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.

My mechanic found that some of the exhaust manifold plugs had corroded out,
so he retapped and replaced them, cleaning up the engine compartment air
(dangerous to be exhausting CO into engine room, I know), and he said that
likely explained my problem: that after a while the engine area filled with
exhaust which didn't support combustion well enough. Running on plane
scooped more fresh air in through the vents and so it cleared up. (Didn't
explain the cool port manifold however...)

The engine did sound much better with the plugs replaced, but the stumbling
after twenty minutes of low-speed operation recurred. I checked both the
water-separating and inline fuel filters, and found a trace of sediment in
the water-separating one, but no water. I cleaned the air filter, and
brightened and tightened the battery connections. The mechanic checked the
distributor by feeling for shocks, but got none. Of course, when I took him
out to demonstrate the problem, it didn't occur, although we went right upon
plane rather than reproducing the experimental conditions exactly.

So, yesterday I changed the spark plugs (reminding me yet again of the joys
of standing on my head for hours in a tiny space in the bilge). The old ones
were blackened, and I checked a few gaps but didn't really dwell on this (no
pun) and they seemed OK. The new plugs were in the 0.032" range. The old
ones, especially at the aft end of the engine which sits lower due to the
engine not being level in the boat (straight-shaft inboard), were oily on
the threads, and I think that the further aft one had oil further into the
block on the threads ... which seems strange to me. They're very hard to get
at with a spark plug wrench, and I'm wondering if they were never quite
tightened in enough. (I was careful not to overtighten, however - having
stripped threads once many years ago...)

I was going to change the leads, too, just for thoroughness, but couldn't
find the right marine set late on a Saturday afternoon. Will have another
look Monday. The distributor cap and electronics control module were new two
summers ago (about 200 engine hours ago), as were the plugs and leads.

Then, I took the boat out for a prolonged low-speed cruise - and everything
worked perfectly. The weather was a bit cooler than it has been here (26C
instead of 32C) and a bit windier, so again my original conditions could not
be exactly replicated, but I'm hoping the problem had something to do with
the plugs.

Summary: was running rough after twenty minutes of low-speed operation, port
exhaust manifold cool, cleared up after a few minutes at planing speed.

Anything obvious that I'm missing?

Thanks again.

Charles

====

Charles T. Low
www.boatdocking.com

====

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

Last season I had a problem with either the carb float sticking and/or the
needle valve sometimes not seating causing excess fuel to "dribble" into the
engine causing the symptoms you describe. I would then have to coax the revs
up and at the higher speed, that extra fuel was not a problem, and the
problem would resolve itself.

I was not that anxious to replace the float/needle valve last season so
thought I'd try something different. I installed a fuel shut off, and ran
the carb dry before storing (I removed the plugs and sprayed the fogging oil
directly into the cylinders and cranked over a few times). This spring
before firing it up, I sprayed carb cleaner into the carb fuel bowl via the
vent and let it sit for 5 minutes ... then started it up. So far no
problems, so here's hoping I won't have to work on the carburator at all.

Something I heard you might try, is install the fuel shut off (if you don't
already have one), and if it starts missing, shut off the fuel and run the
carb dry. Then tap on the carb (to free a stuck float/needle valve and
gently), then turn on the fuel and see if the problem is gone. I have a
mechanical fuel pump ... maybe if you have an electric pump, just pull the
fuse???

And if the problem goes, then I guess the decision would be to repair the
carb ... or not.


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.

15 years ago I had a 55 hp evinrude that ran very rough . Repair shop
did a tune up but could not find anything amiss. Next time out same
thing happened. Once up on plane , hitting wave tops , engine began
missing and stumbling. By accident I jiggled ignition key , found it
was loose. Turned out ignition switch was making/breaking in rough
water.
First thing I check now on every trip out.

Keith in BC

I'll remember that one

Turned out ignition switch was making/breaking in rough
water.
First thing I check now on every trip out.

Keith in BC

Thanks, Mike,

So far, I replaced the spark plugs and since then have had no trouble. That
doesn't mean the trouble is over, but preliminary indications are good. The
electrodes or whatever they're called were black, and there was oil on the
screw threads, moreso the further aft on the engine (which sits a bit lower
than the front) ... what this means I have no idea and so far no one else
I've asked does either. I checked a few of the gaps and they seemed about
the same as on the new plugs, around 0.032".

I'm also going to replace the leads just for thoroughness.

The engine was compression-checked four years ago, about 500 hours of
running time, so a lot might have changed since then. But, although it uses
oil, it doesn't use much. I put in a litre only every 50 hours or so (which
is about when I should be changing it anyway).

Thanks again.

Charles

====

Charles T. Low
www.boatdocking.com

====

"Mike G" wrote in message
ews.com...

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

Thanks. The carb remains a source of mystery to me, although I've read about
how they work and looked at diagrams - I think I need to see it disassembled
in front of me and be talked through it once. I have thought of a carburetor
problem. I do have a fuel shut-off. Anyway, it's working at the moment, but
I'll have to give this some more thought, because reliability is so
important. My mechanic didn't mention the carbutetor, but I also didn't ask
him.

