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Discussion Starter · #1 ·
Can the Existing fuel Petcock be converted to non-vacuum? - Speedo repair?



Has anyone tried removing the diaphragm from their fuel petcock and plugging the vacuum lines and perhaps the fuel overflow to convert the petcock to a full manual petcock?





I took my “new to me” 81 GL SilverWing out for around 400 miles this weekend. On several occasions, after running for 30 minutes or so at a steady pace of about 6k on the tack the bike behaved as if it were out of gas even with an almost full tank. The cure was to pull off the road and at this point the engine will die unless the choke is pulled full on. I’d turn the bike off sit for about 1 minute pull the choke the motor will start with the choke on but not rev until the carbs fill with gas. Now all is well until it happens again usually 30 or 40 miles later. (Well that was Saturday) On Sunday the problem became more progressive – this also does not happen in stop and go traffic.





I checked the gas cap vent and it seems clear and no vacuum sound either when I pull the cap. The first couple of times this happened I pulled the gas cap and after checking the vent I stopped removing the gas cap.



My theory is the diaphragm in the petcock is old and slowly losing its ability to hold the vacuum and let gas flow.

Has anyone tried removing the diaphragm from their fuel petcock and plugging the vacuum lines and perhaps the fuel overflow to convert the petcock to a full manual petcock?



I also had a 2nd issue – the speedometer started making a loud racket and the needle is jumping all over the place. It’s not the cable and not the gear at the wheel, it is the Speedo instrument. I pulled the cable to avoid further damage to the speedo. Has anyone tried repairing their Speedo?



Thanks for any thoughts!



Mike
 

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Discussion Starter · #3 ·

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Discussion Starter · #4 ·
Thanks Phantom, your info is worthy of printing and keeping - the carb info is a nice bonus!



Mike
 

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I have had my hands on or in a decent amount of speedometers and the one thing that has to be thought of is has the cable housing stretch making the smallest gap between the square gearing and the tapered square head. Other than that there isn't really much inside the speedo. There's the input with a bell like magnet on the other end. Sure there are a few gears but they are very simple and should chatter.
 

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What about the cable? I placed liquid graphite down the jacket and the cable to smooth it out. Like we did for the old cars when the needle started to get jumpy.

Well When I Was typing my thought, the picture showed up and now makes me want to open up the speedometer from the 80 parts bike. It is a bit rusty so it should not matter to much if I goof up.I better not goof up.
 

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What about the cable? I placed liquid graphite down the jacket and the cable to smooth it out. Like we did for the old cars when the needle started to get jumpy.

Well When I Was typing my thought, the picture showed up and now makes me want to open up the speedometer from the 80 parts bike. It is a bit rusty so it should not matter to much if I goof up.I better not goof up.




Well in your case just take the speedo out and cut the ring holding it together across on the underside. I usually use a hacksaw for this and then it opens just fine. When removing the trip knob if it's still there you will probably have to hold the rod after entering the speedometer with some needlenose pliers and turn the knob clockwise to remove it.



It's also difficult at times to remove the needle. Sure they are only pressed on but some have a needle like head. Those are the easiest ones to remove. I usually use a fork to get it off. But some have what looks like a needle but really it's a needle with a ball head on it. Those require a bit more patience. A fork can work but a thin blade screwdriver might work better. Or a butter knife. No technical tools for this.
 

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in addition,make sure you are running with an in-line filter......it will protect the carbs
 

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Check the rubber vacuum tube for split ends, and vacuum loss. This weakens the opening of the vacuum diaphram, and reduces fuel flow.
 

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Discussion Starter · #13 ·
The fuel delivery problem was an issue with the vacuum petcock and my current solution was to move the spring to hold the diaphragm open. The vacuum line and overflow line are in their original configuration. After moving the spring originally I plugged the vacuum at the carb and ran a short piece of hose to connect the petcock vac and overflow together which would seem to plug both lines. This worked fine in the garage where I tested by draining a full tank of gas into a gas can – however on the road the suction caused by the gas moving through the petcock pulled the diaphragm closed even against the spring which killed all gas flow. (Go figure? – I did not see that one coming) fortunately I had some lengths of hose with me and got it worked out so I was not stranded.



My speedo seems to be working OK now and the cure was to remove the speedo and blast some air through it via my compressor and then turn the speedo upside down and smack it against a 2x6 a few times. Nothing seemed to blow out of it with the air – but it is working fine for the moment. Guess I just showed it who the Boss is.

If it acts up again I will cut it apart as SuperTanker illustrated with pics.



Thanks to all for the help.



Next project will be new fork seals and Master Cylinder rebuild. However, it’s a good rider now so I’m only doing small projects that won’t take it off the road for long as the weather here in Florida is great for riding this time of year.
 
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