Hot Rods Edelbrock afb leaking fuel in intake

Hey guys. So I have been searching and found lots of threads on this issue. But none have been solved and none have the same concerns I have. So I have an edelbrock 600 afb style carb. After it sits for a day or 2 it starts hard. I have determined the carb goes empty. I have also determined that it is leaking into the intake. I started the car, ran for a few minutes, shut it off, then loosend the 4 nuts that hold the carb down. I then slipped a thin price of cardboard between the carb and the base gasket and let it sit overnight. Today I pulled out the cardboard and it was wet with gas. I looked at the boosters and they looked as if they have been dripping. So it must be siphoning. Plugged vent? One it starts it runs fine. No issues. I've heard that the gas percolates but I only ran it for 5 minutes before the cardboard, it was in my garage last night and it was 57 degrees in there this morning. I have a 750 edelbrock on another car that hasn't ran all winter. I got it out yesterday, with a few pumps she fired up no problem. What gives?

 

What is your fuel pressure? Too much will push the needle off the seat and overflow the carb. Needs to be5 or so on AFB or EDEL.

 

It's a stock small block chevy fuel pump, but shouldn't be pressure when it's off

 

see above--ck fuel pressure these don't like more than 5 pounds--stock fuel pumps can be well over 5=the pressure is probably there til it bleeds off

 

there are plenty of threads here about modern fuel evaporating out of AFB carbs, when left sitting for a few days. It's how things are.

Holleys have the accelerator pump at the very bottom of the float bowl, so they usually have enough fuel left in them after sitting, to be able to start, and get the pump going again. Quadrajets have a tiny float bowl, so they fill up with just one or two squirts of the fuel pump, when you start cranking the engine. But an AFB has two huge float bowls, and the accelerator pump needs the second bowl (the farthest from the fuel inlet) to get over half full, before the accel pump will start working So, you have to crank and crank.

btw, there isn't any way for the fuel to leak out of the bowl on an AFB....it can only evaporate. Take the carb apart, study it, see if you can find any way for it to leak, if you don't believe it.

 

I was gonna post that it must have a hole in it. I thought better of confusing things so I didn’t do that.

 

Well I've heard of fuel evaporating, so I covered it COMPLETELY with an upside down bowl and sealed it tight. No change. I also have another car with a 750 afb. (Same basic carb) in the same garage that hasn't ran all winter. Couple pumps and that car started. Garage is about 55 degrees, so I don't see fuel evaporation being the issue. Also, like I said earlier, I sandwiched a price of cereal box cardboard between the carb and intake and it was wet this morning, I could also see gas on the butterflies, and maybe wet in the boosters. Would too high of a float level cause it to start siphoning?

 

I don’t know any other way for fuel to leak out of the float bowl of an AFB unless there is a pinhole in the casting. There’s no other thing that makes any sense at all.

 

Stock fuel pumps will vary on fuel pressure

 

Well I just lowered the float level, so we will see what happens. While I had it apart I cleaned and blre threw every passage I could find. Nothing really looked put of place. Put it back on, fired it up. Ran fine. So time will tell.

 

I've had a couple that did this. If you shut it off you'll see the fuel dripping from the boosters and flooding the motor. You gotta hold it on the floor to get it to fire back up after it sits a few minutes. I found a diagram online from edelbrock that showed the air bleeds in the venturi boosters, i believe there is three in each one. They advised to make sure those were clean as they will stop up with sitting for a short time. I had already dropped my floats to 1/2" instead of the 7/16" they recommend with no luck. After cleaning the air bleeds, the issue stopped.

 

Here it is

 

Hey Lloyd, thanks!!! When I had it apart to lower the floats I also blew carb cleaner threw those air bleeds. Not sure if they were plugged or not but they blew clear. So hopefully I'll be good.

 

If it still gives you problems, go back at the bleeds with a tip cleaner. I blew mine out, thought they was good, but kept suffering. When i found that article and went back in, there was crud in a couple of them. Hope you get it lined out

 

Hi there Gus68, a friend of mine had a 600 edelbrock on his ot corvette that would run fine but when he parked it, after a couple of days he would come in to his garage that was stinking of fuel and his intake covered in wet fuel. He looked on the interweb and decided that the carb pump rod was the problem as the fuel was bubbling out of there. Changed it, same problem. Bought a knock off rebuild kit, put that through it, same problem. Got the shits and bought a new 650 AVS style edelbrock and the problem was gone. Gave the Carb to me. I put a genuine kit through it and hooked it up to a test pump on a bench and ran for 30 minutes and then turned the pump off. No problem. Put it on my car, still going strong no probs. Found out later that when my friend put the kit though it he only changed the needles, not the seats, cause someone told that the new seats in his kit would not fit the carb. My guess is that the needle and seats were not shutting off, combined with wrong float settings and the fuel was bubbling out the pump rod seal. So my advise is put a genuine kit in the card, double ckeck the floats cause maybe that’s why you’re seeing fuel “leaking” into the intake.


