carb piston comp vacuum


Information and questions on GL1500 Goldwings (1988-2000)
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B_knight99
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carb piston comp vacuum

Postby B_knight99 » Sun May 26, 2013 3:49 pm



Hi all, I have a 94 aspencade that boggs when I accelerate mostly noticeable at hwy speed. If I open the choke it accelerates . I took the air filter off and noticed the left piston comp vacuum not pulling back like the right side. I can move it back hold slightly open and it feels like it wants to close instead of open. I can feel it wanting to close in sink with the right side opening. Is there a vacuum hose reversed? Any help would be greatly appreciated. Thanks in advance.



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ct1500
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Re: carb piston comp vacuum

Postby ct1500 » Sun May 26, 2013 7:47 pm

It is possible about the vacuum hoses reversed. Could be the right is opening too much also and the left one is OK, tough to tell from this distance. :D

There should be 2 or 3 vacuum hoses attached to the front and rear of carbs. Compare vacuum hose numbering on one carb to the corresponding ports and hose numbering to the other carb. Also check where they connect near right front before going to the air jet controllers under right pocket. Air jet controllers will have hose numbers decaled what number goes where.

The left front of LEFT carb will correspond to the right rear of RIGHT carb.
The left rear of LEFT carb will correspond to the right front of RIGHT carb.
This is what I do
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B_knight99
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Joined: Sat Apr 02, 2011 7:09 am
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Re: carb piston comp vacuum

Postby B_knight99 » Sun May 26, 2013 8:43 pm

I will check the hoses tomorrow. Hopefully I will find an error that was done the last time I had it in the shop and correct it. I really don't want to go back to using the choke

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ct1500
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Re: carb piston comp vacuum

Postby ct1500 » Sun May 26, 2013 9:50 pm

The air jet controllers (AJC) operate to help with driveability and emissions and act directly upon the slides of the carbs. I have not gotten into them as yet and do not know at what speeds or under what conditions the controllers are supposed to be doing exactly.

So yes the AJC's if hoses are misrouted could cause slide difficulties I believe.
This is what I do
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B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Sun May 26, 2013 10:59 pm

Thanks agsin CT1500. Hopefully I will be able to find a misrouted hose and resolve ththe problem. I will let hou know my findings tomorrow.

B_knight99
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Joined: Sat Apr 02, 2011 7:09 am
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Re: carb piston comp vacuum

Postby B_knight99 » Mon May 27, 2013 1:39 pm

We CT1500 I just went over looking at the hoses to the carb and from what I can tell there is nothing reversed :cry: Of course I'm going by the parts diagram that I D/L from the site and not a actual service manual which hoh can't D/L. Any other ideas??

B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Mon May 27, 2013 5:06 pm

Well I managed to D/L the service manual. From what I can tell from the service manual #18 hose should be the top hose and the #19 to the bottom hose to the carb which was reversed. Unfortunately that did not effect the movement of the left vacuum piston.

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ct1500
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Re: carb piston comp vacuum

Postby ct1500 » Mon May 27, 2013 5:57 pm

You can narrow down the problem by following this.

viewtopic.php?f=6&t=17014

AND SOME MORE SPECIFIC TESTING

A good quality carb clean spray (Cyclo) non foaming with straw is a valuable diagnostic aid and I keep a can in the bag.

Bike dies on the road: While cranking spray a little in air intake, if bike wants to fire, fuel problem confirmed.

Vacuum leaks?: Spray a little around suspect area, if idle increases or smooths out found source of leak. Pinch off vacuum lines at source to confirm for downstream leaks.

Lean carbs?: Spray a little directly into its individual intake, idle increases or smooths out lean carb confirmed.

Rich carbs?: Spray a little directly into its individual intake, idle decreases
rich carb confirmed within reason.

Quick confirmation of pilot adjustments: Consistent idle (RPM) response when a little spray is introduced to each individual carb intake.

High speed miss?: Spray a little into intake stream, if smooths out and picks up lean condition confirmed.

Avoid overuse around composite parts. (1500 slides for sure) Starting fluid is too volatile and messes things up. When revving the engine you want to confirm vacuum slides are moving in tandem on the 1500 and that all air bleeds are free and clear with good accelerator pump shot.

