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help! carb / petcock vacuum line

Old 01-18-2006, 11:56 AM
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help! carb / petcock vacuum line

I'm in the process of re-assembling the crashed SH I recently bought, and I'm hitting a snag. I believe I'm missing the vacuum line that connects to the petcock. I have the honda shop manual, and all the fiche parts diagrams, and I still can't figure out where on the carbs it connects to. Can anybody out there help me out?
I'm planning on ordering the hose from honda, unless it's a standard size I can buy locally. If you happen to have your tank off, a pic would be great, but I'm sure I can figure it out based on a simple explanation. Thanks in advance for the help!
-Jay
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Old 01-18-2006, 12:15 PM
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Re: help! carb / petcock vacuum line

It comes off the rear intake manifold, there is a small spigot for molded in for the vacuum hose.
Depending on what emissions equipment is still on the bike it might T off along the way but just follow the tube that comes off the rear cylinder manifold.

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Old 01-18-2006, 06:40 PM
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Re: help! carb / petcock vacuum line

Kai Ju-
Thanks for the help. Turns out I'm missing the "spigot" on the manifold. I found the small threaded hole for it. I also have none of the corresponding hoses. Can I route the hose straight to the petcock, or are there addional pieces I'm missing? Thanks again.
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Old 01-18-2006, 06:55 PM
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Re: help! carb / petcock vacuum line

I'm not sure without looking at the manual but as far as the fuel valve actuation goes all you need is the vacuum hose.
There should be another spigot just like it on the front manifold if you need one.
What you can do is to remove the front one and replace it with a 5mm screw and gasket and install that one on the rear or simply run a longer hose from the front manifold to the fuel valve.
Why anybody would remove the rear spigot in the first place escapes me.
The spigots are also used to connect a vacuum gauge for carb synch.

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Old 04-01-2006, 04:21 PM
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I went to sync my carbs today and I found the rear spigot but on the front, Honda Service manual said remove the screw and washer and "install the vacuum gauge attachment into the vacuum port". Am I missing something? My carb sync'ing device has two tubes, nothing else. Kai, you said there is a spigot on the front manifold, is it possible the P.O. removed this for some reason?

Main question, for those of you who have sync'ed your own carbs, these are the right two places to attach your vacuum lines to, correct?
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Old 04-01-2006, 08:00 PM
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Re: help! carb / petcock vacuum line

The front manifold hole is plugged with a screw and you will need to remove it and screw in a hose adaptor/ spigot.
The rear manifold already has a spigot because it actuates the fuel valve.
Make sure that you have the engine fully warmed up and T into the rear manifold so that the fuel valve still gets vacuum.

Usually carbsticks come with both 5mm and 6mm adaptors, if you don't have one you must have purchased a used one.

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Old 04-02-2006, 06:36 AM
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Re: help! carb / petcock vacuum line

Sounds like you are going to need at least one fitting but go ahead and get two. The one on the front manifold can be blocked off and be handy for carb sync's.Rear one is needed for petcock.On the rear hose install a "T" fitting with a length of hose that you can block off and also use to sync carbs.This way you can check sync with out fooling with tank.2 min. job.If memory serves me correct the fittings show up on maniflod pic on parts blowup not carb picture.Order 2 fittings and 2 new crush washers.Should be under 10 bucks.Do a search on vacum or carb sync. Someone posted a picture with a nice little plate and fittings for real quick hook up.Hope this helps------------------Stay Well
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Old 04-02-2006, 01:39 PM
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That's interesting, luckily for me, I have a spare VTR engine sitting around, so I just took the spigot off of that, and I'll use that in the front cylinder. As far as the rear cylinder is concerned, the Honda SErvice manual says to pull off the rear hose (at the rear cylinder) and clamp it with a hose. Then attach your carb sync line to the spigot. Well, if you clamp the petcock hose it won't get vacuum and theoreticallly your fuel supply is stopped. Is this right?

This sounds right to me, because you wouldn't want the vacuum going to the tank AND your sync gauges, but what do you do if you need more than 30 secs of fuel to correctly synch your carbs? I've never done it before and I doubt I can get them synched before my fuel runs out! I won't start this for another about 45 min so if someone gives me input fast I can modify my procedure.
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Old 04-03-2006, 06:01 AM
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The easiest thing to do is to run remotes for these. On the front, buy the spigot and run a hose off it. For the rear, install a t-fitting in the existing vacuum line. Then run the hoses to a convenient place, insert barb fittings and cap those with vacuum plugs.

Mine are zip tied to the frame near the choke. Not particularly pretty, but absolutely convenient.
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Old 04-03-2006, 07:48 AM
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You know what? I didn't read your post until after I was done, but that exactly what I did! You're right, it is going to be so convenient for next time.

Question on Carb Sync: When I first hooked mine up to the mercury manometer (power steering fluid instead of mercury, but good color and safer) there was almost a 24 inch difference between cylinders. I got them to dead even, except when I revved the engine, they didn't stay the same, one would go up and the other down. When you sync, would you prefer to have the idles dead on or the levels the same throughout revving? It seems virtually impossible to sync at 3000 revs like I've seen suggested somewhere on here before.
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