The Stovebolt Site Forums The Shop Area Engine Shop Fuel in my engine!

Here’s an interesting one. I have a 1971 Chevy C20 with a Jasper 350 and Edelbrock 1406 4bbl carb. About a month ago, I noticed it was running rich. Checked the carb and saw the secondarys were wet and there was fuel in the side troughs. Took the carb off and rebuilt it, checking the floats (good) and replacing all needles, seats, etc. Put the carb back on and it ran good for about 10 minutes, then started to run rich. Shut it off and once again, secondarys were wet. Also, my inline, clear filter was bubbling. Ran out of time, so left it sitting for a few days. This is where it gets interesting.

Yesterday (5 days later) I still smelled fuel. Looked under and saw gas dripping from the fuel pump. Dripping fast. Pulled the line from the tank and blocked it. Still dripping fast. Pulled the line to the carb; still dripping fast. Loosened gas cap, large hiss indicating pressure in the system. Pulled off the fuel pump, and as the bolts were loosened, gas started squirting out of the block (about a quart). Pulled the dip stick, strong smell of gas. Pulled a spark plug, gas poured out (about two ounces). Pulled the rest of the plugs and gas came out of one other cylinder (2 out of 8). Drained the oil and I swear, 3 GALLONS of gas and oil poured out!! Assuming about one gallon was oil, that means 2 more gallons of gas made it’s way into the engine.

Every post I’ve found on these forums talk about a few ounces or traces of gas in their oil. None mentioned having gallons! How could the system have pushed that much gas into the engine with it not running?

My plan is to rebuild the carb again, checking everything even more closely, replace the mechanical fuel pump with an electric one, prime the engine with oil to re-lube it, change out that oil and put in more oil. Is there anything I’m missing? Does this make sense to anyone? It is so strange that there was gas below (likely pump problem) and above (carb problem) the cylinders.

Any ideas would be greatly appreciated.

I'd disagree with installing a electric fuel pump. I'd make sure that you have the correct mechanical fuel pump on your engine. Does your truck have a charcoal canister to vent the fuel system? I'm not sure what year trucks went to a 3 line fuel pump. Its possible that you are not allowing the fuel system to vent? Sealed fuel cap and then a return line going to tank and pressurizing the system causing the needle and seat to not hold and letting the fuel run into the crankcase until it bleeds off enough pressure to let the needle and seat to hold the fuel back. Just a idea.
Good Luck

The pressure in the fuel tank due to the lack of a vent is overriding the needle valve in the carburetor, allowing the gas to drip down the intake and flood the engine. It's also possible there's a pinhole in the fuel pump diaphragm that's dumping gas directly into the crankcase. All tanks have some sort of vent, either one that's open to the atmosphere, or with a charcoal canister in the vent line. Find the restriction and fix it, and replace the fuel pump if you think it's bad.

An electric pump conversion is a guaranteed flood situation, unless you install an oil pressure sensing switch and some other safety circuits along with it.
Jerry

Thanks to both for the reply. I hadn't thought about pressure until you brought it up, but I recently bought a new locking gas cap and have noticed a lot of pressure released when removing it. I live in NC and it's been pretty hot lately. In fact, I wonder if the buildup in pressure not only forced gas thru the carb, but also blew the diaphram in the fuel pump. That would explain gas both above and below the pistons.

I don't know how the system is supposed to vent, but I'm pretty sure there's not a charcoal system as described. I think that came later. If anyone knows how/where it's supposed to vent the build-up in pressure, I could definitely use some hints on that.

Thanks again!

There should be a vacuum hose diagram somewhere on the underside of the hood, or possibly on the radiator support. Just about any vehicle made after 1968 will have some sort of filter on the gas tank vent, and a charcoal canister is the most common situation. A vent line will come from the top of the tank and run forward to the front inner fenderwell area. The flex lines from the tank to the frame can collapse, or the canister can get clogged to the point it can't vent pressure. Intake vacuum is supposed to go to the charcoal canister every time the engine starts to purge the trapped vapors out of the charcoal. Repeatedly topping off the gas tank until it's overfull can fill the canister with liquid gas, and keep it from venting pressure properly. If someone has changed carburetors and/or manifolds, it's very possible the canister purge line was not reinstalled correctly.
Jerry

Just to check, drill a hole in the fuel filler neck, (HAND DRILL ONLY). Use some teflon tape to make a small brass fitting fit pretty snugly. Run a line to a stock charcoal evaporator cannister if things seem to work. I'd leave the cannister venting to atmosphere at first, but there should be a connection to the carb if you like the setup.

Why not just leave the gas cap off? Stick a rag in the filler neck to keep varmints out!
Jerry

Where's he going to get a locking rag? ;}

Chain a pitbull with AIDS close to the gas filler. If that doesn't impress a potential gas thief, introduce him to the guy who gave the AIDS to the pitbull!
Jerry

I think the problem is pretty simple from a technical standpoint. You have simply installed too many components on your vehicle that are made to increase your mileage. This happened to me also.

For example, I installed headers that were advetised to increase fuel efficiency by 25%, a fuel saving carb that was supposed to increase mileage by 50%, a fuel efficient camshaft - 20%, high rearend gear ration 15%. It was great for a while, I no longer needed to buy gas! The problem was that I was saving so much that I had to stop every few miles and drain all the extra gas out of my crankcase where it had backed up because my fuel tank was so full!

I learned to live with it but it was a pain. Whenever I parked I had to post those "No smoking within 50 feet" signs.

Yeah. What he said.

does anyone have a vacuum hose diagram for a 72 cheyenne w/ac? there is supposed to be a hose or two going to the gas tank, from the cannister i think,to vent the tank.