Weak spark in Flathead with SBC Distributor

Chopshop13

Chopshop13

Member
Hi
Ive installed a remanufactured and modified SBC points dizzy in my flathead and its giving a very weak spark and is missing intermittently, sparks so weak my timing light doesnt pick it up at all. i havent touched the points, they are at .008" could be the problem? plugs are NGK B-6L gapped at 30 thou. its running 12v neg ground, the coil is borg warner 27290 2.0ohms and 1.9ohm balast resistor. I have swapped out the condensor without improvement and bypassed the balast so as to give all 12v to the coil. No change here. checked earths. any other ideas?:mad:
 
Point gap is .016. About the thickness of a book of matches.
You have 12V coming to the coil?
The Positive side of the coil is wired to 12V (or from the ballast resistor = 9 volts)
Negative side goes to the distributor.
What is the resistance of your coil?
 
Ive never heard of points being set .008 seems awfull close.You could contact Charlie NY on here. Hes the expert on these units. ken ct.
 
wga, The coil and balast are both clos to 2 Ohms and therefore voltage is around 6 volts over each.
I just hooked the coil up to 12 volts to see if there was any change and wassnt so its back to 6. All my wiring is good, new 12 volt loom and strong battery/altinator.
I know .008 is low and usualy a sbc would be 18-19 thou. I just wanted to find out if anyone else has encountered this.
 
That .018 - 19 is kinda on the fat side. Start with 016". Let us know what happen with the change. Initial timing set correctly? How about the high tension wire - coil to cap - making good contact?
 
Yeah, HT's are good, initial timings reasonably close, engine runs, just that the spark is so weak the timing light doesnt even pick it up! and it runs terribly.
 
I do not know about GM distributer in a flathead but in a Chevrolet the Dwell is *30 at 600 rpm if i remember right. It is definetly *30 Marv
 
Sounds like points are too close and there's too much resistance in the primary circuit giving you low voltage at the distributor. It would be nice if "Bubba" would chime in here. Ignitions are his specialty.
 
Set the dist as/GM specs, I believe .019 or 30* dwell check the spec on the coil to see if it needs a resistor or not. I use the GM spec with a 12V coil that dojes not need a resistor. Laurie
 
If the points/cond are new try another brand ---I just had a car towed in with no/intermittant spark the new pointset was chromeplated over the point contacts, in 500 miles the chrome plating started coming off, if it is the chev "window" dist and the points/cond are 1 piece (uniset) I have had them bad out of the box, on other points the new production condensers were bad in a short time

You can take a voltage measurement from the point side of the coil to ground at the battery, engine not running, with points closed it should be less than 0.5 volt, with the points open it should be close to battery voltage ---this will help you decide if you hjave aconnection or grounding problem.

It could be an immune system problem trying to reject the chevy part transplant --have you tried distracting it with a shiney new hood ornament??
 
Make sure you do not have the coil wired in backwards. Example, If you have a negative ground car the negative coil pole wire goes to the distributor. Second open the points up as specified by the distributor conversion.
 
The Chevrolet V8 distributor is one of the best units out there and usually run forever. However sometimes the points do wear and close the gap etc...
The factory setting with a feeler gauge is .019 for new and .016 for used .
We set them on a machine at 30 degrees of dwell allow them to run for a few minutes and then readjust to 30 degrees . They will wear in a little bit as they run.
Your coil and ballast should be fine ( as long as they did run good once upon a time , right ?).
Let us know hwere you are in this problem as we go.
Glad to help....
 
Thanks everybody, so much good info. First things first ill set the points at .019 give em a quick tickle and try again. Thanks bubba, the coil and balast worked with the flaty dizy but as sugested i might try a 1.5 Ohm coil and balast to reduce primary circuit resistance (also being new...). After that, check leads gain, check dwell.

If im going to coil which requires no balast, what resistance should i be looking for? and are there ones designed to run 12v but still work with a coil?

Cheers
 
These are napa #s
IC66 Volkswagon 1963-1969 +
truck and buses IC 712,IC64
These coils are 12 volts,and run with no resister.
Neg grd, neg to points.
NOS usa coils maybe best.
 
Chopshop13 said:
Thanks everybody, so much good info. First things first ill set the points at .019 give em a quick tickle and try again. Thanks bubba, the coil and balast worked with the flaty dizy but as sugested i might try a 1.5 Ohm coil and balast to reduce primary circuit resistance (also being new...). After that, check leads gain, check dwell.

If im going to coil which requires no balast, what resistance should i be looking for? and are there ones designed to run 12v but still work with a coil?

Cheers
Click to expand...

If the coil and ballast worked with other distributor it should work with the Chevrolet. Your unit has the highest quality contacts (echlin cs786) and should be ok , if you need I can ship you another set ?
 
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