I think it's more likely something affecting only some cylinders, because of
the coolness of one manifold while the problem is active, resolving as the
problem disappears.

Charles

====

Charles T. Low
www.boatdocking.com

====

"Bowgus" wrote in message
...
Last season I had a problem with either the carb float sticking and/or the
needle valve sometimes not seating causing excess fuel to "dribble" into
the
engine causing the symptoms you describe. I would then have to coax the
revs
up and at the higher speed, that extra fuel was not a problem, and the
problem would resolve itself.

I was not that anxious to replace the float/needle valve last season so
thought I'd try something different. I installed a fuel shut off, and ran
the carb dry before storing (I removed the plugs and sprayed the fogging
oil
directly into the cylinders and cranked over a few times). This spring
before firing it up, I sprayed carb cleaner into the carb fuel bowl via
the
vent and let it sit for 5 minutes ... then started it up. So far no
problems, so here's hoping I won't have to work on the carburator at all.

Something I heard you might try, is install the fuel shut off (if you
don't
already have one), and if it starts missing, shut off the fuel and run the
carb dry. Then tap on the carb (to free a stuck float/needle valve and
gently), then turn on the fuel and see if the problem is gone. I have a
mechanical fuel pump ... maybe if you have an electric pump, just pull the
fuse???

And if the problem goes, then I guess the decision would be to repair the
carb ... or not.


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.

OT but may be worth sharing: And something else I once heard ... spark plugs
are subject to vibration, and the ceramic insulation may crack over time,
resulting in carbon tracking and reduction/loss of ignition spark. To sum
up, the story is that plugs may look good, but may in fact not be. So
replacing then every couple of seasons is I'm thinking not a bad idea ... I
think I'll include bi-annual plug replacement in my preventive maintenace.

I think it's more likely something affecting only some cylinders, because
of
the coolness of one manifold while the problem is active, resolving as the
problem disappears.

In my V6, there's a ball/spring mechanism in the cooling system that I come
across every fall when I pull all the water lines for draining/winter
storeage. I've just now looked through my Seloc manual, and don't see it. It
may have something to do with controlling water flow to each manifold ...
dunno ... I'll keep looking for info on that. If one manifold is cold, that
says to me that's where (most of) the water flow is going.

And it could be you have 2 problems. Perhaps you had/have some water in your
fuel/tank ... gas line antifreeze (alcohol) would absorb any water allowing
it to pass through the system. Gas treaments apparently also absorb water.
One reason I picked a carburated engine is that they're much more resistant
to water in the fuel ... may stumble a bit, but the water tends to make it's
way through the carb eventually ... unlike an injected system which I
understand may have to be torn down to get the water out. So, a water
separator is a "shall" for injected systems.

Charles T. Low wrote:

So far, I replaced the spark plugs and since then have had no trouble. That
doesn't mean the trouble is over, but preliminary indications are good. The
electrodes or whatever they're called were black, and there was oil on the
screw threads, moreso the further aft on the engine (which sits a bit lower
than the front) ... what this means I have no idea and so far no one else
I've asked does either.

And this is an interesting point. Taken together with your
consumption, it could be sucking oil from the guides on start/warmup
that's sat in the head (proportionately moreso aft), and eventually
fouling the plugs. Have you checked for any smoking at startup? You
could also pull your new aftmost plug after a brief startup/shutdown to
see if it's likewise getting oily. If it were the case the problem
would resurface after awhile & let you know.

Nice book, BTW.

Thanks and to the several others who have offered recent help.

And although I had hoped the problem was fixed, it recurred yesterday. As
soon as it started to stumble, after trolling around for a while (teaching
my daughter how to dock!), I took her up on plane and the whole thing
straightened out in very short order. Very weird.

I haven't quite got the innards of an engine visualized to the extent that I
can see how guides and spark plugs inter-relate, but no matter - all food
for thought, research, and further discussion with my mechanic.

Thanks again.

Charles

P.S. And thanks for the kind words.

====

Charles T. Low
www.boatdocking.com

====

wrote in message
oups.com...
Charles T. Low wrote:

So far, I replaced the spark plugs and since then have had no trouble.
That
doesn't mean the trouble is over, but preliminary indications are good.
The
electrodes or whatever they're called were black, and there was oil on
the
screw threads, moreso the further aft on the engine (which sits a bit
lower
than the front) ... what this means I have no idea and so far no one else
I've asked does either.

And this is an interesting point. Taken together with your
consumption, it could be sucking oil from the guides on start/warmup
that's sat in the head (proportionately moreso aft), and eventually
fouling the plugs. Have you checked for any smoking at startup? You
could also pull your new aftmost plug after a brief startup/shutdown to
see if it's likewise getting oily. If it were the case the problem
would resurface after awhile & let you know.

Nice book, BTW.