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Subject: Spark

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Roger    Posted 03-16-2017 at 09:31:11 [URL] [DELETE]        [Reply] [No Email]  
  • Spark
  • I just replaced the points and charged the battery on my '47 8n. When I put an in line spark plug test light between the plug and plug wire I get a big, hot spark on the first crank and then either a much dimmer or no spark after that first crank, even when I have an jumper assist on the battery. It is original 6V setup. Any ideas?

    Bruce (VA)    Posted 03-16-2017 at 16:51:43 [URL] [DELETE]        [Reply] [Email]  
  • Re: Spark
  • First, get rid of the spark test light. Get an adjustable gap spark checker & open it to 1/4". :


    Meanwhile, you have a weak spark. The most common cause of a weak spark is a weak battery. Charge it (see tip # 60) and check it .(tip # 49)

    Be careful jumping it; see tip # 43).

    Other causes of a weak spark, in no particular order and probably not all inclusive, bad grounds/connections, worn plug wires or carbon core (automotive) plug wires, wrong plug gap, wrong plugs or burned plugs, worn out rotor/cap/points, incorrect point gap, worn insulator on the side of the distributor, incorrect or burned out resistor & a worn out ignition switch putting resistance in the circuit. Rarely, a bad coil..

    Tim Daley(MI)    Posted 03-16-2017 at 11:46:04 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark
  • HiYa Roger-
    Will engine turn over at all? Did you check everything else when you did a point replacement on your front mount? New rotor and condensor too? Check the pigtail on coil to ensure it is making contact? Points gapped at .015" Timing set correctly? On Bruce(VA)'s 75 Tip list, check #13 and #43. By 'even with jumper assist on battery' do you mean jumping from your car or truck 12 volt battery? Are plugs fouled? If so, dry off with an electric matchstick or torch, run a brass wire brush over tip, gap at.025 - .027 and reuse.

    Tim Daley(MI)

    Roger    Posted 03-16-2017 at 12:16:33 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark
  • Thanks, Tim. I replaced the condensor but not the rotor. My old one looked to be in good shape and fit better than the new china one. Pigtail to coil is good (all wires are only about a year old), gapped points and plugs, but didn't mess with the timing since it ran fine before. Engine has about 95 lbs on all cylinders, which I know isn't great, but it should still run? By jummper assist I mean using a 6V charger/jumper box which spins it slightly faster. Just seems odd that the first crank gives a hot spark, then little to nothing. Carb is good as it was recently rebuilt and ran fine on another tractor.

    r geiger    Posted 03-16-2017 at 12:58:48 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark
  • You may be seeing the results of the ballasts resistor. as it heats up, it reduces current flow which would reduce the spark.
    Does the tractor start and run?

    Roger    Posted 03-16-2017 at 13:10:12 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark
  • Tractor doesn't start. At most it sometimes pops on the first hot spark, then nothing.Starting fluid doesn't seem to have an effect either.

    Tim Daley(MI)    Posted 03-16-2017 at 15:26:13 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark
  • There are three basic things needed to run: Fuel, Spark, and Compression. 95 ain't that bad and will run a lot less than that. So, let's concentrate on the first two things; basic problem solving methods apply. Verify fuel first, it's easy to see if carb is getting fuel. With engine COLD, not a problem since you can't get it running now anyway. Loosen the fuel line at the carb brass elbow inlet and point down into a container like a coffee can. Open fuel valve two full turns at the sediment bowl assembly. Observe fuel flow as a steady, pencil thick stream uninterrupted. Hesitation, starts and stops, or slow drips indicate problem is in fuel tank and sediment bowl, not carb. If fuel flow looks good, move on to spark, if not good, time to clean the two screens in the sediment bowl assembly. You'll need to drain the gas tank before pulling sediment bowl assembly to get to the internal screen soldered on the top of sed bowl line in. Careful cleaning and blowing off. I've had some screens blow right of the assembly. Large half-dollar size brass fine mesh screen lies horizontal on top of assembly can be removed, cleaned and blown off with compressed air. Once fuel issue is eliminated, we can concentrate on spark. I'd go back to distributor and go over everything once again and at least check timing. Sometimes that copper strip gets twisted or mangled and will be the culprit. A simple continuity tester will suffice to check for shorts while unit is on the kitchen table or workbench. My money is on the distributor but eliminate the fuel issue first.

    Tim Daley(MI)

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