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Put a temporary gauge on it to get a true psi reading, I had two on a blown SBC, the base's of the carbs when shut off would be damp/wet.... Once I set the reg. To 4 1/2psi. Problem solved... Good luck
PS: stock mechanical pump!

 

Well... update. I seems no one ever finishes these things. So like I said last week. I took it apart and checked the needles and seats. I blew on the inlet and opened and closed the needles and seats and they held. So I lowered the float levels, and blew out everything that I could, just in Case something plugged. So yesterday was the test and...SUCCESS!!!!! Fired up and ran. I did notice before I tore it apart there was gas in the little wells by the secondary butterfly weights. Now there is none. My THEORY is that the floats were too high so fuel spilled out the secondary boosters or air bleeds and once it started it kept siphoning. Hope this helps someone.

 

Great !
hamber Gus68 wins
Nano-tech smart gas - big fat zero

 

Too high float level makes a lot more sense than having a leak. Great to hear that you fixed it.

 

Glad it's fixed and thanks for coming back and filling us in.

 

Well I hate to come back with my tail between my legs. But I've been busy for the last couple weeks and haven't touched the car. I went to start it the other day and no dice. Cranked and cranked, nothin. I pulled the air cleaner and worked the throttle and no pump shot!!!!! Seems I didn't have this thing wooped like I thought. But now I'm totally out of ideas. I had to give it a shot of carb clean and got it going. After that it was fine. Had pump shot, started every time after for the test of the day. I'm not home to mess with it, but it's on my mind. Any thoughts?

 

Perhaps all the fuel evaporated out of the carb, like we said?

That's exactly what happens to my wife's OT Dart, when it sits more than a few days. Pouring fuel into the float bowls gets it to fire up right away.

 

It has to be the fuel evaporating in the carb. I have 5 different cars and they all do the same thing after setting for a day or two. This summer I'm going to buy some racing fuel and try that in one and see how that works. These cars all have afb's or Edelbrocks.

 

I had two E 500's on an old Offy 360 aluminum intake on the 283 in my roadster. That car never ran over 185, but as soon as it was shut off, no matter how long it'd been run, I could actually HEAR gas percing in the carbs. Like yours it was hard to start when warm, flooded by fuel collecting in the intake plenum. I fixed it by making carb insulators out of some 1/4" Lexan I had in the shop. No problem after that, all it needed was that little bit of insulation from the heat of the intake manifold.

 

All good tech guys - the two barrel Carter also has pretty much the same set up with those tubes. I've rebuilt many 2 and 4 barrel Carters building pretty much the same. Get lucky on some and some I don't. Built one for my old 318 poly wagon - not sure what I did but that dang thing would crank up with just a slight turn of the ignition switch -it was pretty dang scary fast.....shouldn't have sold that old wagon.......good day all !

 

Lots more smarter guys on here than me but this is what i found. The carb acts as a heat sink. it will draw heat into it AFTER car has cut off. Hence fuel percolating.(junky fuel)
Go to summit ,buy one of their 1" carb spacer,(10 bucks i think) put between carb and intake. worked like a charm for me. and like above keep us posted. BE SAFE

 

Gus, you never told us the manifold or if it is or not heated by an internal exhaust x-over. Older cars with exhaust manifold butterflies and leaded gas would plug these passages up causing many goofy problems. My aluminum manifold is heated with the butterfly tied open and phenolic 1/4 spacer under the carb because of the new style gasoline percolating out. I was able to hear it and it quit after the insulating plate was added. Bought on eBay. Good luck

 

Did it have a mechanical or electric fuel pump? If it was mechanical, did it always start right up after sitting for a week or so?

 

Ever since most "Stock" mechanical fuel pumps are now made offshore NEVER assume that the fuel pressure is also stock,this has come up on numerous forums some as high as 15 psi+ and causing all kinds of issues.

 

I've had an Edelbrock 600 on my '34 since not long after they came out and they just leak down. I don't run a choke. I spin the motor until I get some oil pressure which also primes the carb. Couple of pats on the old throttle then hit the starter and it starts. You do a lot throttle pumping on a non running motor then you are washing down your cylinder walls with raw gas. Running a wood or plastic spacer between the carb and intake will greatly help on hot starts.