8n will start and idle fine but missfires at half throttle to full! PLEASE HELP

[mbryant51375]

I'm still of the mind you've got ignition issues.
I only threw out the very rare problems I've encountered over the years. They can and do happen but rarely.

Back to ignition.
I assume the original plug wires were/are solid core wires? You didn't put some after market silicone resistor wires on it did you? Some ignition systems don't like that.
I've run into rotor buttons brand new out of the box that have given symptoms you describe, try another one.
Double check those points.

I will look at the wires today, I purchased them in a kit when we put the tractor back to points. It had been converted to to electronic ign which burnt up and was the cause of it being left to sit and be neglected. Points are hitting flat I have had them gapped at 15, 18 and 20 currently I put them back to 15.

Thnx for the replys and help.

 

[rsallen]

I think Utopia was referring to the polarity of the coil itself.
If you have a neg. ground electrical system the live feed (+) will go to the positive post on the coil.
He's right, it'll work in either direction. He also right that reversing the polarity can cause issues.

 

[mbryant51375]

I think Utopia was referring to the polarity of the coil itself.
If you have a neg. ground electrical system the live feed (+) will go to the positive post on the coil.
He's right, it'll work in either direction. He also right that reversing the polarity can cause issues.

It has been switch to a 12v neg ground. The front distrib can only be positive, correct?

 

[Utopia Texas]

Yes, I was referring to the wires at the coil. Here is a Model A ignition page that shows how to use a pencil to determine if the polarity is correct. Look about 3/4 down the page...
http://modelabasics.com/Ignition.htm
There are also YouTube pages showing the correct spark polarity....

 

[8N Ren]

Go to ytmag.com and look though it. They have an entire forum for 2,9 and 8N's. Check out the 75 tips page, there is tons of info. Don't go opening up the valve covers or taking off the head just yet.

Those new plug wires you put on are they copper core?

They have wire diagrams for the entire electrical system as well, 6 and 12 volt, side or front mount what ever your flavor.

 

[Midniteoyl]

Yes, I was referring to the wires at the coil. Here is a Model A ignition page that shows how to use a pencil to determine if the polarity is correct. Look about 3/4 down the page...
http://modelabasics.com/Ignition.htm
There are also YouTube pages showing the correct spark polarity....

Nice page..

 

[grainger12002]

mbryant,check the main jet in the bottom of the carb,if u can remove it and pass a wire thru it,the spray it and pass wire thru again,then reinstall and report,they can be a bear,it runs too god to be anything else,

 

[mbryant51375]

That is a great read! So here is the update this moring I closed the gap on the plugs to .006 made no difference. The electric system is 12v neg ground and the square coil has positive wire from the resistor via the ign switch, so no reverse polarity issue. The plug wires are 7mm thinned copper core j2031 " cut to fit". I gapped plugs to 25 and induced some propane to carb with no change.

 

[Soundguy]

It has been switch to a 12v neg ground. The front distrib can only be positive, correct?

your statement does not make sense.

ground polarity is defined by which battery post is tied to the chassis.

What ignition coil you run also makes some difference.

on a round can ignition coil with 3 conenctions, you can orient the primary to the same polarity as the electricl system by swapping wires. on the front mount with the square coil.. that is harder to achieve as 2 connections on t he base are fixed so that the coil cannot be reoriented. thereare ways areound it.. but in a properly functioning system, the polarity mismatch, if it exists, is of negligible concern.

 

[Midniteoyl]

Cut to fit wires... double check those end crimps..

Question: do you have the wires separated good? They are not zipped tied together are they? Long runs of parallel wires tend to induce voltage into one another... Just a thought.

Did you ever vary the distributor a little to see if it change the misfire? Misfires such as this are usually miss-timing or weak ignition. New coil and condenser or not, I would check those by swapping with a known good. Same with the plugs. One way to help a weak ignition at speed and under load is to reduce the plug gap. At high RPMs the coil has less time to saturate before collapse and that means less 'umph' to span the gap. Smaller gaps equal less umph needed.

I dont think you answered if you are using a ballast resistor.. ?