In Reply to: 8n issues (6V, front mounted distributor) posted by Tony on May 16, 2020 at 08:27:56:
Thank you, everyone, for your thoughts and recommendations.
I just cut the grass again yesterday and confirmed that the tractor does seem to bog down in spots with heavy grass and/or when climbing a hill. It ran for about 75 minutes and did not sputter or die this time. As before, I needed full throttle in 1st gear to get the job done. I tried 2nd gear on a flat area, and while the tractor was moving slightly faster, the engine was definitely working much harder at lower RPM.
Since we have very little information about how it was maintained over the past 70+ years, here's what we have done over the past few months to try to improve the starting and running of this tractor:
* Followed Bruce's recommended starting sequence & procedure
* Checked circuits with a meter, and compared the values to what is in Bruce's list of 75 tips
* Bought shop & user manuals
* Replaced the starter with a new one when the original had stopped turning altogether (kept the old one for rebuilding as a spare)
* Replaced the starter switch with anew one
* Replaced the Zenith carb with a new one of Marvel-Schebler design, along with a new inlet screen; The Zenith did not look like anything we had seen in any 8n reference pictures, and had additional adjustment screws for which we did not find any adjustment information; initial settings on the new carb per recommendations from Bruce (kept the Zenith for rebuilding as a spare)
* A few weeks ago, we noticed liquid bubbling out of the center head bolt between spark plugs #3 and #4. We pulled the cylinder head, replaced the bad head gasket with a new metal one, cleaned the block, pistons and the visible surfaces of the valves; had the head tank-cleaned and honed .010 by a local shop, reinstalled head with torque wrench to factory specs in the correct order; copper-core spark plugs cleaned and reinstalled with correct gap, non-resistor plug wires reinstalled correctly
* Cooling system drained, replaced with water and coolant flush, will drain and replace with proper coolant after running additional hours; presently no thermostat, but we have a new one to be installed after the coolant flush is complete
* Oil & filter changed
* Removed and cleaned the front-mounted distributor, installed new points and condenser, points gapped to .015 as per spec, all new gaskets
Here's our plan:
* The battery cables will be replaced with #1 gauge, since good cables are critical to getting the most efficient use of the 6V battery
* Have the battery tested under load and replaced if needed
* We were thinking about a tachometer in order to see what RPM range at which the tractor is actually running. For example, if the red line is 2,200 RPM at WOT and IF we are only getting 1600 when mowing flat ground, we need to find out why (allowing for parasitic drain from mower deck); what is the acceptable RPM range while mowing?
* Compression test, compare to factory spec and consistency between cylinders
* Check the screens in the glass fuel bowl and replace if necessary
* Check the point gap again to ensure it is correct
* Fine tune the carb idle mixture and non-idle mixture
* Follow recommendations made in this string of the forum
* Run through all of Bruce's 75 tips again
One other issue, relatively minor, the throttle lever will not stay in one position, it wants to go back to idle unless I hold it while running. While this is good for an automobile, it's a pain while mowing. We cleaned the little detentes on the quadrant, as previous paint jobs had filled in the crevices. No improvement. Any ideas?