TOPIC:

I have a KZ200 -80 with original rebuilt carburetor.
It starts easy cold and runs with a decent idle, but when warm the idle goes down and if I stop it its hard to restart. If warm I can start it by running with the bike, but not with the kick and hardly with the electric starter. If it cools for 10-15min it start easy.
 

When was the oil last changed ?
Can you do a compression check when hot (could be a sticking valve)
Hot starting issues would often be down to one of the below

• Weak mixture
• Poor compression (siticking valve etc)
• Engine is tightening up when hot (possibly too hot) then eases as it cools

Hi,
oil changed ~1300km
Spark plug a bit dark an fuel consumption a bit high, ~0,5l/10km
Maybe not right term in english? Flat grinded cylinder head ~1mm
Compression ~7kg
Ignition adjusted after fixing cylinder head.

The bike has never run better than now, easy 90km/h with me ~100kg

Hello Lasse i guess you are from Norway to. Are you sure you have the right sparkplug i think it should be b8es wich is a hotter plug.

B9ES Possibly a too cool plug.
Try a set of B7ES. They will run a little hotter and keep the electrodes cleaner which will allow a cleaner spark which is required at lower revs. . 
Just make sure you don't have resistors in plug caps and resistor plugs (BR((resistor)) 7ES). Only one resistor at most in any one ignition line. 

The compression of 7 bar is a way to low, check the valve clearence!


 
 
 
 
 

@ Rolf1976_KZ900
hi Rolf, I'm from Sweden.

@ Warren3200gt
I think I just looked at what spark plug was in the engine when I bought a new one, in my doc it says B7ES.
I'll buy a B7ES and check what happens

@ Scirocco
ok, I'll check the valve clearence, but wouldn't you here if the clearence is to small (valves not closing) when you pull of the gas handle?
I guess it could also be piston rings, but it doesn't smoke black.


 

LasseT wrote:

@ Rolf1976_KZ900
hi Rolf, I'm from Sweden.

@ Warren3200gt
I think I just looked at what spark plug was in the engine when I bought a new one, in my doc it says B7ES.
I'll buy a B7ES and check what happens

@ Scirocco
ok, I'll check the valve clearence, but wouldn't you here if the clearence is to small (valves not closing) when you pull of the gas handle?
I guess it could also be piston rings, but it doesn't smoke black.



 

You wouldn't necessarily "hear" anything but the valves would be closed for less time so the motor can't build pressure (same as long duration performance cams lower static compression for the same reason)
 

Hard to start when warm is a classic example of poor compression, commonly caused by overly tight valves.  

First things first: DO ALL maintenance.  Waiting for the bike to fail before doing maintenance, can cause damage.

I've checked the valve clearance and it is between limits.
Oil level a little low but between marks.

Try a squirt of oil in the plug hole and redo the compression test when hot (only a little squirt) are you checking compression with a wide open throttle ?

I did a new test.
Cold engine, open throttle 10bar
Warm engine, open throttle 10,5bar