1978 70HP Johnson runs cruddy. help?

External Since: May 21, 2004 Posts: 1

I've got a 78 Johnson 70HP that runs crappy at slow speeds, and has
trouble transitioning to high RPMs.

When the motor is cold, it will run for about 5 seconds then die. I can
save it by hitting the choke. Everytime I hit the choke, it will run a
little longer before I have to hit the choke again. After about 10
iterations of this, it appears to have warmed up and will stay running.
Is this normal?

After this warm up period, it will idle pretty decently. However, as
soon as I put it into gear, it wants to die again, unless I hit the choke
every 10 seconds or so. Between these choking periods, it does seem to
run pretty well, but then starts sputtering and dies unless I choke it.
It does this warm or cold.

Once I get it above 3000RPM, it seems to be fine and runs great.

What's going on here? I've had it to two mechanics and neither of them
could figure out what was wrong.

Any help appreciated.

--
I never did give anybody hell.
I just told the truth and they thought it was hell.
Harry S. Truman

External Since: May 21, 2004 Posts: 11

"Werner" <werner.DeleteThis@cubbyhole.com> wrote in message
news:c8jo2i$knl$1@carlton.cubbyhole.com...
> I've got a 78 Johnson 70HP that runs crappy at slow speeds, and has
> trouble transitioning to high RPMs.
>
> When the motor is cold, it will run for about 5 seconds then die. I can
> save it by hitting the choke. Everytime I hit the choke, it will run a
> little longer before I have to hit the choke again. After about 10
> iterations of this, it appears to have warmed up and will stay running.
> Is this normal?
>
> After this warm up period, it will idle pretty decently. However, as
> soon as I put it into gear, it wants to die again, unless I hit the choke
> every 10 seconds or so. Between these choking periods, it does seem to
> run pretty well, but then starts sputtering and dies unless I choke it.
> It does this warm or cold.
>
> Once I get it above 3000RPM, it seems to be fine and runs great.
>
Tank the carb first (NAPPA auto parts has a proffessional grade carb
cleaner) Leave it in the cleaner for at least two hours.
Reassemble and check the motors operation. If still weak mixture at low
speeds, bend the floats to allow a slightly higher fuel level.

Expect the engine to have problems at the temp extremes (cold and hot). Too
rich at hot and too lean at cold. That's what the thermostat is for in the
engine. BUT thermostats and salt water don't mix so they are extremely
unreliable.

I had a 79 115 HP Johnson that I had to bend the floats. It now works OK,
after a good run and the engine is hot it idles perfectly. When attemting
to pull novice skiers, I have stalling problems as they take too long to get
set up and the engine cools down. My cure is to gun the engine out of gear
to clear the carbs.