KZ 650 Will run perfectly until it hits 6000 rpm

Hi,
Just aquired a KZ650 F2, to get me back into biking after 16 years absence. It idles, starts and accellerates well until it hits 6000rpm under load, at which point it justs hits a massive flat spot and will go no further.

Have cleaned, checked and balanced carbs and diaphrams, checked ATU and connectors, and even tried a replacement igniter box.

Has anyone had a similar problem or a solution, as I have a lot of fun to catch up on? Like 16 years worth.

Any advice would be gratefully received!!!!

wyliewix wrote: Hi, Just aquired a KZ650 F2, to get me back into biking after 16 years absence. It idles, starts and accellerates well until it hits 6000rpm under load, at which point it justs hits a massive flat spot and will go no further. Have cleaned, checked and balanced carbs and diaphrams, checked ATU and connectors, and even tried a replacement igniter box. Has anyone had a similar problem or a solution, as I have a lot of fun to catch up on? Like 16 years worth. Any advice would be gratefully received!!!!

Hello, wyliewix, and WELCOME to KZr!

Might aid diagnosis to have more details about "hits a massive flat spot and will go no further."

Meanwhile, here's a link where a service manual may be downloaded:
jarlef.no/Kawasaki/Series/Z/650/z650files.htm

What's "ATU?"

Good Fortune!

Many thanks for service manual link.

By massive flat spot I mean when you're doing 6000revs and open the throttle the engine does not respond, so if you if you've opened throttle fully it'll 'fluff' as in not respond but if you ease back to say 3/4 throttle it'll start creeping up in speed again, to maybe 6500 but definitely no more.

by ATU I mean advanced timing unit.

If not already done, might consider possibility of fuel starvation from such things as a clogged vent in the fuel tank cap, or clogged petcock screens, or clogged petcock internally, or a clogged in-line fuel filter.

Could test fuel tank cap venting by running at speed with the cap loose (not snapped down).

What type air filtration is fitted? Airbox? Pods? Filter style/brand?
As applicable, would assure air box isn't blocked by something stored underneath the seat,and that the filter isn't over-oiled.

Does adding a little choke seem to either reduce or worsen the condition?

Good Fortune!

It's running on a standard airbox, which seems free of obstruction and has a new air filter. Haven't thought of fuel cap vent so will give that a try.

Have tried using choke and that makes no difference at all.

Must say not too sure how airbox to carb should be set up. Originally carb 1 and 4 were blanked off, with 2 & 3 having breather to aibox and fuel breather pipe attached.

After my Mate has had a play he has now blanked off 2,3 and 4 leaving fuel breather on 1 and no air box pipe to carb connected. Tho that said either combo has made no difference to my 6000 rpm prob!!:pinch:

Haven't checked fuel tap yet as being tight I am waiting for tank to run low!!!!:blush:

wyliewix wrote: Must say not too sure how airbox to carb should be set up. Originally carb 1 and 4 were blanked off, with 2 & 3 having breather to aibox and fuel breather pipe attached.

After my Mate has had a play he has now blanked off 2,3 and 4 leaving fuel breather on 1 and no air box pipe to carb connected. Tho that said either combo has made no difference to my 6000 rpm prob!!

I think a photo would be helpful here as this is really confusing. What is being blanked off? Also, knowing for sure which carbs you have would help, again a photo could help us determine that.

.

Right I'll try my best.

Have got photo's but not sure how to upload.

Carbs are cv type. By blanked off I mean a cap has been put on carb vents/nozzles found on the top.

The bike is definately a F2 checked frame. As it was an import I'd say it is one of the last 'Z's as it has aquired a lot of the 750 trimmings. It is declared on log book as a 1977 but I know this is not so as it has electronic ignition and cv carbs, so if I discount frame no details which definately say KZ650F-2 lets say it's an F1

Pretty sure nothing should be capped off from the factory. But others who have the 650 with CV's will pipe in, I'm sure. Check the manual download linked above - it may provide some clues.

Lots of good info on kawasaki.com, including parts diagrams, part numbers, models sharing same part, availability, etc.

Here's a link for help with navigating the site and finding information.

kzrider.com/index.php?option=com_kunena&...w&catid=13&id=376734