Sputtering when flooring it

[RescuedElk]

Hello and thanks in advance! I have slowly been learning and building a 78 el camino, with a abc 350/th350. I managed to get the engine running and finally took it out on the road. At first take off car felt fine but when I floored the gas the car begins to sputter and feels sluggish. On idle car feels fine has powers, if I slowly press on gas it’s fine, but when flooring I get the sputtering. Any ideas or help, things I should look for? All help is appreciated.

Note: I am no mechanic , but a student of YouTube and forums haha

 

[John Canon]

Hello and thanks in advance! I have slowly been learning and building a 78 el camino, with a abc 350/th350. I managed to get the engine running and finally took it out on the road. At first take off car felt fine but when I floored the gas the car begins to sputter and feels sluggish. On idle car feels fine has powers, if I slowly press on gas it’s fine, but when flooring I get the sputtering. Any ideas or help, things I should look for? All help is appreciated.

Note: I am no mechanic , but a student of YouTube and forums haha

It sounds like the accelerator pump on the carb. Here is a quick test: engine off, ignition off, remove air cleaner, hold choke valve open. Look inside and fully move the throttle once. You should see a good squirt of gasoline going into the throttle bore. Watch for splashes! If nothing, then try again. The accelerator pump gives that extra bit of gas when you press the throttle quickly and give it more air.
P.S. Actually we are not students but prisoners. You are lucky, when I first learned mechanics, I would go to the library each evening to read service manuals while my friends hit the pubs.

 

[airboatgreg]

Check fuel filter

 

[RescuedElk]

Thank you all. I swapped out the fuel filter, fuel pump, and then the gas tank prior. I just swapped the filter again since it appeared to have sand like sediment. The fuel looks clean now.

Im going to test the accelerator pump. I’ll get back you

 

[Clone TIE Pilot]

You also want to manually depress and release the accel,pump plunger to see if its sticking. Pretty common for cheap accel pump seals to swell when exposed to modern E10 gas.

 

[64nailhead]

What carb?

 

[69hurstolds]

Apparently it still doesn't work since he's not back yet.

🤔

Sputtering...probably the technical term for a fuel issue? Or is it a bog? If it runs fine at idle, the idle circuits seem to be good.

Be nice to know more info....original engine? 4bbl or 2 bbl? Assuming 4 bbl. EGR? No EGR? HEI distributor, I assume?

TIMING. Make sure your ignition timing is set right. Not saying this is it, but if you know that's good, check it off the list. No crossed wires as far as firing order, right? Ignition problems like a messed up coil or other components could be causing the sputtering.

FLOAT LEVEL. Has to be high enough to sustain maximum fuel draw without running dry. This coincides with the dirty fuel filter path, fuel pump pressure correct, etc., as mentioned.

DID YOU F**K WITH IT? Did you adjust anything or tweak some screws or any of that once you started having problems. Not saying you did, but it's good info that might be important to help.

One other thing to consider is the reaction spring, plunger delay spring, or whatever you want to call it. The TOP spring above the pump cup. If it's weak or broke, you can try and pump fuel, but it'll just allow the return spring (lower spring in the bottom under the cup) to keep the pump cup right about where it starts. The plunger still goes down, but the cup doesn't move or barely moves and you get a poor or no pump shot. Only way to tell if it's working is if you see a healthy pump shot to the primaries when you stroke the throttle blades while looking into the top of the carb (ONLY DO THIS when engine is OFF).

Another possibility, and since I'm not there, can't see it or have video....(assuming good gas, and good mechanicals) is that a secondary accelerator tube or both tubes have come loose and are sitting in the float bowl. These accelerator tubes act like an accelerator pump for the secondaries allowing extra fuel to shoot into the secondaries just as the air flaps start to open but before good fuel flow starts through the main secondary fuel circuit. Without them, you could cause hesitation, but I doubt it would be sputtering.

 

[RescuedElk]

It’s an edelbrock manual carb, 4barrel. I took the carb to my nearby carb shop. Should be getting it back at 3.

As for timing, I’ve tried getting timing with the timing whistle , every time I think I have it at top dead center the line on the pulley doesn’t line up to the mark on the plate. I use the timing light and I see the line right at the 12 o clock mark. Whenever I try to adjust it to the Mark the car turns off. The distributor rotor points at the #1 spark plug. Not sure if the previous owner ever worked on the car. Again, I’m new to all this mechanical stuff, so I may be saying the wrong terms. My bad. I appreciate the help!

 

[John Canon]

If you are concerned about your ignition timing, then do a few small steps before firing it up . First, confirm you have the correct #1 cylinder location, and mark the wire clearly at the cap and on the cap and the dist body. Then bump the engine to point the rotor at the mark. Remove the #1 plug and use a long skinny screwdriver to touch the top of the piston. If you remove all the plugs it is easier to turn the engine by hand.

Manually turn the crankshaft a bit each way while you sense the highest position using the screwdriver. You can get a pretty accurate TDC point. Look at the timing mark ... it should show TDC. If you don't have that you may have to look deeper. If you engine conks out when you turn the distributor then you may have a short or a loose something in the dist. If the dist shaft has play and if the point gap is way too small, then you could have stalling when you move the dist.

Don't forget to do the various checks for the accelerator pump and other things mentioned above.

 

[RescuedElk]

Issue resolved! I picked up the carb from the shop. Turned out the carb was clogged, and the secondaries were stuck. The el camino is alive. Now on to the next issue. Thanks a lot everyone.