When cold start engine sputters and tachometer needle jumps up and down

Hi and thanks for using 2CarPros.com.

I realize the carburetor had been rebuilt. However, has the metering needle been adjusted? It sounds like it is dumping fuel. What I would suggest, and it has been awhile since I did one, is to remove the plastic cap at top and locate the orifice adjusting screw down inside the carburetor. Next, turning the screw clockwise will lessen the amount of fuel to the engine (make it a leaner mixture). Turning it counter clockwise will increase the amount of fuel. Based on your video, it sounds like this is where the problem lies. When you make the adjustment, I would recommend no more than half a turn at a time on the orifice adjusting screw. Once you get it to run properly, then there is nothing more than a throttle stop screw to adjust.

Try this and let me know what you find. If you have other questions, let me know. One last thing, make sure there are no vacuum leaks to the engine. Here is a link which shows how to locate them:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Also, this could also be related to the electronic ignition. Let me know if the adjustment works.

Joe

Have you rechecked the needle and seat as well as the float level? Has anyone changed the fuel pump type? It is dumping fuel as you already know. Either the needle valve is not closing off the inlet of fuel, the float is set too low, or for some reason there is too much fuel pressure (in the event the pump type was changed).

Let me know.

Joe

Have you replaced and set the points, condenser, cap, rotor and plug wires? Also, can you pull the new plugs out to see what they look like. Do all cylinders and take a video of them please.

Cheers, Ken

It is good the spark plugs are new. I need to see the electrode color to see if the engine is lean or rich? Also, do you have nex plug wires? Do you install EI? Because that car came with points and condenser.

Okay, if we can see the plugs I can tell you which way I would go. By the way, I have had nothing but problems with some aftermarket systems. What is the brand name?

I am a little carburetor oriented.

My thoughts on the super videos you sent are either:

A vacuum leak or a fuel issue. I am leaning towards a fuel issue.

This quick test might verify both possibilities.

Get you a sacrificial squirt bottle capable of stream or mist.

Load it with a few ounces of fuel.

I really suggest doing this outside away from other precious things with a first line of defense (big wet towel) and a second line of defense (fire extinguisher).

Remove the air cleaner and crank it up.

Start by misting fuel into the carburetor throat.

Does running improve?

If yes, we may still have a carburetor issue or a vacuum leak.

Before tearing into the carburetor for a problem.

I would rule out the vacuum leak possibility.

Check those hoses for cracks/ being unhooked/ swelled on the ends letting air by.

Here is how to really check it out:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Who built the carburetor?

Who adjusted the carburetor (on vehicle) Or was it just put on as is?

Keep us posted on results!

Maybe some closer pictures of the carburetor?

The Medic