80 AUTOMATIC FUEL VALVE

twinegar · Post by **twinegar** » Wed Nov 04, 2009 6:03 pm

This morning I smelled fuel and found that fuel was leaking from the automatic fuel valve vacuum vent hose. Does that mean the rubber valve inside has a hole in it? I went to a lot of trouble finding the valve and mounting it properly and would like to be able to use it so hopefully I can find a kit or replacement part. The petcock is passing a small amount even when off and I have the parts to drill it and replace the rubber seal but I still need to get the auto valve fixed.

twinegar · Post by **twinegar** » Mon Nov 09, 2009 2:23 pm

I bought a 80-81 CB 750 900 C F K Automatic Fuel Shut Off Valve and as I thought is identical to the 80 CBX with the exception of the top fuel feed cap and the mounting bracket. All I have to do is fit the top piece off the CBX and screw on the bracket and go.

alimey4u2 · Post by **alimey4u2** » Mon Nov 09, 2009 6:53 pm

I'm listening Twine...

Lots of em out there are taking notes so keep em coming....

twinegar · Post by **twinegar** » Mon Nov 09, 2009 7:40 pm

Here are pictures of the CB900 valve:
http://www.spookytoms.com/SpookyTom-CBX-80-1-RB36.html

alimey4u2 · Post by **alimey4u2** » Tue Nov 10, 2009 9:29 am

EMS · Post by **EMS** » Tue Nov 10, 2009 9:41 am

The valve and petcock was still available from Honda not too long ago. They sold it as a retrofit kit for the 79. Ever so often one pops up for sale on ebay. I have a brand new kit in my spare parts stash.

twinegar · Post by **twinegar** » Tue Nov 10, 2009 11:51 am

Hang onto it, it's like gold now. I did a lot of looking and asking before buying the used one and found nothing. What is the part number on the retro kit so I can look further? My used one passed the test but with two bikes that use them, 82 CB750 & 80 X, I would like to have extras. I intend to put the valves on both 79 X's and my 79 CB750 also.

twinegar · Post by **twinegar** » Wed Nov 18, 2009 4:27 pm

Problem solved. Winter weather parked my bikes so I pulled the valve and after disassembling discovered that the spring is missing so I installed it and after a quick check I am finished. I now have a spare that might go on my 79.

EMS · Post by **EMS** » Wed Nov 18, 2009 4:35 pm

I know a lot of people do not have problems with it and claim their bikes fire right up, but....
My Prolink is a lousy starter after sitting for a longer period of time.
I blame it on the vacuum valve.
When a bike sits for a while, the fuel in the float bowl evaporates.
It will not start easy unless the fuel has a certain level.
It is very difficult to get to that level if flow through to the carbs only happens when the engine intake creates a vacuum.
That is one reason that many vacuum controlled petcocks have a "prime" position which bypasses the vacuum shut-off.
As the CBX vacuum valve is a separate part, this is not possible.
You will crank. And crank. And crank. And maybe stop cranking because of a low battery.

I will not put a vacuum valve on my '79.

twinegar · Post by **twinegar** » Wed Nov 18, 2009 5:23 pm

That is why I installed clear fuel line so I can see if fuel is getting to the carbs. My 82 CB750 came with the valve and it fires up after a few seconds even with empty float bowls. If everything is set right there shouldn't be more than 15 or 20 seconds for the engine to fire. For anyone that wants the valve an easy way around is to use a syringe stuck in the vacuum line to open the valve until the float bowls are full, hooking the line back on the carb and go. I have made the mistake of leaving my 79 on the side stand too many times to take a chance and I definitely wouldn't have the funds to repair the engine damage caused by a cylinder full of fuel.

Terry · Post by **Terry** » Wed Nov 18, 2009 6:32 pm

EMS wrote:I know a lot of people do not have problems with it and claim their bikes fire right up, but....
My Prolink is a lousy starter after sitting for a longer period of time.
I blame it on the vacuum valve.
When a bike sits for a while, the fuel in the float bowl evaporates.
It will not start easy unless the fuel has a certain level.
It is very difficult to get to that level if flow through to the carbs only happens when the engine intake creates a vacuum.
That is one reason that many vacuum controlled petcocks have a "prime" position which bypasses the vacuum shut-off.
As the CBX vacuum valve is a separate part, this is not possible.
You will crank. And crank. And crank. And maybe stop cranking because of a low battery.
I will not put a vacuum valve on my '79.

Will turning over the motor with the kill switch activated create the vacuum needed to add gas to the carbs w/o trying to fire?

EMS · Post by **EMS** » Wed Nov 18, 2009 6:56 pm

Terry wrote: Will turning over the motor with the kill switch activated create the vacuum needed to add gas to the carbs w/o trying to fire?

Yes, Terry, it will. But what do you achieve? You still wear down the battery.

Terry · Post by **Terry** » Wed Nov 18, 2009 7:00 pm

I don't have the problem but what would I acheive? Full floats I expect but how long would it take spinning over the motor to get the floats full enough? How long does it take for the gas to evaporate anyway, months? My 82 is only hard starting after not running for awhile due to the worn starter clutch.

Rick Pope · Post by **Rick Pope** » Wed Nov 18, 2009 9:35 pm

On the back of the vacumm valve is a little nipple. Put a length of vacumm hose on that nipple and stow the extra under the tank. When you want to start the bike after storage, blow into the hose. It will have the same effect as cranking to generate vacumm o the other side of the diaphagm.

This is a tip from one of the really olde phartes, Dave Ditner.

Don · Post by **Don** » Wed Nov 18, 2009 9:39 pm

. . . . . or, just put a '79 valve on your '80 or ProLink ;)

Don