1971 slant six 225 no spark or weak spark at plugs?

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adam83

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I just finished refurbishing the completely stock 225 in my duster. Took it down to long block, then cleaned & painted everything, replaced all seals & gaskets, and rebuilt oil pump/power steering pump/carb/alternator etc. It ran fine before I did the work, but was getting to the point where everything needed attention, so I decided to do it all. The carb is the 1920, the distributor is points, which are also new.

Got everything hooked back up finally, and today I tried to start it. It cranks all day but no start. No backfire, misfire, or stumble, or any indication its trying to fire. I believe its no spark, or weak spark.

I checked carb, choke is working and the gas squirts when throttle lever is moved. so, its getting gas. Its not flooding either as far as I can see.

The coil, points, plugs, plug wires and cap and rotor are all new. I verified all plug wires are in correct positions on cap, the rotor is in place, and that the coil is hooked up correctly. With my timing light on #1 spark plug wire, it will not flash when the motor cranks. It reads battery voltage but does not pick up voltage through the plug wire. When I put the ignition key in RUN, I initially see 5.5 Volts at the + side of the coil, and it steadily drops to about 4 Volts over a short amount of time. When cranking, I see about 8 Volts at the positive side of the coil. I put an inline spark tester light inline with the plug wire from the coil to the distributor cap, and it flashes while cranking, looks slightly weak though. I put the same tester light inline with the #1 plug wire, and it does light up, but looks weak. I put my timing gun pickup on the plug wire from the coil to the distributor cap, and it flashes while cranking, but when I put it back to the #1 wire, no flash. I checked dwell with my dwell meter, its at 34.

I believe my dwell is too low, but that shouldn't stop the car from at least trying to fire right?
Shouldn't I be getting 12V to coil when cranking?
Is there possibly a problem with my cap and rotor? My timing light shows spark from coil to distributor cap, but nothing coming from cap to plugs.

Any help or suggestions appreciated
 
Bear in mind that points with high resistance, bad/ partially bad condenser, weak coil, poor grounds in the distributor, low voltage to the ignition system can all cause this.

BEST way to test spark is to use a WIRE core coil wire, even a piece of non spark wire, if you can "hang" it out in the open away from metal. "Rig" a spark gap, plug, or buy a gap type ignition tester. When cranking WITH THE KEY it should generate at least 3/8 and usually 1/2" nice snappy blue spark

Clip your multimeter to coil + and ground, and turn key to "run." you should see 6-10v or so. NOT full battery if the points are closed, and you want them closed for this test---but don't leave the key on for long, you can burn the points

Then crank engine using the key, and read meter while cranking. Note that reading, then read battery voltage while cranking. They should be very close to same

Anybody that uses breaker points really should use a dwell meter for several reasons. You can find them used. They will generally check points resistance, voltage to the coil, and of course points dwell.

Find out if points switching is actually working. "New" does not mean "good" parts. After measuring coil voltage, hook meter to coil NEG. Turn key to run. Voltage with points closed should be low, lower the better, perhaps 1/2 volt. Manually open points. Voltage should go to full battery. Manually operate points and see if you can get a spark that way. If not, with points blocked open (light cardboard) short them closed with an alligator clip wire or screwdriver Should get a spark

If you can switch open points, if the voltage checks out, and no spark, I'd try a different condenser, and if no, another coil
 
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All the above plus if you want try a jumper wire from the coil (+) to the battery (+) and see if you get a better spark. That voltage seems really low to me. Just remember if the car starts pull the jumper to shut off the car.
Syleng1
 
Syleng1 said:
All the above plus if you want try a jumper wire from the coil (+) to the battery (+) and see if you get a better spark. That voltage seems really low to me. Just remember if the car starts pull the jumper to shut off the car.
Syleng1
Click to expand...
The "run" may not be, the cranking, YES, low
 
Use another battery [ such as your every day driver ] to power the ign.
Remove ALL wires from the coil [+] terminal. Other battery: connect [-] terminal to Duster battery [-] terminal. Other bat [+] terminal: connect to coil [+] terminal.

If no spark, you have an ign problem. If spark, but no spark, mechanical problem such as ign timing, valve timing/adjustment.
 
did you put the engine to body earth strap back and if you did did you put it back onto fresh painted areas.
put a spikey washer under the cable eye if the K or Body was just painted. make sure connection is good

should get better sparking and easier starting if this is a problem and you correct it.

if it is the problem you should probably change out your throttle cable as it has been acting as earth and will have arcked and weakened

Dave
 
YEP. First off, check to make sure you have a GOOD ground from the engine to the body & engine to K frame.
 
