Gas help!

[Security guy]

No, not that kind of gas! I finally got my carb issues figured out, but I'm having problems with getting gas to the carb. Its a 402 with a fuel pump from an earlier car. The pump only has two lines, one in and one out. It ran great with another carb, but the other carb was running to rich. I put a little smaller quadrajet on it and it runs great on take-off. The problem is at 55-65 mph. It starts cutting out and almost dies. If I stop, it fills up with gas again and I can go another mile or two. I have a clear fuel filter just before the carb (not a glass one) and I can see the fuel coming in the filter. It works great when the engine is cold. After the engine gets hot, the fuel just barely dribbles in the fuel filter which is probably why the carb is starving for fuel. What is causing this? I thought vapor lock, but I've heard that is very rare with todays fuels. Is the pump going bad after it gets hot? Its a stock pump from advance auto parts. I think the feed line is clear because when its cold, it gets plenty of fuel. It just seems to do it when the engine is warm or hot (140-195 degrees). Any thoughts? Just replace the fuel pump?

[tim21391]

my 72 was up on highway running about 75-80 mph.. and it would bog down and cut off and starve for gas..then i go to neutral and its fine... found out it was all in my distributor.. points..rotor condensor and cap is what i replaced..dont know if its the same as your problem or not..

[ed2552]

I would look at the fuel pump. Get a new one, they're not that expensive.

[68gmsee]

I had the same problem last year and it turned out to be clogged filter in the carb. I went ahead and replaced both, the one before the fuel pump and the one in the carb. Don't overlook the sock filter inside the fuel tank.

Some years earlier, I had a low fuel problem, which turned out to be a badly restricted fuel line from the tank to the pump. I guess years of sitting and gunk in the tank caused it. I wound up replacing the fuel line.

If you have never replaced the pump or looks like it's pretty old, go ahead and replace it. They're pretty inexpensive.

[67ChevyRedneck]

How many in-fuel filters do you have total?

[Security guy]

I've just got the one fuel filter before the carb. Brand new dizzy cap, rotor, plugs, wires filter is new (less than 75 miles). Is there a filter in the tank? Like a sock type filter? I've got a factory tank behind the tank. The fuel pump itself is new also. I've only put about 150-200 miles on it. I've taken it to the alignment shop and muffler shop and to the auto parts store about three times. Everything is new except the tank itself. Thats why I'm thinking a defective pump. Is there a spring in the pump that is failing after it gets warm?

[67ChevyRedneck]

The tank has a sock looking thing that keeps big chunks of stuff out of the line, but will let all of the silt and fine stuff get by. It's not uncommon for the sock to break off inside the tank.

What CFM is the new carb? Maybe it's not "big enough" for the big block which could be why it's choking down on the highway?

[Security guy]

I originally had a 800 cfm quadrajunk on it, but it kept flooding out and ran real rich. I put a quadrajunk (sorry quadrajet fans) off a 350 on it (i think 650-700 cfm?). It runs great on start up. No hesitation. When i take it out on the highway and get on it, it just dies until I let off and then it will come back. It runs great under 40 mph, but any faster and it dies like its out of gas. When I pull over and pop the hood, the fuel filter barely has any gas in it. Its not getting gas. I haven't checked inside the tank. That could have something to do with it. When its cold or has sat for a while, it gets gas fine. Maybe there is something inside the tank getting sucked in the fuel line?

[pumpgas]

Sounds more like vapor lock then anything to me. Do you have any fuel lines anywhere near heat? If it runs fine cold then has issues when warmed up it isn't a fuel pump or filter issue.

[Security guy]

Thanks for all the help guys! This is giving me some ideas and things to look for. As far as vapor locking, none of the gas lines is touching anything. Its mostly new metal line except for about 6" of rubber gas line. If it is getting to hot, would putting a larger rubber line around the metal line help insulate it? I'll check some other things also, but I think I've got a good idea on where to go from here.

[pumpgas]

Originally Posted by Security guy

Thanks for all the help guys! This is giving me some ideas and things to look for. As far as vapor locking, none of the gas lines is touching anything. Its mostly new metal line except for about 6" of rubber gas line. If it is getting to hot, would putting a larger rubber line around the metal line help insulate it? I'll check some other things also, but I think I've got a good idea on where to go from here.

I don't member the temp but gas boils at a rather low 1 so lines don't have to be touching anything for the fuel to get hot. I would also look at the old reused rubber line to make sure it isn't breaking down or collapsing.

[Andy4639]

I would try and get rid of as much of the rubber line as possible. It may be sucking closed on you while driving. The hose maybe bad on the inside and not obviouse from the outside.
Have you cranked it up and gotten under the hood and looked at while you work the gas, just to make sure nothing obviously is wrong.

[LockDoc]

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Your local Chevy dealer has the sock filter that goes on the end of the fuel pickup tube (or they can order it). Part #5651705. It is listed as a "Filter". As posted earlier there is also a filter in the carb inlet fitting. I would replace it. I would also take the line off where it goes into the fuel pump and at the tank and blow through it with an air hose.

LockDoc

[d10s69c10]

Originally Posted by 68gmsee

I had the same problem last year and it turned out to be clogged filter in the carb..

cant stress how common this is to be over looked. if you have checked it and no its not there it could be many of the above ideas.

i know i tried everything all the way to the point of taking the carb apart and when i found that thimble of a filter i blew in it turned red in the cheeks threw it and that motor has ran great ever since.

[69halfton]

i have a 4cyl Honda Civic stock car.

the car ran perfect, lots for power, but would fall on its face at exactly 7000rpm in the last quarter of the straightaway (oval track car)

i swore it was heat related. we changed everything, distributor, coil, wires, heck we blew the first motor up, swapped in a new one and still had the problem.

you know what it was...when we put the NEW rubber line on the fuel pump, it peeled a little rubber off the inside of the line, and it wasn't until the motor needed all that gas that it sucked the little piece of rubber over like a flap, shutting some fuel off (it never really killed the engine, it was more like a stupid rev limiter)

seeing as you have all new fuel lines, inspect your rubber hose to make sure it hasn't been sliced a little when you put the stuff together. I know how you feel, our problem lasted the entire season, it didn't run good until the final race of this season, talk about ripping your hair out.