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Discussion Starter #1
I believe that I have a vacuum leak that is serious enough to cause the bike to simply stall once the choke is turned off. Starts great, revs great, but once the choke goes off, it just dies. I did discover that if I put my hand over the air intake it will continue to run, but take hand off or even open the fingers and it dies. Those things convince me it is a vacuum leak. I want to do a smoke test, but need direction on where to inject the smoke. Anyone have any experience. I have heard of doing the ether test, but spraying flammable stuff around a running engine, especially in such a tight spot seems not the safest thing in the world. Any advice and guidance would be welcome. Thanks in advance for your help.
Terry
 

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Have you tried turning the idle speed up? You could put smoke in the ports where you connect the gauges to synch the carbs, Pull the vacuum line off on the left center intake and the plug in the right center intake but there is so much you can't see without pulling the carbs I don't know if you could find where the smoke is coming from.
 

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If you don't like to use flammable liquids to find a vacuum leak you could sportz water instead. When you get the right spot the engine will still change pitch or die. Same as any other liquid. :)
 

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It's a 1500 right..so many tubes under the carbs; to fix it you'll have to pull the carbs anyway. Most likely the 90* bend tube..?? But replacing all of them is the way to go.
 

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It could be just gunk in the idle port of the carb. Have you seafoamed it yet? If not you might want to add some for the next 4 tanks of fuel to see what happens. It certainly won't hurt the bike to have some run through it.
 

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Was going to suggest the propane torch, used sparingly. Propane is heavier than air and "pools", which is why you see propane explosions from time to time. (Natural gas will rise and dissipate more readily.) Don't be worried that it's going to explode as soon as you start using it, just don't use it in a closed up closet for half an hour then light a cigarette.

I made a smoke tester for the P-car out of a Harbor Freight "liquid transfer" hand pump and a cheap Tiparillo cigar. I put the cigar on the inlet side, then ran the outlet side of the hand pump to a piece of PVC and silicone pipe that I fashioned to fit over the throttle body. Worked great, and I found work O-rings and seals in a couple of places.

Try to have the bike in a dark area with bright side-lighting, and you'll be amazed how accurately you can pin down where the smoke is coming from.
 

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Discussion Starter #9
At this point I have most of the plastic off and even the air box. Started it tonight and sprayed ether to see what would be. No doubt there is a leak. Sprayed at the front of the carbs and it without doubt it surged. I still cannot see any broken lines. In the next few days I am going to try the smoke test. Going to use lines 16 and 17 white, by taking one at a time off from the right side of the fairing, what would be under the right fairing pocket. I think that is an air control valve I will take the tubes off of. I will let you know how it goes.
 

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Here's your problem sir....just like mine. 1991 GL1500. 80K miles. Surged and stalled off idle.
This little wonder is a common failure in 1500s. Sits under the carbs, in the manifold so it cooks over time. There is a matching hole on the INSIDE radius of the tube as well. Large enough to easily see light through. Perhaps you have a different leak but I understand the ninety degree tube leak is common.
To replace, you'll need to get under the carbs by removing them and from experience I'll say You Tube is your tutorial friend.
Good Luck !
 

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I agree with Stans. More likely than not it is the primary vacuum lines coming off the base of the carbs. Not only leaks in additional air, but screws up the entire vacuum system. Well, at least half of it, if only the 90 degree one is leaking, but I guarantee that the other primary vacuum lines are cooked to death and need replacement; up to where you hit the grey vacuum hoses. It's a design thing, including the Farkin' heat-trapping mat on top of the engine. It ain't the easiest job to fix, but there are videos to help. Whether they mention it or not I'll give you a tip to make the job far easier: Remove the two radiator fans and it all becomes quite doable. Re-synch the carbs when the primary vacuum system is replaced. Instead of buying OEM parts, simply put "sweeps" in the new vacuum hoses, get rid of the farkin' heat-trapping mat while you're in there, and I'll bet you'll never have to deal with it again.!:grin3:
 

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Instead of buying OEM parts, simply put "sweeps" in the new vacuum hoses, get rid of the farkin' heat-trapping mat while you're in there, and I'll bet you'll never have to deal with it again.!:grin3:

supposedly, that mat is to prevent Heat Soak on the carbs during brief shutdown periods.... causing the carbs to boil over while you are inside the DQ
 

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supposedly, that mat is to prevent Heat Soak on the carbs during brief shutdown periods.... causing the carbs to boil over while you are inside the DQ

That's exactly what the mat is for, and having it in there is good for start/stop downtown Tokyo traffic in summer. But if, like most of us, you prefer to be out on open roads instead of putting around downtowns it is pointless, and I'd say a negative. All I know is that after I performed the primary vacuum system/isolators replacement and while in there replacing the OEM carb gasket and took the bike for a ride all he had to say was, "Thank God you got rid of that farkin' mat; it was stifling me!" True story.:wink2:
 

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Discussion Starter #15
Next update. The carburetors are off. I have checked all the vacuum line below as everyone has suggested and have found nothing wrong. From the looks of things I am going to say that the lines look pretty good and I think maybe they have already been changed at least once in the life of this bike. I think that because of how good they look and because I found a piece of the top of a number 18 tube with its little clamp at the bottom of everything. But I am not sure I am stumped and again here is why. Once I got everything unhooked and loosened the screws to the carb boots I was absolutely stunned when the left side was just loose and the right side I had to pull and tug and jerk before it finally popped off. The left carb, from the underside is caked with all sorts of dirt, oil and such while the right side is absolutely clean. My conclusion is that the left carb was never seated properly whenever the previous work was done and it just took this long for it to work loose enough to cause real problems. Any thoughts? I will be ordering new boots and maybe a new mat as I might have chewed the other up a bit. I have one hose to replace because I ripped it getting it off and then we will assemble everything and see if I am right. I will still continue to check, look, examine, and scope out all the lines as I wait for parts to arrive.
 

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If it was me, I would go ahead and replace that hose that has the 90° bend in it that is pictured in post #10. I would replace it "just because" and you are already there with your hands on it.
 

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The good news is if your left carb was not seated into the insulator that would be a likely point for your lean running condition.


If your grit on the carb is similar to this then the bad news is you likely have a leaking float bowl gasket.
 

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Yes and yes. The loose "isolator" (what Honda calls the carb boots) is the likely source of the leak and yes, I'd replace all the hoses while in there. Hoses are cheap, especially since I just use the right size hose, not the OEM 90 degree angle jobs. As I'm about to post re a GL1200 carb question, I'm so anal after dealing with vacuum leaks that when I rebuild carbs I use mini zip-ties to make sure they're sealed tight.:blushing:
 

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Pulling the carbs might be your option. Have a 92 A which cruse control stopped working. found a solft #6 vac line. replaced all I could reach. And that included pulling the carb. The one under the carbs was colapsed and had a large hole in it. Back together again cruse working . Cruse used to light up but not kick in. Now it does . As the Kid Dragon often says "take that deep breath and dive in."
 
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