76 KZ 900--Where do I start

My 76 KZ900 A4 is in the shop to get a new rear tire. That's the easy part. Why it runs like crap and figuring out what to try first to fix it is the hard part. It fouls plugs (NGK8ES), and cuts out around 4K rpm when it is running. I'm not much of a mechanic. I've been reading comments and problems that many of you are having or have had that are very similar to my problems I'm having with my bike, and hope someone can help. I've had it in several bike shops over the last 32 years I've owned it and nobody can seem to fix the problem permanently. I've tried stock Mikuni 26 carbs, 28 carbs, and then back to the 26's--which have been totally rebuilt. I've added Dyna ignition, went back to the stock airbox from individual filters. I bought it in '78 with a Denco left exit 4-1 header. I've tried packing the baffle to increase back pressure but ended up taking the baffle out again and am presently running it unrestricted. With fresh plugs it will fire right up (with full choke) and run at high idle just fine for about 2 minutes, then foul up and only run on 2-3 cylinders. I've had the top half rebuilt about 1000 miles ago--rings,valve guides, valves,intakes,cut valve seats--also cleaned carbs, put in 17.5 pilot jets, replaced cam chain, plug wires, and TS(?) relay. I'd like to narrow it down a bit for the mechanic to start the process of elimination. I've paid a lot of shops a lot of money over the years and still have same problems. So, if I'm going to spend some more money, I'd like to make sure I'm throwing it in the right direction. Any suggestions on where I have him start: check coils for correct output, compression test,go back to individual air filters, re-pack the baffle and put it back in, or start messing around with carb adjustments? I'd like to be able to just ride it whenever I feel the need for some g-force. I want it to run like the screamin' banshee it used to be before all these problems. Thanks a lot for any help.

Order a set of the copper wired sparkplug cables/leads, replace the sparkplug caps with non resistor ones for better spark. I think www.z1enterprises.com sells the Dyna brand sparkplug wires.

Do you have the original ignition coils or are you running the Dyna ones?

What does the compression look like hot and cold?

Others will be along with advise too..........

before u try something more complicated,try something simple.Regap ur plugs from the .032 setting to a .040 setting and see if that improves things or not.bj

ZTop wrote:

My 76 KZ900 A4 is in the shop to get a new rear tire. That's the easy part. Why it runs like crap and figuring out what to try first to fix it is the hard part. It fouls plugs (NGK8ES), and cuts out around 4K rpm when it is running. I'm not much of a mechanic. I've been reading comments and problems that many of you are having or have had that are very similar to my problems I'm having with my bike, and hope someone can help. I've had it in several bike shops over the last 32 years I've owned it and nobody can seem to fix the problem permanently. I've tried stock Mikuni 26 carbs, 28 carbs, and then back to the 26's--which have been totally rebuilt. I've added Dyna ignition, went back to the stock airbox from individual filters. I bought it in '78 with a Denco left exit 4-1 header. I've tried packing the baffle to increase back pressure but ended up taking the baffle out again and am presently running it unrestricted. With fresh plugs it will fire right up (with full choke) and run at high idle just fine for about 2 minutes, then foul up and only run on 2-3 cylinders. I've had the top half rebuilt about 1000 miles ago--rings,valve guides, valves,intakes,cut valve seats--also cleaned carbs, put in 17.5 pilot jets, replaced cam chain, plug wires, and TS(?) relay. I'd like to narrow it down a bit for the mechanic to start the process of elimination. I've paid a lot of shops a lot of money over the years and still have same problems. So, if I'm going to spend some more money, I'd like to make sure I'm throwing it in the right direction. Any suggestions on where I have him start: check coils for correct output, compression test,go back to individual air filters, re-pack the baffle and put it back in, or start messing around with carb adjustments? I'd like to be able to just ride it whenever I feel the need for some g-force. I want it to run like the screamin' banshee it used to be before all these problems. Thanks a lot for any help.

first off... Welcome!!......if it were me , i would start by checking the charging system...get a cheap multi-meter and put it on dc volts 20 and put neg on neg and pos on pos and rev bike to 4k......should get low 14s.....if you only get in the low 13 s....charging system no good....that would account for crappy run at 4k....you must have a known good battery for test.....if it is aftermarket and more than 4 years old, it is suspect....if you let it sit for 2-3 days and test it again not running on dc volts 20 and shows less than 12v, it s junk....get this squared away and you can start with mechanical basics.....good luck

What is a TS relay?

