Chehalis Jeff wrote:
Hi I know you guys like to argue a lot about politics, but perhaps you
could take a moment to help me out with my problem, and here it is:

I have a 1972 Evinrude 85HP V4 Outboard that has been running fine
until it overheated (didn't seize) when the water pump disintegrated.
After the WP came apart, pieces of it messed up the thermostat (or
whatever it is OMC calls it) so I fixed that and the cooling system
works. I took the boat out for a test run and it starts good, idles
good but when you give it full throttle, it seems like the ignition is
severely missing -but only under load- because as soon as the boat gets
on plane, it seems to run fine. It's like spark is jumping to ground
(somewhere other than it should) on one or two cylinders when under
load.

I inspected the Spark plug wires and the coil wire and I don't see
anything obviously wrong. I ordered some new wire and new plugs (old
plugs look OK, perhaps a touch blacker than they ought to be, like it's
running a touch rich) I looked into the spark plug holes and pistons
look good and compression is pretty even on all four cyl. I haven't put
in the new wires (waiting for them to arrive UPS) or plugs but I
wondered if anyone else has seen this behavior before.

Thanks

JM
Chehalis, WA


HI JM

As others have said a good tune can't hurt, new plugs, check leads etc.
Sorry to be the odd one again but feeling here is you might have a head
gasket/joint leak so once water really gets flowing it kills a cyl or
cyls from firing.

Below is a paste of a very old prior post which should help you tune it
if you want without spending.

K


As the others say & if you do the full tune below might help (it's
a paste from a prior inquiry so sorry about the setout etc;-)) even
if you get a manual they're a bit obtuse at times;-)

OMC V4

(i) The basic idea, & the names used for the bits is below &
it's OK
for most of the older style 2 strokes is;
(a) THROTTLE ARM The throttle cable moves a
"throttle arm"
(big arm on the side of the engine) back & forth
(b) ADVANCE STOP ADJUSTMENT SCREW The top of the
arm is
directly linked to the armature plate under the flywheel so any
movement
will change the spark timing, there is the "advance stop
adjustment
screw" just under the flywheel's ring gear.
(c) IDLE SPEED ADJUSTMENT SCREW The second screw
down
(about 2") the "throttle arm" is the "idle speed adjustment
screw"
(d) THROTTLE CAM The next (3rd) thing down (another
say 1")
from the top is a link which transmits the "throttle arm"s"
movement to a
"throttle cam".
(e) THROTTLE CAM YOKE or THUMBWHEEL The link
(above)
between the "throttle arm" & the "throttle cam", is adjustable
for
length, either by a threaded on "throttle cam yoke" or a
"thumbwheel"
(f) THROTTLE CAM TOP MARK The "throttle cam" has
some
markings on it (raised or on some models embossed) the top
(smaller) one
is the "throttle cam top mark",
(g) THROTTLE PICKUP When the "throttle cam top
mark" is
positioned in the centre of "cam follower" (roller) it's the
"throttle
pickup " point.
(h) CAM FOLLOWER (ROLLER) As the "throttle cam"
moves, it
comes into contact with, then starts to move a "cam follower" (a
little
roller)
(j) CAM FOLLOWER SCREW The "cam follower" is
connected to
the carbs' throttle shaft(s) so it opens & closes the carbs. The
"cam
follower" is connected to the throttle shaft(s) by an adjustment,
this is
the "cam follower screw"

(ii) The best thing to do is have someone work the throttle
very
slowly back & forth (engine off) as you just watch what happens,
till you
are familiar with it & the various adjustment bits involved, what
you
should see is;
(a) At dead idle, the "idle speed adjustment screw" is
against
the crankcase with the throttle cable not holding it up nor the
cables
lying too loose, the "cam follower" (little roller) is probably
not even
touching the "throttle cam" & the top of the "throttle arm" is
well over
making the spark timing retarded. You can see that idle speed is
almost
totally controlled with spark timing (retard)
(b) As the throttle is slowly advanced you'll see; the
top of
the "throttle arm" advances the spark timing then after some
movement,
the "throttle cam" will come into contact with the "cam follower"
& JUST
start to move the carb throttle shaft(s)
(c) The "throttle cam" is connected to the carb
throttle
shaft(s) by an adjustable link, sometimes an arm, others just
rods etc.
(d) Tell your assistant to stop there, you should see
that the
"throttle cam top mark" is exactly in the centre of the "cam
follower"
(roller) if so then that part of the 'synchronisation" is OK, get
your
assistant to continue to slowly open the throttle.
(e) Now as the throttle is increased, the carbs are
starting
to open , as the spark timing continues to advance till the
"throttle
arm" can move no further because it's resting against the
"advance stop
adjustment screw" this is WOT (Wide Open Throttle)
(f) With the air silencer off look in at the carb
plates, they
should be fully open & the linkage shouldn't be trying to over
open them.

