The Stovebolt Site Forums The Shop Area Engine Shop exhaust popping in '66 283 engine

I found a '66 C10 in south texas that was in a barn on blocks. the guy who owned it parked it there 20 + years ago and says that it ran good when parked. We changed the oil, put a new fuel pump on it, put in new fuel and it fired up and sounded pretty good. Very good oil pressure and didn't smoke very much at all. It would pop through the exhaust and through the carb every so often. The enginie only has 80K on it. I have taken the engine down to a long block cleaned it up, put a .447 lift / 222 @ .050 camshaft into it with new lifters, roller rockers, and pushrods. New sparkplugs, new timing chaing, new edelbrock 4 barrel carb, new hei distributor, new wires, etc. I also put in umbrella seals on the valve stems, no broken valve springs, everthing looked good. I fired it up and broke in the camshaft and everything looks pretty good except for a couple things. It has periodic popping through the exhaust on the even side of the engine. I am guessing a sticking valve. The best vacuum that I can get is 13 to 14 inches that is pretty steady. I am guessing the long duration cam is the fault there. I have done a compression test and all of the cylinders cold registered between 120 to 150. I am thinking that it probably just needs some Rislone and driven a few miles to loosen everything up. I am sure that there is a lot of carbon build up in it. I have ran decarbonizing fluid through the carb and it really helped a lot, except for the periodic popping. When it pops it throws flame out. That is why I am thinking sticking valve. I have double checked the valve setting and it is right. I set them all a half turn past zero lash. (It is a hydraulic cam). Am I on the right track here or do yall think there is some other problem going on here ?

I see your not getting any replies here. Just a thought, it's possible a valve is hanging up, periodically, in a guide. Does it matter if the engine is hot or cold?

Check to make sure the exhaust isn't plugged up.

I see where you say you installed new umbrella valve seals.??.....Were the valve guides cut to accept these.??...You can not use umbrella seals on small block Chevys unless the guides are cut down to accept Perfect Circle type seals...Regular umbrella seals will hang up on the inner valve spring which your emgine must have...If your getting flame out the exaust that means an exhaust valve is not closing completely during the compression stroke...bent valve stem...weak spring....sticking valve stem..etc....

Hey guys, Thanks for the input. I checked with Federal Mogul about the seals. I told them exactly what I was working on and they put me on hold and looked up the part number that would work. They said that I could install these without modifying the guides. I was going to use positive seals, but they told me that I couldn't use those without modifying the guides. I am going to see if I can isolate the cylinder that is causing the popping and then check it out further. I will post what I find out in the next couple days..

Well, you are not going to believe this. The friggin thing was popping and running crappy because it was running out of gas. It finally ran out completely and after a while of trying to figure out why it wouldn't run, I realized that it was out of gas. I filled the tank and it all seems good now. Boy, I feel a little bit stupid, however the gas gauge doesn't work, so I guess anyone could have missed it.

Don't tell anyone, we'll keep this to ourselves. LOL!