Author Topic: Vacuum Tap  (Read 136 times)

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Offline Clive

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Vacuum Tap
« on: September 14, 2018, 09:01:09 AM »
Good day
Please advise me where I can purchase a vacuum tap kit for my CBR 750 which fits at the rear of the fuel tank (See attached Picture),as mine is leaking.
Is there another Honda motorcycle which has a interchangeable vacuum tap.

Offline robvangulik

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Re: Vacuum Tap
« Reply #1 on: September 14, 2018, 13:11:16 PM »
That is a difficult one, I haven't been able to find that part for any other bike.
To be honest, I wonder what would happen if you went directly from fuelcock to carbs with a fuel line, on the very similar CBR1000F, with the same fuelcock, there is only a fuelpump inbetween that and the carbs....
I'll keep looking, and will put the schematic on here, maybe someone else knows more. Number 11 you're looking for.

Offline Clive

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Re: Vacuum Tap
« Reply #2 on: September 14, 2018, 15:10:08 PM »
Thank you robvangulik for the reply.I appreciate all the help I can get.I have looked online for a kit for the vacuum tap to no avail.In the interim I have bypassed the vacuum tap,the only problem is that I have to close the tank fuelcock everytime I park the Bike, as there is a possibility of the carbs flooding.

Offline robvangulik

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Re: Vacuum Tap
« Reply #3 on: September 15, 2018, 17:01:15 PM »
That's more or less what I suggested too, at least you can ride.
It seems this is one of the few parts specific for the CBR750, I can't find it in any other bike database, so
I have initiated a parts search at several parts websites, if you put your e-mail in your profile they can reach you directly....

Offline xpd153

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Re: Vacuum Tap
« Reply #4 on: September 17, 2018, 15:27:32 PM »
According to my understanding, vacuum tap is a kind of safety mechanism.
So you can connect fuel tap hose with carb fuel hose. Of course, this is unsafe, like a hand gun without safety mechanism.

I saw someone said 'no longer CBR750 vacuum tap is availablle' at some Japanese BBS. But I did noy confirm it with Honda dealer network. Because my CBR has no prob.

If one of your hobby is 3D printing, you can design and make CBR750 vacuum tap by yourself. It is quite simple valve mechanism.
                                                 vacuum hose
                                           +-----------------------------------
      fuel tap hose                 |
   ===============Vacuum Tap
                                            ||
       =================    ======================               
         hose to L carb                     hose to R carb
                           




Offline robvangulik

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Re: Vacuum Tap
« Reply #5 on: September 17, 2018, 18:01:29 PM »
I think the membrane would be difficult to make yourself.
Wouldn't this part be (more) available in used condition in Japan?
No longer available is what you get at all parts suppliers, and I tried many!

Offline xpd153

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Re: Vacuum Tap
« Reply #6 on: September 18, 2018, 01:32:30 AM »
I think new each internal parts of CBR750 vacuum tap is not available.
Because original parts maker is forbidden to sell that product without Honda's permission.
Of course, someone can make dead copy of internal parts, but it will be not cheap.

Only remaining choices are
1 Used entire CBR750 vacuum tap
2 Used other model's vacuum tap. Same or larger ID of fuel tap hose.
3 Design and make completely new compatible vacuum tap by 3D printer

Regarding #1 option, most popular place is Yahoo auction. But I could not find it at this point.
But I found https://page.auctions.yahoo.co.jp/jp/auction/w238969146
Obviously hose layout is different.

I also found a NV750 custom's vacuum tap at ebay.com. But it is expensive new parts.

 

Offline xpd153

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Re: Vacuum Tap
« Reply #7 on: September 18, 2018, 08:33:19 AM »
After prior posting, I researched about internal of vacuum tap.

It consist of
 two large shells. membrane sheet+valve, spring, O-ring between two shells, four halve bolts

 Possible symptoms are
1 imperfect fuel block at no vacuum. It means broken membrane sheet or worn spring.
2 insufficient fuel passing at vacuum. It means broken membrane sheet or broken vacuum hose.
3 fuel leaking. worn O-ring or broken membrane sheet or valve.

 The most difficult cause is, broken membrane sheet.
 If worn O-ring, spring or hose, you are lucky because those are generic parts.

 So you should decompose your vacuum tap and find out which internal part is broken.


Offline robvangulik

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Re: Vacuum Tap
« Reply #8 on: September 18, 2018, 09:20:18 AM »
 :thumbs: That is good advise,, if it can be taken apart there is a good chance the parts, like that membrane, are similar to those used in other bikes, and therefor better obtainable than the tap itself!
And as Clive has already bypassed the tap temporarily, he can take it apart without disabling the bike.