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Discussion Starter · #1 ·
Because the fuel is flowing into the cylinder and past the rings to the oil when the bike is cold, I am guessing the problem is the float. But reading a lot of forums folks also recommend that the petcock could be the problem. I don't understand what does the petcock have to do with the above issue, does the petclock have any restrictions on the volume? My understanding of the petcock functionality is that it's just is to just ration fuel, and on occasion shutoff flow.

Please let me know if I am thinking about it incorrectly.
 

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Let's make it easy and use 3 positions of a petcock:
1. ON
2. OFF
3. PRI [prime]

There is a coin size rubber button with 4 holes in it, just like a button on a shirt. Just make those 4 holes larger in the round rubber coin. On the face of the main petcock, is a blank, or no hole drilled for any flow. The button gasket can be installed in any position so it's not confusing, no complicated to make a one way sealing gasket fit the same using either side.

The button is molded in a way to have those 4 holes look like an oring raised at those 4 holes. When the handle is installed, it squeezes those 4 raised protrusions and seals off each of the 3 holes. By moving the lever to ON from OFF, it eventually tears the raised oring(s). Because the holes of the rubber gasket are so big and close to each other, that tear will flow for either ON or PRI and leak in the crankcase that way.

The Float on the other hand can sit on its side, [side stand down] lower the one side of the float and with 14.7 pounds of pressure on top of the gas in the tank, you have that pressure on the float, where the float itself with the float needle are not damage, needs no adjustment, but points to a petcock constantly on with a cut button gasket.
 

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Discussion Starter · #4 ·
Let's make it easy and use 3 positions of a petcock:
1. ON
2. OFF
3. PRI [prime]

There is a coin size rubber button with 4 holes in it, just like a button on a shirt. Just make those 4 holes larger in the round rubber coin. On the face of the main petcock, is a blank, or no hole drilled for any flow. The button gasket can be installed in any position so it's not confusing, no complicated to make a one way sealing gasket fit the same using either side.

The button is molded in a way to have those 4 holes look like an oring raised at those 4 holes. When the handle is installed, it squeezes those 4 raised protrusions and seals off each of the 3 holes. By moving the lever to ON from OFF, it eventually tears the raised oring(s). Because the holes of the rubber gasket are so big and close to each other, that tear will flow for either ON or PRI and leak in the crankcase that way.

The Float on the other hand can sit on its side, [side stand down] lower the one side of the float and with 14.7 pounds of pressure on top of the gas in the tank, you have that pressure on the float, where the float itself with the float needle are not damage, needs no adjustment, but points to a petcock constantly on with a cut button gasket.
My understanding is that a petcock with Prime does not have a OFF position, because it's OFF when the suction stop (in other words engine is off).

The manual petcock on the other hand needs to have an OFF to be able to stop all flow.
 

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99' Valkyrie/North Central Indiana
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So with all this great feedback, how in the heck can anybody answer the question correctly without knowing your bike size, year, and model is beyond me but I'm not here asking just to up my post count either.
 

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Discussion Starter · #9 ·
So with all this great feedback, how in the heck can anybody answer the question correctly without knowing your bike size, year, and model is beyond me but I'm not here asking just to up my post count either.
Sorry about that. I have a Honda Shadow 750, 2007.

I was looking at my petcock today and I can see two hoses (a large and small diameter). So I guess I have a vac assist one with a bad diaphragm. All my fuel in the tank drained to the oil tank.

But at the same time, if I have a vac assist petcock shouldn't I also have the prime option available on the petcock?
 

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It's technical discussion. That means generic an no need for a year or model. It's basic vac-assist-integrated petcock diagnosing. We know nothings can walk up to any bike and look at the generic parts that transition to other brands of bikes.

Take FI for eggzample. FI = Forget IT.

More the generic squids that own bikes like myself would keep the lever on ON all the time. Then the factory would have to unbend the C the crank made of the rod when it hydraulic'd and ohshit, we better de-squid the movement, or those bikes are not going to move out the dealer door no more.
 

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In the event the petcock is bad and all the fuel drains down the oil tank. Do I have do do anything besides just fixing the petcock and replacing the oil?
That's pretty much it. Say you rode around, belched the air cleaner some. Then it's check the air cleaner and see if it's dry and clean. Spark plugs are how old? That's my list of don't F'around. Oil/filter, AC element, set of 4 plugs. Done.