Other bikes can use sync gauge ports for rich or lean checks. Control the uncovering of ports when screw removed idles up it is rich, spray directly in for lean check while sealing area around straw with your fingers.
This is what I do
Local and need repair help with your 1500, Valkyrie or ST please PM

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virgilmobile
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Re: carb piston comp vacuum

Postby virgilmobile » Mon May 27, 2013 7:12 pm

Posting late on this one...sorry.
If I read correct,you have one slice that does not move.....
The slides are indeed vacuum operated but not in the way you think.
As air passes under the slide,air is sucked out of the upper chamber,kinda like a spray gun sucks out paint.
The upper cylinder is sealed from outside air by a diaphragm.
Obviously your slide is not stuck and it is spring loaded .
You'll need to pull the Carb out to get the cap off,but it sounds like he diaphragm has a hole in it.

B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Mon May 27, 2013 8:18 pm

Virgilmobile, firstly thanks for responding. Would a hole in the diaphragm cause the slide to feel like it wants to close if held open slightly as mentioned in my original post and how difficult isit to remove the carb? I in the back of my mind the possibility of a hole was there but wanted to rule out the easiest possibilities first. Is the slide / piston and diaphragm one piece or bought separate?

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virgilmobile
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Re: carb piston comp vacuum

Postby virgilmobile » Tue May 28, 2013 6:54 am

A tear or hole in the diaphragm will stop it's movement when you rap the throttle and yet when you manually push the slide,it will move free with spring tention pushing it back,Just like the other one.
Removing the carbs took me 3 hours the first time.Now i can have them out in under 2 hours.
Yes you do have to drain the radiator too.
2 special tools are needed...2' long #2 phillips and a 18" pair of angled needle nose pliers.
I've not had to purchase a diaphragm,so I have no idea about replacements.
Be prepared for a long weekend with it.

B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Tue May 28, 2013 6:10 pm

Quote "and yet when you manually push the slide,it will move free with spring tention pushing it back".

When I manually push it back there is the resistance of the spring. When the throttle is rapped I can feel it closing in synch with the right on opening. Does that sound correct?

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virgilmobile
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Re: carb piston comp vacuum

Postby virgilmobile » Tue May 28, 2013 6:30 pm

On my 88,when I rap the throttle I see both pistons jump equally open as air rushes past the bottom of the piston.
They don't move much,maybe 3/4" or so.One moves left the other right.The carbs are opposing each other.

B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Tue May 28, 2013 7:14 pm

That's what the right side does and I can feel the left slide when lightly held open pushing to close when throttle rapped instead of opening when the air rushes past the bottom.
Sorry for being a pain. Just trying to best explain whats happening so if someone had the same symptom and ended up being something else than a hole in the diaphragm. Just trying to make sure (even though deep down I think your correct about the hole)
I would hate to remove the carb and replace the diaphragm and still have the problem. I checked one place online and the part is about $100. :o

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virgilmobile
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Re: carb piston comp vacuum

Postby virgilmobile » Tue May 28, 2013 8:17 pm

I do understand what you mean.As air flows past the bottom of the piston,it is pulled closed rather that open.
In the bottom of the piston,there is a small hole.As air rushes past it,the air Flow creates a pressure drop in the hole.That pressure drop is replaced by the volume of air contained in the piston cavity.As more air is being drawn out of the slide chamber,if sealed up,it rises.
If the diaphragm is torn,Air passes through it filling the chamber and creating a cylinder that is simply being sucked down as it is now a source of air flow.Kinda like your fingers if held over the intake.
By your detailed description and my analysis,if correct,you have a hole in the diaphragm.

Personally,I'd take the carb out,verify it and then order the parts.
Hey,it could be a loose screw holding the cap on for all we know at this point.

B_knight99
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Re: carb piston comp vacuum

Postby B_knight99 » Tue May 28, 2013 8:30 pm

Thanks virgilmobile, I guess I will remove the carb and check it over.I currently have the seat, side covers, etc removed so I'm partially there already. I'll h as ve ry o pivk up the 2 tools mentioned. you say 2 - 3 hrs to remove, is that after you have removed the seat, dide cover, etc.

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virgilmobile
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Re: carb piston comp vacuum

Postby virgilmobile » Wed May 29, 2013 6:46 am

The first time...from seat bolt to carb on the bench was 3 hours.I had no idea what I was in for.
I'd never said "you got to be kidding"so many times.
If you'd like,I can share the details.Pm with a contact.




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