Vacuum Piston Questions


Information and questions on GL1000 Goldwings (1975-1979)
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Ten4321
Posts: 10
Joined: Fri Jul 29, 2011 5:30 am
Location: Newcastle, CA
Motorcycle: 1979 GL1000

Vacuum Piston Questions

Postby Ten4321 » Wed Aug 03, 2011 6:59 am



I have a 79 GL1000 project that I bought with the carbs completely disassembled. The carbs came to me in pieces in a bag. Because of this I do not know what vacuum piston goes with what carb. The vacuum piston covers were marked so I was able to match them up. Is there anyway that I can tell what piston goes with what carb? Is there some procedure that I could do to make sure that the pistons don't stick? I've re-built all four carbs and they are all connected back up together. Also, one of the vacuum piston springs is a little longer than the rest. You can tell its the right spring it just looks like it got stretched out a little bit. Will this affect anything? And finally, the rebuild kit that I used included jet needles that are larger than the stock ones. Does anyone know why?



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virgilmobile
Posts: 7663
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: Vacuum Piston Questions

Postby virgilmobile » Wed Aug 03, 2011 7:18 am

The springs should be the same length.One different spring will change how far up the slide can move with engine demand,causing a imbalance in fuel delivery on that one cylinder.That said,you could stand it on the table,add something on top to compress it half way,measure the distance off the table,then compare to the others.It would be ideal if all the slides had the same spring load so they responded the same.Kind of a crude test.How much taller is it?Count the turns,is it just stretched a little?Make them all the same...
As far as the slides are concerned,there's not much you can do now but polish them up good and test them installed.Put one together,stick your finger down the throat and gently lift the slide.It should move very smooth and not stick anywhere.
The jets being larger will allow more gas into the engine.Better or worse? depends on your needs.Personally I stay with the factory specs.It's your call.

Ten4321
Posts: 10
Joined: Fri Jul 29, 2011 5:30 am
Location: Newcastle, CA
Motorcycle: 1979 GL1000

Re: Vacuum Piston Questions

Postby Ten4321 » Wed Aug 03, 2011 7:55 am

Thanks for the info. I'm going to go back to the original jet needles, there's nothing wrong with them anyway. I know that spring is going to cause a problem because if you turn the whole assembly upside down the piston with the odd spring in it doesn't drop as far. Is there anyway to acquire replacement springs? I'm in for some major added time here. Doing the math shows that there are 24 different vacuum piston and carb combinations. Can the vacuum piston covers be removed with the whole manifold installed on the engine?

Thanks

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virgilmobile
Posts: 7663
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: Vacuum Piston Questions

Postby virgilmobile » Wed Aug 03, 2011 10:43 am

I've never tried just removing the caps on the bike,they need to lift about a inch.They may hit the frame?
From a engineering point of view,obviously different slide movement will result in different fuel mixture.I suppose that different springs were made to accommodate fuel requirements,altitude,etc.The carb for California would be different than Colorado.
Can you rob from a local salvage yard?
How anal are you about getting the exact ones for your altitude?

Maybe someone here has a junk set they will part with?

For a good running bike,they need to be matched.If the springs are the wrong tention,it will run a bit rich or lean.Not the worst thing but not perfect either.

Ten4321
Posts: 10
Joined: Fri Jul 29, 2011 5:30 am
Location: Newcastle, CA
Motorcycle: 1979 GL1000

Re: Vacuum Piston Questions

Postby Ten4321 » Fri Aug 05, 2011 8:21 am

I'm not that picky about getting perfect stoichiometry in all four cylinders I just want to be sure that the bike will be able to start. It has been sitting for 7 years and I want to be sure that everything is ok when I try to start it. It would seem that the weight of the piston itself would provide the vast majority of the force. I've been swapping pistons around and they all seem to fit with the vacuum chamber covers. It would seem to me that if a piston were to stick it I would be able to tell by sliding it up and down withing the chamber cover. I maybe noticing subtle clearance differences between pistons, or I maybe just imagining it. Anyway this has been how I have been deciding where to put each piston.

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scotterichmond
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Joined: Fri May 06, 2011 3:49 pm
Location: Marblemount,wa
Motorcycle: 1975 GL1000
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Re: Vacuum Piston Questions

Postby scotterichmond » Fri Aug 05, 2011 10:22 am

They need to "seal" AND slide freely that's they're function in life.

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virgilmobile
Posts: 7663
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: Vacuum Piston Questions

Postby virgilmobile » Fri Aug 05, 2011 11:52 pm

Cary on mate.It will run.You just have to will it.I guess that slight differences won't mater that much if you only have 2 throttle settings,Idle and wide open :mrgreen:
Don't forget 0 to the speed limit can take just 2 gears and 3.6 seconds. :D Major grin factor.




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