what is the purpose of the petcock?

why cant i run the fuel line directly to the carb?

Re: what is the purpose of the petcock?

you could.. but how to shut off fuel?

a petcock is a valve .. normally has three setings, on, off and reserve.

"On" or "Main" means fuel is entering a short tube that extends up into the tank a few inches..

When fuel level drops below the top of that tube, you must switch to "Reserve" to drain the rest of the tank (gives you time to get to a gs station). Reserve fuel feeds into a hole on the petcock body.

Off is self explanitory .. the Main tube and Reserve hole are protected with a wire mesh screen.

Re: what is the purpose of the petcock?

on my suzuki fa 50 there is only off, prime, and reserve. no off. so the petcock does not regulate the amount of fuel delivered to the carb?

Re: what is the purpose of the petcock?

nope.. a petcock doesn't regulate flow.

Most carbs have a float bowl and a float (operates much like a like a toilet bowl, where water enters full blast)

fuel travels through the fuel hose and enters a hole in the float bowl (called a float needle valve). The float rises and closes the valve with a "float needle".. so fuel shuts off when it reaches the proper level.

float level partly determines how much fuel is mixed with the air streaming through the carburetor..

Re: what is the purpose of the petcock?

Leon Swarmer /

"off, prime, and reserve. no off" HuH?

on, prime and reserve???

Generally the petcock does not regulate the flow. It is either on (from main tank or reserve) or off.

The off postition is used mainly for parking the bike so you don't lose all the fuel if the carb develops a problem.

On your bike the Prime setting adds more gas to the carb for cold starting. most peds just use a choke and decrease airflow to increase the fuel air mix.

Leon

Re: what is the purpose of the petcock?

My motorcycle only has on and reserve.The petcock is vacuum operated.if the engine isn't running to create a vacuum,no gas fows through the petcock.Things have come a long way.The '66 Triumph Bonneville I had a looong time ago,would drain the whole tank of gas out onto the ground,if you forgot to turn the petcock off,because the carbs leaked so bad.And even if you did turn the petcock off,you would still loose a few ounces,because the petcock itself leaked.Then there was the oil.It leaked oil out of everything but the headlight,and that didn't work,because it was made by Lucas.You guys now don't realize how lucky you are.

Re: what is the purpose of the petcock?

on the side of the bike it says to never run it on the prime position, but that is the only way it will run. i want to just bypass it all together and run a line directly to the carb from the tank.

Re: what is the purpose of the petcock?

im not familiar with your bike.. which is a.. ??

if you don't know why it works that way or if it's supposed to work that way, find out.

And if it's broken, fix it..

you do want a reliable bike that gets you there and back, no?

Re:OT the purpose of the petcock?

Leon Swarmer /

OK yea, Then who was in my garage today adjusting the valves on a 73 Triumph GT6. The carbs weren't leaking because they've been disconnected for months.

Headlight switch is labeled off/dim/flicker.

Leon

Re:OT the purpose of the petcock?

PRIME = ON

Reserve and off are what they are...

The only regulation of fuel flow is in the bowl. That's where the float comes into play.

The regulation of fuel going into the motor is dependent on, A. Size of the main jet in the carburator. B. Size of the carburator itself. C. The size of the inside diameter of the intake manifold.

The petcock is there because it's VERY BAD to store your moped with the fuel constantly ON. You could cause leakage in the carburator, and also corosion can get into the carburator due to condensation developing if left for a long period of time.

When storing your bike or leaving it over night in a hot/cold climate, turn the petcock OFF and let it run out of gas on it's own. Then in the morning when you go to kick it over, turn the petcock to PRIME or ON and flick the choke ON. It should start right up in a couple of cranks.

Go nuts.

DannyMoped07

Re:OT the purpose of the petcock?

Danny I agree with you on the petcock being that prime and on are the same.

Although I disagree with "and let it run out of gas on it’s own". This is not only bad for the motor (from what I have been told by my mechanic every time I run out of gas, and he comes to the rescue). It is actually worse to leave the carburetor empty of gas. Gas by its nature repels water, leaving gas in the bowl will in fact keep rust from occurring in the carb or anywhere else for that matter. The lack of gas causes condensation (water) to form on the inside of the carb and will cause oxidation (rust) of all the parts. If you have ever noticed when a metal gas tank starts to rust it does so from the top down, not the other way around, that is because there is less gas at the top of the tank more often, thus allowing condensation and oxidation to occur more often.

If your going to store something use stable, either that or go and start it about once a month and let it idle for about 15 minuets. Either method will keep rust and gumb (caused but the gelling of gas) from building up in your carb.

Re:OT the purpose of the petcock?

This is true, gas does repel water, however going from hot/cold situations is what creates condinsation. My old Kreidler used to build up a ton of condinsation in the fuel every fall/winter because of the extreeme weather changes from riding it around in the snow all day to parking it in the warm cellar. I had to drain my tank and clean the carb 3 times last year and eventually resorted to using a small amount of dry-gas to add to my 40:1 mix.

