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Old 02-17-2014, 04:43 PM   #1
mechanic350
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problems running

so ive had my 72 swb chevy for a few months now and it has been running great. no issues at all. and in the past week it has started sputtering while im driving and then dying. sometimes she comes back on her own other times i have to start her back up after keeping my foot on the gas while i turn her over. i just swapped the spark plugs this morning and put carb cleaner in my tank to see if that would help. i have new wires too. my only thought at this point is that because the fuel filter is before the fuel pump that it is some how not getting enough fuel in addition to possibly dirty fuel and a dirty fuel filter. any thoughts on other causes would be great help.
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Old 02-18-2014, 12:37 AM   #2
leftybass209
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Re: problems running

Sounds like you have a pretty good idea of what to check. Start with the filter, consider cleaning your tank if there's a lot of junk in it.
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Old 02-19-2014, 02:08 AM   #3
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Re: problems running

i was gonna try either draining the tank or trying to burn through it before swapping out the filter although i have 3 spare filters for it. im not too happy about it having a glass cylinder around the filter so i might get a new filter setup. and a buddy had a holley 75ocfm carb to swap out with my edelbrock carb that i have right now. we will see what happens though.
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Old 02-25-2014, 02:19 AM   #4
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Re: problems running

so ive swapped out the fuel filter and my tank is getting near empty and i thought that my truck was running better but she died out again on me today. looks like it might actually be the fuel pump. so gonna get a new one to put in and see if that fixes it
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1972 Chevrolet swb fleet side. 350 with 4 bolt main. Tremec T56 magnum 4/6in drop. 18" boss 338's, wilwood 13in brakes. 4.11 gears with Detroit TrueTrac Limited Slip

Link to my build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=607303
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Old 02-25-2014, 10:52 AM   #5
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Re: problems running

Is your filter full of trash....
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Old 02-25-2014, 11:31 AM   #6
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Re: problems running

The old filter was a little junked up but the new one still looks good. I've got a new fuel pump and a few other parts on the way so I'm hoping that fixes it.
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1972 Chevrolet swb fleet side. 350 with 4 bolt main. Tremec T56 magnum 4/6in drop. 18" boss 338's, wilwood 13in brakes. 4.11 gears with Detroit TrueTrac Limited Slip

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Old 02-25-2014, 11:37 AM   #7
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Re: problems running

Check your gas tank for trash. I had that problem a couple of weeks ago. New gas tank but had crap in it clogging up the pick up tube. I replaced many ignition and fuel delivery parts before I figured it out. I initially wrote off the tank being an issue since it was new.

Remove the inlet line from the gas tank at the fuel pump. If you aren't getting a full solid stream of fuel through that line, blow air through it with your compressor. When you hear the gas bubbling in the tank, stop the air, and reattach the gas line to the pump. Pull out the float and shine a flash light in the hole to see if you can see any trash.

I still don't know what was in my tank. It was a dark red color and disintegrated when I tried to pick it up to look at it. Removed the tank flushed it with water and let it dry two days before I reinstalled it. So far no more problems.

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Old 03-07-2014, 02:40 PM   #8
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Re: problems running

Yeah still not too sure what's up. I siphoned most of my tank down and it was all clear. Put in a different fuel filter with a plastic window rather than glass. My buddy is hooking me up with a holley 750cfm carb so I'll see if tha helps. I'm having a hard time finding a new mechanical fuel pump with a return line on it. Most don't have that and I was wondering if that would affect her running. I just want to get back to driving her again.
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Old 03-07-2014, 03:07 PM   #9
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Re: problems running

Clogged needle and seats, or the accelerator pump isn't pumping fuel. When you move the throttle does the accelerator pump squirt fuel into the primaries? It should be a quick shot of fuel. If it is weak and dribbles out then the pump in the carb is shot. Quadrajet carb?

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Old 03-07-2014, 08:13 PM   #10
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Re: problems running

It usually looks like it is dribbling out but I'll check it when I get back to my house. I can drive her hard around the block but a casual cruise down the street to work or back and she cuts out and I have to restart her. Hopefully your right and it's the pump in the carb. Yes it is an edelbrock 4 barrel in it right now.
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Link to my build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=607303
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Old 03-07-2014, 08:16 PM   #11
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Re: problems running

Not sure you are supposed to have the filter before the pump.
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Old 03-07-2014, 09:02 PM   #12
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Re: problems running

I do have the filter befor the pump. So I don't think hat is the issue
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Link to my build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=607303
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Old 03-07-2014, 09:14 PM   #13
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Re: problems running

Having the filter before the pump may be causing issue (is what I meant above).
Does the problem only happen after the truck has warmed up?
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Old 03-07-2014, 11:23 PM   #14
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Re: problems running

Yeah it usually does happen after she is warmed up. I have yet to have it happen while she is sitting in my garage idling. Hence why I'm at a loss.
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1972 Chevrolet swb fleet side. 350 with 4 bolt main. Tremec T56 magnum 4/6in drop. 18" boss 338's, wilwood 13in brakes. 4.11 gears with Detroit TrueTrac Limited Slip

