KZ900 A4 Could it be the kits?

Hi,

My bike is a mystery here in Spain. A second Mechanic has now had a go at getting the bike sweet. The Carbs have new kits, are balanced, float/tab levels purrfect and all clean as a whistle including the tank. Again it runs sweet for about 5 minutes and then the plugs start to foul. (we've checked theres no gas in the crankcase). This is interesting - adjusting the air intake screws makes no difference, it literally feels like there no effect from allowing more air in the mix and the plugs foul up again. Could it be the kits?

Things to know:

The bike has sat for a couple of years but I started her up every 2/3 weeks.
Though the start-up and running wasn't perfect before -this fouling didn't happen before the new kits.
The Carbs look in great condition - not too many miles on this one.
Floats are fine
Points are all set up good.
I have the original airbox etc.

Lastly, if it could be the kit, can anyone recommend a nailed-on reliable carb kit brand I can buy, with jets, needles, gaskets etc.?

I'm not a fan of "carb kits". They are full of aftermarket jets that may or may not actually interchange with your original jets. If you look at the service manual for a lot of bikes you will see that Kawasaki adjusted jetting quite regularly year over year but the "carb kits" claim to fit a broad range of models and years. And who knows if the orifice in these carb kit jets flow the same as the original Mikuni jets too. Plus, to properly clean a set of carbs they need to be taken fully apart and carb kits don't have all the parts you need to do this anyway.

If you still have the original Mikuni jets I'd start by cleaning them properly in carb dip and/or an ultrasonic cleaner. Then reinstall them. Do this after you verify all the passages are clean and there are no broken pilot screw tips in the carb bodies etc. I'm not familiar with those particular carbs but just go back to the basics like checking fuel level with the clear tube method etc. It sounds like you have a bad needle that's not sealing and too much fuel is getting through to the engine. I rebuilt a set of similar carbs a while back and had to bend the float tang a LOT in order to get the proper fuel level. I suspect someone used some crappy "carb kit" float needles in them though.

Thanks Nessism, Sadly I don't think the old jets are original Mikunis, another kit job I think.

.

Hi

Empty Message?

Sorry about that. I had a question, but by the time I hit enter it had been answered. Ed

Have you checked the valve clearances, and the coils if valve clearances to tight you will end up with blow by and poor running and if your coils are duff they may be breaking down, another thing to check will be plugs and caps, if they are both resistor type you most definately will have problems, how old is the petrol you know our European stuff is like piss and goes off in no time at all, i don't know what the mechanics are like in Spain but most of the young ones in the UK don't even know what points and condensers are, which is why i do all my own work.
Carb settings for European A4
Carbs VM26ss air screw type
main jet 115-r
pilot jet 17.5
needle jet 0-6
jet needle 5DL31 on groove 3
Air screw on carb sides 1 and 3/8 turns out = or - 1/4 of a turn

Thanks Kevski, I'm going to check the carbs with another mechanic and then get down into the valves and points like you say.
The petrol is new so It's not that, the mechanic is about the same age as my bike . What about electronic ignition?

dave3d wrote: Hi,

My bike is a mystery here in Spain. A second Mechanic has now had a go at getting the bike sweet. The Carbs have new kits, are balanced, float/tab levels purrfect and all clean as a whistle including the tank. Again it runs sweet for about 5 minutes and then the plugs start to foul. (we've checked theres no gas in the crankcase). This is interesting - adjusting the air intake screws makes no difference, it literally feels like there no effect from allowing more air in the mix and the plugs foul up again. Could it be the kits?

Things to know:

The bike has sat for a couple of years but I started her up every 2/3 weeks.
Though the start-up and running wasn't perfect before -this fouling didn't happen before the new kits.
The Carbs look in great condition - not too many miles on this one.
Floats are fine
Points are all set up good.
I have the original airbox etc.

Lastly, if it could be the kit, can anyone recommend a nailed-on reliable carb kit brand I can buy, with jets, needles, gaskets etc.?

Are you sure the pilot jet is the correct size? the air screw when fully turned in should cause the bike to stumble. I would start with that circuit. check a parts fiche and make sure the carbs are assembled correctly.

To be honest, the mechanical timing, valve clearances, points set-up and static timing of the ignition really need to be done before delving into the carbs, battery condition?, a video of the bike running may give us an indicator of your problem. As for electronic ignition i use a Dyna-s on my 78 thou, it's pretty much plug and play, there is also Boyer- Bransden in the UK, they are a good system and easy to install. The air screw type and not a lot happening when screwed right in is not unusual as this is really just a fine adjustment, it's hard to diagnose on a forum as it could be one of many things and really needs people to be present to actually get it right.

adjusting the air intake screws makes no difference, it literally feels like there no effect from allowing more air in the mix and the plugs foul up again. Could it be the kits?

If turning the pilot air screw doesn't affect idle speed, the pilot air circuit could be obstructed.

Good Morning! Might be a silly thing to check but? If the carbs were taken fully apart, choke plungers removed. Make sure the "pads" under the plungers are still intact and seating. The old Berrymans formula would melt the pad. Made it handy when replacing, easy to remove but bad for reuse.