Sluggish Motor

Q: Sluggish Motor

I am experiencing a problem with my motor running sluggish. While accelerating it runs fine but when you ease off to a cruising or constant speed, it seems as if it is missing and surging. I have replaced plugs, wires, points and condensor, and even taken the carb off and made sure there is no vaccum leak to the manifold. I am stuck! The only thing that I remotely have left is the distributor. Could this be the problem? Has anyone experienced anything like this? I appreciate any help.

A: Two things come to mind.First if there is excessive ignition advance it can cause the problem you describe.To find out,try disconnecting the vauum advance hose and plugging it then test drive the car.If it is now O.K. check the initial timing, amount of centrifugal advance and amount of vacuum advance.It is unusual but I have seen the internal limit “stop” in the vacuum advance can break allowing the rod to move way too far.You will need a vacuum pump and a “dial-back” timing light to do this check.The other thing is if it is running too lean a fuel mixture at cruise it will cause a surging condition (it would be better under acceleration due to the power system) This is a little trickier to test for.The easiest way would be with a gas analyzer which the average person doesn’t have access.A crude way of finding out is remove the air cleaner and plug and vacuum hoses removed then run the engine at 2000-2500 rpm (engine must be warmed up and choke fully off) Now partially resrict the air horn either with your hand or by partly closing the choke valve and see if the rpm increases.If the rpm picks up sharply and the motor sounds smoother you likely have too lean a mixture.The reason may be a number of things which I could only guess at with out more info.This test is admittedly a bit crude and requires a bit of experience to interpret the results of.

A: If your car has a Quadrajet, your throttle slide (the little brass cylinder that pulls your metering rods up and down) may be sticking. This happened on a 350 I had. Try pulling the top off of the carb and us a Scotchbrite pad to buff it up and see if that helps.

A: I found the problem with the motor surging on my bird. I pulled the distributor and found a wire to be dangling off of the vaccuum advance module. I dont know what purpose this wire served but one end had a screw which held it onto the module itself and the other end was bare just laying in the bottom of the distributor. I went to a local salvage yard and picked up an HEI distributor for 20 bucks and installed that in the car. (Much better than points system). Didn’t even have to beat the firewall in, went right in. I am soooo relieved. I was starting to think it was something mechanical. I thank everyone for the help you have given me.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.