the carb, should there be any resistance? No
2- if you take out one of the fuel lines out of the petcock and apply vacuum to the petcock, how long should the fuel be flowing until stopping? Is it normal for the fuel to flow for 30-60 seconds? I would think that as soon as vacuum has ceased the valve would close.
thanks!
06-08-2020, 01:06 PM
#3
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Thanks!
Yes, it does have a number of issues:
1- after longer rides my crotch smells like gas, and then a few days after the petcock region keeps smelling like gas (my bike has the petcock in front of the saddle)
2- it's been requiring a fraction of throttle to cold start on 1st try, apart from full choke (until last year it only took full choke)
3- when it's very hot and the gas level is low the bike sometimes stalls at idle
4- at low rpm, especially when very hot and at mid to low gas levels it does some jerking and carb farts (before it only did that very rarely)
5- rather frequent exhaust backfire when hot and rolling with the throttle off after high rpm (before it only did that very rarely)
To me this suggests that either the petcock doesn't provide enough flow with low rpm/low vacuum (and even less after it gets hot), and/or the carbs are starting to get clogged. The bike runs fine otherwise, but I'll also buy a starting spray to rule out false air (I know many swear by it but I won't spray WD40 anywhere at the engine or intake).
Starting with the easiest, I begun checking the petcock. You are correct- found a video of a vacuum petcock demo and indeed it closes as soon as you stop the vacuum. Mine doesn't- a few seconds of vacuum was all it took to get gas all over myself.
Took the petcock apart and it did have some very tiny cracks on the edges of the rubber and limestone like deposits all over. I had bought a repair kit last year when it had some stalling issues due to a moth cocoon inside the tank vent tube. Now that kit has somehow evaporated by sitting in a box so I've just ordered another one.
No fuel in the oil, no indication of leaky carbs, no visible leaks anywhere.
If anyone wants to suggest any additional checks please say. The bike will stay offline and with a fully empty tank for at least 1 week until the petcock repair kit arrives, and hopefully I get it right the first time.
Man I wish this bike was FI... I have done a number of major repairs over the years, but apart from refitting the choke cable on a chainsaw, I have zero experience with carbs.
Yes, it does have a number of issues:
1- after longer rides my crotch smells like gas, and then a few days after the petcock region keeps smelling like gas (my bike has the petcock in front of the saddle)
2- it's been requiring a fraction of throttle to cold start on 1st try, apart from full choke (until last year it only took full choke)
3- when it's very hot and the gas level is low the bike sometimes stalls at idle
4- at low rpm, especially when very hot and at mid to low gas levels it does some jerking and carb farts (before it only did that very rarely)
5- rather frequent exhaust backfire when hot and rolling with the throttle off after high rpm (before it only did that very rarely)
To me this suggests that either the petcock doesn't provide enough flow with low rpm/low vacuum (and even less after it gets hot), and/or the carbs are starting to get clogged. The bike runs fine otherwise, but I'll also buy a starting spray to rule out false air (I know many swear by it but I won't spray WD40 anywhere at the engine or intake).
Starting with the easiest, I begun checking the petcock. You are correct- found a video of a vacuum petcock demo and indeed it closes as soon as you stop the vacuum. Mine doesn't- a few seconds of vacuum was all it took to get gas all over myself.
Took the petcock apart and it did have some very tiny cracks on the edges of the rubber and limestone like deposits all over. I had bought a repair kit last year when it had some stalling issues due to a moth cocoon inside the tank vent tube. Now that kit has somehow evaporated by sitting in a box so I've just ordered another one.
No fuel in the oil, no indication of leaky carbs, no visible leaks anywhere.
If anyone wants to suggest any additional checks please say. The bike will stay offline and with a fully empty tank for at least 1 week until the petcock repair kit arrives, and hopefully I get it right the first time.
Man I wish this bike was FI... I have done a number of major repairs over the years, but apart from refitting the choke cable on a chainsaw, I have zero experience with carbs.
06-09-2020, 05:29 AM
#4
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SuperBike
Join Date: Sep 2010
Location: Bisbee, AZ
Posts: 1,874
I too wish the bike was FI.
One thing at a time. Rebuild the petcock and see if that helps. Some of the issues you stat sound like a lean condition. Not unlike what others have reported with a failing
When my crotch smells like gas it’s usually because of something I ate.
One thing at a time. Rebuild the petcock and see if that helps. Some of the issues you stat sound like a lean condition. Not unlike what others have reported with a failing
When my crotch smells like gas it’s usually because of something I ate.
06-19-2020, 08:07 AM
#5
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Cleaned the housing ends with #1000 and #1500 sandpaper as it was no longer sitting entirely flat due to deposits- maybe that was also a factor.
Bad news- the rebuild kit was junk, the parts were smaller than OEM so neither the fuel or vacuum offered more than a partial seal.
Good news- after cleaning the old rubber with some hand soap and water it was good to reuse. Bike started quickly with NO throttle applied, after sitting for almost one month- this hasn't happened since last year. Didn't ride it yet, but maybe the rest of the issues are also solved.
Still, the old rubber isn't in great shape. Can anyone confirm to fit a certain brand/model of rebuild kits? Or suggest an universal replacement vacuum petcock?
It seems that those honda bastards haven't ever offered a rebuild kit for this petcock, and the cheapest new OEM petcock I could get (incl shipping and tax) would be around 250USD, which would be beyond absurd to pay for. A Chinese scooter petcock retails for 1-2USD.
Bad news- the rebuild kit was junk, the parts were smaller than OEM so neither the fuel or vacuum offered more than a partial seal.
Good news- after cleaning the old rubber with some hand soap and water it was good to reuse. Bike started quickly with NO throttle applied, after sitting for almost one month- this hasn't happened since last year. Didn't ride it yet, but maybe the rest of the issues are also solved.
Still, the old rubber isn't in great shape. Can anyone confirm to fit a certain brand/model of rebuild kits? Or suggest an universal replacement vacuum petcock?
It seems that those honda bastards haven't ever offered a rebuild kit for this petcock, and the cheapest new OEM petcock I could get (incl shipping and tax) would be around 250USD, which would be beyond absurd to pay for. A Chinese scooter petcock retails for 1-2USD.
06-20-2020, 07:40 AM
#7
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Thanks!
Yes, it does have a number of issues:
1- after longer rides my crotch smells like gas, and then a few days after the petcock region keeps smelling like gas (my bike has the petcock in front of the saddle)
2- it's been requiring a fraction of throttle to cold start on 1st try, apart from full choke (until last year it only took full choke)
3- when it's very hot and the gas level is low the bike sometimes stalls at idle
4- at low rpm, especially when very hot and at mid to low gas levels it does some jerking and carb farts (before it only did that very rarely)
5- rather frequent exhaust backfire when hot and rolling with the throttle off after high rpm (before it only did that very rarely)
Yes, it does have a number of issues:
1- after longer rides my crotch smells like gas, and then a few days after the petcock region keeps smelling like gas (my bike has the petcock in front of the saddle)
2- it's been requiring a fraction of throttle to cold start on 1st try, apart from full choke (until last year it only took full choke)
3- when it's very hot and the gas level is low the bike sometimes stalls at idle
4- at low rpm, especially when very hot and at mid to low gas levels it does some jerking and carb farts (before it only did that very rarely)
5- rather frequent exhaust backfire when hot and rolling with the throttle off after high rpm (before it only did that very rarely)
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