Technical Truck bucking.. starved for fuel

Have an old 60's stepvan with SBC 350. When driving...out of nowhere truck starts to what we call 'buck' almost like it is starving for fuel. Doesnt matter if uphill, downhill or flat ground.. could happen on any of those. Plenty of fuel but it is in a custom gas tank mounted in a compartment built into the side of the stepvan..not under the back end anymore. Old owner says no baffles in the tank. I thought maybe it is sloshing around but had truck idling for 20 mins in one spot. It died...and trying to restart it sputtered and died about 5x. Then finally started and ran as long as i didnt step on gas.

I drove 5 miles on normal streets no bucking. Got near highway after sitting at light for 2 mins..starts to buck. Get on highway and after 2 mins of bucking i drive 30 miles at 55mph no issue. Get off highway..go 2 miles and bucking again around 30-40mph but I cant pin it to that speed range. Another minute of bucking where I baby the gas...and it is fine for another 5 miles to home.

Brand new battery from interstate.

Does battery have anything to do with it as we did have an issue where when this happened, truck died and could not restart it. Seems the battery got down to 11.7v and it would not start again. Jumped it off one of those portable jump start battery power boxes and it started right up.

Odd.. frustrated as I dont know what the issue is. Not sure if there is a fuel filter on the line..will have to crawl under truck and trace out line.


thanks for any advice

 

Sound like carburetor could be something to look at like the float could be getting stuck at times or maybe the timeing could be off or distribiter jumped.

 

I would check for a clogged fuel filter. How old is the gas? {might be crud in the tank} Been there with most of my older station wagons. Try blowing thru the fuel line to clear it after disconnecting it from the fuel pump.I hope this helps.Bruce..

 

I have no clue...old owner said no issues of course lol. I will trace out the line and see if there is even one in the line! Shame on me for not knowing. I thought it was only when i put gas in this happened but drove today 50 miles and didnt put gas in there. Could be crap in the tank/line. WOuld some sort of carb cleaner/gas treatment help or not really. Im wondering if something is in there clogged without fuel filter on the line..then what? But why would it run well for 30 miles then all of a sudden start.

The distributor/carb suggestion is probably out of my expertise. So will have local mechanic work on that angle.


thanks

 

90% of fuel/carburetor problems are caused by the ignition system. what does it have for ignition? point distributor? HEI?

as for fuel starvation..it takes very little fuel to run at idle, if there is a restriction in the fuel system, it could be idling fine then not run very good under load. The old carburetors had a filter built into the inlet of the carb, where the fuel line screws in, there is a big 1" hex nut that holds in the filter. Check to see if it's there, and if so, replace it. Be sure to use a "flare wrench" on the fuel line, so you don't round off the hex on the nut

 

All original .. not sure even when the ignition system was checked last. Will have mechanic look at this as Im not well versed in this area.

It was idling fine for 20 mins... and then just died. Restarting it sputtered...started then died 5x. I would hit gas after it started and then died. Last time i started and let it idle without touching gas and it stayed running. Sorry for my basic explaining of the situations.

 

custom tank? i bet it doesnt have a vent....

 

Would have to check.. i guess i assumed too much that it was running well and after our trusted mechanic looked it over for 4 days lol.

for the dummy over here.. what effect would that have on the truck..?

 

Well a strong vacuum would develop where fuel left the tank and air was not allowed in to displace the missing fuel.

 

If you have a timing light or can borrow one put it on and see if it is missing any sparks. Gary

 

what would i need to get a check value and hose to put on top of gas cap?

 

vented cap.

 

No vent causes a lock. As the fuel exits the tank, the volume that the fuel took up must be replaced with air. A vent or a vented cap allows the air to enter and prevents the fuel from escaping. If the tank is not vented the fuel will not flow unrestricted.

 

Would also put a fuel regulator in line. Even on mechanical pumps, the surge can overwhelm the float valve. Mine likes up to 4 psi only

 

I had a similar problem years ago with my '53 F-100 that was powered by a 327 SBC. Turned out that the fuel line was rubbing against the floor of truck where the line left the tank. The rubber body mounts had shrunk over time allowing the floor pan of truck to wear a hairline crack on the top side of the fuel line. The fuel pump would suck air through the crack sometimes.

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I doubt it's a problem with the tank vent, but you can test real easily by removing the gas cap, see how it runs.

 

Cracked rubber hose between the tank and the metal line can cause this too, or any other kind of leak in the fuel line. Or a plugged line, you can't see the rust that's on the inside. A weak fuel pump, a bad ignition condensor, badly adjusted points, etc, etc, etc there are lots of possible causes. Gotta check one thing at a time, until you find it.

