Backfire, Flames and 2 cylinders

i think you have a coil problem ....maybe....

triggerbilly wrote:

...it seems to be dripping slow and constant on the 'on' 'res' and prime position (my carbs have been leaking ever since i bought the bike, so I'm guessing this has something to do with it)....

As known, without vacuum supplied from a running engine, a vacuum petcock in ON or RES position is supposed to prevent any fuel flow (same as a manual petcock in OFF position). The internal spring holds an o-ring in position to block fuel flow.

A running engine supplies vacuum to the diaphram which overcomes the spring pressure and thereby allows fuel flow.

Am thinking dirt inside the petcock or a damaged part (o-ring, valve gasket, or spring) is improperly allowing fuel flow in ON or RES position even when the engine isn't running.

Disassembly and cleaning might resolve the problem. Or replacement of damaged parts may also be required.

Z1E carries the diaphram with small o-ring, separately, or a full repair kit including these plus the valve gasket and other o-rings.

Would also assure correct float bowl fuel levels, using the clear tube test. A too high float bowl fuel level may contribute to an overly rich mixture and consequent plug fouling.

If not already done, would also assure good fully charged battery with correct fluid levels, and clean tight terminal connections, including good tight ground connection where negative cable attaches to engine or frame. A weak battery may contribute to weak spark and consequent plug fouling.

Good Luck!

[Click on image to enlarge view]

so should there be gas traveling down the vacuum hose ?

this is my second petcock (i thought i'd buy another used one as the one i got with the bike was making the carbs overflow just the same as this one ????)

Also might want to double check that butterfly valves are all synched

Update:
I'd lost the vac cap form the top of carb #3
so there must be a big vacuum leak ??

but it don't explain cylinder 1 & 2 not firing or the gas running down my vac hose on carb 2 makin my carbs overflow

???? Does it ????

Are the flames shooting out of the exhausts or are the flames shooting out of the carbs.

I am interested because I am experiencing the same problem and believe it is the result of the cam chain jumping a couple of links so the exhaust port is not fully closing.

triggerbilly wrote:

so should there be gas traveling down the vacuum hose ? this is my second petcock (i thought i'd buy another used one as the one i got with the bike was making the carbs overflow just the same as this one ????)

There should be NO gas traveling down the vacuum hose. If any gas is entering the vacuum hose, something is wrong inside the petcock.

The petcock is supposed to block flow when in ON or RES position until vacuum removes the block. And when vacuum removes the block, fuel should flow only through the fuel line (never through the vacuum line).

PRI position allows flow regardless of vacuum, but supposedly through the fuel line only (never through the vacuum line).

Z1E carries petcock repair kits.

triggerbilly wrote:

Update: I'd lost the vac cap form the top of carb #3 so there must be a big vacuum leak ?? but it don't explain cylinder 1 & 2 not firing or the gas running down my vac hose on carb 2 makin my carbs overflow ???? Does it ????

There's a risk of causing engine damage by running without all vacuum caps in place. Z1E carries good high quality long-lasting impossible-to-lose vacuum caps.

As to possible reasons for lack of combustion in cylinders 1 and 2, see above posts regarding valve clearances, and float bowl fuel levels, and float needle/seat interface.

Faulty petcock allowing fuel into vacuum hose would explain flooding of cylinder fed by carb to which the vacuum hose is attached.

Good Luck!

So could i put a vacuum cap on #2 carb and one on the vacuum nip of the petcock. Would it then run like a manual petcock ?
just switch it to 'prime' when it's running and switch to 'on' when not running
would this work (until i save up and buy a new petcock !!)

triggerbilly wrote:

So could i put a vacuum cap on #2 carb and one on the vacuum nip of the petcock. Would it then run like a manual petcock ?
just switch it to 'prime' when it's running and switch to 'on' when not running
would this work (until i save up and buy a new petcock !!)

Capping vac nipples on carb and petcock will certainly eliminate unwanted fuel in a then non-existing vacuum line.

PRI allows direct flow through fuel line from tank to carbs. Same as having no petcock. And no reserve function either, so good luck on not running out of gas again. :ohmy:

Where ON and RES fail to block fuel flow through fuel line without vacuum, such unblocked flow will continue regardless of whether engine is running or not running. Same as just leaving in PRI position.

Could use vise-grip pliers to squeeze and clamp off fuel line when engine is not running, to block fuel flow through fuel line. Or incorporate an inexpensive lawnmower style manual on-off fuel flow control valve in the fuel line to block fuel flow through fuel line.

Good Luck!

triggerbilly wrote:

... carbs have been leaking ever since i bought the bike....

When the float needle seat interface is functioning as designed, there should be no excess fuel allowed through the interface, and therefore no excess fuel entering the floatbowl to overflow from the floatbowl.

But due to age, wear, crud and grit, the interface becomes no longer "perfect" and may then allow some fuel to slip past and on into the float bowl even when the interface is supposed to be sealed closed by the pointed tip of the float needle pressing into the seat orifice. Good reason for using an in-line fuel filter.

Deminimus fuel leakage past the interface usually doesn't cause too much of a problem while running, because enough fuel is being consumed to burn the slight excess flow getting past the interface.

But the problem then arises while parked, often overnight in the garage, where the petcock isn't positioned to block fuel flow from the tank, and fuel gradually seeps past the interface into the float bowl, overfills the float bowl, and escapes through the overflow circuit > float bowl nipples > overflow tubes > around swing arm > underneath bike > garage floor.

All good reasons to have a properly functioning petcock whereby fuel flow from the tank is positively blocked from entering the fuel line while the engine is not running.

Good Luck!

I think i'm gonna go this way !!
www.z1enterprises.com/detail.aspx?ID=1742
Then go for a $20ish harley petcock

clean my seats/needles too !!


might take this petcock apart later today and give the spring a stretch etc..(worth a try)

triggerbilly wrote:

...might take this petcock apart later today and give the spring a stretch etc..(worth a try)

Perhaps discover a damaged or dirt-clogged part inside the petcock. And would closely inspect the valve gasket, and rubber o-rings.

Hoping a good internal cleaning might suffice.

Good Luck!