1979 Special Fuel Issue

[MPittma100]

I removed both front petcock lines that come from the octy and turned each petcock to on position trying to verify that octy is working.

Octy is working when I check it with a vacuum gun.

The problem is this: (both front petcock lines removed). When I turn the left petcock to on position, fuel runs out of the right petcock front port? If I turn the right petcock to on position, fuel runs out of the left petcock front port. What am I missing?

[TopCatGr58]

Hey Mike,

Well, the special petcocks are supposed to be gravity feed. When in the on position the fancy 4 holed rubber valve and the handle is supposed to let it flow from the rear spigot, but not the front one since that's just for Prime. However I haven't inspected and diagrammed the handle/valve and petcock combinations, so not sure about the pathway of the front spigot and what is in the way to prevent the fuel from flowing when just in "ON"?

The way it's acting almost makes me think that the gas cap vent is clogged, and so when one petock is in on, it causes a vent action of some sort and fuel somehow can flow out??

Are you sure the petcocks are in the correct position/side ie. Left on Left, the handles have been known to get swapped with the bases when removed and disassembled and then reassembled mixing the parts!?

T.C.

[MPittma100]

Fuel Flow

I did not think about the cap vent. I will look at that. The petcock covers and handles match I.e left-left, right-right. I did not look at petcocks themselves to see if they may have been switched. I guess that it is possible to have a right petcock with left hardware, but I'm not certain if that can actually happen?

I can unplug the vacuum line to the octy while the engine is running and it will eventually run out of fuel and shut off like it should. This just doesn't add up.

[jetmechmarty]

How can this be? I can't wrap my brain around this one. You take the PRIME lines off the petcocks, and left petcock ON. The right petcock is OFF? How can fuel be running out of the PRIME port? It can't.

[Rasputin]

I did not think about the cap vent. I will look at that. The petcock covers and handles match I.e left-left, right-right. I did not look at petcocks themselves to see if they may have been switched. I guess that it is possible to have a right petcock with left hardware, but I'm not certain if that can actually happen?

I can unplug the vacuum line to the octy while the engine is running and it will eventually run out of fuel and shut off like it should. This just doesn't add up.

Yes that can happen as I do it on purpose to make the valve handles work in the direction I prefer. You can switch them around to front off or back off or even which carb line you want to have live. Just have to study the path they take.

[MPittma100]

Possible?

Yes that can happen as I do it on purpose to make the valve handles work in the direction I prefer. You can switch them around to front off or back off or even which carb line you want to have live. Just have to study the path they take.

Is it possible that the right and left petcocks can have the opposite hardware installed in them? I.E. right petcock with left handle and plate?

If so, could this be causing this phenomena?

Marty - my brain won't rap around this one either.

Mike

[Buckmaster79]

Petcock fix forever

I put Pingel petcocks on they are not cheap and I have no reserve but no more
leaking and they turn very smooth.

[Schming]

Is it possible that the right and left petcocks can have the opposite hardware installed in them? I.E. right petcock with left handle and plate?

If so, could this be causing this phenomena?

Marty - my brain won't rap around this one either.

Mike

Hi Mike, the following pic is of my SF right petcock, notice the "R" in the middle of the handle and between the "RESV" and OFF.

If those are on the right petcock, on yours, you got it right

[MPittma100]

Correct

Hi Mike, the following pic is of my SF right petcock, notice the "R" in the middle of the handle and between the "RESV" and OFF.

If those are on the right petcock, on yours, you got it right

That is the may they are on mine. Just can't figure out the gas coming out the petcock front (prime) port on opposite sides when fuel is turned on?

Mike

[jetmechmarty]

I believe you're going to have to take the petcocks apart to learn why the outlets are bussed together. I can't imagine why, but perhaps there has been tampering involved.

[Schming]

Just now looking at my SF I noticed that the petcocks themselves are labled with an "L" and "R" on the front side.

If all parts are installed on their respective sides I believe your problem may lie within the hose routing or the vacuum valve.

I haven't been able to dive into my SF yet but out of curiosity, I examined the hose routing I got the bike with and it's wrong so it's a no brainer why it wasn't running correctly.

[jetmechmarty]

When PRIME is selected, the vacuum shutoff (octopus) is bypassed. At least, that's the case if plumbing is correct. That eliminates that valve as a possibility.

[Schming]

I believe this is the correct plumbing or routing:

Left petcock rear line goes to #1 on octy

Left petcock front line goes to tee and one side of tee goes to #3 on octy and other side to fuel tee between carbs 1 & 2

Right petcock rear line goes to #2 on octy

Right petcock front line goes to tee and one side goes to #4 on octy and the other side goes to fuel tee between carbs 3 & 4

If this is correct, then the Clymers manual isn't.

[MPittma100]

Fuel Delivery

All of the fuel "octy" hoses are in their proper position. Cap vent is good. I have not looked at the petcock body markings, nor have I taken them apart to see if they have been "modified'.

But the fuel definitely runs out of the ports as I described.

Further inspection is required.

MP

[CatatonicBug]

I believe this is the correct plumbing or routing:

Left petcock rear line goes to #1 on octy

Left petcock front line goes to tee and one side of tee goes to #3 on octy and other side to fuel tee between carbs 1 & 2

Right petcock rear line goes to #2 on octy

Right petcock front line goes to tee and one side goes to #4 on octy and the other side goes to fuel tee between carbs 3 & 4

If this is correct, then the Clymers manual isn't.

You have them mixed up a bit.

Left petcock:
Front port (prime port) goes to Tee, and Tee goes to #1 on octy and left fuel port on the carbs (this can be switched to the right port if you choose - makes no difference)
Rear port goes to #2 on octy - this port is vacuum-controlled

Right petcock:
Front port (prime port) goes to Tee, and Tee goes to #4 on octy and right fuel port on the carbs (can be switched to left if you choose)
Rear port goes to #3 on octy (vacuum-controlled)

I think (not 100% positive) that if you turn on the Prime port, fuel will flow from BOTH ports, which means that the ports are plumbed together inside the petcock. The two rear ports are definitely plumbed together inside the octy. This means that if fuel is being pushed out of the rear port on the petcock by turning on the flow of fuel, fuel will flow from the rear on one side, through the octy, INTO the rear port on the other side, then out the front port. That is why there is an OFF position on the petcocks - that is the only position where fuel is not flowing somewhere.