So where does everything go?

Trebek wrote:

It wasn't much of a leak. I just drove her a couple miles and it isn't leaking now. It is running less than perfect now, in fact I had to leave the choke on the entire time. my guess is that either, my fuel line is pinched somewhere, or/and I need to get the carbs synched....

Perhaps a fuel starvation issue is being partially overcome by choke. Might result from clogged vent in fuel tank cap. Could confirm being a vent issue by test running with fuel cap ajar (not fully snapped down) to determine whether fuel starvation diminishes and ability to run without choke.

Other possible causes of fuel starvation besides mentioned fuel line kinking include such things as clogged petcock pickup tubes up inside fuel tank, clogged petcock filter screen above sediment cup (if manual petcock), and/or clogged inline fuel filter.

I don't suspect poor syncing as reason for choke being required to keep running.

Let us know if fuel leak persists, as the source is sometimes difficult to locate. Could be loose fuel pipe, cracked line, bent tab ear on float bowl, defective gasket, loose floatbowl screw, loose drain screw, defective drain screw o-ring, sloppy fuel line connection at petcock nipple or at carb or at inline filter, etc.

Good Luck!

Probably the most common cause for needing the choke on to keep running is clogged fuel passage or pilot jet in the carb primary circuit.

Earlier posts include other possibilites besides internal carb issues. You know, the easier stuff.

Good Luck!

I re-did the fuel-line set-up and put a higher capacity see-thru fuel filter between the petcock and the carb fuel hose. The fuel seems to be slowly funneling thru the filter when switched to prime and reserve. When the petcock is switched to on, the fuel barely drips out. There are no leaks at all, but the trickle of fuel flowing thru the see-thru filter, causes me to think, that either my petcock is blocking the fuel from flowing freely, or my vacumn lines are compromised (shouldn't the filter just be full of fuel and not looking like a small trickle flowing thru with lots of airspace?. The bike still only runs with the choke wide open, and I have to keep a bit of throttle to keep her running.

Trebek wrote:

I re-did the fuel-line set-up and put a higher capacity see-thru fuel filter between the petcock and the carb fuel hose. The fuel seems to be slowly funneling thru the filter when switched to prime and reserve. When the petcock is switched to on, the fuel barely drips out. There are no leaks at all, but the trickle of fuel flowing thru the see-thru filter, causes me to think, that either my petcock is blocking the fuel from flowing freely, or my vacumn lines are compromised (shouldn't the filter just be full of fuel and not looking like a small trickle flowing thru with lots of airspace?. The bike still only runs with the choke wide open, and I have to keep a bit of throttle to keep her running.

May test for ample fuel flow being available to carb fuel pipe. Test done with engine cold and not running.

Petcock in position to disallow fuel flow.

Assure sufficient fuel in tank. Open fuel cap to eliminate any issue with tank venting, and leave the cap open for duration of test.

Disconnect fuel line at outlet side of in-line filter.

With shop rag handy, turn petcock to ON (if manual petcock) or PRI (if vacuum petcock), whereby petcock is supposed to allow fuel flow.

Watch for ample fuel streaming from in-line filter. Catch fuel with shop rag. If ample fuel flow, the test is over. Return petcock to position disallowing fuel flow. Reconnect fuel line to filter. Close fuel tank cap, and done.

In no fuel or very little fuel streams from in-line filter, there's a flow problem upstream (problem with filter, line, or petcock, or insufficient fuel in tank). If tank fuel cap was left snapped down during the test, there might be a cap vent issue.

Transparent inline filters typically appear less than completely full, and do have visible air space.

Good Luck!

Downstream of the inline fuel filter. Fuel is supposed to enter carb through the fuel pipe (T-connection where fuel line attaches).

Fuel is then supposed to flow past float valve until rising to proper level is floatbowl. An obstructed float valve might impair sufficient fuel flow into floatbowl. But the reverse is more typical, where an obstructed float valve fails to completely close and keeps on allowing fuel to pass when it's no longer supposed to.

May test entry of fuel into float bowl by removing a float bowl drain screw and watching for ample discharge of fuel from the drain hole. Replace drain screw.

Also, a too low fuel level inside floatbowl usually causes an otherwise perfect carb to run too lean. If not already done, would perform clear tube test to assure correct service floatbowl fuel level.

From fuel bowl, fuel goes into enrichment circuit (choke), pilot circuit, and main circuit.

Where fuel level exceeds specs for whatever reason, (such as leaking float valve, faulty float, incorrect assembly. something binding, etc.), the excess fuel is supposed to escape via the floatbowl overflow circuit and discharge from the overflow tubes routed to underneath the bike.

A too high fuel level inside floatbowl usually causes an otherwise perfect carb to run too rich.

Poor idle and low rpm performance often results from a problem in the pilot circuit, which is influential mostly during first 1/4 throttle opening, until the main circuit (throttle slide, jet needle, and needle jet) assume command from 1/4 to about 3/4 throttle. And the main jet rules the roost at wot. Past 1/4 throttle, the pilot circuit has very little influence on carb performance.

Good Luck!

Thanks again Patton, you really know your stuff. One more detail is that the petcock pretty much shuts off when turned to "ON" and flows freely on pri and res.

