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Discussion Starter · #1 · (Edited)
Hi guys, im a noob here, but a pretty experienced d.i.y mechanic.

First things first, the bike has new rings, size 40 instead of 38 pilot jets and 3 turns, Fuel float height was set to 16.75mm instead of 17mm (slightly richer) , the float valve needle-tips are squished at the rubber tip not a perfect pyramid , And it did sit for months after the rebuild with the petrol cock left to prime and flooded the engine oil with petrol, but i caught onto that and drained the sump and reinstalled fresh oil, and installed an inline tap to the petrol cock to shut off when its not in use.

Valve adjustments were done when cold, not sure if need be done when hot, but they were not jammed open, i had clearances on all 16valves

The Bike runs pretty good, except for its erratic idle bouncing up 250rpm and down., so i assume now it must be the carb sync, they were synched by eye by me before i re-installed the carbies after i did the rings and valve adjustments..

Heres the kicker, I cant just plug off cylinders 3 and 4 and sync one and two together with a t-piece to a vac gauge. the bike wont start / or idle, it kicks over but wont start,


(all ports are blocked off at this stage) 1 and 2 with a T-piece to a gauge and 3 and 4 seperate lines that are blocked with a thick-screw.....And it wont start,

Then i switch it around and try and just see what vacuum #1 cylinder is pullin by itself, the other 3 vac-ports blocked individually,.. no go-er again,

Then i switch it around again back to stock with 1 and 4 synched up with its original hose and 2 and 3 to a T-piece as it is stock but the 3rd line that operates the petrol-cock diaphragm disconnected and plugged into the gauge, and it gives me a reading of about 15 cfpm and it starts/idles fine...

And when i connect 2 and 3 up like it is stock and then block the fuel vacuum line up with a screw and I then T-piece #1 and 4cylinders to the gauge it reads about 20cfpm vacuum,


Why cant I do each LEFT and RIGHT bank individually does anyone know?,

From what Ive been told by a mechanic you synch in #1 and 2 with its screw inbetween,
Tthen synch in #3 and 4 with its screw, then synch in the middle screw (between 2 and 3) obviously with a 4 vac-gauge setup,


But i cant even run the engine with its vacuum lines blocked , i have to run stock hose-routing, somethings up here, Ive sprayed starting fluid around the intake boots 'carb to head side' and nothing fluctuates so no leaks i assume, and i did spray a liberal amount....

Anyone with some helpful advice would be appreciated,

Am i running too rich with the richer+ leaking fuel bowls that it causes some issue or is the not being able to block off the vac ports separately other than stock factory setup something entirely different?


:frown2: *bangs head
 

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The mechanic advise you were given is correct, synch 1 & 2, then 3 & 4, followed by Left to Right bank

If i'm comprehending correctly???...why are you connecting to 1 & 2 **OR** 3 & 4.....why not connect vac gauge to ALL 4?

I recently did a ZX750 valve adjust (requiring pulling both cams) with zero issues synching.
 

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Discussion Starter · #4 ·
Are you not hooking up 4 gauges at the same time?

I dont own a 4-guage setup, just 2 gauges.


What I am implying though is the bike only wants me to test 1and 4 together or 2 and 3 together, and if i test 1and 4, 2 and 3 must share a common line , and if hook 2and 3, 1 and 4 must share a common line, If i alter any of those 2 pathways ...say to sync 1 and 2 together, then hooking up 3 and 4 to nothing at all but a capped tube -separate tubes. she doesnt run, and if i get wise and hook 3 and 4 up with a common tube (sharing vacuum) it still doesnt run.


It is an absolute nightmare.
 

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Discussion Starter · #5 ·
The mechanic advise you were given is correct, synch 1 & 2, then 3 & 4, followed by Left to Right bank

If i'm comprehending correctly???...why are you connecting to 1 & 2 **OR** 3 & 4.....why not connect vac gauge to ALL 4?

I recently did a ZX750 valve adjust (requiring pulling both cams) with zero issues synching.

