Need a second opinion on this matter. Finally installed a tach, and at idle, the engine burbles. You can hear little "puh-puh's" out of the exhaust, and the tach needle spikes to 1500 or so along with the puh-puhs. At idle when this is going on, the negative side of the coil measures between 7.9-10.5 volts. Jumps alll over the place. At 2000 rpm, however, the voltage only jumps between .3 and .5 of a volt, and the puh puh's are pretty much non-existant. Also, the tach reads steady at anything above idle.

What I'm thinking is the distributor shaft is worn. I haven't gone outside to wiggle it yet, but will soon. Just curious if anyone has another idea, or would that be a decent idea? Any other parts that might make the engine behave like that? Timing is set, carb is set, and everything of the sparking system has been replaced EXCEPT the distributor itself.

 

If you've replaced all the tune-up parts ie: pionts, condensor, rotor and cap then the only logical thing is something is moving that shouldn't be. You can see if the dwell is jumping also or pull the cap and give the shaft a wiggle. You might want to check the breaker plate also but that usually gives you a mid range miss when the vacuum advance comes on.Good luck, Rich.

 

Check the following for loose or worn components: timing gears and chain, camshaft (rare), leaking vacuum advance, slop in the carb butterfly rod and/or throttle plate, and worn mixture screws/seats.
Worn carb components can affect the timing if isn't holding the vacuum steadily, ditto for the vauum advance itself.
You can check the timing gears and chain using the timing marks. Rotate the engine by hand one direction until the pointer is on 0 or TDC. DO NOT reverse the motion if you pass it. This action tightens the chain up in one direction, so if you reverse it before setting the timing pointer on the timing marks, you will get a false reading.
Next, remove the distributor cap. Have a second person observe the rotor.
NOW, reverse the direction of the crank until the rotor begins to move.
STOP when the rotor moves. Read the difference in the timing marks, and that will tell you how many degrees off you are. If you started at 0, and it is now at 18, you have 18 degress of slop in your chain. You should have no more than 10, and even then, that's too much.
Do this several times to ensure an accurate reading. Depending on the engine's rotation direction, you might need to reverse the direction you start in.
This procedure works equally well on gear and chain driven timing systems. Of course,this is only an indicator, but it saves tearing down the front of an engine just for a look-see.

 

That's way cool. Such a simple thing, but I hadn't thought of it, and I was curious about the timing chain. I've got 4 degrees of play. Sounds good to me, but what do you think?

The engine runs great and since it was rebuilt in 94 and it doesn't burn a bit of oil, I'm figuring they must have done the timing chain at the same time. It sat for a year, so 6 years is all he had time to run it, and I know from the condition it was in that it didn't do more than run around town. So I'm figuring the rebuild has at the very most 60,000 on it, but probably less.

 

Good to hear it worked for you! 4 degrees isn't bad at all. Now, we need to figure out what's wrong - and it sounds like the coil voltage is an issue. I would try another condenser, and then another coil first. Use a used one that you know isn't bad, if you have access to one. (New parts DO come bad out of the box occasionally.) If that doesn't work, try this: with the engine running apply a full 12 volts using a jumper wire to the coil, and see if that momentarily cures it. If not, then it is most likely the distributor. If it does cure it, my money would be on the condenser, the coil, or the resistor block.
Good Luck!