All,
I have a '49 8N, no serial number on the block, front-mount distributor.
I recently replaced the head gasket, complete wiring harness, plug wires (copper), new points and condenser, new plugs and added the missing thermostat. Replaced the governor with a new unit as all parts in the old one (including the housing) were bad. I also replaced the distributor cap and rotor and added the missing gaskets.
Seriously, there were no exhaust manifold gaskets, carb manifold gaskets, no gaskets at all in the distributor (not even the cork under the coil). I think the previous owner had a phobia about gaskets.
I very carefully checked the static timing. Since I had the head off it was easy to see when #1 was at TDC and use a continuity tester to monitor when the points begin to open. All seems good.
After all of that work, it started right up and has been running beautifully for a couple of weeks. I've been mowing about 25 acres that is covered in golden-rod and other stuff with fluffy seeds. I have to stop periodically and empty the cyclone air cleaner (new cyclone to oil-bath gasket) and blow out the radiator. I also check the oil-bath and replace the oil when it contains fluff.
So...
In the last couple of days it has started to backfire through the tail pipe when under load. At idle or at light load (driving on smooth flat ground) it only backfires once every 15-30 seconds. Under heavier load, like driving uphill or when the brush hog hits heavy weeds, it backfires quite frequently ~ 3-10 times or more in 15 seconds. The backfire seems to be a new behavior in the last few days, and it did not backfire at all for the first couple of weeks after the major servicing.
I'm not comfortable with this many backfires, so stopped and checked whatever I could think of. Today I cleaned the oil bath, pulled and checked both of the air filter bird nests (they looked quite clean to me), verified that the plug wires are tight to the plugs and firmly seated in the distributor. Fresh gasoline, no issues in the fuel filter, really nothing that seems out of place.
So, if someone could tell me what is wrong I would really appreciate it! :^)
If not, I would love some hints on where to look or what kinds of diagnostic tests I could perform to identify the issue.
Thanks for your help, and any thoughts would be appreciate.
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Jon
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