Car Surges, or Stumbles While Cruising

This can be caused by many things. I'll list some of the things to check, not in any order.

• Too much fuel, or too little fuel - check the float level. Don't fudge, set the float at specifications.
• Power valve leaking. This might show up on the power level also.
• Main discharge leaking - If running smooth at idle, then this probably isn't it, but at idle look down the carburetor. If gas is dribbling out of the venturi, then you have a leaky discharge.
• Take a couple of spark plugs out and look at the color. If tan, or light brown, then they are burning correctly. Black indicates too much gas and white indicates a lean situation.
• Main jets don't wear out, but if something changed on the carburetor, high performance parts added, carburetor is a transplant, or moved in elevation (5000 ft), then the jets may not be sized correctly.
• A vacuum leak can cause this. Check around the carburetor base, all vacuum lines and the intake.
• Ignition problems can also cause this, distributor, plugs, etc.
• There is the possibility a passage is plugged. Spray carburetor cleaner through each passage to make sure it goes through.
• The fuel pump may be too weak, look for 5 lbs prox. This can show up at higher speeds.
• Replace the fuel filter. A partially plugged filter will restrict gas flow.