86 Sub not running well

tfpary · November 12, 2002

Friend has an 86 Burb, 350, quadrajet, 230,000 miles. Was parked for 5 years (brakes were bad, not worth fixing said the previous owner). We changed fluids, add fuel, new fuel pump, fuel filter, plugs, wires, cap, rotor, air filter. Finally got it started after considerable cranking. "Popped" through the carb under load. Idled smooth. Now it seems to be backfiring through the exhaust. I would guess its running lean (he is getting a carb kit - I am sure it needs a good cleaning after 5 years with fuel evaporating in it) but the plugs are black, sooted up. Checked compression on number 1 cylinder 135psi warm. Haven't checked the timing yet, but its next on the list (too #### cold). When we changed oil, we put a can of seafoam in the oil to help remove sludge and free up sticking lifters (if any were). Any tips would be helpful. I am hoping the carb rebuild and timing make this thing run decent, cause it's sitting in my yard!

Thanks

tad

Larry · November 13, 2002

I have brought back a few old chevy’s from the dead a time or two. Sound like you already replaced all the obvious stuff but if it were my newfound treasure I would first defiantly rebuild the carburetor. At 230,000 miles it is probably time for a lot of things but a timing chain would be a cheap worthy addition if your friend is hoping to squeeze a few more miles out of this mill with it running halfway decent. A decent small block Chevy Cloyes double roller timing chain can be bought for about $20 but it takes a minimum of 4 hours of labor to replace it. Might as well screw on a new water pump and radiator hoses while you have them off to replace the timing chain.

I would also replace the rubber fuel lines from the metal frame mounted lines up to the carb as well as all evap fuel lines. From experience, I can tell you these fuel and evap lines will be the first thing to leave you scrambling around in your garage searching for a fire extinguisher at the most inconvenient time when this thing decides to leak and burst into flames.

If this old pig starts to blow blue smoke at start up you will want to replace the valve stem seals. Valve steam seals are very cheap but again, a lot of labor…probably about another 3 to 4 hours to replace all 16-valve steam seals if you are slow. Replacing the valve stem seal means you will have to fill each cylinder (one at a time) with air and remove the rocker arms to gain access to the valve steam seals….16 times. Once your are done you will also have to adjust the rocker arms. If it hasn’t started blowing blue smoke at start up it will very soon especially after sitting for that long.

135-psi compression is pretty good for half worn out 350 but the biggest clue of this engines worthiness is if all have the same compression on all 8 cylinders within 10%. If you have a cylinder or two with more or less than 10% of the highest reading the engine will have a miss at idle or tip in that you will never be able to get rid of. If this engine starts smoking like a train and has compression readings all over the board I would just throw it back in the water and fish for something better or face the fact that you will have to sync a lot of money into it. And that was only for the engine….you still have to check the brake lines, brake linings, wheel seals, wheel cylinders…the list goes on and on……

If this rig is 4wd save it but if 2wd...you may want to throw it back in the water!

tfpary · November 14, 2002

Thanks for the tips Larry. Got a carb kit, now just have to put it in. I find it kinda fun, but not when its 20 degrees! Timing chain might be next - I have done a few of those, and your right its just time consuming. One other thought is that he took all the plug wires off at the same time, then I put the new ones on - I'll have to double check the firing order. As for the brakes, we already have completely rebuilt the rear brakes (it was not fun getting the rim off the drum, or the drum off the hub/studs!). Transmission was rebuilt shortly before it was parked. I'll have to check the compression on all the cylinders (only checked one the first time - as I was unscrewing the gauge I noticed the tire on my wifes car was flat - gotta have priorities)

Thanks again

76BBSub · November 19, 2002

Backfiring is almost always ignition related. Check your plug wires, as you mentioned, especially #5 and #7. Also, make sure the initial timing is correct, and check for correct operation of the mechanical advance, vacuum too. And check the vacuum at idle to see if you have a valve problem or vacuum leak. I'm sure the carb needs to be rebuilt, but the backfiring is probably ignition.

Let us know what you find!

Jeff

tfpary · December 13, 2002

76bbsub - you know your stuff, I had the #5 and #7 wires mixed up on the cap. Swapped them, she started right up. Replaced everything but the lines in the brake system, and it runs pretty darn good, all things considered.

Now, can you tell me how to tighten up the steering? On the slightest movement of the wheel it wanders all over heck. Some of that is the tires, I know, but some has to be in the steering components. I will be checking all the obvious wear spots, but I seem to recall reading something about adjusting the steering box somewhere. Any tips?