Hi all
I installed overflow tubes in my carbs a few years ago. I presume this is the cause of fuel evaporation from the bowls if the bike is unused for a few days in hot weather. I seem to have to use the prime position alot more than I remember. I have thought about putting a dab of grease in the drain holes that would dissolve if an overflow occurred and would reduce the evaporation. Any thoughts or other ideas...?

Hi all
I installed overflow tubes in my carbs a few years ago. I presume this is the cause of fuel evaporation from the bowls if the bike is unused for a few days in hot weather. I seem to have to use the prime position alot more than I remember. I have thought about putting a dab of grease in the drain holes that would dissolve if an overflow occurred and would reduce the evaporation. Any thoughts or other ideas...?

Instead of dabbing grease, which may end up as a plug, simply create a 'loop' with the drain hose used, and dribble some motor oil into the loop, to create a 'trap'where the oil seals the bottom path of the loop, kinda like a 'sink drain trap'.

Thanks..sounds like a plan

What's stopping the vapour from escaping via the air box?

There are 2 vent tubes coming out at the top of the carb bank.The fitting of overflow tubes introduces an air path from the bottom of the bowls up past the fuel in the bowls through the carbs and out the the top.Hot air rises and Carbs are aluminium which is great at transmitting heat.This is an effective way of increasing evaporation of fuel particularly on a hot day. That's my thinking on it..

Another thing you can do is get some of those rubber caps that are used to cap off vacuum lines. Many sizes available at your local auto parts store. Easy on, easy off.

Dan

Another thing you can do is get some of those rubber caps that are used to cap off vacuum lines. Many sizes available at your local auto parts store. Easy on, easy off.

Dan

ummmm... capping the drain lines kinda negates what they are for, if capped, they cannot drain, and Hydrolok will occur during a float valve failure, just as if the anti hydro mod was never done...

There are 2 vent tubes coming out at the top of the carb bank.The fitting of overflow tubes introduces an air path from the bottom of the bowls up past the fuel in the bowls through the carbs and out the the top.Hot air rises and Carbs are aluminium which is great at transmitting heat.This is an effective way of increasing evaporation of fuel particularly on a hot day. That's my thinking on it..

the 2 clear upper vent lines are there to prevent a sealed "container" scenario, as a sealed system, will not allow fuel to flow into it... has nothing really to do with the hydrolok mod, it is, and has been, (has to be also) since this carb design was started. basically you cannot flow a liquid into a closed container, unless the displacement of air is allowed... I've seen dozens of people capping these off, and the bike won't run... duh... they need to be free and open up top, to allow fuel to flow into the carbs. (I've also seen a bunch of hoses, blocked by spider egg sacks, which blocked them...they didn't work either..)

ummmm... capping the drain lines kinda negates what they are for, if capped, they cannot drain, and Hydrolok will occur during a float valve failure, just as if the anti hydro mod was never done...

Yeah, true. Been away from the C10 so long, my memory gets a bit fuzzy...

Dan

Yeah, true. Been away from the C10 so long, my memory gets a bit fuzzy...

Dan

that's ok Dan, you and me both...
that's why they coined the term "fuzzy logic"..
peace, ride safe...

  I have overflow tubes on my carbs and a loop in the hose about halfway to the back. My C10 usually sets for a couple of months without starting. Takes about a minute or two to fire up. No prime and petcock is always set on run.

     Here's some interesting info. After installing overflow drain tubes, indeed the evaporation rate of the fuel increases. I have seen bikes on the lift that are hot, when shut off you can see the gas vapor literally shooting out - downwards - from the bowl nipple.  The fact the carb vent tubes are open makes a kind of backwards chimney effect... the air can come in from the vent to help speed the evaporation. But on the other hand... the overflow tubes alone act as carb vents, and at that point the actual vents become redundant and not needed.

  To prove, take a set of carbs with no overflow tubes and while idling, block the stock vent tubes. the bike will immediately shut off because the air can't move in and out of the bowls to balance the fuel displacement.  Now do the same test with a set of carbs that have overflow tubes. They are unaffected by the vents being blocked, gthe bike will continue to run, unaffected.

   I have known this for a lot of years, but this is the first time (to my recollection) that I've written about it. I have found often giving information like this just sets some folks off, and the end result is more confusion than if I'd have left it alone. So now I'll guess we'll see what happens      Steve

Steve
Thanks for the info..where overflow tubes are fitted would blocking the two upper vent tubes be worth a shot? The way I figured was the overflow tubes allowed an air path upwards past the fuel in hot bowls and out the upper vent tubes. You have seen it going the opposite direction. I will block the vents as a trial
Dan