Kawasaki Motorcycle Forums banner

1 - 20 of 20 Posts

·
Registered
Joined
·
62 Posts
Discussion Starter #1
I was trying to fine-tune the carbs on my '78 KZ650 with a Carbtune, but what do I do with the vacuum tube coming off the No. 2 carb? The manual and Carbtune instructions just say to hook up the lines, but that #2 carb is being pesky...can I just block off the vacuum line - stick a golf tee in it or something, and then adjust to That carb, or...?


I'm pulling 16 bars Mg off carbs 1, 3, and 4, but #2 is just not behaving. I also put new carb holders on and did a spray test, and that was fine. The idle is set currently at about 1500, which got rid of that rattle I mentioned in a previous post, so it was probably set too low.
 

·
Registered
Joined
·
1,348 Posts
I suggest you check the compression to make sure #2 isn't lower than the others. If it is adjust the valves. I don't know what you have done to the bike already.
 

·
Registered
Joined
·
91 Posts
Yes. Plug the vacuum line. Balance all 4 to as close to all the same reading. The reading itself is not important. Just get all the same. Changing one will make others change too. All the same, or close, is what you want.


Sent from my LGMP450 using Tapatalk
 

·
Registered
Joined
·
62 Posts
Discussion Starter #4 (Edited)
Compression runs 155 - 165 each cylinder, so that should be okay...and thanks Mike! Is that what it should be pulling, about 22.5 Hg? What idle?

For what it's worth, I have the idle adjust all the way back off the stop, and it's still running about 1500 rpm... turn each adjuster IN to richen, and OUT to lean, yes...?
 

·
Registered
Joined
·
91 Posts
The specific reading is NOT important. Just get them balanced. When syncing increase your idle rpm high enough so it runs smoothly, then adjust each carb. Turn the adj screw and see which way the gauge moves.. It's an art in itself. Some say black magic.. Do it on a running temp engine. If its air cooled.. Put a fan on it so you don't overheat.

Sent from my LGMP450 using Tapatalk
 

·
Registered
Joined
·
62 Posts
Discussion Starter #8
Yes, this is my first time, and it's a little trickier than I thought - I set the idle at around 1500, but then couldn't get them all in line - I would adjust one, and doing so would cause another channel to rise, or lower.

I adjust #1, and #2 and #4 don't show anything. I get #'s 1 and 2 equal, and 3 and 4 are flat. Adjust those, and #1 and 2 go down, or Waaay up, and 3 and 4 barely show anything...tighten 3 and 4, and 1 and 2 collapse - or 1 and 3 go up, and 2 and 4 go down - - I'm all over the place !

Adjust one, the idle picks Waay up; screw that one back down, all four drop out...it's like playing carburetor Whack-A-Mole! I did wind up taking the carbs back out and bench-synching them again, and tightened down the allenheads on the carb holders, just to be sure I was on a 'baseline', and I was...the carb is really sensitive.

Technical note, though - the #3 carb appeared to overflow, Just Once - a big puddle of gas came out of the #3 overflow tube - I assume because I probably inadvertently closed the slide and it backed up - but what do you think?
 

·
Registered
Joined
·
91 Posts
Your description sounds correct for a 1st timer! Turn the idle up a bit and the others moving when adjusting one will decrease. 2000 or so rpm is ok. Do this all at opreating temp. Put a fan on the motor. Loosen the lock nuts just enough to move the adj screw. SMALL adjustments. Think 2 moves ahead. If #1 moves up when you move 3 up, adj #1 down then adj #3. And presto.. #1 moved up to match where you moved #3 to! Lightly snug the lock nuts during the process. Lightly blip the throttle also to settle in the slides after adjusting one. If the idle gets too high as it tends to climb as you get balanced, just turn it basc down some. A special carb tool is also very helpful. It lets you work the lock nut and adj screw without putting pressure on the slides.

https://www.z1enterprises.com/carb-adjustment-tool-set.html


Sent from my LGMP450 using Tapatalk
 

·
Registered
Joined
·
62 Posts
Discussion Starter #10
Sure; easy for You to say...! ;) So do you do #1 and 3 first, and then 2 and 4? Or does it matter?

And I do have that tool you included. I used to use it on my Virago and CX500, but this is the first time I've ever tried to do a whole BANK of them! It's amazing how much fuel it uses...


I think it's amazing how such little adjustments can affect the flow characteristics of the fuel - doing this gives you a real appreciation of just how finely machined carburetors are. Just like life, sometimes a little adjustment can effect a big change in performance...or, conversely, cover you in fuel and burn you to death. Either/or...:)
 

·
Registered
Joined
·
62 Posts
Discussion Starter #11
Ha! I did it! That adjustment tool referenced above was a big help, too. made it a helluva lot easier than a No. 8 wrench and a screwdriver.

But you fix one problem, and another rears its ugly head: while the bike was idling, as I was Carbtuning it, the #3 carb 'peed' out of its overflow tube...I had that happen yesterday too, but thought it was me ham-handedly adjusting the slides. Just the #3, none of the others.

I changed the oil, took it out for a brief run up the street and back - which was awesome considering the last time the bike ran was sometime in 1986 - and it ran great! But I notice that when it sits and idles, every 12 seconds a good spurt of fuel would squirt out of the #3 overflow tube. I turned the bike off, and watched it do it repeatedly, every 12 seconds. Got quite a nice-sized puddle before I took off the tank and watched my petcock continue to dribble, as well as glances at the fire extinguisher on the wall...


