Carb question

[MAFED]

Hi out there,

On going problems with my 1977 Z1000 rebuild, fitted an electronic ignition unit but still having problems, difficult to start without choke, often just cuts out & absolutely refuses to tick over, had a go at cleaning out the 4 Mikumi carburettors when I noticed another external jet underneath each carb adjacent to the float bowl, similar to the air screw, it has a slot in the head for adjustment, anybody recognise what this may be for?

Thanks

Mark

[zoro]

Sounds like the float bowl drain screws.

[MAFED]

Hi Zoro,

Thank you for the info, but having removed one of the screws it looks more like a brass needle or jet, similar to the mixture screw on the side of the carb, could this be an idle screw of some sort?

Cheers

mark

[zoro]

Are we talking about a 1977 KZ1000 with four mikuni carbs?If so,do they have pod filters or the stock airbox?Can you measure the ID of the carbs on the engine side?Im trying to determine what carbs you have.

[MAFED]

Hi Zoro,

Yes you are correct, they are definitely mikumi carbs on a 1977 Z1000 engine squeezed into a custom frame, the carbs have pod filters, and I will remove these tomorrow and look at the carb ID numbers, you suggest I measure the ID is this the internal diameter of the throttle opening on the engine side?

Thanks, your help is very much appreciated!

Cheers

Mark

[MAFED]

Hi Zoro,

The internal diameter of carbs on engine side is 28mm. I have downloaded a few photos showing the screw head for the jet in the fuel bowl & and the jet removed.

Cheers

Mark

[weedy64]

Is this your Carb?

http://www.pjmotorsports.com/Jets%20Pics/expvm29.gif

If so the item on the bottom is the pilot jet and the angled screw/needle is a pilot air screw (2.5 turns out from lightly seated to start with)

Are you certain that the jets are clean and the carb passages are clean. After much soaking and with the aid of an ultrasonic cleaner I still found I had a jet the needed prodding with a wire to clean it. I also had a passage that I had to introduce cleaner with a needle to reach the clog. I could only see it with a magnifying loop.

Good Luck

Glenn

[bad 79 kz 1000]

dont no if helps but on my 79 bottom screw is air 1/4 turn out runs like a raped ape with air pods and jet kit do not have side screws

[MAFED]

Hi Glenn,

I have given all four carbs a second clean & generous soak, set the pilot screws and just managed to get it to run, but only at 2000+ rpm! As soon as I start to adjust the idle to settle it down it coughs & splutters and cuts out! Ready for scrapping the carbs and getting hold of a set of decent second hand ones!

Many thanks for all your guidance

Mark

[MAFED]

Hi Bad 79,

The ¼ turn adjustment must be the only one I haven’t tried, will attempt tomorrow in a last ditch attempt to get it to run!

Cheers

Mark

[MFolks]

Go to this website and see if your bike would benefit from doing this simple to wire ignition bypass: wiredgeorge motorcycle carburetors - Vintage Japanese Motorcycle Carburetor Sales, Rebuilding and Restoration - Home His website has a similar forum for questions. This envolves a 40 amp auto relay, relay socket,some wire, wire splices an about an hours time.

To check your ignition coils primary side input voltage, remove the gas tank, and with the ignition switch on but the bike not started, read the voltage at the coils with a meter(at the smaller wires). If the battery is fully charged the voltage should be the same minus a very small amount. If it's down around 8 volts, your bike has a big voltage drop.

Many guys have done this ignition bypass with great results at KZrider.com - Home. They have reported a one kick start, and with electric start, barely having to hit the start button.

[OKC_Kent]

Are you using compressed air to blow out the passages? Is air or carb cleaner coming out the other end of the passage with force?

[MAFED]

Hi OKC Kent,

Good question, yes I have used compressed air and carburettor cleaner, when using the compressed air I did not notice much pressure coming from the passages? Yesterday was a slight improvement managed to get her to tick over at 1000-900 rpm only for a minute then it cut out! The bike revs smooth at above 2000 rpm, just a pig to start and will not tick over??

Thanks for your help

Mark

[OKC_Kent]

Maybe those little passages are still clogged. As long as it runs you can try Seafoam in the gas and maybe it will clear up; else I think it's back to another cleaning session.

[MAFED]

Hi OKC Kent,

I have not tied the Seafoam, but it is certainly an avenue worth exploring, as I am running out of options!

Thanks for your advice

Mark

[Mike900]

After you try starting are the spark plugs wet or dry?
If they're wet then I'd try another set of plugs.
How did you set the timing after switching systems?
Have you checked compression?
Plenty of fresh gas?

[MAFED]

Hi Mike900

Thanks for your questions; the plugs are always dry after it eventually runs, usually black and sooty, but I put that down as needing the choke to start it even when hot.

The timing question is interesting because I did fit the a new Boyer-Brandson ignition unit and after a weekend of attempting to get it to run & tick over I thought that the timing may be out because since fitting the new ignition unit the bike would still not idle (I fitted this in the first place because the engine was lumpy, difficult to start and would not idle in the!)

So I decided to turn the magnetic rotor anti-clockwise (advanced) the ignition and the bike started up and miraculously allowed me to settle the idle to 1000rpm, I then decided to turn it off and restart, there was a little running on but she started at the first push of the button!! But then it all turned sour when I adjusted the pilot air screws, as she cut out & refused to start!!!!

I have not checked the cylinder compressions yet but the fuel is clean & new.

Any ideas will be well received

Cheers

mark

[Mike900]

Hi Mark,

1st thing I'd do is try to set the timing. It sounds like you're going to need a timing light & set it per the instructions that came with the unit.

Hopefully you can put in a new set of plugs & get it to run long enough to use the timing light. Make sure you check it twice. Once with the light connected to either the #1 or #4 plug wire & again with it connected to the #2 or #3 wire. Also double (triple?) check that the spark plug wires for #1 & #4 cylinders are going to the same coil. (They're very hard to start on 2 cylinders -trust me )

If you get it started but can't keep it running then carefully (don't burn yourself) check the exhaust pipes to see if all 4 are hot. If not then let us know which cylinders are cold.

Mike

[OKC_Kent]

Originally Posted by Mike900

Hi Mark,

If you get it started but can't keep it running then carefully (don't burn yourself) check the exhaust pipes to see if all 4 are hot. If not then let us know which cylinders are cold.

Mike

Use a spray bottle with water. A running cylinder will turn the water to steam, a dead cylinder will let the water run down the pipe.

[tark48]

You know sometimes those old carbs are just worn out!
I have worked on many KZ sometimes a good cleaning will work and other times not!
Mikuni RS flat sides are real good option.
Early suzuki katana 750 cv carbs work great, with the larger intake boots which you can get at Schnitz Motorsports, Inc they just need some jetting, the dynojet stage 3 is a good starting point.
But even on a stock motor the RS's really make the motor come alive!