[Limegreenninja]

A friend at work has a 1978 KZ400B1. A little about the bike; I have checked the compression and the cylinders are 6psi apart from each other on a dry test well within spec of the Clymer service manual. It has a bright orange spark with a hint of blue to both spark plugs. It's a single coil same firing so swapping plug wires makes no difference.

The Problem: starting the bike when it's cold is like every other bike, it starts and runs fine. The bike works great until it is good and hot and then it's like someone flicked a switch. It bogs out like it's flooded with any throttle opening except idle. It will idle all day at this temp but if you try and use any throttle it dies. But it will fire up instantly right away. If you don't let it cool down, it will only start to run on the left cylinder, the right one stays dead.

One other note, the right turn, low beam and some other light I can't think of doesn't work. This I'm sure is a ground problem behind the headlight.

This bike does have the emission control diaphrams on both carburators. Anyone have some ideas?

LGN

 

[Limegreenninja]

Bump

 

[Loudviking]

Check carbs as they can be plugged. Check or replace fuel filter just cause.
Sounds to me like it could be coils packing up when it gets hot. Not much
help but I would look at those items first.

 

[Limegreenninja]

Yesterday I tore the engine down to the crank. Cleaned all the carbon off if the pistons and rings. The pistons are .050 overbore. There was excessive carbon on the valves and shit so they were removed and cleaned. I re-seated them with valve grinding compound.

I checked cylinder bore to piston clearance and they were in spec in all areas and positions.
I could not get any pistons or rings as Kawasaki only makes a .020 and a .040 and no stock sizes. I cleaned everything thoroughly and reassembled the engine. I have 145 psi in the left cyl. and 132psi in the right. When the bike is running it only runs on the left.
It will bang and pop on the right with a quick throttle opening but that's about it. Swapping the plug wires doesn't do anything. When the right plug is pulled it's wet. Both plugs are new. Changing the float height in either direction makes no difference. There is nothing wrong with the needle and jet as swapping them with the other carb makes no difference.

On stock internals kawasaki says 22psi difference between the two is the limit so my question is, since the pistons are over bore and this decreases compression, is 12-13psi too much difference?

Limegreen

 

[Limegreenninja]

Yeah that's exactly what I thought too.