77' KZ750 - Leaking fuel, stalling and running on

KZ 750B2 - 1977

I bought this bike last week and I love it already. It has some problems. Oil leaks from the tach input, some asshole that had bought and returned it put sugar in the tank, oil leaks a lil from the oil pan.

It's been running after I cleaned the tank and put a shop towel on the tach cable. The oil leak isn't bad so I just make sure it has oil.

But today she almost gave up the ghost on me.

I was cruising at about 75 when she started running really rough. I pulled into a lot and it looks like she is only running on one cylinder and there is gas leaking from the same side carb.

I have driven the bike 500 miles since I got it with no problems. Does anyone have any suggestions on this? I am thinking a carb rebuild kit and an engine gasket set from Z1 as soon as I can afford it. The better half let me buy it cause it is supposed to be my daily commuter.

Here are some photos of the two plugs I pulled out if it helps. The black one is from the side that isn't running right and is leaking fuel.

It sounds like a stuck float valve - no big deal, just pull the bowl and clean the float valve needle & jet and see if it stops leaking. If that's all it is you don't need to remove or rebuild the carbs; you can remove the bowl with the carbs still on the bike. Oh, and buy some spark plugs; what are those things from a lawn tractor? :laugh:

I pulled the bowl off and it had some sugar in it so it's possible that it got in there and messed things up. Yea I was looking at the plugs and wasn't sure what they were.

What kind of plugs do these things take?

If you have the owners or service manual they will show which plugs to use, otherwise maybe someone here with a 750 twin will chime in. I would definitely put a fuel filter on the bike in case there's other crap in the fuel tank. Ed

Welcome Tested.
Stock plugs are NGKB8ES or NDW24ES-U.
KZINFO tab at top of page has a list of specs for various models. 1976 KZ750 should be the same as your 1977.

Good luck,
Jim

The factory spec for the 1979 750 twins was the hotter NGK B6ES or ND W20ESU plugs. The fours ran the colder B8ES plugs.

Today I put in new NGK B8ES plugs, a new 3 ohm ignition coil and new wires. I also disassembled the carb (again) and cleaned all the jets and fixed a problem with the diaphragm. It ran great for a little while but it is still leaking fuel from the overflows. Now this is really bad because fuel under the bike is bad.

Is this a problem with the float or with the needle? What happens if I plug the overflow tubes from the bowl until I can get it fixed?

From what I read on the Kawai Twin forum the guys were saying that the B8ES plugs were better for these bikes.

Do even think about plugging the overflows! If you do, all that gas will go through the intakes, around the piston rings, and into your crankcase. Bad karma! You need to figure out what's going on with the float valve or floats or you risk a fire. Ed

Tested, are you getting a flow of fuel from the overflow, or just a drip? If it is a drip it could be your overflow tube is damaged and letting fuel seep out, instead of it being an overflow situation from the top of the tube. If your float level is good then this is what most likely is happening. I just had a crack in my overflow tube which was causing a drip. Thanks to some friends here I was able to find it and solder it (I was careful not to solder the tube shut). On the other hand, if it is flowing out faster then a drip then once again the float needle or float setting is suspect. Just food for thought.

It's a flow from one tube and a drip from the other. I am really starting to think that it has something to do with the float and or needle.

I would think a drip would not be a stuck needle or improper float setting. But others here can shed light on that. Therefore, the dripping carb could be a damaged overflow tube. You can take the bowl off and fill it 3/4 of the way with fuel. If it drips you will confirm the tube is damaged. As for the carb having the flow instead of a drip, it is most likely the float setting / needle problem.

I rebuilt the carb and over adjusted the floats. But hey it doesn't leak. Now just to set the floats right and I should be good to hook.

Thanks for letting me know what happens if the overflows are blocked. You guys educated me and several of my friends that are new to this stuff.