Mom has a 74 nova with a 250 straight 6 and 1BBL carb...a new problem arouse the engine sputters...i suspected low compression in a cylinder especially when it read 12 to 15" of vacuum...now before i can confirm that the engine desperately needs a rebuild what else should i look in to.

New wires and plugs
New Carb
New Cap and coil
No Cat but Glasspack muffler in good condition

No oil or coolant leaks but puffs out black smoke

 

You gonna drop that 250 into your car, and put a V8 into the old Nova?

The reason I'm asking is because the moderators sometimes frown on non-thirdgen questions. And because a 250 under the hood would be pretty cool!

That engine probably does NOT desperately need a rebuild. It may need a head gasket, but you need to do a compression check, wet and dry, and write the numbers down for each cylinder. After you figure that part out, the rest will be a piece of cake.

Good luck.

 

I'd pull the plugs and find out which are fouled out... If the engine is puffing black, there's a good chance that a couple of the plugs are also black. Find out which ones before you go and do anything else, as you can knock the problem down to a couple of cylinders that way. I6's are notorious for being too rich towards the center of the engine or wherever the carb is and too lean at the extreme ends of the intake manifold due to the design of the manifold.

What is probably the reason the vacuum is low is because of the a/f mixture... A compression test would help, but I would guess that there is a problem with the induction. There are ways to tell with the vacuum gauge, you'll need to find the booklet that came with the gauge. Or get a book from a library or something that shows the gauge readings.

 

Unfortunately, I have to lock this thread, because it's not only not 3rd gen related, but asking about an engine that is not even offered in a 3rd gen.