Help! KZ wont take gas.

Hi fellas! Ive read through these forums and yall know your stuff. So, lets see what yall can come up with. I have a 1980 kz750 G1. When I bought it it wouldnt start. The guy I got it from said it just needed carb work (yeah right). Took it to a local bike shop, they wouldnt touch it. Took it to the other place and they did some work. Shimed a tight exhaust valve, installed new points, fixed starter gear... Got it idling with choke on. Thats as far as they could get. So brought it home, downloaded the service manual (thanks bis!) and got to work. I dismantled the carbs, removing pilot jet, main jet, and float needles (both looked perfect).
Adjusted floats to within spec.
Blew them out with carb cleaner and compressed air.

Didnt work. Same problem. Slightest throttle it dies like its running lean. So went on down the list.
Changed plugs, they showed rich but turns out they had put wrong ones on at the kaw place.
Checked coil and wires with ohm meter- it was right on spec.
Re-adjusted points as per manual.
Cleaned petcock- fresh gas.
Inspected boots for leaks, unfortunately none.
Cleaned carbs again today just to make sure. Yup they are clean.
Only things not perfect- pinhole in diaphragm repaired with tiny bead of gorrilla glue, and someone had stripped out a drain plug and replaced with larger thread screw. Same length shaft so not obstructing the airway.

Im stumped and turns out cussin it doesnt help at all.
What else could it be?

Hello, FortPayne750g1, and WELCOME to KZr!

Here's a carb diagram from kawasaki.com for reference.

If not already done, would assure #47 main jet plug screw isn't missing.



Good Fortune!

That doubles as float drain on this model. That is the one that was replaced with a larger thread screw on one carb.

After stumbling round a little bit came across coil power mod. Might try that tomorrow.

Thanks Patton

Are you using the stock airbox and air filter? Ed

Also make sure the slides #19 in the diagram are supper free and slide very smooth and free. If they hold up they wont let in the fuel.

FortPayne750g1 wrote: ...Adjusted floats to within spec....

If not already done, would assure correct fuel levels by performing the clear tube test.

The mechanical float height measurement is notoriously unreliable.

Before resorting to the coil mod (which simply assures battery voltage to coils without correcting issues causing the loss of voltage between battery and coil), would visually observe spark on removed plugs, looking for fat blue spark.

If fat blue spark is present, the coil mod likely won't help much.

Would also assure proper function of the timing advancer.

Good Fortune!

If it idles pretty good, but dies when you crack the throttle i'd check the condensers, had same kind of problem on my CB550. My uncle owned it before I got it and he had changed them, they were grounded out on the points plate, so it was like they were not even installed. so maybe throw a set on and see what happens, if it's been setting for awhile they could be bad. There is a way to check them with a DVOM by charging and then reading the amount of time it takes them to discharge but I don't know the Specs on how long it should take or whatnot.

Carbs, air box- stock.

New points assembly, but will check condenser 2mrw just to make sure.

Did not inspect timing advancer, might be a good idea. I assume service manual shows what to look for in a bad advancer, ill let yall know what i find.

Thanks guys!

FortPayne750g1 wrote: That doubles as float drain on this model. That is the one that was replaced with a larger thread screw on one carb.

After stumbling round a little bit came across coil power mod. Might try that tomorrow.

Thanks Patton

don't go with the "Coil Mod" as a fix. But you can of course test with something going to the coils from the battery. If you find the voltage low on the Yellow/ Red at the coils. Check also the Brown wire at your voltage Regulator/ Rectifier assy. Low here will cause charging issues, overcharging if voltage is low. The way the circuits are feed, the white wire from the Main Fuse goes in to the Ignition switch, then when on the switch powers both the coils and R/R. So check both sides of the Main Fuse Holder, wires, clips, fuse, for voltage drop.
Here is the link in "File Base" for your Diagram: www.kzrider.com/filebase/cat_view/99-198...3-kawasaki-kz-750-g1

FortPayne750g1 wrote: ...Did not inspect timing advancer...assume service manual shows what to look for in a bad advancer....

Function is best checked with a strobe type timing light.

Visually observe advancer quickly move back and forth as rpm is varied by blipping the throttle.

Good idea to put a drop of oil on each pivot point.



Hoping the advancer doesn't look like this: :pinch:



Good Fortune!

Well while on my way to take the points assembly off i turned the engine over with the wrench and heard bubbling.:huh: Upon further inspection it was coming from the boot between carb and engine intake. I had removed them previously to check for cracks and dry rot and found nothing. I had also ran the starting fluid test and the rpms stayed the same. I think turning the shaft counterclockwise pushes pressure out the intake but im just guessing though. So what I did was make a gasket from gasket material and add just a tad of black gasket compound to ensure a good seal. Takes 24 hrs to fully set up and think ill wait it out. If she takes throttle ill order new boots and be good. If not ill proceed with timing advancer inspection.

Thanks for the great advice guys!

P.S. - you were right about skipping the coil mod. After checking my voltage im at 11.48 v. Not enough for significant coil performance drop I dont think.

GOT IT!!! Patton your awsome. Thanks guys for the great advice!

After waiting several hours tried out new seal on carb boot, it was a no go. So straight to the timing advancer; it looked like pic 2:ohmy:

So a can of wd40 and some steel wool later...:woohoo:

Crazy thing is kawa dealership had to look right at it when they installed the new points. Oh well, it works now and cheaper this way.

Knew yall could figure it out!