'79 750 Carbs Draining Fuel

Bloody Mary

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New to me '79 LTD with 5300 miles. Have put about 50 miles on the bike so far since purchase in November. I typically turn the fuel petcock off about a mile from home and put bike away after it stalls out. Today, turned on the petcock and fuel began draining from the tubes attached to the carb bowls. Thought maybe the drain screws had loosened, or perhaps the drain seals for the screws had not sealed properly....loosened, then tightened again, but the fuel still drains. Looks like all four are draining, but haven't confirmed. Perhaps floats stuck? I do not have the ability to remove and rebuild carbs (you might ask why I have a 40+ year old motorcycle).
Any advice or recommendations appreciated.
Thank you.
 

amc49

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Ethanol in your local fuel does it. Take carbs apart and simply touch the needle and then it comes unstuck, they stick on the rubber because ethanol attacks it ro make it sticky. My 550 does it too if bike sits more than a week. You are running the carbs dry and then the ethanol sticks the needles where they end up, or wide open. Ethanol also increases the evaporation rate of fuel in the bowls by like 500%, it dries up much quicker.

I developed a procedure to not have to yank carbs, simply yanking main entry fuel line to put some small amount of air pressure in to knock the needles loose works. I use a portable air tank to do it but you have to be careful not to allow full air pressure in, it will bend needle settings. The needles can stick open or shut depending on circumstances.

Ethanol in gas plays bloody hell with earlier things like motorcycles, which have open vents to the atmosphere unlike cars which now have to travel venting forever before it gets out to save problems with ethanol. The bike carbs vent so easy it is nothing for air to get in to evap the ethanol to cause troubles. Check a bowl in a week that WAS full; it won't be even over that short a time. Spill some fuel in the hot summer, it dries up while you watch in seconds and much faster than it did with no ethanol, the alcohol content really increases the evap rate.

Why I say the use of ethanol in fuel is transparent if you use the vehicle every day, but let them sit and the problems begin. You won't ever hear the oil companies tell you that though.
 

amc49

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You might even try filling carbs up till they overflow out the hoses and then turn petcock off and wait 24 hours. The new fuel exposed to the needles tips may melt the sticky off to go back to working loose. I had some limited success doing that.
 

Bloody Mary

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Thanks, amc49. When I got the bike in November, I filled the tank with non-ethanol fuel, and drained the carbs completely for winter storage. There is NO rust in the tank. Taking carbs apart way above my pay grade. Might try your filling and wait 24 hrs. suggestion. This fuel draining happened once before, but stopped before the incident yesterday. I thought that perhaps the drain screws have o-rings that dried out. I am puzzled how fuel drains out if the drain screws are closed tightly and properly sealed. Checked Partzilla and it appears there is a gasket or o-ring on the drain screw.....although listed as part of a $35 gasket set.
As always, thank you kindly, sir, for your expertise.
 

amc49

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Lucky you with no ethanol in fuel, I'd kill to get some. Do they even use any ethanol in the fuel there at all? If so, the stuff may be leaching into the fuel lines for non if like here. News reports of regular fuel buyers getting premium if the last guy before you got it, some stays present in the line system to come out with the next fill even though switched to another type. The premium users here b-tch when they are not getting all they pay for. And with the help we get now there is no guarantee the tanker guy is putting the right fuel in the right station tank. Premium being often made using ethanol now makes even the fuel supplier suspect too, they get it cheaper than the gas itself due to the subsidy on it. And the mileage drops making it that way so they sell more too.

If the seats are good the drain plugs will seal by themselves, the o-ring then needed to seal from bowl leaking on top of motor when the drain is opened up. It also provides backup seal if the drain seat leaks a bit.

Yes, let it sit. I have rebuilt carbs before to have them leak with pretty fresh o-rings, let bike sit one day to let the fuel get to the rings to swell them and everything fine and never leaked another drop. ALL rubber parts swell a bit when the fuel hits them, when they shrink from drying out; if you do not disturb them and they do not shrink enough to crack often they will swell back up to be fine.

A LOT of people have complained as well about the mostly Chinese carb replacement parts we get, the fuel needles often have issues with swelling due to a lesser grade of rubber tip being used. Even normal non-eth fuel can make them act up if they are not original, and if they ARE original then I would expect them again to act up due to age.
 

Bloody Mary

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Yes, there is a local gas station...less than 10 miles from me that sells non-ethanol fuel, however only 90 octane...which I think will be fine in the Honda. I removed the drain screws from the bowls of the two throttle side carbs...the only ones leaking. O-rings looked ok. Saw a related post here from a few years ago saying that removing the screws and blowing some compressed air through the drains might dislodge any debris blocking float needles. Low and behold, that worked....no more leaking.
Was considering adding an in-line fuel filter to help prevent any more debris going to the carbs. Any suggestions for such?
Thanks again!
 
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