12v Coil on Kubota

[fredbear241]

Is it possible to 'bypass' the Kubota ignition unit on a single cyl engine & use a 12v Automotive Coil? I'd still need something to replace 'points' and act as a 'switch'....any ideas? The flywheel has a magnet, the existing coil is there, there is a lighting coil inside the flywheel..... I suspect the orig coil might be cause of starting problem & wanted to test by bypassing it.
TIA for any input - Fred

 

[RichNJ]

What engine is this? From what machine?
In general it's easiest to find the problem and fix it.
Test the points with an ohm meter. Sand or file them gently to remove any corrosion. Check the gap.
If there are no points and it's a coil sensing a magnet on the flywheel then connect a high impedance volt meter to the coil and turn the engine by hand with the plug removed. As the magnet passes the coil it will 'kick' the voltmeter.
Test the condensor with an ohm meter. Set it to times 1 million or X1M and put the test leads across the disonnected condensor. The condensor will charge up from the meter's battery looking briefly like a short and then stopping high up in the megohm area. An analog meter is best for this test.
Check the spark coil with the ohm meter. The primary winding will be very low around (I don't remember extactly) 2 or 3 ohms. The secondary (going to the plug) will be quite high around a few thousand ohms.

 

[fredbear241]

Hi Rich,
Its a GH400V single cyl Kubota. No Points or Condensor. Large flywheel with magnets & external ign pickup. Magnets Pickup all cleaned up. 2 leads from ign coil, HT lead & a LT(?) lead. LT lead has ~ 1v when engine is running. Should it have 12V? or is the 1v correct? I suspect coil (U shaped with 'back box' in center) maybe 'breaking down when it gets warm. Before replacing it I wanted a way to test confirm that it is the cause of the problem. I checked ohms on coil and seems like it should be OK. (ie it's fairly close to spec). When engine runs it runs great. When it decides to stop working....it's good at that also. It may decide to work in 5mins, or not for 12 hrs!..sounds sort or organic eh? Is this typical of kubota ign unit probs?

 

[hayden]

I'd just replace the points, condenser, and spark plug. It's probably no more than $10 in parts and is a cheap way to avoid problems.

 

[fredbear241]

Hayden,
trhanks for reply, but there are no points or condensor. Its got a Kubota sealed "black box" in the middle of the pickup (apprx 2" across) which sits on outside of flywheel, which has magnet on it. What I wanted to do was to hook up a std Auto Coil to replace the Kubota 'black box'. Only prob is finding something to work in the same way as 'points' in a old fashioned (pre black box system) would. ie how to get the flywheel magnet to activate the coil.

 

[RichNJ]

If you wanted to replace the system I would suggest going to the junkyard and getting a system out of a 1980s Toyota, Datsun, etc. The typical system consisted of a magnetic pickup in the distrib and a metal box w/the electronics mounted to the standard looking coil. You have to be careful as some were still points and some were magnetic and some were optical. You will also need the wiring diagram from the car in order to wire it correctly. I have used this replacement system a couple of times on older cars where no replacement parts were available. It's time consuming but one way of fixing it.
You would have to mount the pickup in the correct spot to maintain correct timing. How much is a replacement from Kubota? How about a used one from a junker?
In order to measure the voltage on the primary of the coil you will need an oscilloscpe. The "black box" will send a pulse of about 200-400 volts to the coil primary.

 

[fredbear241]

Hi Rich.
Sounds like it's getting expensive / messy to set up as a test. If I knew the coil/'black box" was the prob, I'd prob just buy one.....but then the thought of somehow 'triggering' a std auto coil seemed easy(?). What am I missing....a coil with 12v applied to +ve. -ve side goes to ground via a "switch"....in this case the magnet on the flywheel acts as the 'switch'...not sure what is on the other 'side' of the switch. Maybe the LT side of the existing 'black box' would work as the 'switch'? My thought is if the existing coil is breaking down under heat, it is the HT side not the LT side that is breaking down (probable or unlikely?) So if the -ve side of auto coil was connected to the existing LT lead, the circuit is completed....timing is taken care of, and ummmm what did I miss? And how can I test this without frying the existing (on the assumption it's not dead after all, and the prob is somewhere else.)

 

[RichNJ]

Are you sure there are no points? Did you look under the flywheel? Is there a wire going from the coil and going somewhere under the flywheel?
This black box sure sounds like a conventional magneto ignition system.

 

[TWINKLE_TOES]

Fred,

I don't think you will have much luck trying to bypass the original system with a conventional automotive ignition.

Are you sure there is no points or magnetic pickup to trigger the spark. Most magneto type ignition systems store energy in the coil when the magnet on the flywheel passes by, about 120 deg of the rotation, the energy is relased to the plug when the points open. Timing is determined by the point gap. A magnetic pickup is often used to sense the position of the crankshaft and ther trigger the spark thru a solid state switch.

Al

 

[kubmech]

Fredbear, The coil is an electronic ignition unit and does not require points, condenser or even 12 volts. The "NT" lead you mention is what grounds out the coil when you shutoff the engine or if your operator present system needs to shut down the engine such as PTO engaged and you come off the seat.
The easiest way to test the coil is to disconnect the shutdown lead, remove the spark plug and turn the engine over with the starter with the high tension lead hooked to a spark tester or somewhere near ground (don't use the sparkplug as a tester unless your sure it's a good one) If you have spark without the ground lead hooked up to the coil the coil is good. You may have a problem in the saftey switch system.