In article oups.com,
[withoutUN] says...
TIA to all.

1978 Chrysler 318 V-8 gasoline engine, www.ctow.ca/Trojan26, hour-meter
coming up to 1000 hours, about half of them in the four years I've owned the
boat.

Recently the engine began to run rough, stumbling quite badly. This happened
several times about twenty minutes out of port, trolling along in the
1200-1400 rpm range. Twice, I have then put the boat up on plane to scoot
home (3200-3400 rpm), only to find that half-way home the whole problem
disappears quite suddenly and dramatically, the engine smooths out, revs
pick up and I have to pull back on the throttle.

One other observation: when misbehaving the port exhaust manifold (I think -
the thing with the risers leading to exhaust hoses, muffler...) stays cold.
Once the problem clears up, both manifolds get warm.


A couple of things come to mind but the top of the list one is that you
are running rich and loading up the engine at the low RPM and the good
run at WOT is cleaning things up.

A compression check probably wouldn't be out of order either since the
second item on the list is a question of how well the valves are
seating. Especially if you do a lot of trolling. five hundred hours of
more low RPM trolling then high speed operation can give you quite a
build up of carbon which may be getting to a point where the seating is
only marginal.

There is always the hotter plug thing but since I'd only consider it if
you were doing a whole lot more trolling then running at WOT. I'd only
suggest it after you gave things a lot of thought and a second opinion
from your mechanic.

I know it doesn't address the manifold thing but.................

Good luck


--
Mike G.
Heirloom Woods

www.heirloom-woods.net