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gld1

  • Thread starter Thread starter gld1
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gld1

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Hi,
Can anybody tell me why my 81' GS1000L leaks fuel out the exhaust? I had the carbs rebuilt last year and had them reset this summer and it still leaks fuel out the exhaust? I put new rings on all pistons, had the head re-honed, #2 clcy. was fowling plugs and a shop up here told me that my bike needed new rings and #2 clcy. needed the 2 valves replaced so I did that to? The bike runs great but I can't stop the fuel from running out of the exhaust?? I'm new to the big and old bike world and after I ran across this sight at 3am this morning I think I found the pot of Gold!!!:)

Thank You,
gld1
 
Fuel flows into the carbs from the gas tank via the float bowls. A float valve controls the amount of fuel in the bowl of each carb. For fuel to overflow the float bowl and flow into the cylinders, the float valve has to stop working.

A float valve stops working when any or all of these problems are present

- float level isn't correctly set
- float doesn't hold air so it doesn't float
- float sticks due to bent float pin
- valve sticks because of wear to the valve and/or seat

There may be other reasons for the float valve failing to properly work, but the net is when the carbs of a bike without a fuel pump and with a properly venting fuel tank overflow fuel, you have some sort of float valve problem.

Each carb should vent through an overflow passage to prevent gasoline from a stuck float valve from overflowing the bowls and running down a carb throat into a cylinder. The overflow vents should be checked for proper function.

If you have gasoline coming out of the exhaust, you need to stop running the bike. If gas fills a cylinder when the piston is at the bottom of its stroke there is significant risk of damage from the cylinder being hydrolocked. Also gas filling a cylinder will overtime find its way past the piston rings and ultimately dilute the oil in the engine creating the risk of bearing failure.
 
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Your mention of #2 cylinder makes me leap to blaming the petcock for some of your woes. When you say #2 you mean the cylinder second from left as you sit on bike?? (#1 being the one under clutch hand lever.)
 
Fouling in #2 would likely indicate a problem with the fuel petcock. Its a vacuum operated switch with cylinder #2 providing the vacuum. When the diaphragm fails, fuel runs down the vacuum hose and into the cylinder hence the fouling.

Not sure about the fuel from the exhaust though.
 
This tells me you need a new mechanic. Not possible to get fuel in the exhaust if the petcock is shutting off correctly regardless of what the floats are doing. And the trouble with #2 definitely points to a leaking diaphragm. Routine valve clearance adjustment would have certainly prevented any problem there.
 
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Yeah, it sounds like you definitely have a bad petcock. Replace it: the rebuild kits are garbage.


You may have additional issues. A few more things to consider:

A very high percentage of the bikes I work on have the float level set totally incorrectly. You're supposed to measure from the "step" in the float, not the top of the float. And it appears that many "mechanics" never really bother to check in the first place.

Secondly, you say that you had the carbs rebuilt. This strongly implies that someone used rebuild kits or aftermarket parts. These kits are widely known to be shoddy junk -- if you look at the FAQs and n00b mistakes on this site, this is one of the most common. Rebuild kits are a dangerous waste of money. In your case, I strongly suspect shonky imitation float valves and seats have been jammed in there with shoddy loose-fitting o-rings. Most of the time, they never seal, and if you do manage to get the bike running, the imitation needles very quickly develop worn spots and start leaking.

Another common cause of fuel overflow is old petcocks. Basically, many people new to the ways of the GS cannot resist the lure of the petcock lever and start yoinking on that which should not be disturbed. (It's vacuum operated, and is never moved in normal operation.) If it's an older petcock, moving the lever will release bits of mung that prop open the float needles and cause overflow. The petcock includes a very effective filter that does a good job of keeping tank mung out of the system, but it can corrode internally over large spans of time.

Lastly, it's very important to remember that it's a very old motorcycle, and there's rarely just one thing wrong at a time. You have to think of the fuel system as a system, everything from tank to exhaust, not just a series of fixes. Every GS needs a new petcock (the rebuild kits are just more shoddy dangerous junk) and every GS will need the carbs disassembled and cleaned (for real, not just spritzing carb cleaner here and there) then correctly reassembled with original or OEM jets, floats, etc. and an o-ring kit from cycleorings.com . Adjust float level and idle mixture correctly, ride regularly, and you will most likely not need to monkey with the carbs again for a couple more decades.
 
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Where are you located? There may be another GSer close by that could lend a helping hand.
 
Mine will un seat a float valve if I forget the petcock is set to PRI. I thought that was normal.....
 
bonanzadave said:
Mine will un seat a float valve if I forget the petcock is set to PRI. I thought that was normal.....
Click to expand...

Yep, that's pretty normal. The float valves are not designed to hold back a tank of gas all night.
 
gld1

You've been taken advantage of so far. There is no reason your bike needed to be rebuilt based upon the evidence you presented

The decades of experience from the above members (and others) can guide you to the correct solution

Step 1. Go by the auto parts store and get a vacuum cap to replace the hose from the petcock to the #2 carb. Pull the hose off the carb and put the cap on the nipple on the carb

Step 2. Figure out how to turn your petcock to prime. You have the infamous leverless petcock and I believe you need to have a screwdriver and turn the nub in the center 90 degrees, Be sure to turn it back to where it is now when you're done riding. Others can offer you more advice on this petcock

Step 3 - go ride and see if the symptoms stop

Step 4 - report back

You have indeed found the pot of gold in the GS world
 
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