The International CBX Owners Association

The picture does not show it, really. The vacuum valve is a device that is installed on top of the carbs. The fuel line from the Petcock goes into this and from there into the carbs.
Honda offered this as a retrofit for the '79 because some customers experineced fatal engine failures due to hydrolock when the petcock was left on open and the carb overflow filled the No 1 cylinder with fuel when the bike wa sparked on the sidestand.

Mosseltje wrote:As far as my (very humble) knowledge goes the petcock valve on my CBX is still 100% original.
But I placed a fuelfilter between the valve and carbs.

I have this crappy photo



Last time I tried to start the engine till the battery had no more juice but the CBX would not start.
15 minutes later after recharging the battery the CBX started right away.

What is the magic trick for cold starts?
Choke out and push the button or do I need to twist the throttle a few times before starting?

.

Twist the throttle a couple times, if your accel pump is working it will prime the motor, when you start the motor hold the choke lever full on while hitting the starter button( the choke will move off full choke if you don't keep pressure on it), take thenbike off choke as soon as you can.

Looks to me like you do have a vacuum valve on the bike. You need to blow into the vent hose for the valve (should find it on the right side inside the frame somewhere near the airbox). Blow into it, holding pressure for several seconds, a couple of times. This will fill the carb bowls, which evaporate gas like no other bike when you shut it off hot. Then quickly pump the throttle maybe a dozen times to squirt fuel into the engine with the accel pump (assuming it works), as Jeff says. Then full choke, no throttle and hit the starter. You also need a very strong battery. The bike WILL start pretty quickly this way.

Dave

Dave Ditner did a great tech write up some yrs ago, he bought one of those rubber photography bulbs that you use to blow the dust off a camera lens, attached it to the vacuum line on the shutoff and would give it a couple squeezes before hitting the stater button, it's small enough to tuck back under the side cover before hitting the road.

You can probably find the writeup in the archived CBXPresses.

daves79x wrote: This will fill the carb bowls, which evaporate gas like no other bike when you shut it off hot. Dave

I beg to differ: The Kawasaki KZ1300's carb bowls evaporate gas on a much, much faster rate than any CBX. Mainly because the motor gets so hot behind the cylinders, you can cook canned food on the block.

EMS wrote:

daves79x wrote: This will fill the carb bowls, which evaporate gas like no other bike when you shut it off hot. Dave

I beg to differ: The Kawasaki KZ1300's carb bowls evaporate gas on a much, much faster rate than any CBX. Mainly because the motor gets so hot behind the cylinders, you can cook canned food on the block.

I thought of suggesting a cooking contest with our motors as the heat source, then remembered our "ringer", JP. I wouldn't stand a chance.

Unbelievable how much fun such an old bike can give you.
After fixing the problems with the carbs the bike runs perfectly.
The only problem is the oil consumption. The bike consumes 1 liter oil every 200km.

But that is a worry for later.

Herewith a sound clip of my CBX some months ago when I had a 3 day trip in Germany.

https://www.youtube.com/watch?v=hG2d5sbQJJI

The sound of your CBX at play is wonderful and it will have to do for the next 5 months.

Mosseltje wrote: The only problem is the oil consumption. The bike consumes 1 liter oil every 200km.

Wow, that is a problem indeed 1 Ltr/200km (1 quart/120 miles) is definitely on the high side. Does the bike smoke much?

The smoke is divided by 6 exhausts so it does not look too bad.
And when people notice the smoke I tell them this is normal for a 6 cylinder 2-stroke bike.


The engine is in need for an overhaul. But I do not have the time right now.
As long I keep the oil level high it should not be a problem.

Man ,I've got to get me a set of 6 into 6 pipes !!!