350 engine stall problems help needed

[raser13]

hey guys i've got a huge problem witch is getting worse fast. i've got a chevy 350 in my 80 CJ5 it has a holley double pumper carb on it. it has a hei distribution system on it. i haven't been able to identify the model num on the carb yet.

on to the issue. it's unfortunately a gremlin.(does it sometimes and not others and never under the same conditions) what it is is you'll be driving along and all of a sudden it will start sputtering like it's running out of gas. the carb also makes a weird noise when it does this. the only way i can describe it is that it sounds like an old kirby vacuum cleaner motor. the motor not a vacuum line off sound.

at first i thought that it might be vapor locking because the fuel lines were running only about 2 inches from the exhaust manifold and the pipes. not the best idea by the PO. well i've re routed those away for the heat and even bent the fuel rail up off the top of the intake to get a little better cooling to the lines.

next i thought it might be over heating because it only has a single core radiator and no fan shroud and a mechanical fan trying to cool such a large motor. and it seemed to do it more on longer trips. i planned to get the mysique set of electric fans to help cool and a 3 core radiator if i can find one. but before i could get around to it it started doing it on smaller trips, say five miles or less and after it had been sitting all day and couldn't be warmed up yet.

i still plan to upgrade the cooling system once i get this figured out. speaking of wich all of the parts stores only list one radiator for this beast and they don't list how many cores they have any more but for the price i'm assuming it's just like mine. where do you get larger radiators for your rig? also any idea where i could get a temp gauge the works more like a stock one on resistance instead of these cheap alcohol filled line aftermarket type where you get one kink and they quit working?

i know some chevy's have a problem sputtering under load or at high rpms but this does it under no load and at high and low rpm. i've taken it on long trips with no problem.(over 400 miles) and like i said i've gone on short trips and have had issues. it does it at every speed. in every temp. in every weather. i've replaced the entire fuel system except the carb. i've looked over the electrical side and it all looks good. but visually inspecting components doesn't tell you what's going on inside.


any ideas as to what this could be?? it's driving me nuts trying to figure this out. especially with it being so random as to when it happens. thanks in advance.

 

[82Laredo]

Is it electric or mechanical choke?

 

[raser13]

manual but it's tied open right now. it's hard as heck to move when it's not. thought it might be the choke in the beginning just falling closed periodically that's why i tied it open just to make sure.



this pics old w/o the tie but it shows you what i'm working with.

here's my photobucket of it. there's a couple more shots of the bay. maybe someone will see something amiss that i haven't. these are from the day i brought it home and i haven't taken newer, better shots. i'm going to do that when my wife gets home with it.

 

[Barry2]

How long does it have to sit not running until it's OK again? And did you check your fuel filter/s?

 

[raser13]

from the fuel tank to the fuel pump in the engine bay is all brand new including the filters.

as for sitting.... sometimes a few minutes sometimes a couple of hours. it's really flaky on how it stutters and on how it recovers. it was stuttering once while i was going down a hill and i depressed the clutch to a)stop the jerking b)make it so i could rev the engine and keep it alive. the engine died so i just dropped the clutch and pop started it. it fired back up and ran fine like the sputtering never happened.

weird stuff like that is what has kept me guessing on this thing.

 

[Torxhead]

You have an issue with lots of possibilities. Pull a spark plug out to check if it is running on the rich side. Does the plug appear to be full of fuel and deposits? When it does start to act up, you could check the fuel float bowl level by removing those brass screws. It should be at the lower level of the threaded hole. On the ignition side, there could be a bad ignition control module, but I am not really sure how to diagnose that other than the symptoms are of it running crappy or not at all.

 

[Old Dog]

On the ignition side, there could be a bad ignition control module.

If you haven't changed this yet I'd try a new one, can't hurt.

 

[mtnwhlr]

You say everything is new does that include the pump? When was the last time the carb was rebuilt? The next time it starts take the gas cap off and see if sucks a bunch of air.

 

[raser13]

the fuel pump was the original one that was on it when i bought the jeep 5 months ago.

as was a suggestion on another site i added an inline fuel pressure gauge and found that while at idle the pump was throwing 5 psi at the carb. with the hood off, my wife driving, and me on the fender going 35 down the road, the pump read 1-2psi after a while and that is what started it sputtering! it should be around five to six psi frome every thing i can find. so i think i finally found the culprit!!!!!!!!! :booze::booze::booze::booze:


BTW I IN NO WAY ENDORSE RIDING IN AN ENGINE BAY OF A MOVING VEHICLE AT ANY SPEED FOR ANY LENGTH OF TIME!!!!!! IT WAS STUPID FOR ME TO DO IT!!!! IT WILL BE EVEN DUMBER FOR YOU TO DO IT!! PLEASE DON'T DO IT

 

[Scooter402]

Good job finding your problem. What is happening is the fuel pressure drops out because the pump can't keep up with the volume demand of the carb/engine. Once the fuel bowls empty out, you've got no fuel to stay running. The carb in a stock/street application needs a constant 5-6 psi.

Glad you made it back in one piece to report the problem. Might I suggest next time (or for anyone else diagnosing this problem) to use a remote fuel pressure gauge? just throwing that out there out of an obligation to safety. Not meaning anything personal there.

 

[Fastatv]

I hope you found it. But I would like to say, you still may have a carb issue...float settings, and air/fuel mixture. Double pumpers are for fairly hi performance engines, and unless you raise "cain" on the asphalt with your jeep, I would think you would run better with a vacuum secondary carb....something no more that a 600 CFM max. Just a thought for you.

 

[duffer]

First, if you're going to actually use the Jeep off-road, that carb needs to hit the junk box. I played with those for 20 years using every trick in the book and there is just no way to make them work when on a steep climb and/or off camber. The carb model number should be on the air horn. Going to be something like 4777, 4779, etc and you can cross that to find the cfm rating. For off-road, something like a 600 cfm Truck Avenger would be my only carb choice but retro fitting a TBI system would be a much more effective use of dollars and time. Fuel injection just can't be beat off road.

Fuel delivery issues are usually debris related, especially the tank outlet if its and old steel tank. Fitting a sock over the pickup will minimize that problem. Also, just because a fuel pump is new doesn't mean it properly functions. If you do need another pump, I would go with Holley's high output version and one of their regulators set at 6 to 7 psi. Those double pumpers also have a sintered brass fuel "filter" behind the inlet fitting. They have a very minimal filter area and the get plugged easily. Best solution is to throw them away and use a good in-line filter.

 

[raser13]

no offence taken scooter. it was a very stupid thing to do. main reason i put that huge bold red at the bottom. i wanted to make sure no one thought it was a cool thing to do. but it was late and the parts houses were closed. and money is getting tight and i want to fix this !@#$%^%$#$%^& problem so out on the engine i went.

as for going off road. right now this is a road rig. but i would like to take it on some minor trails. maybe tear through a muddy field) so i plan to get new carb or tbi when i can afford one.

 

[Torxhead]

I hope you are not using an electric fuel pump, if so that is probably your problem. The main problem with those things that are externally mounted is an ability to get enough fuel to them, causing them to burn up. It can be done quite well in fact, but they have to be mounted correctly and require a vented fuel tank. A carbed engine can run quite well with a mechanical pump.