Vacuum petcock vs non vacuum

  • mjkawa
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Vacuum petcock vs non vacuum

23 Oct 2009 10:00
#329139
I have two kz650's, a 77 b, and a 78 d2. I am in the process of rebuilding rejetting and tuning both sets of carbs. I was thinking that it could be a very usefull diagnostic tool if I could switch the carbs back and forth. It could help me diagnose both problems w/ the carbs, as well as other potential probs.
Both bikes have pretty similar setups, (4-1 pipes, and stock airbox) so will probably be jetted the same.
But the 78 has a petcock w/ the vacuum, and the 77 has a petcock w/o the vacuum.
Could I simply change the petcock on the 78 to one w/o the vacuum, and plug the vacuum line?? Or will this affect how the carbs perform??
I know that I could just switch the tanks and petcocks with the carbs, but if I can, I would like to make it as easy as possible to switch back and forth.

Thanks for any ideas.

MJ
82 KZ-1000-J
77 KZ650 B

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  • TeK9iNe
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Re: Vacuum petcock vs non vacuum

23 Oct 2009 16:03
#329182
I've had nothing but leak problems (eventually) with the vacuum operated pets.

I don't mind turning my fuel on and off. :P

B)
Motorcycle Shop Owner/Operator

79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors ;)

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  • Patton
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Re: Vacuum petcock vs non vacuum

23 Oct 2009 16:32
#329184
Should be easy to simply cap off the vacuum nipple not needed for manual petcock.

Where vacuum petcock replaces manual petcock, just add vacuum hose from any vacuum nipple to the vacuum petcock.

Good Luck! :)
1973 Z1
KZ900 LTD

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  • deftones5792
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Re: Vacuum petcock vs non vacuum

18 Nov 2009 09:16
#334461
I am brand new to this forum and brand new to motorcycles. I bought a 1980 KZ550LTD this weekend and the petcock leaks. The previous owner installed the rebuild kit but it did not fiz the problem. I have ordered a replacement manual petcock and adapter plate from z1enterprises.com. I have no experience with bikes and am wondering how to plug the vacuum line. I have a service manual that gives an OK walkthrough of draining and removing the tank and removing the petcock but I am not confident. Can anyone provide a walkthrough of how to do this and what I need to be careful of. (i.e. I read that failing to plug the vacuum line properly can cause a holed piston). Many thanks

Ryan

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  • RonKZ650
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Re: Vacuum petcock vs non vacuum

18 Nov 2009 09:57
#334468
Plugging the line is simple, just find something to stuff in there. A piece of wood dowell, old screw in appropriate size ect. Anything the basic diameter of the hose can be used to plug it. Not plugging the line will cause a vacuum leak and it won't idle right, no other big deal. I doubt holing a piston has ever happened from a vacuum line on a KZ.
321,000 miles on KZ's that I can remember. Not going to see any more.

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  • JMKZHI
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Re: Vacuum petcock vs non vacuum

18 Nov 2009 13:10
#334479
deftones5792 wrote:
... I bought a 1980 KZ550LTD ... the petcock leaks. The previous owner installed the rebuild kit but it did not fiz the problem. I have ordered a replacement manual petcock and adapter plate from z1enterprises.com. ...
By any chance do you know what brand of rebuild kit the po installed? Some are made in China. Others are made in Japan.

Install a good vacuum cap from the auto parts store - they usually come in packages of 4 or 5. The aftermarket fuel valve screen may not fit into the tank's opening. If you decide to ream out the hole a tad, keep in mind that it's a fuel tank & a spark could cause an explosion.

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  • Patton
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Re: Vacuum petcock vs non vacuum

18 Nov 2009 13:22 - 18 Nov 2009 13:23
#334481
RonKZ650 wrote:
Plugging the line is simple, just find something to stuff in there. A piece of wood dowell, old screw in appropriate size ect. Anything the basic diameter of the hose can be used to plug it. Not plugging the line will cause a vacuum leak and it won't idle right, no other big deal. I doubt holing a piston has ever happened from a vacuum line on a KZ.

Correct.

As also noted, one option is to simply cap off the now unused vacuum nipple at the carbs.

Another vacuum plug just like the others should do just fine.

The high quality set from Z1E comes with 5 plugs.

Click here > Z1E Vacuum Plugs

Good Luck! :)
1973 Z1
KZ900 LTD
Last edit: 18 Nov 2009 13:23 by Patton.

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  • YUKABODOS
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Re: Vacuum petcock vs non vacuum

18 Nov 2009 14:26
#334500
I have both a 78 w vaccume petcock (replaced with Suzuki from z1) and 77 with out vacume.

I would much rather have the vacume operated petcock. Easy to forget to turn off the gas. Plus swapping over the tanks takes all of 2 mins (1 for each tank) I would just swap carbs and tanks. Christ, if you can work on carbs then you can swap tanks.

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  • deftones5792
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Re: Vacuum petcock vs non vacuum

19 Nov 2009 10:58
#334630
Thanks for all your help everyone. I'll be ordering those plugs just to be safe. Also, sorry to mjkawa for hijacking his thread

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  • chance
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Re: Vacuum petcock vs non vacuum

19 Nov 2009 11:12
#334632
Patton wrote:
Should be easy to simply cap off the vacuum nipple not needed for manual petcock.

Where vacuum petcock replaces manual petcock, just add vacuum hose from any vacuum nipple to the vacuum petcock.

Good Luck! :)
Correct ..Your bike will perform as well with either petcock you use ..Patton has the easy swap for you.:)

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  • bluej58
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Re: Vacuum petcock vs non vacuum

19 Nov 2009 11:42 - 19 Nov 2009 11:45
#334636
Patton wrote:
Where vacuum petcock replaces manual petcock, just add vacuum hose from any vacuum nipple to the vacuum petcock.

On the kz900 carb are the nipples on the 1 and 4 carbs considered vacuum ?
1280
78 KZ1000 A2A

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Last edit: 19 Nov 2009 11:45 by bluej58.

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Re: Vacuum petcock vs non vacuum

20 Nov 2009 02:25 - 20 Nov 2009 02:37
#334791
bluej58 wrote:
Patton wrote:
Where vacuum petcock replaces manual petcock, just add vacuum hose from any vacuum nipple to the vacuum petcock.

On the kz900 carb are the nipples on the 1 and 4 carbs considered vacuum ?
1280

The 1976 LTD carbs have 4 vacuum nipples, one on each carb holder. (Not shown in the above pic.)
The vacuum nipples are used when syncing the carbs.
During normal engine operation, all four nipples are sealed with a rubber cap on each nipple.
The 1976 LTD was fitted with a manual petcock from the factory. The manual petcock doesn't have a vacuum nipple.

A vacuum petcock does have a vacuum nipple to receive vacuum which operates the petcock.

Where the manual petcock is replaced with a vacuum petcock, any one of the vacuum nipples may be then used for supplying vacuum through a vacuum hose connected between it and the petcock vacuum nipple.

In the above image, may be looking at one of the two carb floatbowl vent nipples, which usually have hoses attached that exit to open air.

Here's a pic of the 1976 LTD carb with a blue arrow pointing to the rubber cap on the vacuum nipple located on the #4 carb holder.

Can also see the two yellow hoses from the vent nipples (which hoses exit to open air underneath the seat).

Good Luck! :)

[Click image to enlarge view]

550
1973 Z1
KZ900 LTD

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Last edit: 20 Nov 2009 02:37 by Patton.

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