Would keep the oem 26mm carbs and airbox.

Need good properly timed SPARK ---
With plugs removed, visually check for healthy blue sparks.
Use timing light to verify ignition timing (or at least static timing with ohmmeter).
"F" mark aligned with case mark.
Advancer working properly (if sticking, likely needs cleaning and lubing.)

Need acceptable COMPRESSION ---
Compression test AND assure correct valve clearances.

Need correct FUEL MIXTURE ---
Assure air filter isn't dirty or obstructed with a shop rag, gloves, or whatever.
Would assure float bowl fuel levels are correct, using the clear tube method.
Test run with pilot air screws leaner (turn out counter-clockwise).
Might be a dirty pilot circuit.
Might be incomplete closure of choke plungers (for whatever reason).

Based on reported history, am guessing ignition and compression are probably okay.
Which leaves fuel mixture as prime suspect.
Am also guessing too high fuel level or dirty pilot circuit.

Good Fortune!

[Click on image to enhance view.]

WEAR PROTECTIVE GOGGLES WHEN USING CARB CLEANER SPRAY.

keith1 wrote:

...must have a known good battery....

AMEN to that!

Also assure battery fluids to correct levels.
And assure terminal connections are clean and snug.

Assure integrity of ground connection where negative battery cable attaches to rear of engine.

Use kick starter.

Remove choke asap.

Test run without headlight.

Good Fortune!

Thanks to you all. I'll have the mechanic start with all your suggestions--copper plug wires, non resistor caps, regap plugs,and charging system check. I just put a new battery in it so hopefully that part can be eliminated, but I'll have him check it just the same. Before I left the shop, the mechanic did say he'd probably do a compression test, even though it's only got 1000 miles on the top end job--you never know.

I'm running the Dyna ignition with new coils but I think I do still have the old coils in my old parts box--along with old carbs with accelerator pump, etc. I'll get up in the attic and take a look.

Thanks again. I appreciate the help and look forward to being able to ride again.

To confirm, 1976 KZ900 oem carbs were 26mm Mikuni manual slide with NO accelerator pump.

Good Fortune!

Thanks Patton. Battery is brand new so I'm hoping that part is good--but I will check the engine ground. I'm assuming your suggestion to kick start it is to save juice used by the starter? Likewise with the no headlight--which I only use when riding (very dim anyway since it's original style (non-halogen). Not sure what the TS relay on my old repair bill means--I just listed it along with everything else that was done the same time I had the top end rebuilt. Remove choke? --use throttle instead then? --not sure it would even start but I can give it a shot. I'll also print out your carb clean diagram and instructions and try that too. Whew--got a lot to do. I'll let you know how it turns out.

Thanks heaps.

Correct--that's the present set-up I have.

ZTop wrote:

...Remove choke? --use throttle instead then? --not sure it would even start but I can give it a shot....

Just meant push the choke lever down asap, to avoid loading up the spark plugs while warming the engine.

If battery is low, running for awhile with the headlight off allows the battery to charge faster.

Good Fortune!

I know I am new here and y'all can tell me to shut up but after reading this thread it reminded me of my old 76 KZ900, dejevue.

Go to the local auto shop and cross reference your plugs with a set of champions. (I do hate them plugs in everything else) I had the same issues and a whole season and a thousand bucks in cool parts with a shitty running plug fouling bike. Last time it ran on 3 cylinders I was right at a parts store and crossed them with anything they had cause they didn't have the NGKs. Only thing was the champions. I swear I didn't have to change them out for 3 years till I sold the bike.

Just for chits and giggled give it a whirl, try to check the gap but I didn't and had enormous success. All the problems simply went away. Had different coils, points, gaps, timing, carbs, smooth bores, hot coils, electronic ignition kirkers etc etc. nothing helped till the plug change.

Jeff