Hello my fellow 3rd gen peeps I’m im need of some big help LOL. 8th cylinder won’t go above 200 ish degrees while engine warmed up

new spark plugs
new plug wires
New distributor (not installed yet)
new carb (Holley 600 not installed yet)

would gladly take any advice

 

Likely, intake valve not opening; some kind of valve train problem. Broken push rod, rocker nut fell off, etc. Up to and including a rolled cam lobe.

Pop the pass side valve cover off and watch the #8 parts as the engine is running. Odds are, something about that one, will look ALOT different from the others. Then all you have to do is identify the farkled part(s).

 

yes I did that earlier today after work push rods are okay I would say I didn’t run it while running I thought oil would squirt out if I did that? Please lmk if I’m mistaken. And i totally agree I think the exhaust valve is stuck which is causing the gases being built up and backfiring through the carb

 

Yes of course, one would hope so.

Nothing a trip to the quarter (dollar bill? debit card?) car wash won't fix though.

A "stuck exhaust valve" would have the EXACT OPPOSITE effect you are proposing. It would get forced open by the MASSIVE force available by way of the cam push rod rocker etc., and the spring would be unable to return it. It will "stick" open, not closed. Will make it pop in the exhaust, not backfire into the intake. Can't say I've ever run across that before however. Not in any kind of modern (post WW2) engine anyway.

A rolled exhaust lobe on the cam will cause the exh valve to never open, thereby not allowing spent gases to escape into the exhaust. Rather, they will spit back into the intake the next time the int valve opens. If your car is doing that (your original post failed to mention that) then an exh lobe down on the cam is a very real possibility. The most likely one, in fact. See my signature for help with the "likely" concept.

Nearly all the SBCs I've had that rolled an exh lobe, it was either the #6 or #8. Which was quite a few, both my own and my immediate family's, as well as ones for customers, before I wised up and quit dinking with 70s blocks altogether. I suspect that that's what you have, now that you've let us in on that little tidbit. Especially if your block is from the late 70s. Seems like The Problem (THAT one, there are MANY Problems of this general sort) was worst from maybe 76 or so up to maybe 80 or 81. Just as an example, I had a 78 and a 79 Z28 that both had it, both on #8 exhaust (although the 78 also had it to some extent on the #6 exh). I traded the 79 in on the 83 I still have after swapping out the cam so that it pretended to run right briefly. Evidently some one of the machines at the block foundry that drills out lifter bores, got out of alignment at about that time; and it took that many years before somebody finally noticed it. The Problem (ahem: [corporateAmerica] "opportunity for a solution" [/corporateAmerica]) is that the lifter bores are drilled kinda sideways and don't point properly at the cam lobe, therefore the cam/lifter interface is incorrect, therefore it all EATS itself. Ah the wonders of 70s domestic auto mfrs' "quality control"... keep the quality under TIGHT control, and never let it get so high that it's out of hand and the customer comes to expect that the next one they buy will be "right" too. Gotta keep em on their toes.

Watch the #8 exh push rod, rocker, etc. while it's running. Shouldn't take more than a few seconds to figure it out. If that one is moving ALOT less than the others, then you have a destroyed cam & lifter, probably LOTS of metal shavings in the oil meaning you'll be needing rod & main bearings before long, and a block that was defective from the day it was made and just keeps getting worse every time another cam wipes out in it and trashes that lifter bore even more. Looking at your 2 push rods, looks to me like the one on the right is the exh, and has been moving less than ¼", whereas the other one has a witness mark from the hole it passes through that's about ¾" long like it should be. They're reversed with respect to each other; the left one is laying there with the rocker end at the top of the pic, and the right one is with the lifter end at the top. Flip the right one over and you'll see.