Hi there,
I have a '78 KZ650 with four standard carbs. the carbs have been ultra-sonically bathed, and all the jets and 'o'rings have been re-newed, but it is still hard to start, mis-fires and drips petrol out one carb ( any more adjustment of the float level shuts the fuel off completely). The man tuning the bike is being driven to distraction. I don't know the true mileage or history of the engine but when it is on song, it flies with no un-toward noises.
Any ideas?

 

Sounds like there might be some electrical issue. Check the coils to make sure they are working properly along with the spark plugs. Also, maybe a stuck float causing the leak? If the O-rings have been replaced, I would look there too.

 

Hola Zbike,

The coils are new, plugs new and timing is set correct. The floats have also been changed but the problem remained so the original floats were re-installed. The misfire occurs in the mid rev range (3,500 to 5,500) which could still be a mixture problem. Outside this range the engine runs smooth. The problem is if the engine is set to run smoothly thru' the rev range, starting from cold becomes a major operation.

 

How do you set the engine to run smoothly?

 

I think your misfire is still related to fuel delivery thru the primary jets. What do your plugs tell you? Run at "primary jet speed" staying out of the mains, then shut off and pull all plugs and inspect. I guessing it's lean. (Maybe the dripping carb has been set a tick leaner than the others?) Coils are replacement OE or are they "super duper converts-to-a-stick-welder" aftermarket jobs?

 

Z650 - to make the engine run smoothly, the air screws (on the outside of carbs) are opened, stopping the plugs flooding.
Jeffzx9 - the coils are om versions.

At the last tweaking, opening the air screws, the misfire has changed to lower revs and gives problems moving off from a standing start. In order to keep the bike moving I using 6-7000 revs all the time which isn't ideal. The plugs are a nice brown/sandy colour except number 2 which is still a little rich but wouldn't cause this much bad running. The exhaust backfires on over run and also occasionaly backfires on acceleration which could be a timing problem.

 

How many turns are you using on the air screws? If it is running lean on the pilots it will backfire. I would not do more than 3 turns if all else is stock. I would say, start at 2 turns and see where this leaves you. The first 1/4 of the throttle openinig is related to the pilot jets (Air Screws). From 1/4 on up its the mains providing the juice. Sounds like either #2 has a stuck float maybe or a bad plug or wire.

 

Interesting read but should point you in the direction to consider. Pro mechanic or not.

 

Hola folks,

Sorry about the delay, lost the spark to plugs 2/3 which turned out to be the electronic ignition unit, then it died altogether. Waiting for a new one coming so I'll let you know how I get on when I've fitted it. Could explain the mis-firing and cold starting problems, fingers crossed.

 

Cool, I thought that in the beginning. Hopefully that works out. Let us know