Gas may repel water, however it CAN mix with water, and water molocules can become suspended in the gasoline. hence why we have dry-gas (ethanol).. this bonds to the water creating a burnable alcohol which thus mixes more thuroughly with the gasoline.

This is why most moped gas-tanks rust from the BOTTOM of the tank, inside-out. The condonsation builds up, it's parked all winter, and the water trickeles to the bottom through the gas and sits on the bottom of the tank. It can only take a couple months for gasoline to lose it's octane level thus losing it's water-repelling properties. During this time the tank is extremely suseptable to rusting. Hence why a full gas-tank can still rust.

Sorry to go on a rant about this. I guess I wasnt very clear with my earlier explanation. Not like you have to worry about condinsation in the summer time anyway! lol.

Go nuts.

DannyMoped07

Re:OT the purpose of the petcock?

Ok from the sounds of it we are reading from the same book Danny, but from different ends. Here is the Short Short version of the book

Short term, Gas is better then empty (1day-1month max) Keeps water out

Long term, Clean and Dry is best, or drygas/stable if can't dry. (1month or more)

Although if you live where it never gets cold (unlike here) you can drive it every day and never worry one way or the other.

Would you agree Danny?

Re:OT the purpose of the petcock?

Lol. Way to make the ends meet Mike :). In all the thinking about what I was going to say I missed out on the particulars. Darn ADD.

Where in Maine are you from? Feel free to add my AIM handle to your buddy list "DannyMoped07"

Re: what is the purpose of the petcock?

the bike is an 84 suzuki fa50, and it is a beater. i just want to get it to run good. right now it is cutting out at full throttle and high speeds because of lack of fuel i think. it may be ignition related as well, im not sure. so i am going to bypass the petcock and run fuel directly to the carb and cap the vaccum line. i will let you guys know what happens.

Re: what is the purpose of the petcock?

My Kreidler used to do that, turns out the points went. Get that checked out.

Re: what is the purpose of the petcock?

no chit.. my Kriedler MP9 used to do it too. After the engine was modified a bit it was definately running out of gas.

Eventually traced it to the float valve seat orifice being too small... the valve in the Bing was removable.. you could press it out. I'm not positive but i think i remember switching it with a larger one from another Bing..

Re: what is the purpose of the petcock?

Wierd. Lol. I had the MP9 too, i brought it to my dealer and he said, well, i can either fix it for 300 or give you 100 on trade in, because they dont make the points for them anymore... So i got a TTLX. Lol.

DannyMoped07

Re: what is the purpose of the petcock?

i resurrected mine from the grave and then drove it to death... finally fried the bottom end .. left the bike laying around for a long time (parts? hehe) and dumped it.. layed off moped for a few years. Found another moped and needed generic parts and regretted dumping the MP9

comfortable, well engineered bike.. crappy carb .. shuddered bad shifting to 2nd..

Re: what is the purpose of the petcock?

Ok, yours shuddered too! Lol.. It must've been the way the bikes were constructed. I know i re-built my carb once when i had it, re-did the exhaust, and changed the tranny fluid 2 or 3 times. It would work really nice for a few miles and then shudder like crazy till the next tranny change.

Re: what is the purpose of the petcock?

i knew little about it and still know almost nothing about wet clutches and tranny fluid and all that.... but from the looks of the rest of the bike (and the whole line of Kreidlers, including fine race machines) i have no doubts that Kriedler knew what they were doing.. engineering was impressive. I bet the factory coulda cured the shifting thing.

btw, Kriedler has made bikes up to this day.. but the Kriedler name was sold to a far east (Taiwan?) company a few years ago..

Re:OT the purpose of the petcock?

Whats a GT6?

Re:OT the purpose of the petcock?

I agree.Never leave a carburetor empty for any length of time.Or a gas tank.If you are going to store it for several months,keep the tank full,and use some type of fuel stabilizer.Jerry.

Re:OT the purpose of the petcock?

Leon Swarmer /

Sorry should have been an OT warning there. it is a two seater sports car. 2 lilter straight 6 OHV Twin carbs. Looks like a Triumph Spitfire with a steel fastback roof.

Leon

Re:OT the purpose of the petcock?

GT6

Re:OT the purpose of the petcock?

Leon Swarmer /

Hey, you even got the color right..just wish mine looked that good. But the pic doesn't show the fuel leaks/oil leaks, brake fulid leaks.

Mine alsodoesn't have the badge bar and the stock wheels

Leon

Re: what is the purpose of the petcock?

one nice thing about the fuel petcock is the reserve setting, without it, yud never know your about out of gas. when the ped dies on the run or on position, you know your boput out of gas, the reserve gives you the added time to get to a gas station or back home

Re: what is the purpose of the petcock?

Leon Swarmer /

Just like the real old VW bugs.

Leon

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