Trebek wrote:

...petcock pretty much shuts off when turned to "ON" and flows freely on pri and res.

Engine not running --- Petcock is supposed to allow fuel flow only in PRI position. And flow until the tank goes dry.

Engine running --- Petcock is supposed to allow fuel flow in any position. Of course, where fuel level inside the tank gets low enough to require RES, the ON position stops flowing fuel. Perhaps the fuel inside tank is down to the RES level. Would add a gallon of fuel, and see whether ON position begins flowing.

If petcock problem persists, disassembly and cleaning might restore it to proper function. Examine the diaphragm for any holes, and for any damage to the o-rings or fuel port gasket.

Might need a petcock rebuild kit from Z1E.

Good Luck!

A tube from a carb sync nipple (or special carb nipple) supplies vacuum to petcock.

Such vacuum allows the petcock to flow fuel in ON and RES positions. It is designed so that the petcock is automatically OFF when the engine is not running. So us senile forgetful old reprobates won't have to remember turning it off.

Good Luck!

Hi, guys. Please forgive my ignorance, as well. I am a Harley guy so I know nothing about these bikes. My friend has a '77 KZ750B twin and we're trying to figure out how they are supposed to be plumbed. The overflows are at the bottom- that we got. There's 2 lines coming out of the petcock- 1 going to each carb inlet...but there's an extra port on the left side of each carb that I have NO idea what it's for(number 1 in the picture-any ideas?). Also, there is a plugged vacuum port on each of :S the intake boots. Should they be connected to anything? Any help would be GREATLY appreciated...:S

harleyguy wrote:

Hi, guys. Please forgive my ignorance, as well. I am a Harley guy so I know nothing about these bikes. My friend has a '77 KZ750B twin and we're trying to figure out how they are supposed to be plumbed. The overflows are at the bottom- that we got. There's 2 lines coming out of the petcock- 1 going to each carb inlet...but there's an extra port on the left side of each carb that I have NO idea what it's for(number 1 in the picture-any ideas?). Also, there is a plugged vacuum port on each of :S the intake boots. Should they be connected to anything? Any help would be GREATLY appreciated...:S

Until more competant advice arrives, I would say the hose labeled #1 is a vent hose for the floatbowl and should be open to outside air, with the open end probably routed to underneath the bike.

All vacuum nipples are supposed to be plugged unless used for a specific purpose such as providing vacuum to a vacuum operated petcock. The pictured petcock is a manual petcock, NOT a vacuum petcock. So no vacuum hose attaches to it.

Vacuum nipples on the carb holders are used when syncing the carbs.

Some later model bikes used one or more vacuum nipples to connect EPA hoses and fittings, of which most have been removed over the years.

Good Luck!

what patton said is dead on the line that your talking about is the bowl vent since the c.v carbs work off pressure differencal that line must not be plugged the plugs on the intakes are for doing carb sync's or for extra vacuam source for a petcock but since you have a manual one keep them plugged as well.

You guys should have explained to him in detail that if the daiphram has a hole in it the bike will run like crap and that it's also the reason the petcock still flows gas when it's off. If the diaphram has a hole in it it will leak air and that small vaccuum leak will make it run less than perfect. Not chiding anyone just think it'll help him out a little. I think you'll want to check the timing next so here's how. Take the points cover off. Clip a test light to the cover housing. Use a light to look inside the space between the points. Using the kick start bumb the motor over little at a time and watch for the 1/4 to appear. Locate the F mark. Stop the motor when when the F mark is 1/4inch from the mark on the engine case. Turn the ignition on. The left hand point set is 1/4. Locate the part of the point set that makes contact with the points rotor. Hold the tip of the light against the side of the contact, (the actual contact itself), you'll notice if you apply pressure to the side of the contact the points will open. You don't want to do that. Apply enough pressure to just get a good ground or contact between the light tip and the side of the contact. grab the kick start with your left hand and Locate the marks again. Gently bump the kick start (don't worry about it breaking) bump it slowly untill the the light comes on. That's when the points break. Note the relationship between the F mark and the mark on the block. If the light came on after the F mark passed the mark on the case you have late timing. If so loosen the three screws and bump the plate counterclockwise slightly. Tighten one of the screws and check it again. If the test light comes on before the F alighns with the case mark bump the plate clockwise slightly. If the light does not come on at the same place with both sets, adjust the points by loosening the screws and sliding them slighty. The same direction applys. If you run out of adjustments using the plate and the points max movement, the points are worn at the rotor. If this is the case changing the point gap on one or both will allows more adjustment. Just keep the gap reasonable and it won't present problem with the spark's energy. If you decide to replace the points check the rotor for smoothness. IT's ok to take it off and polish it. This will make adjustment enterverals much farther apart. And I dare someone to laugh at you for carrying that light with you when u ride. You can pull it out of your back pocket in public places and point it at people,,,WAAAAA!! They'll think your the coolest cat in town. I've gone one step further and had the operation. The llight bulb was surgically installed into my nose and the ttip exits through my finger. A slight studder is all I get after a points adjustment. And my nose blinks on and off when I talk. Comes in handy for diagnosing under the hood of a car at night. Chicks dig it too.