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Fuel petcock Routing

Fuel System: Gas (Petrol) tanks, Carburators
Brent
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Posts: 4
Joined: Thu Jul 19, 2007 3:57 pm

Fuel petcock Routing

Post by Brent » Thu Jul 19, 2007 4:06 pm

I'm helping to restore a '66 CB77 with my nephew, and the bike starts easily, but only runs on one cylinder. I've removed the drain screw on the right carburretor while the bike was running, and nothing comes out, so I've obviously found why the right cylinder isn't running. The reserve line on the petcock has been blanked off. To what is that tube that runs from the petcock reserve supposed to be attached?

Thank you for any help or advice you can offer.

...Brent

piecutter
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Location: Maryland

Post by piecutter » Thu Jul 19, 2007 9:16 pm

Reserve line? You should have one line running to the right carb and one to the left. There should be no reserve line. Unless the petcock is from a different tank that had a cross over from a nipple on the opposite side. Do you have any pictures of the petcock and tank? Does your petcock have a brass siphon tube extending up inside the tank?

Brent
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Joined: Thu Jul 19, 2007 3:57 pm

Reserve line tube

Post by Brent » Fri Jul 20, 2007 10:41 am

Yes, there is a brass siphon tube that goes up into the tank, and there are two outlets for the left and right carbs, but there is also a third outlet that angles upward that the parts manual calls a reserve line with a short length of tube attached to it. I can onlt assume that this tube attaches to an outlet at the bottom of a fuel tank. However, this tank doesn't have such an outlet, so I guess the petcock is from a different model.

I still can't find out why there's no gas getting to the right carb, though...

piecutter
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Joined: Wed Aug 18, 2004 2:03 pm
Location: Maryland

Post by piecutter » Fri Jul 20, 2007 1:50 pm

It seems there were some earlier tanks with crossover tubes. I guess your fuel cock is off of one of those. Just leave it blocked and don't worry about it.

Brent
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Joined: Thu Jul 19, 2007 3:57 pm

Petcock fuel flow

Post by Brent » Sat Jul 21, 2007 8:21 am

With the fuel lines detached from the carburretors and the petcock in the on position, should the gas flow be the same from each line? When I do this the left line gushes, and the right virtually stops. If I put my thumb over the left hose, the right line flows freely. Again, it would seem this the source of my problem, but what would cause this?

Thanks again.

piecutter
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Posts: 326
Joined: Wed Aug 18, 2004 2:03 pm
Location: Maryland

Post by piecutter » Sat Jul 21, 2007 12:41 pm

Deposits in the petcock passages usually. Sometimes carb cleaner alone won't work and I have to disassemble the valve and use a dental pick to clean it.

kustommusic
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Location: Goshen Indiana

Post by kustommusic » Sat Jul 21, 2007 6:38 pm

Brent, Just a thought on your reserve question. On CB77s you should have a nipple on the right side of the tank(toward the rear of tank) that the reserve hose goes to. The hose routes under the frame backbone to the opposit side of the tank from the petcock. That is on all CB77s. Good Luck, Kustommusic

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