fastjeff
Gold Medal Contributor
I've posted this little problem on other sites and no one has a solution yet that makes sense. Here goes:
1958 vintage Mark 78 converted to late model (mid-70s in-line six) electronic ignition. Motor ran super for two years and, seeing it was over 50 years old and original, I rebuilt it over the winter. Motor started instantly, but it was running rough, smoking (had lots of oil in the cylinders) and idling roughly at 3K with the throttle set to idle.
What the hell?
Distributor’s gotta be off a tooth, I predicted, but it wasn’t. I then backed the idle stop screw off a TON and fired her up. I also rotated the distributor by hand to the idle position and no difference. Still idling very high and rough as hell.
What the hell?
The carb butterflies gotta be open somehow, I thought. Checked and readjusted, fired it up and—no difference; still running rough and screaming at 3K.
What the hell!
Having nary a clue as to what was going on I started messing with the idle adjustments—I had to try something. Still no difference. Suddenly, while I trying to figure what to do next, it smoothed right out and dropped down to a nice 1K idle. For a moment I though it had dropped a cylinder or two, but no--all six were running fine.
What the hell!!!
From my 60 years of messing with motors, I've never seen a screw up of some kind (like fuel or ignition) that caused a motor to rev HIGHER--lower or stalling right out at idle is normal.
The next day I took it to the river. Started up fine, then did the high, rough idle thing again. Rapped the throttle a few times (and good!) and it suddenly dropped to a nice, 6 cylinder idle at around 1K. Snicked it into gear and she took the gas immediately without a hint of a bog. Ran the boat then and she ran normally for the rest of the day. Ditto the following day with no problems at all.
So what on earth caused that problem? I'm at a loss. Thought it might be the switch box (somehow) so I changed it (and the coil) before taking it to the river. I THOUGHT that had cured it, but the problem returned so......................
Any suggestions will be gratefully accepted.
Jeff
1958 vintage Mark 78 converted to late model (mid-70s in-line six) electronic ignition. Motor ran super for two years and, seeing it was over 50 years old and original, I rebuilt it over the winter. Motor started instantly, but it was running rough, smoking (had lots of oil in the cylinders) and idling roughly at 3K with the throttle set to idle.
What the hell?
Distributor’s gotta be off a tooth, I predicted, but it wasn’t. I then backed the idle stop screw off a TON and fired her up. I also rotated the distributor by hand to the idle position and no difference. Still idling very high and rough as hell.
What the hell?
The carb butterflies gotta be open somehow, I thought. Checked and readjusted, fired it up and—no difference; still running rough and screaming at 3K.
What the hell!
Having nary a clue as to what was going on I started messing with the idle adjustments—I had to try something. Still no difference. Suddenly, while I trying to figure what to do next, it smoothed right out and dropped down to a nice 1K idle. For a moment I though it had dropped a cylinder or two, but no--all six were running fine.
What the hell!!!
From my 60 years of messing with motors, I've never seen a screw up of some kind (like fuel or ignition) that caused a motor to rev HIGHER--lower or stalling right out at idle is normal.
The next day I took it to the river. Started up fine, then did the high, rough idle thing again. Rapped the throttle a few times (and good!) and it suddenly dropped to a nice, 6 cylinder idle at around 1K. Snicked it into gear and she took the gas immediately without a hint of a bog. Ran the boat then and she ran normally for the rest of the day. Ditto the following day with no problems at all.
So what on earth caused that problem? I'm at a loss. Thought it might be the switch box (somehow) so I changed it (and the coil) before taking it to the river. I THOUGHT that had cured it, but the problem returned so......................
Any suggestions will be gratefully accepted.
Jeff