Two ways of doing this:
1. Yes, oil and filter. Yes, if ALL rubbers are available to rebuild, add up the parts needed.
2. Option here is the same change out of the oil/filter, a new petcock and be done with it.
3. Since you have the parts added up, the cost of new petcock vs the rebuild, how much are you really saving is always your call.
 

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My understanding is that a petcock with Prime does not have a OFF position, because it's OFF when the suction stop (in other words engine is off).
Correct. Prime is to not drain the battery down using it to fill up the carbs first with the diaphragm assist.

The manual petcock on the other hand needs to have an OFF to be able to stop all flow.
Correct again. That would be ON/OFF/RES or PRI.
 

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Here's a couple of functional diagrams of

Vacuum petcock:
Font Parallel Rectangle Symmetry City



and Carburetor Float Valve (4&5 below):
Font Parallel Design Diagram Drawing


As has been previously posted, the vacuum petcock is either at the outlet of the fuel tank, or in-line in the fuel hose.

The Carb. float valve is at the inlet(s) to the carburetor(s). These two valves restrict fuel flow in series, when functioning correctly.

However, fuel can also enter the engine through the Vacuum line that actuates the Vacuum Petcock, if its diaphram is compromised. This vacuum line is usually sourced at the intake manifold, past the carburetors, ( above point 7 in the diagram above). This is a particularly insidious potential source of engine damage, (fuel hydrolock), in my opinion. I make it a point to always shut my MANUAL petcock OFF, whenever my machines are parked.
 

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Fact is not all models of SHADOWS have vacumm operated petcocks thus not knowing which Shadow model is relevant.
 

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Let's make it easy and use 3 positions of a petcock:
1. ON
2. OFF
3. PRI [prime]
That's interesting! I've only seen manual petcocks with On/ Off and On / Off / Reserve. Priming, back in the day, was done with a "tickler" that opened the carb. float valve to get a richer mixture for starting.

The vacuum shutoff valve on my VLX is plumbed inline, after the manual petcock, and has no manual controls. It's supposed to be on or off only.
Circuit component Font Auto part Machine Electronic component

I found this picture online, which looks to be what you are describing:
Nickel Metal Fashion accessory Wood Titanium


You didn't get into the functioning, but I assume that in the PRI position, the diaphragm operated valve is either pushed open, or bypassed? The three positions we can see in the picture are labeled PRI / FUEL / RES. Is the last position that is obscured, a mechanical OFF position?
 

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Usually when I work on a bike, it's always pri or res, depending on the petcock. This way I know it has gas, don't need to look, don't need to pop the gas cap to know if it has a gas level for ON position? Kind of forgo all of those moves.

Lots of combinations of uni-body, remote vac-remote petcock. NO petcock, just hose end nipples brazed into the tank. No way to shut it off, short of the correct sized cap off rubber ends ready in hand and ready. Unless nothing has changed since first year fuel injection, petcocks turned obsolete off the shadow's gas tanks.

There are a lot of generations and combinations between manufacturers when it comes to petcocks. In the era of petcocks, it either vacuum only, gravity fed only, vacuum assist w/shutoff lever, and next generation is probably none on the future generations of tanks to come, starting in 2010.

A siphon hose is in your future.
 

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Discussion Starter · #20 ·
Usually when I work on a bike, it's always pri or res, depending on the petcock. This way I know it has gas, don't need to look, don't need to pop the gas cap to know if it has a gas level for ON position? Kind of forgo all of those moves.

Lots of combinations of uni-body, remote vac-remote petcock. NO petcock, just hose end nipples brazed into the tank. No way to shut it off, short of the correct sized cap off rubber ends ready in hand and ready. Unless nothing has changed since first year fuel injection, petcocks turned obsolete off the shadow's gas tanks.

There are a lot of generations and combinations between manufacturers when it comes to petcocks. In the era of petcocks, it either vacuum only, gravity fed only, vacuum assist w/shutoff lever, and next generation is probably none on the future generations of tanks to come, starting in 2010.

A siphon hose is in your future.
what is the difference between vacuum only, and vacuum assist w/shutoff ?
 
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