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Old 03-07-2014, 11:34 PM   #15
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Re: problems running

Dosent the filter Go after the pump? that may be the issue
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Old 03-08-2014, 08:16 AM   #16
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Re: problems running

I run filters before and after the pump with no problems. if you run one before the pump it needs to be a high flow filter. I run a 10" stainless filter from speedway .if you run a standard universal paper filter before the pump it doesn't take much to stop or severely restrict the flow from a mechanical fuel pump. I would also check your fuel pressure, my autozone mechanical pump was putting out 10psi so I had to run a regulator with it
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Old 03-08-2014, 03:53 PM   #17
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Re: problems running

I'm running a k&n stainless right now. It's pretty small. Before that it was a mr gasket with a glass cylinder so I swapped that out. I do want to run filters before and after though.
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Old 03-08-2014, 06:45 PM   #18
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Re: problems running

Process of elimination, you might consider taking the fuel filter before the pump off and see if the problem still persists.
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Old 03-08-2014, 08:08 PM   #19
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Re: problems running

Tried that I'm on my third filter and all three have been different. Problem still exists
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Old 03-08-2014, 09:01 PM   #20
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Re: problems running

You've removed the filter entirely and ran it with only one filter (after the pump)?
I reread your first post - You poured carburator cleaner inside of the gas tank?
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Old 03-09-2014, 01:20 AM   #21
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Re: problems running

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so ive swapped out the fuel filter and my tank is getting near empty and i thought that my truck was running better but she died out again on me today. looks like it might actually be the fuel pump. so gonna get a new one to put in and see if that fixes it
When my trucks gauge is near empty the tank IS empty, are you sure your even getting gas to the fuel pump and into the carb?

Take the hose off the fuel pump that feeds the carb and put on a length of hose and point it to where it go's into a container, start cranking the engine and make sure your getting gas into the container, if not the problem is before the pump, maybe the pre filter sock inside the tank. if your getting gas the problem is after the pump.

If you know the fuel pump pumps ok then the next time it starts to die don't try to keep it running, just let it die, Then take off the air cleaner and see if by moving the throttle it squirts gas into the primaries, if not its a supply problem, needle and seat float related, or between the carb and fuel pump.

You mentioned that it dribbled? If it doesn't squirt then you found part of the problem. If it does squirt it would point to dirt in both the idle circuit and main jets, they rely on the vacuum to pull the fuel into the primary's or secondary's, if there is dirt in there the orifices will get plugged. My bet says that you just need to pull the carb apart and clean it up because you have a lot of crap inside plugging it up. I don't know if your engine is stock or built but a 750 Holley may be a little too big.

Got another question for you to think about, when it dies have you checked for good hot spark? just because you changed the plugs and wires doesn't mean you have good spark, if your still running points and condenser they could be in need of changing, and if the coil is getting hot it could create enough heat to generate enough resistance to weaken the spark as well, while your there look for any possible frayed wires running to the coil.
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Old 03-09-2014, 10:39 AM   #22
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Re: problems running

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Old 03-09-2014, 12:04 PM   #23
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Re: problems running

This post is interesting, I'm having very similar issues (post - Carb disassembled, cleaned, still runs poor please help!).

I haven't seen anyone mention carb issues aside from the one comment on accelerator pump. Have you tried cleaning the carbeurator to make sure all passages and jets are free? I'm having the same issue, once it warms up it runs like crap and hesitates briefly off the line, but then seems to run fine through the rest of the power band. But as soon as you take your foot off the gas, it wants to die.. I have yet to find my solution- timing is unchanged, carb/jets appear to be clean, fuel filter is clear, etc..

Something else to think about, could it be a vacuum leak? Haven't found one on mine but sounds like a possibility here too.
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Old 03-09-2014, 06:13 PM   #24
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Re: problems running

well there is about 5 gallons of gas in the tank right now so im sure there is fuel. when i took off the connection for the pump inlet fuel free flowed out of that pretty well with no efforts. i havent tried moving the filter after the pump just yet. i agree that the 750cfm holley is gonna be a huge carb for this motor but it was free. so that is always nice. yeah i do need to check if its a vacuum leak too because that would cause a few issues as well. on a side note anyone know what this is on my intake below the carb. showed it to a few buddies but no one has seen plates bolted onto intake runners before. btw its an edelbrock manifold
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1972 Chevrolet swb fleet side. 350 with 4 bolt main. Tremec T56 magnum 4/6in drop. 18" boss 338's, wilwood 13in brakes. 4.11 gears with Detroit TrueTrac Limited Slip

Link to my build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=607303
Instagram: https://www.instagram.com/72c10shortbox/?hl=en
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Old 03-09-2014, 06:16 PM   #25
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Re: problems running

It is a heat shield. You should remove the filter BEFORE the pump, not after.
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