This may be the wrong area but, I have a 55 caddy 331 with a dual 4 intake. Everything is new but runs like a pos. Sounds and runs like the egr valve is stuck open, which would be an easy fix if it had one. Just wondering if any of the grey beards have experienced these intakes cracking in the heat passage. Idle is shitty but runs great when you bring the rpm up around 2000. Thanks in advance...
Mine ran like that until I opened all four idle screws 1/2 turn at a time starting with about one turn. Hope that is all it is.
are the carbs new? I always double check all the ignition first. I even adjust timing by ear in case the marks are wrong, on a car with running issues. If all that is Ok, are the carbs progressive? If it was a moderate vac leak into the exhaust or not, and if it does not get good until 2000, then that size leak should make it almost impossible to set the idle rpm screw to anything below 1000-1200 without stalling. If you can get an idle, (but crappy), at 800 or less, I doubt "a" vac leak could prevent it from getting ok until 2000. Also, if you end up suspecting a carb problem, I'd make a block off plate to seal off the base for one carb at a time.
Make sure rockers adjusted properly. If they're too tight it will labor at idle and run generally bad. Just one of dozens of possible remedies.
This came to me as a rebuild. The carbs have been overhauled (didn't need it) by me (it's what I do for a living) so it's not an issue. What I have found so far is the crush on the lifters was WAY too much, .088... I have shimmed the stands .060 and that has helped a lot. My concern was, do these intakes crack in the exhaust cross over? Cuz that's the way it seems to run, like the exhaust is purging the intake. The ignition is pertronics and I've spun it in the dist machine. The rotor to segment clearance is .025. The plugs are new gapped at .042, the wires are new and checked with a dvom. I'm going to pull the intake tomorrow and block off the exhaust passage. I'll let you know how it works out... Thanks for the input...
I've had mine so hot it cracked a head and the manifold is still good. Try spray on copper seal on the gaskets when you reinstall the manifold.
The ignition is pertronics and I've spun it in the dist machine. I would double check this but I also suspect a vacume leak
Started a fire with carburetor cleaner looking for a vacuum leak. Use the propane torch now with better results. Can't find that "good" carburetor cleaner any more anyway. Ron
i use oxygen from my unlit torch. idle goes up nicely when it gets sucked in. carb cleaner is messy and takes paint off. don't have to take the intake off to block the heat passage. just loosen the fasteners and lift up with a prybar enough to slip in a piece of shim stock, tin can, etc.
OK after a couple different jobs I got back on the caddy. The leakdown showed 18% loss at #7 so I pulled the left head. I took the head to my buddy Johnny Cleveland and he dialed the seats in that cylinder. .008 out of round on both seats in #7. Previous machinist error. Also noticed the fuel was a dark orange color, so I drained the tank of old fuel and added 10 gals of new fuel with some nitrolube fuel conditioner. I also ran a straight file over the intake to head mating surface and found that someone (probably the same machinist) had used a 3M sanding puck to clean it before me, lots of divets. Fortunately they came out pretty easy. The new intake gaskets were steel shims so I used liberal amounts of Permatex #3. Final result, it runs on all 8!! Thanks to all for your input. PS. ran a boroscope thru the intake and found no signs of a crack...
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