carb synch, vacuum variable at idle normal?

866 Views 11 Replies 6 Participants Last post by Dagon7, Oct 18, 2006

bluenote

Discussion Starter · Oct 16, 2006

I'm hunting for the cause of my surging bike, and I've had carbs & fuel suggested to me a few times. I checked out what my dealer service manual had to say, (nice 4 port digital tool incidently) and got myself a vacuum gauge.

My problem is, at idle, the vacuum is completely unreadable because it oscillates around so much. At 2000 rpm it begins to firm up and 2500 - 3000 it is pretty rock steady.

Does this indicate I have a vacuum leak? Could this be indicative of fuel supply issues? I tested 1st and 4th and got the same behaviour and then called a halt since I didn't know how to interpret the data.

Is this normal behaviour?

thanks for any insight

Cory

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Stewy

· #2 · Oct 16, 2006

Your vacuum should not be floating around that much at idle, or any RPM range for that matter, it should remain fairly steady. I leak wouldnt typically appear as frequent variations in vacuum, but more so as a drop in the overall reading.

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Danke

· #3 · Oct 16, 2006

Want more fun,,,,,,,?

Most carb stix aren't calibrated so you need to check them.

Connect two of the gauge lines to one of the bikes vacuum taps at the same time, they should read the same.

The reason they do not is the glass or plastic tubing that is used is not the exact same dia in the ID so they read differently.

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bluenote

Discussion Starter · #4 · Oct 16, 2006

Danke said:
Want more fun,,,,,,,?

Most carb stix aren't calibrated so you need to check them.

Connect two of the gauge lines to one of the bikes vacuum taps at the same time, they should read the same.

The reason they do not is the glass or plastic tubing that is used is not the exact same dia in the ID so they read differently.

I don't actually have the neato 4 in 1 tool (but thanks for the tip). Anyone want to hazard a guess on what's causing my vaccuum fluctuation, or if Im doing something wrong??

Cory

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Danke

· #5 · Oct 17, 2006

Could be a bunch of grit and grime in there now, looks like you've got some sort of old ZX-6, have you checked around to see if there's a dedicated Kawi forum in North America or the UK?

Could also be the idle mixture screws (if it has them) Maybe turned in so it's not giving enough fuel/air to stay consistent. Of some other carb change that's not allowing the idle circut to function properly.

Probably time to pull that bank of carbs, clean and inspect them, make sure they have all the right breather hoses hooked up, all the jets and needles are OK etc. Heard of one guy who put in a kit, and the needles hadn't been machined properly.They vibrated during use and milled out the mains so you couldn't do anything but pony up for new carbs (ZX-9).

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bluenote

Discussion Starter · #6 · Oct 17, 2006

Danke said:
Probably time to pull that bank of carbs, clean and inspect them, make sure they have all the right breather hoses hooked up, all the jets and needles are OK etc. Heard of one guy who put in a kit, and the needles hadn't been machined properly.They vibrated during use and milled out the mains so you couldn't do anything but pony up for new carbs (ZX-9).

I got some advice last night that it could still be a vacuum leak and that I should check using an unlit propane torch, I'll probably do that today and if I can't make progress there, then what you suggest is my next step. thanks for taking an interest

Cory

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gordopolis

· #7 · Oct 17, 2006

bluenote said:
I don't actually have the neato 4 in 1 tool (but thanks for the tip). Anyone want to hazard a guess on what's causing my vaccuum fluctuation, or if Im doing something wrong??

Cory

What tool *are* you using?

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bluenote

Discussion Starter · #8 · Oct 17, 2006

gordopolis said:
What tool *are* you using?

A regular old vacuum gauge (the only one to be had at canadian tire yesterday morning)..

Cory

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gordopolis

· #9 · Oct 17, 2006

bluenote said:
A regular old vacuum gauge (the only one to be had at canadian tire yesterday morning)..

Cory

Are you sure it's up to the task?

Maybe before you start trying to diagnose an (assumed) problem with your bike you should test again with a proper carb synch tool? (Ie. beg borrow but don't steal?)

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bluenote

Discussion Starter · #10 · Oct 17, 2006

gordopolis said:
Are you sure it's up to the task?

Maybe before you start trying to diagnose an (assumed) problem with your bike you should test again with a proper carb synch tool? (Ie. beg borrow but don't steal?)

I tried to eliminate the gauge as a part of the behaviour and could not re-create the oscillation without actual vacuum oscillation so I feel (fairly) confident that it is reading true (ie: the gauge itself is not faulty/insensitive/too sensitive). I *am* keeping that fact in mind though, unfortunately I have more suppositions guesses and inferences than facts at this point :/

I'd love to hear if anyone has experience with seeing this kind of thing before?

Cory

EDIT: to answer your question, I wouldn't turn up my nose to use a proper tool (especially when its time to actually synch) but I dont have convenient access to one so for now I'm proceeding like I've got a leak to find before synching if needed

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Commander Keen

· #11 · Oct 18, 2006

You'd be surprised how accurately regular vacuum guages read. Mines been faithful for years, best tool ever for finding idle a/f mixture. Erratic vacuum, I'd have to check again but can't that be an indication of improper cam timing, or even bad valves?

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Dagon7

· #12 · Oct 18, 2006 (Edited)

I just did a carb sync myself, I used motion pro stix, but I was told to do it one carb against the master at a time. This is diff. than the service manual and would not explain the need of 4 sticks, also what is the little tube in the back for? I assume breather? SO anyway my bike is running worse than before and the exhaust smells of gas. Also for lack of Honda 5mm adapters I used a universal valve checker to connect the intakes, not sure in retrospect if it was airtight enough for an accurate measurment. I think I'll take it in or anyone want to bring there adapters to my place in PoCo? I'll buy the beer.

"EDIT: to answer your question, I wouldn't turn up my nose to use a proper tool (especially when its time to actually synch) but I dont have convenient access to one so for now I'm proceeding like I've got a leak to find before synching if needed"

I've got the tool if you have 5mm adapters!

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