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another airbox breather gas leak thread

  • Thread starter Thread starter d.bradley
  • Start date Start date
D

d.bradley

Guest
Okay I need to make sure I know what's going on here. This is my first day with a bike, a '83 GS450T. After the transaction a friend drove it about 2 hours or so on some back-country highways to deliver it to my place. I took it out for about 30km of subdivision practice riding...my first time on a bike ever! Fun times, and I didn't notice any problems while riding.

I was disappointed this morning to see gas dripping from the underside of the bike. In the excitement of getting going, I had left the bike in Prime on the petcock, and stored it overnight.

Carbs were just cleaned, bike was certified. How can I check if I am having carb leak problems, or if I was just stupid with the Prime setting and the carbs are fine?

I was reading this thread:
http://www.thegsresources.com/_forum/showthread.php?t=107140

and got confused about whether the Prime setting will let the gas leak from the engine, into airbox and then hose, or if that's not supposed to happen. I'm also not sure if it would keep dripping a bit if I turned it back to ON due to leftover gas in that part of the system.

I was rolling the bike backwards down the slope of my driveway if that changes anything.

Sorry I know this has been covered before, but I'm new, have studied the Hayes and searched a bit, and need some dumbed down answers.

valve.jpg



Thanks all,
Damian
 
Last edited:
i think the float valves should close the gas supply even if you leave it on prime
so, your floats may be set incorectly or the float valves don't close properly

as a temporary measure, you can set the tap to "on" and drain a little gas through the bowls (screws at the bottom)

check your airfilter and re-oil it if the gas diluted the impregnating oil
 
My bike 78 750 will leak gas if left on prime every time. gas gets in the oil (if left on long enough) but everything in the carbs a fine. I'd just leave it on ON or RES. and change the oil. cheap easy prevention. also good luck with the bike.
 
Thanks guys, I really appreciate the help. I've checked the air filter, and will change the oil. I'll leave it in ON and see if the leaking persists. If so, I will definitely look into the floats / float valves.

Worst comes to worst, I hope to get it working well enough to ride to the shop :) Will post with my results.

Thanks again,
Damian
 
Technically if the carb floats are sealing properly it will *not* matter if you leave it on prime; no leak should occur.

That said, if the floats are sealing 99%, that's basically good enough and it's not a big deal if they *slowly* (very slowly) allow gas past when closed. In a situation like that you'd probably use gas while riding faster than it leaks past the valves.

The float valves are not designed to hold back full gas "pressure" for extended periods with perfection; they are designed to regulate fuel height in the bowls while riding. Hence the vacuum petcock which turns off fuel flow when the bike is off.

So a leak after leaving it on prime overnight and a leak while riding are different animals. You want those valves sealing as well as possible, though, so here's what I'd do:
1) I tried this the other day and it cleared up a leaky float: disconnect the fuel line and find the float bowl vent lines. Blow on these three hoses a bunch. Squirt some carb cleaner down them perhaps. They all lead to the bowls and the fuel line is on one side of the valve while the vent lines are on the other, so you can put some air pressure on both sides by blowing and perhaps coax any debris away from the valve seat.
2) Put a goodly amount of SeaFoam in the tank and go ride, letting the SeaFoam work its magic.
 
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