Vintage and Classic Hondas

How bad is...?

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Honzilla

How bad is...?

Is it bad for the engine to keep the fuel pet-cock switch open all the time???

runabout879

Re: How bad is...?

I'm sure it's not bad, but if you are worried that your carbs might flood or leak, it would be best to turn it off.

dave Esch

Re: How bad is...?

In reply to this post by Honzilla

My carbs drip if I leave the fuel on. One post said something about this being a symptom of an issue, but i don't remember what it is. No engine damage will occur though. The fuel is on, but it isn't running into the motor if the bike is off. I leave the fuel on with my other bikes and never have an issue, but much newer bikes. The 750 is the only one that leaks if I leave it on.

runabout879

Re: How bad is...?

In reply to this post by Honzilla

I believe it's the float needles not seating properly that causes it to overflow. If it's leaking out of the top of the bowl, then the o-rings are needing to be replaced.

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Re: How bad is...?

Administrator

In some cases the gas could run into the cylinder, and past the rings contaminating the oil. However it is not a problem on the CB 750s. If you have gas coming out the overflow tubes. try tapping the float bowels with the handle of a screwdriver. If that does not stop it, you should replace the needle valves.
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)

GreenerGatsu

Re: How bad is...?

This sounds a lot like what I have going on with my 77 cb750. I also leave my switch on and it appears to have a small leak. The problem I am trying to trouble shoot though is that it runs strong for about 40 miles then slowly dies. It has happened twice while coming from the same place driving the same distance and dying at the EXACT same point in my trip. Help please?!

Cabreco

Re: How bad is...?

In reply to this post by Honzilla

Honzilla wrote

Is it bad for the engine to keep the fuel pet-cock switch open all the time???

It depend on the year CB750 you have.
On the DOHCs a diaphram shuts the fuel flow when the engine is turned off.

FIONA
1981 CB750K

Andy
Tennessee

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Re: How bad is...?

Administrator

In reply to this post by GreenerGatsu

Sounds like your vent in the fuel cap is clogged.
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Rodgil

Re: How bad is...?

In reply to this post by Honzilla

My 1982 CB750Z has had the vacuum shutoff removed. I never turn the fuel off, and have never had a problem with fuel leaking. Obviously, my float needles and seats are in good condition. If you have a DOHC with a working vacuum shutoff, you have the fuel turned off by just switching off the motor.