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1991 zephyr 750 question 10 Dec 2023 06:45 #892514

  • Robby2894
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A couple months ago i bought this 91 zephyr 750 as a project bike. When I bought it, it struggled to start, but would with a little finess, I rode it home but was only able to use about 75% throttle anymore and it'd just bog at a bit lower rpm then at 75% throttle and wouldn't go past around 85-90mph. 

Because of that i was going to bypass the evap cannister and vsv, because i figured without the emissions and vacuum bullsh*t it will start easier and run better just like any engine when you get rid of all the emissions bullsh*t. I still need to know if I should cap all 4 carb vac nipples after I remove the vsv and cap the ports where the two hoses connected the vsv to the valve cover? 
I have put new main jets and diaphrams in the carbs aswell.

I was also wondering if they came stock with a fuel pump and regulator or where the stock cvk32's gravity fed? It did not have a fuel pump or regulator on it when I bought it. 
If they didn't come stock with a fuel pump and regulator. Would it be a good idea to install one? Was wondering if it would make it have constant even flow, and possibly make it start easier and run better? Thanks

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1991 zephyr 750 question 10 Dec 2023 08:06 #892517

  • Stereordinary
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I can’t answer your second question, but for the emissions removal you need to block off all of the remaining holes. I think that’s only 3 of the 4 on the carbs, two on the engine top cover, and one at the airbox. 

Love the Zephyrs, post pics sometime. 
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1991 zephyr 750 question 10 Dec 2023 13:11 #892548

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There is a lot to reply to…
-No, they never came with fuel pumps or regulators. A properly functioning fuel tap will provide more fuel than the motor can consume. 
-As mentioned, the vacuum port closest to the fuel petcock has to be used for the fuel petcock. The others have to be blocked off with the correct rubber caps. (Autozone vacuum caps will rot apart in weeks as they are not fuel resistant.)
-If you remove the “clean air system” on the valve covers, loop the two reed boxes together with a hose or buy a block off kit. Plug the giant hole left in the air box. 
-Zephyr fuel tanks are notorious for rust. Like really really bad. So remove your petcock and make sure it isn’t full of rust particles. If it IS full of rust, then tear down the carbs all the way. (As in separate every carb body.) The fuel distribution pipes between carbs are where the ultra fine rust particles settle and then plug everything up.
-Thoroughly clean the carbs. (Jets, emulsion tubes, air jets, all of the many idle ports….all of it.) Check that the float heights are correct. The CVK32 carbs on the Zephyr use the exact same rubber o-rings and other parts as the Zx600a/b/c, Concourse touring bikes. So I found sites that sold complete Viton o-ring kits for cvk carbs that I couldn’t through Kawasaki. 
-Verify that someone hasn’t put in a Sigma jet kit.  The “cheap” jet kits require that you drill an extra large hole in the diaphragm slide. If done/drilled improperly, those carbs will never work properly ever again. (Pod air filters do not physically fit in the 750 Zephyr frame, so don’t try to go that route) 
Factory Pro is the only jet kit for the 750 Zephyr that doesn’t require drilling. 
-Zephyrs use a computer to control the ignition advance and not governor weights like the older 750’s. So just look to make sure the Ignition box looks stock and the wiring looks factory. If someone hacked another ignition box in, that would also cause high rpm issues.

My best guess is that you have rust plugging something up somewhere in the fuel system. 

Let us know what you find. 
 
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1991 zephyr 750 question 10 Dec 2023 22:53 #892581

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-If you remove the “clean air system” on the valve covers, loop the two reed boxes together with a hose or buy a block off kit.
Correct. Or you can also go find yourself a non-US market valve cover off of eBay that doesn't have the reed valve ports in the first place, and slap that puppy on there. Makes for a cleaner look.
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1991 zephyr 750 question 16 Dec 2023 06:57 #892781

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-If you remove the “clean air system” on the valve covers, loop the two reed boxes together with a hose or buy a block off kit.
Correct. Or you can also go find yourself a non-US market valve cover off of eBay that doesn't have the reed valve ports in the first place, and slap that puppy on there. Makes for a cleaner look.
It would also be a good idea to tap the ports and block them with grub screws.
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1991 zephyr 750 question 16 Dec 2023 08:53 #892784

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Agree on the grub screws...and non-air injection valve cover.  I'm running the valve cover from a 750 Turbo.

P1020013 by nessism , on Flickr
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1991 zephyr 750 question 27 Dec 2023 04:23 #893161

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Do you by any chance have a link to where I can get the reed valve block of covers/kit?

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1991 zephyr 750 question 27 Dec 2023 05:06 #893162

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Do you by any chance have a link to where I can get the reed valve block of covers/kit?
A google search turned up this...www.6sigmajetkit.com/kawasaki-ais-block-off-kit.html

APE sells them for the 550 and J head 1000/1100...kzzone.com/billet.html

 
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Last edit: by Nessism.

1991 zephyr 750 question 27 Dec 2023 09:19 #893164

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Should I keep the reed valves installed when I install the plates?

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1991 zephyr 750 question 27 Dec 2023 10:21 #893171

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Should I keep the reed valves installed when I install the plates?
I'd ditch them.  They won't work anyway.

Are you going to install grub screws in the ports?

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Last edit: by Nessism.

1991 zephyr 750 question 27 Dec 2023 18:59 #893176

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Ok. I'm not sure yet. For now I'm going to just plug the ports and will decide later on what I'm going to do. Still trying to decide whether I'm gunna go with the plates or splurge and order a euro valve cover.

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1991 zephyr 750 question 28 Dec 2023 05:39 #893186

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Cheapest option is to run a piece of hose between the two ports.  That will seal them off.  It reduces the clutter, but not as much as other options.

Here is a reasonably priced valve cover...

EDIT: the parts fishe shows the Zephyr uses a different valve cover gasket than the early 750's.  The valve cover linked below, may not fit.

{remove underlines}

https___://www.ebay.com/itm/315039636689
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Last edit: by Nessism.
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