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Intermittant run problem

F

FrankS

Member
Friend has a 901 Ford that will start and run fine then suddenly either not start or miss terribly. 12 volt conversion with resister and 6 volt coil replaced with a new NAPA 12 volt. New condenser. Points look good and gapped at .025. Coil to distributor wire is metal and clean. Was out 2 days ago after my friend said it ran with a horrible miss. I checked the voltage to the distributor side of the coil when open and get 12.46. Coil primary read 3.8 ohms. Secondary 8,500. I thought I should get around 3-3.5 volts to the points when closed. I got 3.2 volts at the distributor (negative)side of the coil the first time I checked but subsequent checks were at .12 volts. Same with just a jumper to the coil +. I didn"t do anything except remove and reconnect the test probes. However the tractor started and ran fine for 2 hours pulling a disk. Parked it and restarted it a couple times no problem. Friend called this morning and says it won"t start.
Carb was rebuilt with a master kit. The shutoff switch on the gas tank will not close off the gas but fuel flows steadily when the line is disconnected. Advise?
 
Wire from output of coil to side of distributor should be near battery voltage with points open, and near zero with points closed.

3.2 volts would indicate points are not making good contact. Problem could be with points or wires/connections in distributor
 

OK thanks. Then is .12 volts acceptable or should it be lower? Perhaps there was some contamination on the points the first time. I had put a piece of paper in between them afterward to recheck open readings so it may have cleaned it off. Several subsequent readings were all at .12 or .11. The tractor started and ran fine. How do you measure how many volts are getting to the points?
 
I have found that intermittent problem like this to be the little carbon tower in top center of dist cap. Some are junk from new. Get Standard brand (USA made) Had same problem with Uncles Jubilee just last week. Dist cap looked brand new inside and out but was junk.
 
rvirgil is correct, the voltage to ground on the negative side of the coil should be 0v with the points
closed.

The voltage to the points will be the same as the voltage to the coil positive terminal. With the points
open, the voltage is simply passing through the coil with no where to go.

Sounds like the points are contaminated or burned. The new points and condensers are prone to quality
problems. A bad condenser, improper adjustment, worn distributor bushings, contamination from oil, grease,
or moisture will cause points to burn prematurely.

Would he be willing to invest in an electronic conversion?
 
Thanks. As you can tell, ignition systems are not my strong suite.
I looked at the points and they looked ok. I'll try replacing them. All the wires and connections are clean and tight.
It could be the distributor bushings. Any way to tell without pulling it? The shaft wiggles back and forth a bit but I don't know if it's excessive enough to cause the problem. Would it show up on the timing?
Is the 8,500 volts from the coil secondary in spec?
What's the cost of electronic conversion?
 
Keep it simple and don't overthink it. Screwdriver in end of coil wire...1/4" from good ground...does it spark? If it does then do same with plug wire. Does it spark? If not replace cap/rotor. Elect. ign. is not going to fix your problem.
 
I presume you mean 8500 ohms resistance from big coil center to either + or -- terminal. Normal resistance for a coil is about 1.5 ohms on 6 volt and 3 ohms on 12 volt from + to --. 8 to 10,000 ohms from either + or -- to center is normal range.

If you read no continuity or extreme high ohms reading you can assume the coil is bad. Other than that an ohm meter won't tell much about the condition of the coil. Windings can be shorted in the high voltage side that can not be detected by ohmmeter.
 
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