Running out of parts to swap... ignition woes

[sirwompus]

Bone stock 521, misfires on acceleration but idles smooth. My hunch is that it's an ignition problem but I guess I could be wrong. Truck ran fine till one day it started missing, saw the points were badly pitted and this is what I've changed with no results:

 

points, condensors, wires, coil, balast resistor, rotor. Plugs look good so I won't change them for now.

 

Since the problem started suddenly I'm not suspecting the carburator. One thing I'm concerned about is that the new points I put in seem to have alot of burnt resedue after barely running around the  block once. Also if I jump the points with the ignition on to test the quality of spark (which is good) I'm seeing a bigger spark at the points then I would expect as if the condensor was bad but as I said they have been both been replaced. Both the old and new balast resistor tested at about 1.9-2 ohms, is that right? When I test the voltage out of the balast resister it's only slightly less then the battery's voltage which seems extreemly high for the new coil which is marked 6V.

 

Of course a matchbox distribuor would be the easy solution but I'd like to think that the art of points is not completly lost.

 

At idle all four exhaust runners are warm and pulling each plug wire makes the engine stumble equaly. After driving for a bit the coil seemed hotter then I'd expect but not to hot to leave my hand on it.

 

Thanks,

 

 

[flatcat19]

I'm gonna take a wild guess on this one...

Only misfires in third?

[sirwompus]

If anything only runs right in third.

 

The primary points are the set closer to the engine? Secondary (third gear) closest to the fender?

[wayno]

Check your valve clearances, the crap unleaded they sell as gas these days will destroy brass seats, I have hardened seats in everything I own that burns gas.

[sirwompus]

Checked valve clearances cold, nothing was far off.

 

I keep coming back to the fact that the primary points get really hot after idling just a few minuits. Another strange thing to me is that with the ignition on the coil always seems to be getting 12v even though this is a stock balast setup and the wiring loom is uncut/stock. Is it possible the hot start relay is stuck in the hot start position which bypasses the balast resistor or something?

[wayno]

Well it is hard to tell certain things not being there, but does the coil get hot to the touch even when the engine is not running with the ignition key on?

Are you sure they sold you the correct coil?

The coil can be wired incorrectly even though the wiring harness is un-cut, I beleave what I am about to tell you is correct, but I am not totally sure anymore as it has been so long, and my truck has a 720 column in it now, and it is wired to the 720 column ignition switch.

 

There are two black wires near the coil area, one is black with a white line, it goes to the ballast resistor, let's call that the "A" end, it is the run wire, the wire on the other end, let's call this end the "B" end of the ballast resistor, it goes to the positive side of the coil.

The other black wire has a red line, this is the hot start wire, it will go one of two places, it will either go to the positive side of the coil directly, or it will go to the "B" end of the ballast resistor.

The black wire with the red line should only be hot when the key is in the start position, in the run position it should have no power.

 

I am fairly sure what I said is correct, if that black wire with a red line has power while un-plugged from the coil while the engine is running, then something is wrong.

[sirwompus]

Your description sounds like what I'm seeing except if I unplug the ballast resistor while the engine is running it keeps running which tells me its not dropping the voltage to the coil. Any chance someone could tell me which relay switches the coil from start to run mode? Every diagram I see leaves out the ballast resistor.

 

As far as the coil being correct, I asked for a 1970 521 coil and it is marked 6v which seems correct.

[DanielC]

There is no relay that switches the coil from start to run mode.

The ignition switch makes two connections in start mode.  White to black with yellow, goes to starter, and white is also connected to black with red, goes to the coil positive.  The white is also connected to black with white, and remains connected to black with white, in run position.

Here is a wiring diagram for a 521.

[wayno]

Which wire are you removing from the ballast resistor, the black/ white line one, or the black and red line one?

If you are removing the black/white line one from "A" end of the ballast resistor and it keeps on running, then something is wrong with the black/red line wire on the 'B" end of the ballast resistor or the positive side of the coil, where ever that wire connects.

Make sure there are no other hot wires going to the positive side of the coil.

 

Black/white line is hot when the ignition is on.

Black/red line is hot when the key is in the start position only.

 

Un-plug these wires from the coil when testing them.

[ggzilla]

Since the problem started suddenly I'm not suspecting the carburator.

-------------

 

Carburetor problems start suddenly in many cases. I would suspect the carb, and I say this after having 30 years experience adjusting Datsun carburetors.

 

 

the coil always seems to be getting 12v

-------------

 

Yes, that is normal -- even with a ballast resistor -- when the points are open at the time you measure. With engine off, rotate the engine until the points close, then turn key ON and measure the voltage. The voltage can only be "cut down" by the resistor if there is load on the circuit.

[sirwompus]

Problem solved. Wayno and DanielC you guys saved the day.

 

PO had wired in an aftermarket ignition switch. While all the wiring under the hood appears stock the black/red and black/white were not rewired as they should have been. The black/red was given constant power and I could find no continuity from black/white to the ignition switch so before getting to crazy with running a new wire from the ignition switch to the ballast resistor I just swung black red over to the blast resistor meaning that I have no hot start circuit. Truck started right up without the choke and after a smooth ride around the block had no overheating of the points or coil. In the future if I have any starting issues I may want to reconsider wireing up a hot start circuit but for now I'm good.

 

Now I can pickup some fence materials...

[wayno]

They usually start fine when warm, the moment you let off the key it hits, but when cold it can run the battery down dead and never try.

You need a hot start wire, even if it is a wire with two alligator clips going from the battery to the positive side of the coil, as this is what I did till I figured out that my black/red line wire was disconnected.

The black/white line wire is supposed to go straight from the positive side of the coil to the fuse block, and that part of the fuse block is activated when the ignition is turned on, you need a volt meter to check your fuse block, make sure things are right there.