Took the tank off, and the petcock is dripping, rather steadily - but why would it be overflowing? That means the floats are dropping(yes??), allowing more fuel into the carb, which in turn goes into the overflow tube, and it 'pees'. Which means gas is somehow escaping(?) from the carb bowl? I changed the oil, the oil didn't smell like gas, there wasn't any fuel in it...the carb itself is not leaking around the gasket...any ideas? Nagging Thought: would the/could the needle seat be installed upside down? I don't think I did - I know what they look like and how they should go - but could that do it?


Also, FWIW, the idle screw is IN all the way, won't go any further; but the bike is idling right where it should be, around 900 - 1050/1100 rpms...would that have anything to do with it?
 

·
Registered
Joined
·
91 Posts
Congratulations on the tuning success! From your description of the #3 carb leaking out the overflow.... That's what a sticking needle or float set to high does... it overfills the bowl. The overflow pipe is doing its job and keeping the overfilling fuel from draining into the crankcase. A common misconception is that a needle will completely stop the fuel flow. Not true. When they were rubber tipped they did much better... so on to the petcock. Fix it, because it must be closed whenever the engine is not running. When fixing/setting the #3 float height, be very careful handling the carb bank and maybe you won't have to sync again. (but you should check them). Two steps forward, one step back!

Sent from my LGMP450 using Tapatalk
 

·
itching to ride
Joined
·
2,215 Posts
I synced my carbs on my gpz with a homemade apparatus two carbs at a time. I was pretty easy and I cross checked all four to be certain. I also gauged the slides to make sure the gap under them was the same. I should have kept that bike.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #14
Re: the floats and the needle - I'll bet it's the needle; I was Meticulous in setting the float height in all the carbs.

At least I'm getting pretty GD good at pulling and reinstalling them...;)
 

·
Registered
Joined
·
91 Posts
Re: the floats and the needle - I'll bet it's the needle; I was Meticulous in setting the float height in all the carbs.

At least I'm getting pretty GD good at pulling and reinstalling them...;)
Setting the float heights is done best by using the "clear tube" process. This gives you a visual certainty that the fuel level inside the bowl is right. There are too many ways to incorrectly set one by measurement of the float height.

https://www.z1enterprises.com/fuel-level-gauge-tool-kawasaki-suzuki.html


Sent from my LGMP450 using Tapatalk
 

·
Registered
Joined
·
1,372 Posts
I synced my carbs on my gpz with a homemade apparatus two carbs at a time. I was pretty easy and I cross checked all four to be certain. I also gauged the slides to make sure the gap under them was the same. I should have kept that bike.
Interesting... I thought a GPz had constant velocity carbs on all models. The openings on the throttle butterflies would be what is used as a gauge of sync and not the vacuum pistons. They will all sit there like a bump on a log until the bike is running and throttle twisted and I doubt it would be possible to measure how far open they are.

Doing two carbs at a time is possible with CV type carbs. You would first sync 1&2 to each other then 3&4 to each other and then connect your double gauge to 2&3 and adjust the center sync adjustment and all four would be then synchronized.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #17
Yes, I have two of those - they did come in handy checking the float height. I built a mount for the carbs and attached it to that, making sure to square it up with a level, and fabricated a auxiliary tank to hang off it; worked pretty well, plus it will be a handy piece of equipment to have around in the future.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #18
Update: I got the carbs off, AGAIN, and opened up #3 and sure enough, there was what looked like a thin blade of grass in the needle seat. I believe it was that that was causing the carb overflow. So, there you have it, I guess. All the others are running fine, I just hope I don't have to re-tune it when I put them back on, but I just might anyway. I'm going to at least flush out the passageways.

And No, I don't have an inline filter in there *yet - I was mainly working on getting the bike going - but I will be putting one in before I re-install the carbs.

All this JUST in time for the freezing weather to get here...! It figures. But, this is the first time in 32 years the bike has ran - it has a 1986 inspection sticker on it - so that's something, I guess.
 

·
Registered
Joined
·
91 Posts
Great report! Now, replace all the fuel lines (if you haven't already) when you add the filter, unless you want more practice pulling the carbs. Replace the vacuum lines also. Great idea on the rig you made for setting the floats w the clear tube. I did something very similar. Use some "Stabil marine" and non-ethanol fuel and maybe spring will bring NOT gooey carbs.

Sent from my LGMP450 using Tapatalk
 

·
itching to ride
Joined
·
2,215 Posts
Interesting... I thought a GPz had constant velocity carbs on all models. The openings on the throttle butterflies would be what is used as a gauge of sync and not the vacuum pistons. They will all sit there like a bump on a log until the bike is running and throttle twisted and I doubt it would be possible to measure how far open they are.

Doing two carbs at a time is possible with CV type carbs. You would first sync 1&2 to each other then 3&4 to each other and then connect your double gauge to 2&3 and adjust the center sync adjustment and all four would be then synchronized.
They are BS34's and you are correct it was the butterfly valves I gauged. It was back in 2009 when I got the bike and sometimes memory gets foggy looking back that far. Any way I looked online and got the idea on the homemade manometer. I thought about using 4 tubes and a plenum of sorts to connect them but figured I'd try the two tube setup first and see how it went. It worked great and I cross checked them pretty much like you said. It took a few tries to get them all four in sync but once dialed in the bike ran great.
 
1 - 20 of 20 Posts
Top