Do this a few times & you'll see how all the little rods,
string &
sealing wax play together to manage the spark timing & the
carb(s)'
throttle opening.

(iii) The spark timing pointer; before you start timing etc,
particularly on an older motor you need to ensure it's actually
"pointing" to TDC. A bit of a fiddle sorry but worth it.
(a) Get an old spark plug & bash the porcelain & spark
tang
out of it.
(b) Put a small bolt & nut in the resultant hole so
when put
in the motor it will hang down a little into the chamber (just a
bit not
too far)
(c) Put it in #1
(d) By HAND & slowly & carefully bring the piston up
till it
touches the bolt then mark the flywheel level with the pointer.
(e) Turn the engine back the other way till the piston
rests
on the bolt & again mark the flywheel level with the pointer.
(f) TAKE THE PLUG OUT NOW!!! Catastrophic if you
leave it
there & turn the engine over;-)
(g) Measure between your two marks, the flywheel's TDC
mark
should be exactly midway between the marks, if it isn't then the
pointer
has been banged & is not accurate so,
(h) Bend to pointer so it points to true TDC. (which
way & how
much is obvious when you are doing it) Recheck.
(J) You did take the butchered plug out..... didn't
you???

(iv) Adjustments;
(a) The carbs throttle plates need to be all against
their
stops at idle, so loosen whatever interconnects them & links them
to the
"throttle cam" & ensure they all snap fully against their stops.
(even
against their stops the system is designed to still flow lots of
air).
Tighten the screw then by moving the "cam follower" (roller) you
should
see all the carb plates move together, if not do it again.
(yours is the
screw on the lower carb lever adjustment )
(b) The "throttle pickup" point should be checked
next,
slowly move the "throttle cam" till it touches the "cam follower"
(roller) & the carb(s)' throttle plate spindles just start to
move. The
"throttle cam top mark" should be in the middle of the "cam
follower"
(roller), if not loosen the "cam follower screw" & adjust so the
carb(s)' plates
JUST start to move
when the "throttle cam top mark" is in the centre of the "cam
follower"
(roller) Tighten screw & recheck.
(c) The throttle cable should let the "idle adjustment
screw"
rest against it's stop, if it's not just touching the stop as the
cable
runs out of travel or the cable is left too slack, adjust the
cable at
the bottom on the air silencer where the cables enter the engine.
(d) The next thing is the spark timing, some engine's,
the
manual specs a "throttle pickup" point spark timing, some don't.
Also if
the engine has a decal or placard which gives spark timing always
use
that over the manual etc.. If your engine specs a "pickup point"
spark
timing you can do it now; put a timing light on #1, start the
engine &
gently increase the revs (you'll need the warm-up in neutral
lever to get
it off idle) till the linkages are in the "throttle pickup'
point, then
check the spark timing. If it's not
correct, speed up or slow down till the timing light is reading
the
specified advance, then turn the engine off without touching or
changing
anything, you can now adjust the link between the "throttle arm"
& the
"throttle cam" so the "throttle cam top mark" is in the centre of
the
"cam follower" (roller) Tighten all, restart & recheck
"throttle pickup" point timing.

(e) Next the WOT spark timing. Bring the engine up to WOT & max
spec revs in the water, be careful OR courtesy of rec.boat's Tony Thomas;

"You don't need a test wheel to do this. Disconnect the throttle
linkage
from the timing advance rod. At idle advance the timing by hand and
check.
I have also had someone drive the boat and check it on a calm day
but the
linkage method is safer."

Easy if you have a tacho if not hmmmm, borrow??. Don't over rev the engine.
Check the max spark advance with the timing light but always follow the engine
decal/placard. If it's not correct, you can adjust it with the "advance stop
adjustment screw" just under the flywheel's starter ring gear.

(f) Engine off put the throttle to WOT & check the
carb(s)'
throttle plates are fully open & the linkage is not trying to
over open
them, adjust if needed.
(g) In the water you can then set the idle speed with
the
"idle speed adjustment screw". Get it as slow as is comfortable
for a
nice shift which doesn't "clunk" too hard.

Good luck.

K