random miss fire

[Chris Newman]

Well I been working on my newly acquired 8n tractor nonstop for
nearly 6 weeks now. It's a front distributor and was supposedly
professionally rebuilt several years ago. at half throttle it Has 40 psi
of oil pressure cold, about 32 psi hot, hot idle is about 12 psi.

I Have fixed a lot of problems but still has a random miss that I can't
seem to get rid of. I think I have exhausted all of the common
potential causes so now I am looking for the really off the wall
ideas. So far I have done the following to the tractor:

New points & condenser
New plug wires, copper core (had incorrect non-copper wires)
Set timing (starts like a champ now, it was way off)
fixed exhaust manifold leak (had manifold surfaced)
Fixed exhaust manifold to exhaust pipe leak
Rebuilt carburator
cleaned air cleaner, replaced air pipe couplers
New AL437 plugs
and of course I have checked the plug wire locations and 3&4 are
not reversed (I even swapped them just to check)
Jumped across the ignition switch to rule out a bad switch
checked spark at all plugs, nice blue flame at each location
Checked fuel flow, confirmed all three screens are clean

Compression check results
dry 95, 95, 80, 90
wet (couple squirts of oil in the cylinder) 115, 110, 115, 115

sometimes the misses come in rapid suspicion, sometimes I don't
have one for 30 sec. Misses more at idle than under load. Look
forward to any ideas anyone may have. Thanks, Chris

 

[Bob Harvey]

I'd start with the plugs. Replace them with new properly gapped, one at a time. HTH

 

[Chris Newman]

I will give that a try. When I changed them a few weeks ago they looked pretty good. I changed them all at the same time, not one at a time though.

 

[Animal]

I am just going to throw something at ya here. Did you replace the wires with the common wires from here or another after market place? I rebuilt my 2n a couple years back and had the same problem, fire was jumping inside the metal tube that hold the wires. I got some good Packard wire and my miss went away.

 

[Chris Newman]

bought the wires from Maple Springs Farm on Ebay. I am considering pulling the coil and generator wires that run through the metal tube and replacing them as well. No telling what they look like inside of the tube? Thought for sure I was on to something when I figured out the wires that came on the tractor were not coper core wires. Unfortunately the new wires didn't seem to make a difference.

 

[POPGUN]

Carefully stretch the pig tail on the coil. Intermittent miss could be the coil or ignition wire. A coil on its way out can cause int problems Even if you checked ign wire if its loose or a short it would show up as a intermittent. The wires in the tube could be shorting out if chaffed. Make sure all ele connections are tight and shinny.

 

[Bob Purinton]

Turn out the lights when you have it running and see if there is a random spark around the tube. I had a bad running welder that lit up like a Christmas tree at night until I replaced all the wires.
Just for the heck of it; try running the plug wires (different set so you won"t have to re-run wires through the tube) without the tube. Just unplug the wires in the tube and run another set outside the tube.
Good luck.

 

[isaacv]

worn distributer?

 

[jerrybigrig]

Years ago my dad had a similar problem on a car eng we ran a mixture of trans fluid and water through the carb while it was running and it cleared up. If you decide to do this don't do it inside a building because it smokes like crazy .we used a small pump oil can w/ a 50/50 mix of water and trans fluid. Good luck

 

[Chris Newman]

Installed fresh plug wires yesterday. I think I will pull a new coil and generator wire next and see what I find. I have been over all of the other electrical connections and they are good. Guess you never know what the wires look like inside the tube till you pull them out. Be a good project for this weekend when it warms up. It's -16 F at the moment.

 

[cbradio]

I was having a miss issue and installed new plugs yesterday while changing the oil. Cured the problem. The plugs were pretty fouled up too.