Hard to start B JD

Mo in NE tex · Sep 4, 2015

I have a 1948 JD "B" electric start, mag ignition and it's a bear to start with the starter, and it's 12V. A short tug with my truck and it starts "lickity split", I know it's either mag or carb, but I've had the mag rebuilt by a reputable mag fellow up in Michigan and it knocks the fire out of me. Is there a chart that tells me the volt/amp output of the mag on impulse and when running? It just seems to me like it doesn't have that umph on impulse. It will start sometimes with the starter, but after trying for a while, and when it does, it fires right off, no miss or anything. Am I looking in the wrong place and need to look at carb instead? Any advise would be appreciated. I am not a electrician, but my brother knows something about it as he works on some big robotic dye cutting machines, he asked about the voltage output.

Blue Jay · Sep 4, 2015

Is the mag snapping on impulse when you turn it over?

Ben.So.Tex · Sep 4, 2015

Check your timing on the tractor if it is off it can be hard to start. Pulling with truck spins the engine faster than the starter and it fires off. there is a mark at 3 oclock on the tractor, rotate flywheel by hand when the mark/dot (left impulse)on the flywheel are next to each other the mag should click. If it is off rotate the mag alittle and check again. Also try a fresh set of plugs and points. Good luck

old popper · Sep 4, 2015

On the late styled B the timing mark is a punch mark on the raised boss on the flywheel that lines up with a hash mark at the bottom of the center cover hole.
Hope this makes sense to you.

David G · Sep 4, 2015

Engine might be spinning over to fast for mag to impulse, make sure it clicks when starting.

Mike M · Sep 4, 2015

I have also seen that before on a 12V converted B with a Mag.

ET · Sep 4, 2015

Your description is a classic weak coil description.

RandyB(MI) · Sep 4, 2015

That would mean it's turning it over at 250 + rpm which is the same as pulling it would do. Faster than 250 rpm and it has enough spark to fire without impulse. I would advise checking compression and timing. If it runs right after starting then it isn't carb unless choke is put together wrong. That would have a #67 which has a spring loaded choke and could be put together wrong and not applying choke. Late "B" with #67 will need a little choke to start even when warm.

mijohn · Sep 4, 2015

I had the same problem, but I had a wico dist. When I switched to a delco dist. my starting problems went away. It starts on about the second revolution. And I also switched it over to 12 volt before I overhauled the wico dist. I think the trouble in my case was the coil was not strong enough. In some of my old farm magazines from the early 1950s wico added an external coil to the XB dist. Just my thinking. John

Mo in NE tex · Sep 5, 2015

Double checked timing and it's right on the mark, mag impulses right on the mark. I've changed plugs so many times that I now own stock in the spark plug companies, all of them (AC/Champion/NGW or whatever). I cleaned up an old pair yesterday afternoon and it fired off on the 2nd revolution. Going to try it again this AM and see what it does, need to get some disking done b/4 it rains (someday).

Hard to start B JD

Mo in NE tex

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Blue Jay

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Ben.So.Tex

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old popper

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David G

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Mike M

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ET

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RandyB(MI)

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mijohn

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Mo in NE tex

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