How does the Petcock operate at WOT?
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How does the Petcock operate at WOT?
So last night i was wondering about my moped problems, and i went back to the fuel system. I was thinking, the petcock takes vacuum to open the valve and let fuel flow.
And i also know that at Wide open Throttle there is little or almost no vacuum. So wont the petcock shut off and stop fuel flow?
That would be why the bike can go for a while at WOT then slow down. It just goes until all the fuel from the bowl is gone then it stops. Once at idle it brings all the fuel back in and it can do it all over again.
So i got a really long vacuum line and hooked it to the petcock, and ran it to my mouth (... ). At WOT when i keep suction on it the bike runs fine, when i let it vent to the air it would do the same thing as usual.
So is my petcock bad? or is this just how they work?
And i also know that at Wide open Throttle there is little or almost no vacuum. So wont the petcock shut off and stop fuel flow?
That would be why the bike can go for a while at WOT then slow down. It just goes until all the fuel from the bowl is gone then it stops. Once at idle it brings all the fuel back in and it can do it all over again.
So i got a really long vacuum line and hooked it to the petcock, and ran it to my mouth (... ). At WOT when i keep suction on it the bike runs fine, when i let it vent to the air it would do the same thing as usual.
So is my petcock bad? or is this just how they work?
94 Elite SR.
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
I've heard the 'usual' way is that when left alone they glue shut, but mine went bad in a way that it never closed all the way, so my carb would leak when the engine was off for a while, like over night. new one fixed that completely, and they're not that expensive (40$ for mine) so if you think it's broken you should just replace it, and do your tubing while your at it, 77 cents a foot for me (plus a 6$ special handeling charge (screw you too motorcity powersports))
Last edited by Ziraya on Wed Sep 03, 2008 4:40 pm, edited 1 time in total.
Are you sure the vacuum hose is good and fits tight? A vacuum leak would cause this same issue. You could try cleaning before buying a valve. You could go borrow a vacuum pump at the auto parts store or buy one at Harbor Freight and apply vacuum and check it that way. I'm pretty spoiled and have all those specialty tools.cf_z wrote:... but mine does not.
so im just gonna assume that my petcocks bad?
is this the way they usually go bad?... or?
Bear 45/70
'83 Aero 80 X 3
'84 Aero 80 X 3
'85 Aero 80
'84 Aero 125 X 2
'84 Aero 125
'84 Aero 125 X 2
'85 Aero 50
'85 Spree
'83 Aero 80 X 3
'84 Aero 80 X 3
'85 Aero 80
'84 Aero 125 X 2
'84 Aero 125
'84 Aero 125 X 2
'85 Aero 50
'85 Spree
I would replace your vacuum tubing and make sure the tank filter is clear before replacing the petcock. Its unusual for one to not open properly - generally they seem to either stick closed (often after storage) or stay open (crud hung up on the valve or damaged diaphragm).
Clive.
Clive.
Lambretta TV-175 (wish I'd never sold it!)
2005 Vento Phantom R4i 125cc (stolen)
1986 Yamaha XC180 Riva
1985 Honda CH150D Elite
1988 Honda SA50 LX Elite
1989 Honda SB50
2007 iScooter 150cc
2006 Roketa 150cc
2006 TNG Venice 50cc
2005 Vento Phantom R4i 125cc (stolen)
1986 Yamaha XC180 Riva
1985 Honda CH150D Elite
1988 Honda SA50 LX Elite
1989 Honda SB50
2007 iScooter 150cc
2006 Roketa 150cc
2006 TNG Venice 50cc
With his symptom of dying at WOT but running at lower speeds I agree, sounds like a bad vacuum hose.Clivester wrote:I would replace your vacuum tubing and make sure the tank filter is clear before replacing the petcock. Its unusual for one to not open properly - generally they seem to either stick closed (often after storage) or stay open (crud hung up on the valve or damaged diaphragm).
Clive.
Bear 45/70
'83 Aero 80 X 3
'84 Aero 80 X 3
'85 Aero 80
'84 Aero 125 X 2
'84 Aero 125
'84 Aero 125 X 2
'85 Aero 50
'85 Spree
'83 Aero 80 X 3
'84 Aero 80 X 3
'85 Aero 80
'84 Aero 125 X 2
'84 Aero 125
'84 Aero 125 X 2
'85 Aero 50
'85 Spree
Also, What would be the harm if it always stayed open? Seems like if the floats were working right it wouldnt mess anything upClivester wrote:Its unusual for one to not open properly - generally they seem to stay open (crud hung up on the valve or damaged diaphragm).
Clive.
94 Elite SR.
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
i dont know, but it seems i have seen people do this before.cf_z wrote:Also, What would be the harm if it always stayed open? Seems like if the floats were working right it wouldn't mess anything upClivester wrote:Its unusual for one to not open properly - generally they seem to stay open (crud hung up on the valve or damaged diaphragm).
Clive.
i have a straight gas line on my old school moped i have have had no problems with that.
"Its not what you ride, its that you ride"
1996--------Honda Elite S-
1991--------Tomos Targa-
And a Bunch of other bikes.
1996--------Honda Elite S-
1991--------Tomos Targa-
And a Bunch of other bikes.
im almost thinking that honda might have put that on there so if you crash the gas wont keep flowing out.
if you lay your bike down the floot would floop over and just let the gas flow and flow and flow and flow. if the petcock is on it, if the bike lays down, the motor dies, gas stop flowing.
if you lay your bike down the floot would floop over and just let the gas flow and flow and flow and flow. if the petcock is on it, if the bike lays down, the motor dies, gas stop flowing.
"Its not what you ride, its that you ride"
1996--------Honda Elite S-
1991--------Tomos Targa-
And a Bunch of other bikes.
1996--------Honda Elite S-
1991--------Tomos Targa-
And a Bunch of other bikes.
thats what i was thinking also. of that if the fuel lines accidently became disconnected that the gas just wouldnt flow out.
it shouldnt effect gas mileage so i think i'll just go ahead and do that if the new vac line doesnt work.
it shouldnt effect gas mileage so i think i'll just go ahead and do that if the new vac line doesnt work.
94 Elite SR.
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
PoliniCorsa+PGlong+28oko+8.44.1+KeliVariator+HiEnergyCoil+Pirrelis
=fast
I'm not exactly sure, but my petcock was stuck slightly open until I just replaced it.
The old one let gas trickle all the time, which, even though it was a little amount coming out, added up and gas would drain out to overflow on the carb.
It wasn't a huge deal because I just unplugged the line to the carb and plugged the end with a screwdriver tip so it wouldn't do that. I had to hook it up every time I wanted to ride.
It did seem to affect my performance though. Once I got the new petcock it was much easier to tune the idle/air and get things working. It also seems to have solved a bogging issue that popped up every once in a while (I assume because the petcock still worked some times, other times it would get stuck closed for a while) So in my experience the faulty petcock did seem to have a negative impact on performance.
The old one let gas trickle all the time, which, even though it was a little amount coming out, added up and gas would drain out to overflow on the carb.
It wasn't a huge deal because I just unplugged the line to the carb and plugged the end with a screwdriver tip so it wouldn't do that. I had to hook it up every time I wanted to ride.
It did seem to affect my performance though. Once I got the new petcock it was much easier to tune the idle/air and get things working. It also seems to have solved a bogging issue that popped up every once in a while (I assume because the petcock still worked some times, other times it would get stuck closed for a while) So in my experience the faulty petcock did seem to have a negative impact on performance.
1984 Honda Aero 50
1986 Honda Spree
1986 Honda Spree