Ignition coil

My forklift has the older, cylindrical shaped ignition coil, with a 12 volt system. The coil was using an external resistor when I got the lift truck. It is now wired to get 12 volts when starting, and it fires up INSTANTLY. It then drops back to the resistor for running. However, after starting the engine with half choke and running for a couple of minutes, I push off the manual choke. As the engine warms up, you can hear cylinders "coming in" that weren't running properly before. A plug check found smutty plugs, but the engine runs relatively well after the "clearing out" occurs. The engine should not be over-choked, because I am just choking it enough to keep it running as well as possible, no black smoke exhausting, etc. I am wondering if the resistor is cutting back on the coil too much, affecting my spark after startup and during running. The coil has no markings. I am thinking about bypassing the resistor to see if things improve, but I obviously don't want to burn up the coil. Does anyone have any info on how to tell if a coil really NEEDS an external resistor? Any ohm readings I can take to tell if it's a coil that can be run without a resistor at 12 volts? Thanks for any helpful info.

RJ

Reply to
Backlash
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The resistor is more to extend point life . Even with a capacitor to absorb the surge , 12v will fry the points . You might try a Chevy ballast resistor . Are you sure it doesn't use a resistance wire to the coil ? Too much resistance will surely weaken the spark .

Reply to
Terry Coombs

Since the resistor is external, you might put a 2nd one in parallel with it, more or less halving the effective resistance. I'd hesitate to simply pull the resistor altogether, the coil would likely overheat if you ran it that way for more than some few seconds.

I'd measure the resistor and find a wirewound of similar resistance good for 10 to 20 watts- Radio Shack might still be carrying them these days. At one point they sold dummy speaker loads- basically just an 8 ohm resistor that could take a good deal of power.

I have automotive coil with internal resistor, shows about 4 ohms on my meter. A resistorless coil should have very low resistance, less than 1 ohm I'd think- I've never measured one. You might doublecheck that your coil doesn't have an internal resistor already- perhaps the original resistorless coil was replaced at some point by a unit w/ internal resistor and now you're running with something like double the resistance.

Gregm

Reply to
Greg Menke

"Backlash" wrote in news:PemdnVhK3eMKZy snipped-for-privacy@portbridge.com:

RJ, You didn't mention who the manufacturer of the engine was, and that would be helpful information. My suggestion is a trip to the junkyard...to find an electronic system from a later model year. Failing that, you could always go with an aftermarket electronic conversion kit for the distributor, and something like an MSD or Jacobs ignition kit. Changing over would provide a reliable, high-voltage, stable spark and performance, better economy, less maintenance. Be sure to open the spark gap up to what the electronic system was designed to run with. (This should gain you some power to boot.)

Reply to
Anthony

You might use a new approach. Put in retrofit electronic points and change to a coil without a resistor.

THIS IS SO MUCH BETTER! I live in MN and I've changed all my old tractors over. Now they all start if the battery can kick it over and I haven't replaced points in years.

This will cost you about $100. Any autoparts store can order them. I couldn't find it, but there's an online website to get them cheaper, just for tractor restore.

Karl

Reply to
Karl Townsend

Thanks all, for your valuable input. Problem is, right now I'm in the middle of loading my entire workshop into a semi trailer I bought, so needed a quick solution. Wife got a promotion, we're moving, and at the same time, a friend bought out my workshop property, so I had to clear that out also. I think I'll measure the resistance of the coil, and see If I think I can eliminate the resistor. I haven't owned the unit that long, and the coil could just already be a more resistive coil. I'll let you all know what I find out.

Well, off to resume loading. A neighbor has just called and offered his lift truck as a backup.

RJ

Reply to
Backlash

Check your plug wires.

Randy

Reply to
Randal O'Brian

I had the same problem with my old 1965 International Scout... I put a super hot yellow racing coil in place of the old one years ago... Its been working great .......

Reply to
Kevin Beitz

Most engines run with a 6 volt coil.The resistor is to bring the voltage down from 12 volts to six volts. Fords use a resistor wire. Chryslers use a ballast resistor. I don't recall what GM uses. When you start the engine the system by passes the resistor so you are running 12 volts to the coil. This is for cold weather starting. Once the engine is running the power is rerouted through the resistor and you are then running the coil with the proper 6 volts. Some cars use coils with the resistor built in.

Richard W.

Reply to
Richard W.

Check the coil primary resistance. If it is3.25 ohms, run without resistor. If less than 3.25 ohms, total of resistor and coil should be roughly 3.25.

Reply to
nospam.clare.nce

Not true. Coils on 12 volt systems with resistors generally run on closer to 8 volts.

6 volt coils are generally 1.14-1.26 ohms. 12 volt coils used wqith a resistor are generally 1.42-1.58 ohms. They range from 1.25 to 1.73 12 volt coils for use without a resistor generally run 3.15 to 3.48 ohms, while electronic ignition coils, particularly CDI, generally run well under 1 ohm, with 0.3 to 0.6 being common.
Reply to
nospam.clare.nce

Take out the resistor. It will run fine. One caveat. Make sure that you do not leave the key on without the engine running. It WILL blow up the coil. Running the higher voltage will give you a "hotter" spark.

My dad, grand dad and I have been putting alternators on IH B and C tractors for years. Of course all were originally 6V systems. We have just switched them directly over to 12V using the original coil. As long as you do not let the coil "soak" at this higher voltage it will not adversely affect it. I am sure it does reduce the life of the coil, but we have run then for an awful long time with out replacing any of them. It isn't actually the voltage that is hard on it, but the higher current that the primary windings take without the resistor limiting the current.

As mentioned, this will result in a hotter spark. This is good. You can run a wider gap and/or get the plugs to jump better if you are burning oil or have likewise poor conditions.

As one other poster mentioned, you could put another resistor in parallel to effectively 1/2(assuming matching resistor) your resistance and bump up the primary voltage. This will work well and limit the potential to cook the coil.

JW

Reply to
cyberzl1

Pertronix (

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) is one company that comes to mind. I live in Karl's neighborhood, and have to agree. A "pointless" system is so much better. At a $100 a crack, they get pricey if you do a lot of them, but they really work well. I have installed one on spray buggy and one in an older car. I think I have the older Ignitor module.

Reply to
cyberzl1

Pertronix (

formatting link
) is one company that comes to mind. I live in Karl's neighborhood, and have to agree. A "pointless" system is so much better. At a $100 a crack, they get pricey if you do a lot of them, but they really work well. I have installed one on spray buggy and one in an older car. I think I have the older Ignitor module.

Reply to
cyberzl1

Coil life may not suffer, but with point ignition, point life WILL.

As for current vs voltage - you can argue both ways. High current can only flow through a fixed resistance with increased voltage - so which came first - the chicken or the egg? You cannot have high current without too high voltage - so it IS the voltage that is critical for a given coil. The only way a ballast resistor reduces the current flow in the coil is by reducing the voltage seen across the coil. It does this by creating a "voltage devider". The resistor drops its share of the voltage, leaving less for the coil.

The net effect is to reduce the current flow through the entire coil primary circuit - including the points.

Reply to
nospam.clare.nce

Chances are EXCELLENT that the existing direct ignition system will out-perform the MSD anyway.

Today's electronic ignition systems are capable of putting out astronomical spark voltages, at pretty sizeable currents.

Reply to
nospam.clare.nce

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