bytor

Working on my backup Quadrajet. I’m checking the fuel bowl for leaky plugs. I set it up on a stand and put a piece of paper beneath it. Then fill it with gas or mineral spirits and let it sit overnight. The next morning, the bowl only has ¼ inch of fuel and no indications of drips on the paper. Also, no wet spots on the bottom of the carb bowl. Where is the fuel going??

Artsvette73

Depending on the weather I would say evaporation

bytor

I wondered about that. I covered the entire bowl with a thick folded towel thinking it would slow down the evaporation. No difference though.

TopGunn

Are the wells on the bottom wet at all?? It might be evaporating before it has a chance to drop on the paper. Maybe you can get a mirror under the carb to look. If it's not coming thru the well plugs I can't think of any other place it would go other than evaporating out the top as Artsvette said

bytor

Well, it gets wierder.. I let the bowl sit as it was for another day. Did not add any more gas or anything. Checked it this AM and it still has 1/4 inch of fuel in it. I would think if evaporation was the problem, it would be completely empty.

So, a recap.. I set the bowl up on a stand. filled it to the normal level with fuel. Let is sit overnight and the next AM, the fuel level dropped so that only 1/4 inch remained in the bottom of the bowl. (No signs of fuel dripping or leaks anywhere) Let it sit for another 24hr, still 1/4 in the bottom of the bowl. Maybe I have a pinhole or crack somewhere causing it to leak down to this level.. Very strange. Any thoughts?

AzMotorhead

Add red food coloring to fuel and retry your test.
Are you putting top back on the carb after filling with fuel?

bytor

I have done this a few times now with the food coloring added and see no fuel dripping,weeping or seeping.. Very strange. I pulled out my old junk bowl, taped and sealed the well plugs and tested it. The fuel level dropped overnight. This can't be normal can it??

1stC3Vette

Take a small cup and fill it to the approximate same level as the fuel bowl and let it sit overnight also. See if the level drops there.

Good luck,
Dino

w1ctc

The easily evaporated parts of the gas did. Whats left is the less volitile stuff. Eventually turns to goo. Put the same amount of gas in another container and see if the same thing happens.

vettephyxer

If you still haven't found your solution to this problem, you might try this. Go to your local home depot or hardware store and get a bottle of snap-line refill. This is blue powder which is very light that you can dust the carb with to see where any leaks might be coming from. Even if you don't see it right away you will see the 'trace' after a few hrs. This stuff usually comes in a plastic sqeeze type bottle with a nozzle making it very easy to dust something. Good luck.

bytor

Took w1ctc's advice and put an inch of fuel in the carb bowl and an also but an inch in a beer can cut in half. Checked about 10hr's later and the level in both had dropped the same amount. ~1/2in. So I guess evaporation is the culprit and just something to live with on carburated cars with modern fuels..

bytor

Finally have had some time to get back to this and I need some help. I've got the car running great now but I have one nagging starting issue and I think I may be a step closer to the culprit. I have noticed that when I take the car out for a spin then park it. The next day, it’s hard to start. I’ve confirmed the carb (Quadrajet) only has about 1/4 inch of gas in it. Now, if I start it (cold) and let it run for a minute then turn it off. It can set for 2-3 days and then start right up. So, do I need some sort of heat shield or is my intake getting to hot and boiling off the fuel on the carb after I park it?

A few other notes. The car is a 78 L-82. I have no overheating problems. Even in hot weather the engine temp never gets above 200*. My heat riser valve is disconnected because when I got the car, it was stuck shut due to a bad temp vac. switch. I am running a Quadrajet with a stock base gasket.

Matt Gruber

a 1/4" or thicker gasket really helps stop heat transfer.
i like electric fuel pumps too. with a prime button under the dash

Artsvette73

You also have to consider putting gas in the bowl on a work bench testing for leakage may work depending on how tight or loose the plugs are. My point is heat from the engine is missing in the test. A carb may not leak on the bench but in the real world on a hot engine it will.

noonie

Let cool down a bit and carefully take carb off and see if there is gas in the plenum. Found leakers that way that didn't show on a stand.

Be safe, plug it properly anyway while it's off.