Steel balls inside vacuum hose - why? | GTAMotorcycle.com

Steel balls inside vacuum hose - why?

Matt Rain

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Another newbie question for the old-school techie crowd.

I'm about to replace the old, cracked vacuum lines on my FJ600 with brand new rubber, and I just noticed that the small line between carbs 2 & 3 is plugged at both ends with a steel ball.

Why? What would happen if I remove those plugs?
 
can the ball move at all or is it tight in the hose? Could it be functioning as a check valve or restriction to control air flow or is it a full blockage?
 
What are the vacuum lines for?

On old carbureted bikes, usually the only thing any vacuum hose between carbs would be for, is for operating a vacuum-operated fuel valve.
 
Maybe those ports were only needed to meet specific emissions regs like California EVAP rules. Or maybe they were off-the shelf carbs that served other uses where those ports were needed. If they're plugged just leave them plugged.

Though I don't know why they'd connect them and also plug them, as opposed to simply plugging them. Maybe it saves having to use a hose clamp?
 
Brian, my bike does have a vacuum-actuated petcock.

As far as I know, the carbs are original to the bike. Mikuni BS32s.

A previous owner messed with the bike's settings to get it to idle even though the intake valves were ridiculously out of spec. I wonder if plugging that line was part of the quick fix.

I'm assuming I can't harm anything by running an open hose between those two carbs? The other vacuum hose goes from the petcock to a splitter and from there to carbs 1 and 4.
 
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Actually, I found a ball inside carb #4's end of the hose as well, so only carb #1 is used to operate the petcock.

?!?
 
It is probably correct that the cylinder #1 vacuum port alone is used to operate the petcock, and that the others were plugged. But most likely the other three cylinders were meant to have the vacuum ports plugged properly using a rubber cap, not a hose with a BB inside it!
 
Cool, then I'll just cap 2-3-4 and run a hose from petcock to 1.

Thanks, once again!
 
Took a quick look at the parts diagrams. It looks like all the vacuum lines are to eventually connect together and then go to the petcock. No balls or caps were seen.
 
Yeah, I'm seeing the same thing on the diagram at BikeBandit. Its two sister bikes from '85 (Radian and FZ) have 3 plugs and a hose from petcock to carb #2, but the FJ clearly shows that it's meant to have a short line between 2 and 3, and another one from the petcock to a splitter and then to 1 and 4.

Will try both setups and see what happens.
 
I used my new rubber to craft the original connection setup and I can't say I notice anything different in the way the bike runs. Seems to hold idle faster after a cold start but that may just be because of the new rubber.

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Someone (not the factory) put the balls in there to block off those lines. Why, so the lines look like they are connected but they are for all practical purposes blocked or capped (emissions stuff looks connected to an inspection but it is not operating--pretty hard to tell this on a visual). Could have also been a vacuum leak causing problems and they used the balls to block off the line, most would just cap them in this case though...

Steel balls (ball-bearings) are found inside of all kinds of vacuum lines on cars, specially the EGR valve (looks connected, not working). None of those balls were there from the factory...

A check valve is different, but that is not what you are describing.
 
Yeah, the balls were definitely added as an attempt to fix something.

Took the bike on the Gardiner after work to give it a bit of a workout and roll-on power seems stronger, but again, might just be the new, non-cracked hoses.

Either way. Bike happy, Matty happy.
 
I know this thread is a little old but this might come in handy for others.

I have an XS650 with mikuni bs34, there are vacuum barbs that are situated on either side that serve no purpose other than to operate the vacuum valve, or to be used to synchronize the carbs. If you have a line that goes from one of the barbs to the petcock make sure the other barbs is blocked off, or if you have a gravity petcock make sure both or sealed VERY WELL
 
In other applications balls are used as "one way" valves. Might be to prevent backflow

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I've used the BB in the hose trick on my Mikuni power jet carbs (RZ 350). I had originally blocked off the jet at the bottom of the bowl. I didn't want to permanently block it off so I just plugged the tube.

I ended up wanting to use the original set up, so I just replaced the tube. Plugging the tube was way easier than filling the port with something.
 
In other applications balls are used as "one way" valves. Might be to prevent backflow

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+1

Check if there are any springs...usually check valves, one way valves, backflow valves, just don't have a 'ball' alone...you need that spring to return the ball back to block the port depending upon which side the pressure differential occurs...
 

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