Carbtuning The Carbs - Vacuum Line?? - Page 2 - Kawasaki Motorcycle Forums
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post #11 of 20 (permalink) Old 11-08-2018, 05:41 PM Thread Starter
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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?
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post #12 of 20 (permalink) Old 11-08-2018, 07:00 PM
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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!

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post #13 of 20 (permalink) Old 11-08-2018, 11:52 PM
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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.
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post #14 of 20 (permalink) Old 11-09-2018, 04:32 AM Thread Starter
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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...
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post #15 of 20 (permalink) Old 11-09-2018, 07:06 AM
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Originally Posted by Dr. Frankenstein View Post
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-l...ki-suzuki.html


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post #16 of 20 (permalink) Old 11-09-2018, 01:58 PM
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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.
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post #17 of 20 (permalink) Old 11-10-2018, 07:53 AM Thread Starter
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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.
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post #18 of 20 (permalink) Old 11-10-2018, 04:52 PM Thread Starter
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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.
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post #19 of 20 (permalink) Old 11-10-2018, 06:00 PM
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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.

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post #20 of 20 (permalink) Old 11-16-2018, 11:55 PM
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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.

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