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Kawasaki ZR750C1 Zephyr 1991
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Discussion Starter · #1 ·
Good day everyone,

Recently I've been given a Kawasaki ZR750C1 Zephyr which sat in a garage for over 10 years.
I'm very happy with the bike and hope to drive a lot of fun and safe km's with it.

Since it didn't run for that long I've had to do some maintenance obviously. Well, suffice to say I renewed everything that was (kind of) worn as well as motor oil, sparkplugs, air filter, tyres, oil filter, brakes (pads and plunger seals) and last but not least gas.
Also, the fuel tank and the carbs have been fully restored and revised.

It runs and drives but there are a few little problems I would like to discuss over here with all you fanatics:
1. If the motor is warm (without choke) it idles at 2500-3500rpm, if I remove the tank and start it it idles at 1200rpm.
2. The left exhaust makes a puffing sound (idling and driving).

Does anyone have a clue what may be the problem? I can't find it and don't know where to look anymore.

Thanks in advance.
The solution for this problem would make my day!!

43219
 

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Usually a high idle after carb work is due to a vacuum leak.

The leak usually comes from the rubber ducts that connect the carbs to the cylinder head. You could try checking for leaks and tightening the duct clamps.

I cannot explain why removing your tank fixes the problem. That is either a total fluke, or there is something else going on. Keep us posted please.
 

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Kawasaki ZR750C1 Zephyr 1991
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Discussion Starter · #3 ·
Is it possible that the high idling RPM could be the result of the tank tap vacuum seal not properly working?
What I mean is that the fuel comes out of the hose even though it's on "on" and "res". Normally this should be sealed by the membrane in the tap, right?
 

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You don't say if had tried lowering the idle by turning the idle knob under the carbs.

Of course, you do realize, if you take the tank off, and start the engine, you would have to plug the vacuum hose to the fuel petcock, or the carbs will be getting extra air from it.

You don't say how many miles on this bike either.
 

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Kawasaki ZR750C1 Zephyr 1991
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Discussion Starter · #5 ·
You don't say if had tried lowering the idle by turning the idle knob under the carbs.

Of course, you do realize, if you take the tank off, and start the engine, you would have to plug the vacuum hose to the fuel petcock, or the carbs will be getting extra air from it.

You don't say how many miles on this bike either.
Yes I tried lowering the idle speed with the knob on the underside of the carbs, but didn't made a difference. And when the tank is off I needed to turn it back to the position where it was because otherwise the engine wouldn't run.

Yes I did that precisely. I plugged the vacuum hose!

Total miles is about 28k.
 

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Check to make sure the throttle cable is not getting snagged. Perhaps by removing the tank it is freeing up the cable?
When you twist the throttle it should not immediately operate the mechanism at the carbs. There has to be a small amount of free play. Check for free play while you turn your handlebars from full left to full right and then in the middle position.
 
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