84 C-20 350 engine help

I just got an old chevy and am having fits getting it right. The engine is original but seemingly professionaly rebuilt but definitly has a cam too big for it. I just threw the old q jet in the junk pile and installed a new 1406 600 cfm edelbrock with the correct edel adapter ( 4 hole) for a spreadbore intake. The distributer appears new but I had to change the cap and rotor a few days ago after finding out the hard way the previous owner put the brush in on top of the rubber seal instead of under it. It shut off on the highway after burning the cap out. I can't use original timing specs thanks to the cam but I got it loping along pretty nicely at 550 rpm in gear 650 neutral with 12 deg timing. It hits 35 deg at about 2500 rpm and I think it is too soon but I have forgotten too much about non computer cars to be sure. Yesterday after the little car radiator exploded I put in a modine 4 row like it probably had in the first place for a 3/4 ton truck and I also put in new ac delco plugs ( r43t was the PN). Now strangly when I get on it from a stop up to highway speeds it is more sluggish than my mule out in the barn. It feels like a army duece and a half with a water tank behind going up the steepest mountain around. Almost gave me flashbacks. If I am cruising along at 50 or 60 and stomp it it will almost spin the tires with all the power it has. This one has about got me stumped. New fuel pump and filter, Didn't mess with the carb other than initial idle and mixture settings. Choke ain't stuck, park brake ain't on, none of the obvious stuff. Do y'all think this cam is just too big for a truck with an auto ( t400) trans or could it be something else?
Oh a couple other things it has a 180 thermostat and flex fan and according to the factory gage runs right at 180 in town and 190-195 on the highway. Lean maybe? Plugs were good looking, brownish light coating from the garbage gas here but not bad looking, We are at 3500 feet though. It also deisels just a bit when I shut it off hot and if it sets more than 10 minutes or so then it cranks 10 to 15 seconds before starting. in the mornings I just tap the gas to set the choke and it fires right up and goes. It doesn't ping and runs like a scalded dog once wound up just no low end whatsoever. The 75o holley I put on the wifes 455 runs fine at this altitude after I went down 5 jet sizes and reset every thing. It always starts right up and runs like it should. Am I missing something on this edelbrock maybe?
I am a mechanic, actualy computer technician, and it really bugs me I am getting whipped by something as basic as a 350 and a 4 barrel carb. I guess trying to keep up with all the modern stuff I really have forgotten a bunch from my younger days. If anyone has any advice to offer on this truck please let me know. I need it to pull the horse trailer soon. A big goos neck horse trailer. A better cam and and edelbrock intake are already planned when I get more money to throw at it. I can definitly use recommendations for a cam. Thinking about one of the extreme 4x4 cams maybe.

You don't mention how it ran from a dead stop before you changed carbs. If you dropped bottom end power after you changed the carb, chances are that is the first place you should look.

If it's the 4 hole spacer that that cuts down to little half moon openings before it goes into the intake, go pull your Q Jet out of the trash and replace it with the spacer, or bite the bullet now and buy a square flange intake. If the engine is slugish chances are its starving for fuel/air because of the restriction in the primaries.

If you want to continue to try the combination, you might want to go with step rods a couple of steps richer and see if that helps at all, it's only a band-aid however.

Before I changed the carb it wouldn't hardly run. I was gonna rebuild the q jet till I found how bad the shaft holes were and that the choke was broken too. Just not cost effective. The spacer is the one edelbrock recommended. It has the 4 holes that exactly match the holes on the carb then devide off to exactly match the intake. Not the half moon shaped one. I haven't seen one of those in a long time. I had an open adapter at first and it actualy pulled off a little better but idle was much worse. It did get worse I think after the plugs I put in to it. They were a much shorter tip design than the bosche that I pulled out. They were sopposed to be original equipment for it. The number was r43t if anyone knows what is sopposed to go in a heavy duty 1984 350 engine. That wouldn't make that much of a difference though would it? I guess this is gonna turn into another winter project.

I'm gonna just take a shot here as I ran into the same prob. not too long ago with a friends rod...his turned out to be a multitude of things but the worst was his dist.- he didn't have a "curve" it was more like a corner. The weights were so light for the carb. that he had installed that as soon as he hit the gas it threw the weights inside wide open. We got a curve kit from ye ole parts store & it improved 1000*.............worth a check huh?

Last night as I was out in the garage annoying the neighbors I started playing around with the accelerator pump and just for the heck of it I moved the link to the other holes and tried it. On the top hole it bogged real bad and almost stalled. On the bottom hole it was much better. It was on the middle. I think I am gonna go and put the calibration kit from edelbrock in it for my altitude and see what happens. Along with the advance kit.
I have had that problem too but with my tractor and not a car engine. It is an old farmall super c and it came with firecrator aluminum high compression pistons as a dealer installed option originaly in 1953. The original owner must have replaced the distributer with the wrong one at some time and it was a dog after I rebuilt everything on the motor. I ended up haveing to get the correct distributer shaft and springs for the application from the IH dealer and it cured it. The aluminum pistons required a much different curve then the more common iron pistons. I am betting that is most of my problem too. The mechanical advance will reach 22 deg max at 1200 rpm and with the vac hooked up it will go to 40 by 1650. What do you think I should shoot for. I'll bet the dist came from auto zone. I might end up having to replace the whole thing with an msd or mallory or something.

Initially, I think I would shoot for about 36 total in at about 2800-3000 rpm (it's hard to say what the truck will like, but I think thats where I would start.)

Also keep in mind that when you are pulling away from a stop sign (under load when actually driving instead of sitting stationary in the garage), you intake vacume will drop giving little or no vacume advance. To trouble shoot it I think I would plug the vacume advance temporally (to insure you don't get too much advance when the vacume raises at cruse speed) and add some initial timing and see if that helps.

