Rough Idle

[cherryelky305]

Recently I gave my 80' elcamino a little gas and now the idle is at a lower rpm and the engine is rougher when climbing the rpm band. I checked the spark plugs, which i just replaced thinking i had flash burned it, nope all look good but two were finger loose, i tightend everything and the problem is still there, next i found a wire going to the carb and it was burned, so i fixed that , the problem is still there. It seems to run ok mechanically, no loud noises. The problem is almost like a misfire. Could it be the cam, someone told me that cams in 305's have a reputation.

[bobss396]

I replied to this elsewhere as a possible burned plug wire and that you should try to isolate the misfiring cylinder. I would replace all the plugs just to rule them out, check the wires and distributor cap, pop off the cap and give it a good look for cracks and carbon up in the tower section.

If you can find out which cylinder it is and everything else has not worked, remove the one valve cover and look for a possible cracked rocker arm, those do fail under hard sudden acceleration. Check for a bent pushrod too. Run it and look carefully at the action of the valves in comparison to the ones next to it. A flattened out cam lobe or collapsed lifter will show up most of the time in a visual check.

Bob

[7D8SS]

Could be a crossed wire. Make sure you have the firing order correct. Jon

[bobss396]

Real simple, you could have a vacuum leak at the carb base. Take off the air cleaner top, let it idle and put your hand over the choke horn. If the idle picks up and it smooths out, you have a vacuum leak somewhere. Look for a hose that is off or cracked from age. Spray some carb cleaner around the carb base to see if it idles faster. If so, you found the leak.

Bob

[SolRaven]

I had the same situation. Turned out a chunk of the carb gasket was missing! it either got sucked in or blown out in a back fire and crated a vacuum leak. the best way to look for vac leaks it with a spray can of fuel injector cleaner. if you spray a little aria and the engine revs on its own thats where the leak is.

[Shoerfast]

The K I S S method is still the best!

What you might want to do is build yourself a Dynamic Balance Tester, the well insulated ones are a little better for the wimpy.

Take a tool like an ice-pick (old school) or a straight seal pick or sharpen an old screwdriver to a very fine point. You just need to run a wire from the shank of your ice-pick to a good engine ground and your set.

Just for grins you could hook up an underhood Vac Gauge, an RPM gauge is cool , but your going to hear your weaker cylinder as you "probe" the plug wire ends as they attach to the Dist-Cap. One by one, compare the amount of drop you get from each cylinder, when you find which cylinder has the least effect when shorted, wha-laa!

If all the cylinders have about the same drop, purposely lean the idle screws just a tad, and with an unlit propane torch, of a can of starting fld (or something that burns) spray any possible vac-leak, when the engine picks up, prove the spot of vacuum leak and repair it.

* A note on your Dynamic Compression Tester, make sure that your elbows and hands are aiming away from the hood, fan-blades or anything that will be in-line it you do get bite by the spark, you will survive the shock, just wakes ya up a little! Jurking your hand-arm is the most dangerious thing that could happen. (a very well insolited well grounded tester will not bite you) If your bothered by the little holes in the plug wire boots, just dab a little silicone form a gsk on the pin-pricks.