 

Check the carb with the vehicle off take air cleaner off and look into the carb and pull back accelerator and see if gas is getting squirted into the carb. If you dont see any squirts going down in there then you need the accelerator pump replaced in the carb. But if your not inclined to do that just let some one help you with that Good luck

 

A home made tank might have rusted inside and block flow as it gets sucked up.

It could have some sediment in the carburetor that moves around. If it has one of the filters with a spring behind it where the fuel line enters the carburetor, the filter can clog and the pressure will push the filter against the spring allowing dirty fuel to get past the filter.

 

My first car, an all original 54 Chevy had the same problem. It would start and run fine. Get me about 10-15 miles from home start bucking and sputter and die. Would not restart 20-30 mins later tow truck would show up. I'd hit the key to start just for shits and grins and it would start right up. Son of a bitch. Tow it home. Get uncle Chilton to help me rebuild the carb, adjust the timing, every thing that could possibly be done I did. Went on for almost a year. Fuel filters were clear and had gas in em!!! Culprit. Gas tank. After rebuilding almost everything on the engine it was the varnished, sludgey, rusty, junky ass gas tank. Would let enough fuel through until the debris clogged the pickup tube. Then settle back to the bottom after a half hour or so. New tank, problem solved. Silver lining was it taught me to work on my own shit. I can rebuild those damn rochesters in my sleep. For shits and grins. Try running it off a marine gas tank or rig up something ( safely). Good luck

 

hmm food for thought. Im looking online and not seeing large universal gas tanks bigger than like 18 gallons. Anyone ever seen or bought a larger one universal type?

 

The fuel tank does have a vent and sure looks super clean inside. Not seeing any sort of inline fuel filter. Gas line is rubber (new) from bottom of tank to a metal line that snakes to middle of truck under motor and then up to carb.

Carb is filthy.. black on it.. just all so dirty. Anything i can do there?

thanks

 

I was going to say the same thing. The bronze filter in a GM carb is known for clogging.

I probably wouldn't have posted a thread until I chased what I knew to chase. if you think you are starving for gas for instance and haven't checked the fuel filter that would probably be a good place to start.

 

Without taking it apart is there a way to tell if my quadrajet has the bronze filter or the long filter? thanks

 

My friend had a similar problem; the vehicle would occasionally starve for gas. We finally had to drop the gas tank and found a white sock (the kind you wear on your feet) floating in the tank. When my friend asked the previous owner he said “he stuffed the sock into the gas fill when he lost the cap to keep stuff out of tank, when he got a new cap he couldn’t find the sock.”

 

i got a good look in the tank as it is in a side compartment on this old truck. looks super clean. The carb on the other hand. .is filthy black! gunk all over it...on springs, outside, inside. Would carb cleaner be the way to go or better way?
Thanks

 

Try carb cleaner at the car wash just before washing the engine. Cover the distributor with a plastic bag or just use caution not to blast it or the air cleaner directly.
Quadrajets do have the small filter mentioned above. Remove the fuel line, then the larger nut that it screwed into. Carefully remove the filter and spring for inspection, cleaning, or replacement of filter.

I found a small piece of rubber (like a cap seal) in a tank once. It would move around and sporadically cover the tank outlet.

 

tried alot of carb cleaner... and no luck. Drove it today. Seems like once engine is warm and it idles in place for a couple of minutes (like I stopped at gas station for a water..left running) it then stumbles. Let off and gently press gas and she goes well. No rhyme or reason when it happens. It actually stalled out after the five minute idle time. Started right up and went 20 miles no issue.

Put seafoam in gas tank..no change. Didnt look at quadrajet filter as i started to try to get fuel line off carb and couldnt.

Returned home.. stumbled every couple mins. Just let off totally on gas, gently press it and she goes fine. Very frustrating.

Biggest issue is the stalling..that could be dangerous on highway!!!

Any thoughts?

 

This thing sound like i mentioned earlyer. you need to check the carb and see if your getting thos squirts inside the carb with the motor not running and if those jets are not working that is what is not giving it that juice for take off. Another thing to check is spark plugs. And see how the timing is set on it amd disconect the vacumme and see if it idels different without the vacume hooked up. If you have stock style distribitor it could be vacume pod on the side of distribitor not working no more. Mainly look into carb and see if the carb is squirting gas. When you pull the throttle. Check that first.

 

But if it only happens intermittently how would the jet test tell me much?
What to check on spark plugs.. fouled?
If timing was off..wouldnt it always run oddly/rough..not once in a while?

Im thinking of telling mechanic to go ahead and replace distributor, wires, plugs, etc. but something telling me it may be a carb issue.