Need some help w/my Plymouth Falthead 6

OK ... I'm gonna come before the collective wisdom and admit that I'm not too up on engine magic. My Plymouth has started acting kinda strangely. I thought I had an exhaust leak because I was hearing this "chug-chug-chug" sound at low RPM and under load. The other day I took it out for a drive and she started feeling underpowered and then gave me a couple of good backfires. I limped home, opened the hood and I could hear the "chug-chug" seemingly coming from the CARB? Now, I know what my "read a lot of books but never opened up a motor" brain is telling me it sound like, but I thought I'd ask the experts! Any thoughts?

Thanks

 

If its coming back throug the carb, you might have an intake valve not closing all the way, maybe a broken spring or you may have lost a retainer, so its ot closing all the way. If you have a vacuum gauge hook it up to the vacuum port ont he intake manifold, then go to secondchancegarage and look at the page they have on reading a vacuum gauge. If you don;t have a vacuum gauge do a compressioin test. If you don;t have a compression gauge, with insulated pliers, with the engine running, pull one spark plug wire at a time. If the engine runs worse, than that cylinder is OK, put the wire back on and move to the next one, when you get to the cylinder with the problem the engine idle won't chage apprecialbly as that will be the cylinder that is missfiring, and causing the problem. You still won;t know what the problem is but at least you will no where to do some more looking. If you isolate the bad cylinder. You can check the valve operation by removing the side covers under the exhaust manifold. The is facilitated by jacking up the front pass side remove the wheel, on the inner fender there is a removable fibre panel to facilitate valve adjustment. Pull that and it will give you access to the thumb screws that hold the side covers on. with the covers removed, you can observe the operation of the valves on the bad cylinder.

Make sure you use jack stande before sticking your head in the wheel well.

 

Sometimes the 'chug-chug' sound is caused by a split exhaust manifold. If you have a cracked manifold it will make this sound. This will cause these two cylinders to run lean (hot). The car won't overheat but you can blow a head gasket between any of the paired cylinders where the head gasket is skinny.