Nice bike :) , well done, I havent got 4way vac gauge and if i did, i doubt it would run because if 1and4 and 2and3 dont share the original common vac-lines she wont run,



its soooo annoying, ive inspected every hose for cracks and holes, nothing, must be some internal damage in the carby ?


, as my above post 2 and 3 share a T piece to the fuel tap from factory, so i just plug in the vac gauge with a double sided 1/4 inch plastic barb that comes with the vac-gauge and then join the gauges vac hose to the barb and then to 2and 3 t-piece setup, ............... the kit also comes with a t-piece barb so i cut the single tube joining 1 and 4 and put the t piece in the middle to the vac gauge,


luckily with further research I see for my 2nd vac gauge which is a hand pumping brakebleed kit essentialy ,..... that I must limit the ammount of vacuum going to that gauge as it jumps around like a yo yo, luckily... as i was saying I have a spare valve that i can restrict air flow which should fit the vac line with a bit of force and i can then have cylinder 1and4 hooked to a Tpiece and 2and 3 to a T piece and to two seperate gauges, but thats not the correct way to sync the carbs,..... its an actual nightmare.
 

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I'm no expert, but I don't see how that is going to get you a true 4 carb sync. You may have better luck going through the carbs getting everything back to stock, and replacing the worn parts before syncing them anyway.
 

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I'm no expert, but I don't see how that is going to get you a true 4 carb sync. You may have better luck going through the carbs getting everything back to stock, and replacing the worn parts before syncing them anyway.
Its not....you need each gauge directly connected to each cylinder...no "teeing" of any of the vacuum paths. Each carbs' vacuum paths are separate and do not interconnect downstream. If 1 gauge is Tee'd to any 2 cylinders...how would synch between those cylinders be possible at all? Think about it.

Look at my photo of proper 4 cylinder mercury synch tool....each tube connected to each carb...enabling synching 1 to 2....then 3 to 4....then L bank to R bank....resulting in perfect synch as pictured. Works every time....twin cylinder to 4 cylinder.

OP needs to follow standard, accepted service procedures written in manual, use proper tools and not try to reinvent the procedure to meet his convenience.
 

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Discussion Starter · #9 · (Edited)
So yeah, just went and showed a seasoned bike mechanic the video of all 4 carbs blocked off individually and a no-start scenario, hes left scratching his head.



He said something along the lines of a XJ 650 (yamaha i take it?) once had a problem with the main shaft connecting all 4 butterflies leaking air somewhere in there on the seals between each carby, but Im left scratching my own head on that one as its his story not mine .


heres the link to the video i showed him, and you can see it tries to start with all 4 blocked off but fails instantly
 

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It not being able to start may be a good reason to get the bike back to stock. A funnel would come in handy to put fuel in the fuel line.
 

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It not being able to start may be a good reason to get the bike back to stock. A funnel would come in handy to put fuel in the fuel line.
Re: all 4 blocked off/no start vid....its obvious you've got other issues to deal with.

A remote, temporary tank is the only way to go while running/synching.

And for the record...you ARE dealing with a "seasoned bike mechanic" right here. Here's a vid of a 1992 Honda CBR600 F2 I did carb work on a few years ago....to show you the remote tank I built in the 70's from an old coffee can no less.....and still in use today.
When brought to me,owner complaint was the idle all over the place..up/down. The vid taken the next day after I received the bike and completed my carb work...21 hours actually.

https://youtu.be/aU0uX8FehA8
 

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@JJ_GPZ_600 quote...."He said something along the lines of a XJ 650 (yamaha i take it?) once had a problem with the main shaft connecting all 4 butterflies leaking air somewhere in there on the seals between each carby, but Im left scratching my own head on that one as its his story not mine."

I did 10 years at a Yamaha dealer long ago....your mechanic friend is referring to Yamaha's long ago YICS system which was used on some sporty Seca models.

YICS....Yamaha Induction Control System....a balance port which connects all four carbs to each other to create a performance enhancing fuel swirl ...