Lots of things to check, thanks for the suggestions.

I just put a spare battery on the slow charger, and we'll see what it looks like when I get home from work. I also can use the known good battery from my daily.

I'll also check the voltage at from the battery positive while cranking and see if it matches the voltage at the positive coil while cranking.

I have a solid connection from body to battery. I did paint the power steering bracket and engine, and the negative battery cable goes to one of the bolts that holds those together, so I'll have to check that too.

@67Dart273 I will try your suggestions too thanks.
 
Battery is still charging, will have to wait til tomorrow
 
Battery was taking to long to charge, so I just removed the good battery from my daily. Before I installed it, I removed my power steering pump bracket and cleaned off the paint surrounding the bolt holes on the bracket and block, and the bolts, to ensure good ground. The same was done with my body ground. I also removed the positive cables from the starter relay and cleaned them up good, as well as the battery posts and cable ends.

With the good battery installed, still no start. Then I decided to put the old cap and rotor back on. Took a bit but the car fired right up. Upon inspection of the new cap and rotor, there is not a single electrical or mechanical marking on the rotor or terminal posts, they were completely clean and looked unused.

Maybe the rotor sits too low? Annoying because this was the 'better' brass option on rockauto, WVE brand. The one I put back on is a super cheap and almost completely wore out duralast from autozone.

Here's a pick of the WVE


https://ibb.co/c84kv2b]
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https://ibb.co/nMV2jZW]
20230519-185757.jpg
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Yep! That does not surprise me at all. You have to be very careful buying aftermarket parts anymore. I've used a WVE part before & will never use them again. Even a long established company like Standard has crappy parts a lot of times. Most things, even aside from car parts, are made in CHINA & it's junk. I would rather have stuff made in pretty much any other Country. I have been very happy with the parts I get from NGK/NTK, think spark plugs, sensors & the like & the more expensive stuff isn't always the best.
Glad you got it fixed though.
 
IIRC there was an "extended rotor " design for the later slants that required a matching cap. Am I mistaking? Measure your new rotor to your old one and even the ID of the contacts from both caps, you may find a variance.
 
Thanks. I've never had this issue, so it was frustrating trying to figure it out. Thanks for advice everyone.

Now my stock radiator is leaking pretty steady from the tubes where they meet the tank up top. Enough to lose almost 3 cups or so overnight, faster while engine is running running. I'm considering trying a radiator seal, but as I just cleaned out the block and put a new water pump on, I'm nervous to put an additive in that may clog something up and not even fix the radiator. Annoying because I really wanted to keep the radiator stock
 
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you could attempt to repair the brass radiator with solder: drain and invert the rad. use a stainless wire brush and clean the joints, apply flux and heat slowly until the flux starts to boil and smoke, then add silver solder and allow it to flow into the leaking joint. Pull the flame away and allow it to cool. It should fill the cracks. Here is an extreme example of applying LOADS of flux and then the solder. Flux cleans and shields the base metal from oxidation. Solder and old rad solder has lead in it so please do this in a well ventilated area preferably standing upwind of the draft. Once the solder has cooled, rinse old flux off work.
 
That looks like a fun project. First thought is I don't know if i could constantly heat the underside of the top tank like he does on the video, his top tank is really skinny and the heat spreads to the underside quickly. My tank is almost 3" tall, I'd likely have to hit it with the heat from the sides instead of the bottom.
 
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After watching that video, and another, I don't think I want my original radiator to be my guinea pig for figuring out radiator repair.

I called Glen Ray and they are 5 months out. My local shop charges Glen Ray prices but doesn't have the same reputation, so for now I'm gonna try some AC Delco 10-108 coolant system seal tabs. Hopefully they can stop the leak. If not, I will likely be buying a champion radiator cc527 to use until the original is rebuilt.


I need to look into the extended design rotors as well, or possibly shim rotor on the wve set, I think it is sitting too low. I don't want to keep running this old cap and rotor much longer, they are getting pretty burnt up
 
All caps & rotors get 'burned' after some use from spark erosion. Totally normal. Without seeing some pics, unable to comment further. A larger rotor gap is good for increased spark performance but causes more RFI noise.
 
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