rough idle

[82chevyk10]

I would like to start by saying hi to all the square body fans out there. OK, I bought my truck about 3 years ago. All the emissions, expect the PCV valve, had been removed, and the stock 305 had been replaced with a 350 4 bolt out of '75 C20. All the vacuum lines from the canister were just hanging there, non of them go anywhere. The truck ran like pure hell. It had an edelbrock 1406 carb, but the electric choke didn't work, the idle screws didn't do anything. It flooded horrible and backfired constently, but I knew with a little tender love and care I could breath some life back into it. The first things I did was buy a new edelbrock 1406 carb and rebuild the distributor, with the exception of the vacuum advance, and module. I also done a basic tune-up. That alone made a major difference in the performance, except the idle continued to be rough. Timing adjustments and idle screw adjustments just didn't get my idle right. A few months later I got on the throttle a little too hard on take off and a rod started knocking. I want to rebuild it someday, so I parked it before it blew. I dropped a new crate 350 4 bolt using a new edelbrock 2101 intake and headers with 1 5/8" primary tubes going into 3" collectors into 3" exhaust pipes with cherry bomb mufflers. I reused my almost new carb, partially rebuilt distributor, and old water pump. The truck has and to this day idle rough, and seems to have a slight miss at cruise. The only vacuum lines connected are the PCV hooked to the center of my carb, the vacuum advace hooked to the ported side of the carb, and brake booster hooked the rear of the carb. I used a fitting off of my stock intake and put in a hole in my new intake between my carb and distributor. I tried plugging it, but my engine would barley run at all. I know that something needs to be done with it because it can't be left open. I can't help but wonder if some of the vacuum lines on the canister were to be reattached if that would help my performance. If so, then where? And what else should I look into? I'm striving for a set up of a 1975 era. My intial timming seems to do the best at 16 deg. BTDC.

 

[crazy4offroad]

16 degrees is a tad too much, 12 would be a higher performance cam, 8 would be nearly stock engine. I'd say the problem lies with the carb. With so much ethanol in gas these days first thing you should do is upgrade your rubber lines at the gas tank and carb to ethanol compliant. Next make sure you have a good paper fuel filter, like a Delco or Purolator. Then I would take the top off the carb and clean out the fuel inlet pipe. Looking at the front of the carb, the far right has a corner that gets a pile of goop stuck in it. A long stiff wire or something similar and a parts washer would do great at cleaning it out, just be careful not to knock your floats out of adjustment. After that, while the top is off I would blow out the idle circuit. The primary jets, toward the front of the carb that the metering rods ride in, are where you apply air pressure to blow dirt out of the idle circuit. Re-assemble and see if it helped. Lastly if you hadn't went deep enough in your distributor I would look into replacing the pickup coil. It is underneath EVERYTHING, a small round looking thing with contact points on the inside and a couple wires. Replace it, I wouldn't even check it if it's original. Also check the distributor weights/springs and make sure the pin and holes aren't shot, or the weights aren't stuck.

Hope something here helps, and welcome to the forum!

 

[82chevyk10]

At 8 deg advance it idle's horrible, to the point of barley running. I replace the fuel filter approx. every 6 months with a basic purilator inline paper filter and run a fuel treatment with every oil change. I know edelbrock 1406 carbs don't like no more than 5-6 psi fuel pressure so I installed a fuel pressure regualator and set it on 5.5 psi. The distributor weights and springs hasn't been change, but the coil, cap and button has. The vacuum advance, and module hasn't been changed either.

 

[Jims86]

At 8 deg advance it idle's horrible, to the point of barley running. I replace the fuel filter approx. every 6 months with a basic purilator inline paper filter and run a fuel treatment with every oil change. I know edelbrock 1406 carbs don't like no more than 5-6 psi fuel pressure so I installed a fuel pressure regualator and set it on 5.5 psi. The distributor weights and springs hasn't been change, but the coil, cap and button has. The vacuum advance, and module hasn't been changed either.

4 degrees is usually base time for a 305 or 350. You may want to pull your timing cover and make sure the cam and crank marks line up...that would be the only other option as you have pretty much gone over everything externally. I would suggest a better carb, like a q-jet.

 

[82chevyk10]

I don't think it could be the cam and crank marks not lined up. It's a new crate 350 that I put in myself. No internal engine work has been done to it. Could the timing tab be wrong for the damper?