BUT....the balance port had to be blocked with a special Yamaha "YICS tool" to synch the carbs....yielding exactly what you've got...1 vacuum port per cylinder...blocked and NOT interconnected....thats no accident that blockage of the ports was intentional to allow synching.
 

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"First things first, the bike has new rings, size 40 instead of 38 pilot jets and 3 turns, Fuel float height was set to 16.75mm instead of 17mm (slightly richer) , the float valve needle-tips are squished at the rubber tip not a perfect pyramid"

FWIW....I'd suggest returning to 38 pilots and use 2.5 turns starting position, 17mm float height after replacing the distorted, defective float valves with new....all 4.

I believe you are overfueling, a factor to your non starting issue.

After completing the suggestions...the mixture screws will also need to be set further, bike fully warm, running, setting for highest RPM per cylinder. Did you replace the orings on the mix screws? If not, do that too. And bowl orings if leaking, hard or flattened.
 

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Discussion Starter · #14 · (Edited)
Thanks BigBadBass, I believe i am over fuelling too as when i pour in petrol down the main filler hose it sucks in a teaspoon every second just at idle its quite thirsty for idling, I think its spose to be 1/4 teaspoon a second not a full teaspoon


For instance that main filler tube,, it will drop roughly 1cm per second, i literally have to top it up every few seconds and im not even riding it, LOL
 

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Discussion Starter · #16 ·
Okies, heres an update, I set the float heights to 17mm, used a steel ruler and a razorblade taped on at 90' set at 17mm , they were all 16mm at least maybe one 15.8ish (pays not to do it by eye without such a device,


I pulled out the main jets they are all clean still and the jet holders holes are all clear,



I took out the pilot jets and they were all still clean enough, i reamed them out with wire just to make sure. (mandolin string)


I took out all the floats and respective float-needles and noticed they arent damaged just a shiny ring making them look damaged, so I suspected float seat seals worn, sprayed them with chain lube , let it soak in, blew air on the fuel line with all 4 float-seats plugged with fingers and there was no air coming through the o-rings on the float-seats so that was great news.


I then used a brand new roller-skate ball bearing and a 5mm through-punch to to locate in the brass float-seat hole tightly and i tapped the ball with a just-over "love" tap with a hammer. A trick i learnt a few weeks ago on the youtube, I was lucky enough to have the equipment on standby.



Lets hope that helps correct any leakage problems i may have had. I then noticed with 2 and a 1/2 turns on the pilot jets , cylinder #1's pilot needle was sticking up 0.75 - 1mm higher than its counterparts on the same ammount of turns, so I then backed off that cylinder #` pilot needle to match its brothers and that requires a further 1/4 turn on the pilot needle "richer" ,



I just got off the phone to my mechanic and he reckons maybe a washer or o-ring is missing on the pilot needle, so I`m going to take it apart in the morning to find out.
 

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Any chance you could put up a link to the video you mentioned, I wouldn't mind checking that out.
 

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Discussion Starter · #18 · (Edited)
sure bro, heres the original video, I have recorded a good 2hours footage i have to sift through for the layman to understand how to take the carbies off a gpz from start to finish , ill try do that tomorrow, its the rendering time that takes the longest, if you want high quality that is.


heres the link to the no-start scenario


Oh man i cant tell you the link without it knowing its a link, take the spaces out and copy and paste


y o u t u b e . c o m / watch?v=1RH15WcadqQ
 

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Discussion Starter · #19 ·
The only thing i can think of why it wouldnt start was the over enrichened fuel from the bowls, once i verify tomorrow whether it has any of its pilot screws missing o-rings or washers then I will know for sure that it is most definitely a flooded scenario
 

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I then used a brand new roller-skate ball bearing and a 5mm through-punch to to locate in the brass float-seat hole tightly and i tapped the ball with a just-over "love" tap with a hammer. A trick i learnt a few weeks ago on the youtube, I was lucky enough to have the equipment on standby.
No, I already saw that video. I want to see this trick. :wink2:
 
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