My mind also keeps going back to your comment about running better with the longer reach plugs. Were asuming that you have the original heads on the truck, but are you sure they are? I think I would pull a plug that easy to get to and see if I could tell what the depth is to insure that the electrode is actually in the combustion chamber. (Another way to do this would be to pull a valve cover and run the casting number to see if the heads are actually correct for that engine.) With the engine combination you have, I would start with the plug that the engine the heads came off call for + 1 step hotter.

well today I pulled all the plugs and checked all the cylinders compression readings. All dead on 150. Perfect according to my book. I guess it isn't an auto zone motor after all. Thank god! I already knew the block was still a 4 bolt main like it should be cause I had to pull the oil pan to fix a leak last week. I also called the chevy dealer with head casting numbers and they verified they are correct. I put in the plugs my books called for and quite a bit of power returned. Still ain't all there but better. It was r45t. I bet the r45ts would have been better with the longer reach but these are what it calls for. The r43's that were in it the past few days were pretty black. Just too cold or the carb too rich or both? I guess I will pull one in a couple days to see. I got a mister gasket advance curve kit today too. I will try to put it in tonight. According to the chart on the back of it the weakest springs it has makes a curve almost exactly like what I have. I will go with the strongest ones first and get it up to 38 at about 3000. That will actualy be where it runs at at highway speed so it should be alright. This truck has a 4.11 locker saginaw full floater in the rear. Boy they made nice rear ends back then.
Oh a moron at the only shop in town that does custom distributer work told me today that the edelbrock instructions that came with the carb are wrong and that I should hook the vaccume advance to the manifold vaccume instead of the timed port. I tried to tell him it will not idle no matter where I set the timing to when I do that unless I open the speed screw up to about 1000 rpm. Then when I put it in gear I hold my breath and hope the drive shaft doesn't come through the floor. That couldn't be a good thing. He tried to tell me that is how it should be. well I guess he won't be getting any of my business. I may be a little rusty when it comes to hot rod chevys but I ain't stupid.

yep, right at 150, well 148-152 or so. Close enough for me. I got a good snap on compression tester and I trust it. If it were an autozone special I would have checked to see if the needle were sticking. I had to do it quick on my lunch break and didn't do it wet. I didn't really see any reason to.
I just put in the curve kit with the stiffest springs. Minor difference in taking off. Big difference in idle and the transition to power mode. Now if I can just keep the vaccume advance out of it while it is floored I think I will have it made. I think I need to get one of them gm things to kill the vaccume to it while floored. I think they close below ten inches if I remember right. It is still getting 38-40 at 1800 or so.
The test strip I am using is quite unscientific, Just 5 telephone poles on a back road and I take off from a stop and when I get to the 5th I look at the speedometer. It was at 45 yesterday and I am up to 55 today with the hotter plugs and advance curve in it. I am just leaving it in drive for testing. If I shift it and let the rpm go up I can hit 70. Not too bad for a 6500 pound truck.
I am gonna try to do the rejetting on the carb and get that vaccume break or what ever they call it before I mess with anything else. Has anyone had any experience with a edelbrock 1406 at 3500 ft altitude? I was gonna get the kit edelbrock recommends in their owners manual but if there is anything else I should know please let me know. The plugs are still black so It needs jetted but I was wondering about reducing the shooter size or anything like that. Or am I thinking about holleys too much. That is all I really have any experience with.
My wife is going in for surgery tomorrow morning so it may be a couple days before I can get back here but I really appreciate all the suggestions so far. Thanks a lot guys.

I'm in AZ at about 4000 feet (good old hot thin air most of the time). I've had a couple of modified engines that ran the best with no vacume advance at all (I ended up just putting a cap on both vacume ports). The way I set the timing is to run it up to about 3000 RPM and adjust the timing untill it runs the smoothest. Thats just where they seemed to run the best here (when I took the cars on vacation to places about sea level they liked having the vacume advance hooked back up).

Read the instructions with the Edelbrock kit well before you start. What I normally end up doing here is to first try a set of lighter springs under the power pistons and see if that helps before I change step rods. After that if its still rich, I start going with larger step rods (if it's too rich). As far as the shooter goes, normally it can be adjusted enough with just the holes in the linkage.

A couple of other things I have found on the Edelbrock at this altitude and temp are

1. To prevent the carb from flooding over the floats like to be set a little lower than the factory calls for. I'm guessing that it's a combination of the high heat and altitude that causes the gas to expand a little more than the factory anticipated. Don't go overboard the gas still has to be high enough to go in the port (slot) that fills the accelerator pump well.

2. Personally, I've never had good luck with the spring loaded needle valves Edelbrock uses. If you have problems, your kit should come with non-spring loaded needles you might want to drop in. If not the cheapest way to get them is to order them separatly from a parts store. What is interchangable are the needle and seats from an AVS of a Chrysler product (like a 1968 383 Road Runner).

Don't expect a lot of miracles you've got a lot for truck and a relatively small motor.

Well I got a bit of news on my problem and this is probably the whole reason I am even having a problem. I took off a valve cover to check valve lash and Much to my surprise it was full of roller rockers. Worse yet for a truck it has solid roller lifters. I hate to even guess the lift on the cam. It has to be huge being solid and roller. Oh well, No harm done. I will swap it all out with one of the extreme 4x4 cams as soon as I can make up my mind wich one. Any suggestions? I need pulling power not top end nascar type performance. I have two draft mules weighing almost 2000 pounds each and a fairly large goose neck trailer I need to pull with this thing. At least the next hot rod car I get I will already have some new performance parts saved up.