21 stud running rough

Blownflatheaddeuce

Blownflatheaddeuce

Senior Member
Hey guys seems to be a common issue with our cars :(

I went for a run in the roadster about a week ago - ran Ok but them progressively began to run rougher, less smooth on the rev up thru the gears and the odd backfire. Barely made it home.

Knowing about the condenser issues, I swapped it out with a spare i had as its a quick change. Instantly back to her old self but lasted all but 1/2 an hour's worth of driving then back to the same crapola.

Hmmm.....

The engine is a good condition 37 21 stud, mild cam, Edelbrock slingshot, shaved heads and headers. Ign is a rebuilt 36 Helmet running 12V with new everything that has now done perhaps 2K miles all up. Coil was new, run with a ballast resistor and has run flawlessly for 2+ yrs.

So I undertook the following checks:

i. Volts at battery: 12.78
ii. Volts going INTO ballast resistor : 12.78
iii. Volts OUT of ballast resistor: 12.78
iv. Ign "ON" Volts at coil+ve post: 12.60
v. check cranking spark at coil COLD: light blue/white spark - HOT: same
vi. check spark at plugs cranking COLD: blue/white spark - HOT running:
same
vii. check plugs: clean no carbon /fouling (set carbs originally with vacuum
gauge
viii. checks dist caps - look fine
ix. check for arcing in the dark : NONE
x. Coil lead resistance: 4.75 Ohms
xi. Coil Pri side: 1.8 Ohms Sec side: 10200 Ohms

Upo these tests I proceeded to pull the distributor and disassemble. Was spotless inside one point set was slightly pitted but pretty much cleaned up with wet n dry. Prob pitted because of the toasted condenser on the first long drive. Rotor looked almost new and no cracks that i could see.

I added some heat shrink (like Ive read on the Barn) to the shaft and reassembled the dist and regapped the points at .016". Fired right away once again when reinstalled but not running or reving up smooth - same as before.

At this point Im thinking even though the 12V late style coil checks out OK, it might be playing up when hot and under load. Would this trash the condenser? The condenser used is the one that came in the 12V conversion plate/kit, was fine for 2+ yrs but not sure of its MFD rating.

I will be swapping out the coil, ballast resistor and get some condensers and decent points from Bubba. As noted in the tests, the wires to the plugs put out light blue/white spark to the plug which I understand is HOT and the way it should be.

Again the car ran great when swapping out the condenser the first time, but soon returned to running poorly with no power :eek:

Have I missed anything here? Any suggestions as to what could be causing condenser failures both times now ? :(

Thanks

BFD
 
Last edited:
Bfd,
I think iii is a problem, Bubba will explore this fer sure.
HOWEVER
Jim Bubba Lindner advised me to try a BOSCH blue coil....Bosch # 00012....
correct resistance is built into this coil. Works like a charm.
The Vertex condenser Terry mentioned, occasionally available from Jim, is the apex in the world of condensers.
Charlie ny
 
Charlie ny said:
Bfd,
I think iii is a problem, Bubba will explore this fer sure.
HOWEVER
Jim Bubba Lindner advised me to try a BOSCH blue coil....Bosch # 00012....
correct resistance is built into this coil. Works like a charm.
The Vertex condenser Terry mentioned, occasionally available from Jim, is the apex in the world of condensers.
Charlie ny
Click to expand...

Charlie does that Bosch blue coil operate without a ballast resistor? I agree, iii. is suspect.

What is the correct method/Ohms to check resistance on a ballast resistor?

Yep will try to get some from Jim.
 
Last edited:
Bfd,
The Bosch blue coil does not require a ballast resistor. Before the blue coil
entered my life I measured volts at the resistor once it warmed up. I can change
a light bulb almost on my own.....for the rest I usually call Bubba.
Charlie ny
 
I had a similar problem which split my coil. I wasn't running a ballast resistor and I guess the voltage was to high. This was on a 12V system. I changed system to Pertronix and even though the coil has an internal 1.5 resistor, I was told I should still run a 1.5 ohm resistor before the coil to keep it running cooler. I haven't had any problems since.
 
Yes JM it is - although the gear was refitted correctly and the cars been running great since the cam install.

I swapped out the coil with a new one, new ballast and new condenser....fired right away and seemed ok in neutral, but I could'nt even make it down my street it was running that rough.

Im running out of ideas can anyone make any suggestions in case Ive missed something ?

Thanks

BFD
 
BFD, I know you have already mentioned this, but I have experienced bad running like you describe and it has almost always been down to the HT side of the ignition going bad.

You might need to swap in a known good rotor, I would have said shrink wrap the shaft but you have already done that.

To keep the loads on the HT side as low as possible, and try to stave off HT side failure, I do the following.
Use solid core wires.
Use solid connectors between the wires and plugs. (No resister type caps)
Gap the plugs at .025.

Oh yeah, one last thing, My diver's helmet distributor became so unreliable (probably due to rotor - shaft shorting) I replaced it with a crab distributor on an adapter. Never looked back after that.

I have new parts to re-try the diver's helmet type, but haven't done so as the crab works so well and is easier to service.

Mart.
 
Hey Mart thanks for the input.

FWIW....

To keep the loads on the HT side as low as possible, and try to stave off HT side failure, I do the following :

Use solid core wires. .....check
Use solid connectors between the wires and plugs. (No resister type caps)......check
Gap the plugs at .025...... check

Done all the above already ;) Spark at the plug is strong, from dead COLD to completely warmed up.

Thought about the crab too (better advance plate) but wanna keep trying to get this nutted out ;)

Gonna swap out the plugs & points ( do I need to "retime" the dist? and move the condenser off the dist to the front of the intake as well and see what happens.

BFD
 
Something is wrong with the ballast resister if it is not showing a voltage drop. Voltage at the coil should be around 8 - 9 volts. If it is putting 12+ volts to the coil it would start and run ok but overheat the coil and the coil would break down. After it cooled off it may or may not restart ok. If you run at 12v very long you may damage the coil and the points may be burnt.

If you are getting 12v+ on both sides of the ballast resister are you sure the wiring is correct? Is it possible that you are getting 12v to the coil side of the resister from some other source?
 
I'll say what I think is right, but I'm not 100% sure.

I don't think you will get much voltage drop across the ballast if the points are open. As there is no load, the resistor don't need to do much resisting. (hard to explain).

If the points are closed, you will be able to see a reduced voltage after the ballast, as it has the load of the coil on it.

I mention this because if it is part of the troubleshooting method you could go up a blind alley if expecting one result and getting another.

Please correct me if I have it wrong.

Mart.
 
I think you are right on, Mart. Also, as the resistor heats up when the engine is running, the resistance increases. If it increases too much, it will cause a problem with the spark.
 
Did you recheck the voltage on the coil side of the ballast resister? If it is not 8 to 9 volts (with the point in the correct position) then there has to be a wiring issue. Is it wired to put 12v on the coil when the starter solenoid is engaged? If so, 12v during startup and then 8-9v at run, otherwise a wiring issue.
 
Guys the voltage on the coil side of the ballast is 8V running, rechecked it with the addition of the the ballast, coil and condenser.

Thx

BFD
 
You must log in or register to reply here.
Back
Top