TOPIC:

Hi all.
Newbie here
So heres the thing. I have rebuilt a 1981 kz750E1 that I discovered in a neighbours garden with grass growing on it. Carbs, pistonrings etc. I replace the cams as shown in the shop manual (outlet first at the Z7EX line then 45 cam chain rivets later, the inlet at the IN line). New gaskets all round, new shocks fork seals etc.
Due to a dearth of parts in the garage, I replace the carb and vacuum switch valve tubing with transparent version of same. I fire her up. At idle, she shows the appearance of ignited gas in these vacuum tubes, heading towards the vacuum switch valve - she also sounds like she is missing a cylinder firing. Spark is there for all four cylinders and I am reminded that when I forst took her apart, I noticed that the air filter, yes the air filter, was melted on the side facing the carbs. I envision that the problem then is one of timing. the inlet valves being open when the gas is ignited. yet I replaced the cam chain correctly.
So I therefore, throw the problem out to all of you wise kz gurus. Is it the ATU, the vacuum switch or something else?
I hope you can help and thank you for your time.
Stalag

Post edited by: stalag, at: 2006/02/22 14:36

did you do anything to the valves?

just cleaned them up but did not 'rout' them I also reset the clearances with my vast collection of unmarked valave shims (nightmare of micrometer use)

If the cam timing was that far off I don't think it would start, let alone idle.

I assume you had the head off, did you check and see if any valves are bent or burnt? Ir really sounds like you have a bad intake valve letting combustion gas escape into the inlet tract.

valves are fine.
I just saw an old thread message that mentions 'back-firing through the carbs'. Sounds like my problem right there. I guess I will strip the ATU first and se if the timing is retarded so badly that the gas ignites before the inlet valves close....

sounds more like a valve issue to me, I dont think the ignition timing can be that far off, not that much adj in it. Since you have a dead cyl, I would run a comp, check on all four.

You were right. The ATU was rusted up and I rebuilt it and lubed. With it back in place the bike was no different.
I will replace the carb holders then pull the top end again and recheck all valves. Thanks all for help

So the carb holders made it a little better but when I crank it by hand the cam chain jumps on the inlet cam shaft. I have never seen anything like this before. Is there a kink somewhere down there? I thought is was just routed under the crank shaft, and over the two cam shafts.....any ideas?

what does the chain adj, look like? is it working or broke?

its workin, i rebuilt it - its the automatic T shaped one

There is supposed to be a lot of chain sag between the cams because there is a cam chain guide (slipper) bolted to the underside of the cam cover. Without the cam cover in place the cam timing is going to be off (I think 5-7 degrees, but I don't remember for sure) if the chain is tight.

More info is available in the GPz750 FAQ

its workin, i rebuilt it - its the automatic T shaped one