85 El Camino with major drivability issues



Jul 22, 2019
This might be kind of long so bare with me. First I have an 85 El Camino with a 305 (not sure if it's the original) I bought it with an aftermarket Edlebrock intake manifold,Holley 750 carb, flow master exhaust with CC delete. I began having an issue with her about a month ago. She ran great and then one day she didn't. She had a tendency to deisel out and when you needed to make a quick get away she would fall flat on her face. But other than that no issues. I have had to replace the starter, alternator. Stupid stuff. Well I ended up running off the road and I blew out a tire. That's all I thought was the issue. Then she started to run like crap. The electronics were cutting out, rough idle, really rough and rough running. So I went to buy a Quadrajet. I put the Quadrajet on and I eventually got it to run but she revs up. The electronics problem was the starter main post was broken. And the rough running I believe was 2 busted spark plugs. The issue is the carb had been messed with so now it's all out of whack. Now I'm pretty sure I have it all dialed in but now she backfires when accelerating, if I try to speed off then she does well until I level the acceleration out then she backfires. I can run her in second up to 50mph and have no issues other then a rough idle. I mean rough. I have no idea what my problem is. I have a new timing chain, I'm going to clean out the carb today, I also have a new complete gasket set for her that I'm thinking about putting on while I'm doing all of this and I hope to get a compression gauge in the next day or 2. I don't know how to use one. But I'll learn. Is there annything I might be missing or any tips. Please. Thank you.
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Jul 22, 2019
Yeah I know that is way to big of a carb but it's what was on it when I bought it. I do have a Rochester 4 barrel 600 cfm for it but it's missing some rod levers and wants to rev up when I install it. Not to red line but way more then it should. I was thinking timing myself. I have a brand new double chain timing chain and gears ready to go. I am waiting on my compression tester and I also noticed today that I have a major major exhaust leak. Think I will fix that first then timing and while I'm doing the timing might do new valve cover gaskets. I have an entire gasket set for my truck. I just want to know I'm on the right path. If this was a motorcycle I could have it diagnosed and fixed before you even finished telling me the problem. I don't know crap about motorcycles. The solution just comes to me. I don't know crap about cars but so far it seems I second guess myself because it is my dream car and I don't want to mess it up but other advise tends too lead me down blind alleys. I will say that it's nice to have others who validate my original thinking. El Camino central was a bunch of who ha. Blind alley after blind alley. Took me almost a month for someone to mention the starter could be the electronic problem. That's what I thought. But was told no since I just replaced it. Thank you all for your help. I'm sure I will have alot more questions so I'll keep this post up to date daily if possible.


Master Mechanic
Aug 23, 2010
San Angelo, TX
Take your valve covers off and have someone crank the engine. Make sure all the rocker arms are moving. You might have flattened lobes for one of the cylinders.


Dec 8, 2019
Vacuum gauge, compression test, timing light and the suggestions above are your friends.
It sounds like timing or some ignition related problem. Do you drive it short distances often? Were your plugs carbon fouled? Try to run some 93 octane thru it. The vacuum gauge is cheap and can tell you alot about your engine. Also im pretty sure you have a squarebore intake and quads use a spreadbore intake.
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