Hysteresis. A properly sized valve would probably create a more consistent fuel level. A bigger valve might let in bigger pulses of fuel. Fuel valves can work linearly, but I think they also can work in a pulsing mode. Exact same thing happens in electronic circuits. The pulsation can be eliminated through damping. Using a smaller valve would be analogous to damping.
Obviously, you have to have it big enough to flow for your maximum needs.
Fuel level in the gas tank is directly proportional to the fuel pressure at the valve. I would expect your symptoms would get worse as the fuel in the tank starts to run low. Also, a slightly more restrictive petcock factors in as well.
So much for my quick top end swap.... no wonder it seemed low on power. The right piston pin was seized in the piston and took a puller to remove. Not sure how it started; further inspection required. the small end of the rod is trashed. Luckily i can remove the rods through the oil pan. but since I have to go this deep I'm wondering if i should pull the motor and go through the whole engine? that's a bunch more work i'd rather not do. There didn't seem to be any big chunks in the oil pan, just a little dirt that fell down when i removed the jugs. I just can't seem to get an easy one on the projects lately....
I am coming in late to this topic. The bike looks super!! Lots of great and innovative work you have done. I am in the finishing stages of my '78 Twin. Sat in a back yard for 12 years with a locked up motor. Thankfully running now but until I heard that first "pop" I was nervous. Love your build thread.
Finally got the easy win I was looking for. New EBC single disk setup. Shaved 4 pounds off rotational mass and an additional 2.5 unsprung with the removal of the extra caliper. I bought a 12mm brembo MC to match. The fitment is super tight. less than 1mm on spoke/caliper and disk/fork leg. I'm digging the new look. Very interested to see how it feels.
Small update, but one of particular interest to kz750 twin owners.
I was cross referencing part numbers and realized the z1/kz1000 share the same head studs as the KZ750 twin. This means you can use APE's heavy duty head studs and nuts which are intended for the z1/KZ1000. I have bought a set and can now confirm, however, you do end up with 4 extra studs and nuts you don't need. These bikes are notorious for head gasket leaks, increased compression will likely make this worse, hopefully this will help address that.
Just some recommendation DoctoRot for your engine rebuild.
Only buy the head gasket part #: 11004-1267, the green one
It´s the last and best cylinder head gasket for the 750 twins
A little gasket history :
11004-071 => 11004-078 => 11004-1055 => 11004-1267
11004-071, recall campaign in June 1976
11004-078, the red one with black middle section
11004-1055, light brown, comes with the first LTD model
11004-1267, the green and the best for the last LTD model
Full story and source but only in German language.
People here in Germany discover that a classic car or bike is like a good investment.
Prices for a classic car or bike,(older than 30 year are tax and insurance reduced), go high as i never seen before. It´s like a must have in every garage. The used classic car/bike market prices goes insane!
Finally got around to making mirrors for this thing. I got these cheap mirrors off ebay for $20, they are actually pretty nice, solid aluminum construction and convex glass. I used the old head studs for the stems, turned a little cap where the mirror attaches, tig brazed it on, and polished it back. I also had some stainless flange nuts that I trimmed down so they wouldn't be so bulky.