78 KZ650B won't run without choke

Hey everyone,

I've got a 78 KZ650 that runs well every once in a while. It ran just fine when I bought it, the next day it wouldn't start. A few repaired connections in the dash and a new dyna-s ignition later, it ran but idled at about 4k RPM, so reading through the forum I learned it was most likely a vacuum leak, so I sprayed starter fluid all around and fixed a few suspect boots, re-sync'd the carbs, and it ran just about perfect for a week. Now if I run it without the choke fully on and give it any throttle it dies out. I've gone back through the carbs and cleaned them as best I can, the plugs were black when I took them out so it seems like it's running really rich and I don't know how to lean the mixture out any. The mixture screws on the outside of the carbs are all 2.5 turns out, but I don't notice any difference whatsoever when I turn them out or in, either in the idle speed or the vacuum gauges on the sync tool. Also noticed fuel spitting out of the boot between the carb and the #2 cylinder, but when I sprayed the area with starter fluid there was no change in idle speed. Is it possible the engine is overheated from running in place? should I run all the adjustment screws on top of the carb down together? what am I missing?

Thanks a lot!

i would think 2.5 turns out would be pretty rich. and the gas coming out between cylinder 2 and carb would be a needle i would think. make sure you floats are set right and that the needle on number 2 isnt worn or dirty

The test for leaking carb holders isn't going to show much unless you can do it with the engine idling low (like below 1000 rpm). If you see gas coming out from between the cylinder head and the carb, I'd say you carb holders are leaking. BTW, are you positive your carbs have "mixture screws?" If the screws are located up on the side of the carbs they are air screws. Turning them counterclockwise increases the air. They are not going to make much difference in the vacuum, that's not how you sync the carbs or adjust the idle. Do you have a Kawasaki Service Manual? Ed

Take your carb off and clean it out thoroughly, it sounds like your pilot jet may be clogged a bit.

Here's a pretty good cleaning method for manual slide carbs with side located pilot air screw:



Wear eye protection while spraying, because the spray always backfires.

Good Fortune!

This is one of the most useful instructions I've ever seen! I haven't had time to take the carbs off yet, probably will this weekend, last time they were off I noticed that all the jets were what the stock should be, but in hindsight the previous owner installed a kerker 4>1 and a k&n filter in the air box and evidently never changed the jets.. In this thread ( forums.kz650.info/index.php?topic=1853.0 ), spudbuddy is running a similar setup with 95 mains and 15 pilots with the needles on the 5th notch; I have jets on hand to run what he's running, so when I take them apart and clean them again I'll try his setup and keep y'all posted on the results

78 KZ650...likely a vacuum leak, so I sprayed starter fluid all around and fixed a few suspect boots, re-sync'd the carbs, and it ran just about perfect for a week. Now if I run it without the choke fully on and give it any throttle it dies out.

Most re-seal jobs on carb holders don't last long, because the sealant soon fails.
Probably need new carb holders.

I've gone back through the carbs and cleaned them as best I can, the plugs were black when I took them out so it seems like it's running really rich and I don't know how to lean the mixture out any.

Would perform the clear tube test, and assure that fuel levels are within specs.

The mixture screws on the outside of the carbs are all 2.5 turns out, but I don't notice any difference whatsoever when I turn them out or in, either in the idle speed or the vacuum gauges on the sync tool.

Indicates something wrong inside the carb, usually an imperfect pilot circuit (due to obstruction)

Also noticed fuel spitting out of the boot between the carb and the #2 cylinder, but when I sprayed the area with starter fluid there was no change in idle speed.

Would sniff-test the crankcase oil, and examine its condition. If the oil is fuel-contaminated, should change oil and filter, and not run the engine until the cause is determined and corrected.

previous owner installed a kerker 4>1 and a k&n filter in the air box and evidently never changed the jets. In this thread (forums.kz650.info/index.php?topic=1853.0), spudbuddy is running a similar setup with 95 mains and 15 pilots with the needles on the 5th notch

Imo, 5th notch is likely raising the tapered jet needle too high out of the needle jet, and thereby producing an excessively rich fuel mixture. 4th position could be an improvement, and the middle position might be best. Recall that mid-range is governed largely by the jet needle position (as set by the notch clip); and that this interrelates with the fuel level.

Good Fortune!

the needles are currently on the third (middle) notch, would the 5th be closer to the blunt or tapered end? Also, spudbuddy is running vm22's, while i'm pretty sure mine are 24's. Should I leave the jets as is? right now they're 15 pilots and 102.5 mains. I've got the carbs off the bike now and just ran out of carb cleaner so I'll need to pick some more up over the weekend, I couldn't smell any fuel in the oil, and what exactly do float levels affect other than not dumping fuel into the engine and how far off can they be before they start affecting performance?
Thanks a lot

Fuel level influences the mixture in all carb circuits, throughout the throttle range.

For example, an otherwise perfectly tuned carb would be expected to start running rich if the fuel level rises above spec.

Good Fortune!

With baffled 4>1 Kerker and air-box K&N, larger main and pilot jets may offer improved performance.
Others having more experience with the particular make and model at hand will be able to offer better jetting advice.

And optimal jetting will remain dependent on having the proper fuel levels.

Good Fortune!

I cleaned the carbs thoroughly according to Patton's earlier post and adjusted all the floats to 23mm while they were open on my bench. I don't have a tool to measure the levels with clear tubing, but I ordered the mfr tool today and it should be here friday. I got the carbs back on and tried to sync them, 2 3 and 4 would sync together or 1 2 and 3, but when I adjusted 1 it would simply raise and lower the engine rpm and not raise the vacuum level to be even with the other three; 4 was backed all the way out and still the vacuum was not low enough to adjust equal to 1. I decided I'd sync 2, 3, and 4 together and assume for now that the vacuum line going to 1 was somehow bad, and it seemed to idle strongly. When I took it out for a test ride, it had no power at low rpms and started popping when I slowed down. New jets? what's my next step? Thanks...

wheresthelove83 wrote: ... adjusted all the floats to 23mm while they were open on my bench. I don't have a tool to measure the levels with clear tubing, but I ordered the mfr tool today and it should be here friday. I got the carbs back on and tried to sync them...no power at low rpms and started popping when I slowed down. New jets? what's my next step?....

Running sync is the final step in a tuning journey.

If not already done before syncing with engine running, would assure perfect functioning of the timing advancer, and visually observe spark quality (looking for fat blue sparks), and assure valve clearances are within specs, and assure correct uniform fuel levels via the clear tube test.

The procedure of adjusting the float height to conform with some measured distance while the carbs are upside down on the workbench, may or may not happen to come close to the correct height necessary to provide the correct fuel level. The fuel level is critical. When the fuel levels are correct in all carbs, it's likely that the measured float heights will vary among the carbs.

Carb performance depends on proper functioning of the other components, and even a perfect carb can't compensate for deficiencies in the other components.

Attempting to sync without first attending to all the other items upon which carb performance depends, is usually an exercise in futility.

Sometimes the clear tube test doesn't require any type of special tool, fitting, barb, or whatever; and the end of the tube itself may be snugly fitted inside the drain hole. Minimal leakage where the tube connects to the float bowl drain won't adversely affect the test results.

Good Fortune!