Can't start 83' KZ750

Can't start my KZ750. Plugs are new, carbs cleaned, spark is good, starter rotates. Pilot screws 3 turns out, choke on. Battery is good. It shows sign of starting but there is no running. Is the ignition timing is controlled automatically on these bikes? I also changed chain tensioner at some point. Could it be something with the chain itself? Thanks.

I had the same problem with one of my old bikes. Went through and did everything you did to find out my petcock was partially clogged.. Sometimes its small things that bite us in the ass.. Good luck tho'... I'm sure someone will be along to help you out further..

Check if the choke shaft turns freely. If you have keihins cv34, the choke shaft is splitted in two shafts. The second one spins by the force of a spring, the first one is mechanical attached to the choke lever.

Some years ago I had the same problem. The bike showed signs of starting but it never started. I discovered the second shaft was not turning, then not closing cylinder 3 and 4 choke butterflys.

Same thing happened to me - choke flaps not moving. Listen for them clicking into place as you operate the choke lever.
After failing to start are the spark plugs wet with gas/petrol?
Could you have flooded some of the cylinders? - remove plugs and allow gas to evaporate
Is it possible that when you changed the tensioner you had the cam chain skip a tooth on one of the sprockets thereby upsetting the cam timing? Probably a long shot want. May want to check valves timing and clearances.
Compression check.?
Just some ideas
Good luck

I would try some starting fluid in the air box to see if you can get it to fire up at least for a second. If it fires, then you have a pretty good indication that ignition is working correctly. I believe that this bike has electronic ignition and not points. Take off your right side cover and make sure the advancer is turning freely and its lubed up. Other than that, I would check that carbs are getting fuel and the float levels are correct.

I had this same problem last week, Ended up being bad plugs. Its annoying but I bet its something really small.

I would try some starting fluid in the air box to see if you can get it to fire up at least for a second.

I would be careful with that stuff.....a little goes a long way when it comes to motorcycles.

OK so my plan is:

Petcock-will check that;
Choke flaps-when I cleaned carbs they very working just fine;
Flooded cylinders-when I removed spark plugs after trying to start they were wet. Might want to allow cylinders to evaporate;
Chain tensioner-I changed it according to manual. Removed it from cylinder head, Rotated the crankshaft to "T" mark, unscrew new tensioner's locking nut, put it in cylinder head, rotated crank shaft couple of turns and screw in locking nut. This is what bothers me could chain skip tooth when I rotated without tensioner;
Compression test-will check that;
Advancer-will check/lube it.

karoliens wrote: OK so my plan is:
...........................
Chain tensioner-I changed it according to manual. Removed it from cylinder head, Rotated the crankshaft to "T" mark, unscrew new tensioner's locking nut, put it in cylinder head, rotated crank shaft couple of turns and screw in locking nut. This is what bothers me could chain skip tooth when I rotated without tensioner;
Compression test-will check that;
.........

I kinda doubt you could skip a tooth but then I'm not a mechanic and am just familiar with my own bike. It might be a good idea to try some fresh spark plugs while you are at it. It will likely turn out to be something simple

You turned the engine after removing the tensioner? If so, that's a good way to bend valves. I'd double check the cam timing. Also, in case you didn't know, these bikes won't run for crap without the airbox and filter installed. Check spark too just to be sure and make sure to adjust the valves before putting any real mileage on the bike. The valves tighten with mileage, and once all the clearance is gone the valves burn shortly therefafter.

So today I checked:
Petcock-OK;
Chain tensioner-actually I rotated the crankshaft after I put chain tensioner and took off valve cover to check timing. Everything seems to be fine there. When "T" mark appears this is how camshaft sits:

Timing advancer-how exactly it is removed to clean and lube it? And which part I need to lube exactly?

By the way I tried to start with air box and filter in place. But with fuel tank remotely placed and with vacuum from fuel tap pluged off as well as same line on carbs.

karoliens wrote: So today I checked:
Petcock-OK;
Chain tensioner-actually I rotated the crankshaft after I put chain tensioner and took off valve cover to check timing. Everything seems to be fine there. When "T" mark appears this is how camshaft sits:

Attachment 1.jpg not found

Timing advancer-how exactly it is removed to clean and lube it? And which part I need to lube exactly?

Attachment 2.jpg not found

The picture below is from the manual and if this is what you are seeing with the correct pin count etc when the T 1 4 mark appears in the window then you should be ok. How is the compression ? No bent valves I hope.
If you still have the cover off you should check the valve clearances as Nessism suggested.

The timing advancer is behind the pickup plate in your second picture and it is the thingy that has the T 1 4 mark on it. To get at it you need to take off the pickup plate. Remove the screws at 12, 4 and 8 o clock in your second picture to remove the plate with the pickup coils and you can see what needs to be lubed as the advancer turns in behind.

Just looking at your first post above and wondering why you have the pilot air mix screws at 3 turns out ? Stock setting is 2.
Have you have the motor running at any time ?