What would different float heights do?

bountyhunter wrote:

The stock bowls have drains at the bottom. Find a clear tube and trim the end so it jams into the hole

OK, so that would be the hole at the very bottom of the bowl? The one with a screw in it and the main jet on the other side of it?

Topper wrote:

bountyhunter wrote:

the spec for the fuel level in the bowls is 5.5mm below the lower edge of the upper body of the carburetor (where the bowl mates against).

Where did you find that spec?

Also still looking for an answer on whether or not I can do the clear tube test without modified bowls.

It's in the manual somewhere. I have done it so many times it's burned into my brain. The actual spec is 4.5mm to 6.5 mm which is 5.5mm nominal. In english measure that's about 0.22 inches. I made a little gauge with two lines on it from an old business card.

Topper wrote:

bountyhunter wrote:

The stock bowls have drains at the bottom. Find a clear tube and trim the end so it jams into the hole

OK, so that would be the hole at the very bottom of the bowl? The one with a screw in it and the main jet on the other side of it?

That's it. I made a clear tube tool by finding a piece of rubber fuel line just the right size that it fits tight in the screw hole and then shoving it inside a 1/4" piece of clear tubing. The fuel line is some really thin stuff.

One other thing: since both the pilot jets and main are in the bowl, hose the heck out of the bowl with carb spray cleaner. It's best to remove the jets and spray into the bowl. WARNING: those jets are in TIGHT and you must have a screwdriver with a tip that fits them exactly or you will tear the jet up. Find a screwdriver with correct blade thickness and then grind it as narrow as needed to fit the head of the jets. Keep this as your special jet tool.

Yeah I didn't have any luck getting the pilot jets out. I hosed them with carb cleaner like you suggest.

Well that seems to have helped a little.

I went to Home Depot with my float bowl and found some clear tubing that I could wedge into the drain hole. I rigged up a funnel with a piece of fuel line to serve as a fuel supply and performed the clear tube test as described above.

One tip for other noobs doing this, be sure you pour enough gas in to fill the bowl and trigger the float. One time I didn't pour quite enough in and got a result that didn't make sense. Fortunately that was easy enough to figure out.

I used the fuel height spec from my manual which said 31mm +- 1 from the center of the bore. That puts it at about the lower level in Patton's diagram.

From the inside of the bowl this meant a distance of 25mm from the top of the gasket to the top of the float. YMMV.

One thing is pretty clear, the fuel levels in each of my carbs were not anywhere close to one another prior to this adjustment. The height of the floats had been off from each other by nearly 10mm. When I was done with the clear tube test they were both right at 25mm.

Put the carbs back on the bike and hooked everything up. It does seem to be running smoother but I won't know for sure until I take it out on the road. It's too late for that tonight.

Of course tonight is the warmest night (50 degrees F) we've had since I bought the bike, that might explain some of the smooter running too.

I'd still like to sync the carbs with a vacumm gauge and I need to check my point gap.

Thanks for all the help guys!

I rechecked my factory manual for 1979 KZ-750 B4 (twin) and the factory spec for fuel level is 4.5 - 6.5mm as measured in the picture shown earlier in the thread and repeated below. I always run mine at 4.5mm as richer gives a little better throttle response.

Thanks. Can you tell me where in the manual you found that spec?

It's in the maintenance section. There is a section on the carburetors.

My grandma liked to say: "If it had been a snake it would've bit you" in situations like this. Page 119 figure 408. I've been looking through the carb maintenace section for days and I don't know how I missed that.

I'd been thrown by the spec on page 114 table 11 that says fuel height is 31mm +- 1 from center of the bore. That's pretty hard to measure.

Fortunately I ended up at about 4.5mm from the lip of the carb body. Might be running a little rich for my tastes, but it's better than it was. I may adjust the floats one more time and be done with it.

here's the figure from my manual: