Fuel in my oil & Engine!

[Bildo]

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 an ounce). 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.

[70rs/ss]

Pressure pushing past the needle and seat, and or tearing the diapham in the pump. I'd guess the pressure pushed past the needle and seat and forced fuel into the engine through the carb, since you said the cylinders were filled up this all points to fuel going through the carb into the intake, but change the pump as well.

[Chevyman680063]

This happened to a friend of mines uncle. He had a 71 Chevy truck with the original 350 in it. The fuel pump went out on it and put gas all in the motor. It ended up destroying the motor so he had to buy another one. Hopefully you caught it in time and won't have to replace your motor.

[airdale94]

I'd just replace the fuel pump and change the oil, and see if that takes care of your secs. also.

[70rs/ss]

I thought about it just being the pump, but the whooosh he got when he pulled the gas cap off and the fuel in the cylinders (hard to fill them from the bottom up with the rings, so I figured it came from the top through the intake?) got me wondering, so replace the pump as we all suggested, but keep an eye on it as a non-vented cap can build enough pressure to cause some problems as well. This is a weird one, but give us an update so we can all have the knowledge of what caused this for future needs.

[truckdude239]

get a vented gas cap and change the pump and rebuild the carb you should be good to go

[steelhorse]

It sounds like your gas tank is building up pressure and pushing past the needle seats.Pull all the spark plugs ang leave them out drain the oil and leave the drain plug out till it quits dripping.Replace the oil and filter.Idealy you would pull the dist and reprime the engine then crank the engine overto push all the fuel out of the cylinders,if you have axcess to an air compressor blow out the cylinders with an air nozzle,replace the plugs and run it for a few minutes then rechange the oil just to be safe.I hope this helps.Dont forget to get a vented cap or fine out if the vent is clogged.

[umwtnt]

With a non vented cap and the heat we have had lately its easy for the tank to build pressure. As the temperatures raises the fuel in the tank expands causing the pressure in everything to raise. The diaphram in the fuel pump can go bad and expell fuel into the engine. I have seen this numerous times. As everyone else has already said, replace the pump and flushed the engine and start fresh. I would also replace the cap with a vented cap. Good Luck.

[BLACK AND BLUE 67-72]

Sounds like you need a vented fuel cap, I ran into a guy the other day with the same exact problem, the pressure would push the gas through the needle and seat and flood his engine until fuel came out of the spark plugs, he changed the cap and it hasn't happened since!!

[Bildo]

Thanks to all for the help. I recently did change to a new locking gas cap, and I'm guessing I got one that's not vented. I'll change that as well as the pump. Steelhorse, thanks for the tip on repriming the engine. Since it hasn't been run at all after the gas flooded in, I don't think I did any damage. Priming it, then changing it again as described is the plan.

Thanks to all for the help, I'll let you know in a few weeks how it all comes out. (Going to Hawaii and Cali for a two week vacation with the family so won't get back to it until end of Aug.)

[Bildo]

One other thing; How is the fuel system on this truck ('71 C20) supposed to vent? I want to make sure I get it right.

[BLACK AND BLUE 67-72]

Well if it has EEC it vents into the passenger side rear of the cab, the tank will have a hose by the gas filler neck and one on the passenger side running up into the cab. If it does not have EEC then it vents out the cap.

[HavinSomeFun]

I have seen this more often with the Edelbrock carbs. To much preasure from the pump or the tank building up preasure will cause this. Another simple fix is a fuel preasure regulator set to 6 pounds max. The Carb will be able to hold that much without it leaking past the needle. You still need a vented cap.

[72-c20]

a 3/4 ton would not be EEC originally.

(at least the '72's aren't.)

[70rs/ss]

Yeah, Edelbrocks don't like more than 5-5.5 lbs of fuel pressure, so in this case 10-15 psi worth of air pressure would easily go past the needle and seat and empty the tank in theory as the pressure is pushing down on the fuel and forcing it out of the tube at the bottom of the tank, that being said, until the fuel is below the pick-up tube the fuel will be pushed out. I don't think I've had a cap fit that good on my trucks, but my 02 Blazer about blew my hand off the other day. I was in Phoenix (117 degrees by the way!) twisted the cap and woooosh!! On the newer ones they have a Vapor recirculation system (basically a vent tube at the highest point in the tank, then a tube goes all the way to the carbon canister and vents into that. I don't think you need anything like that on your truck, but a vented cap at least, you'll just smell gas??


For 68GMC454, get a pressure regulator on that pump as the edel don't do good over 5-5.5 psi!!