1995 Johnson 70hp starts then dies

[Johnson70hp]

Good day Folks.

I am thinking, I need a new fuel pump but looking for confirmation.

95 Johnson 70hp outboard, here is the scenario.
Was running great the other day, all of a sudden it started acting like it was running out of gas but never actually quit and after 30 seconds it picked right back up no issues for another 20 mins or so until I docked for the night. Next morning go out, starts right up, warmed up. got 200ft from shore and quit. It will start but dies after 3-4 seconds.

This is what I have found so far.
Gas tank is full fresh premium gas mixed 50-1 no leaks or plugs in the hose from tank to motor
Compression is 150-160 across the three cylinders
spark plugs were replaced a couple days prior, and show no signs of fouling.
no fuel leaks any where around the engine.
fuel filter is new
pumping the primer does not help. nor does it loose prime.
I can get the motor to stay running if I engage the fuel primer with the key switch.
if start it and let go of the key it dies. if I hold the key in like when cold starting, it stays running.

Since the motor dies completely like it runs out of gas and not just one or two cylinders I don't believe the issues is related to one of the 3 carbs. Since it starts and runs when gas is injected Spark is not an issue.
Unless I am missing something the Fuel pump would be the only other component that would limit the fuel to all carbs.

Am I on the right track here or am I missing something. ?

 

[flyingscott]

Did you put oil in the cylinders before your compression test? Thats more compression than it left the factory with. What happens if you pump the primer ball on the fuel line when that is happening?

 

[Johnson70hp]

I did not, didn't know I should. As for the primer ball on the fuel line, it makes no difference if I squeeze or don't. it stays firm,

 

[oldboat1]

It sounds like a carburetor issue if using the primer system keeps it running. They may need rebuilding (or another visit).

 

[Johnson70hp]

It sounds like a carburetor issue if using the primer system keeps it running. They may need rebuilding (or another visit).

I find it strange that all 3 carbs would plug up at the same time.

 

[racerone]

The electric primer valve put fuel directly into the engine.---This fuel does not go into the carburetor bowls.-----This fuel bypasses the metering circuits in the carburetors.-----This strongly suggests that carburetors need attention !----You have replaced the water pump impeller ?-----Motor might be overheating and going into S.L.O.W. mode.----Up to you to do some simple trouble shooting.----Make no assumptions.

 

[saltchuckmatt]

I find it strange that all 3 carbs would plug up at the same time.

Did the motor sit with fuel in it for a long time? Sounds like the vro was removed?

 

[Johnson70hp]

The electric primer valve put fuel directly into the engine.---This fuel does not go into the carburetor bowls.-----This fuel bypasses the metering circuits in the carburetors.-----This strongly suggests that carburetors need attention !----You have replaced the water pump impeller ?-----Motor might be overheating and going into S.L.O.W. mode.----Up to you to do some simple trouble shooting.----Make no assumptions.

Yes I understand how the electric primer works,
the impeller was replaced at end of last season, and seems to working.

other than pulling each carb off and cleaning what troubleshooting do you suggest still?

 

[Johnson70hp]

Did the motor sit with fuel in it for a long time? Sounds like the vro was removed?

the VRO has been disconnected for years by previous owner. Since i bought it 5 years ago its ran great and I've been mixing 50.1 in the tank.

the last 3 years it has been in the water all spring summer and fall. Basically ice out to almost freezing. and runs weekley or some times multiple times a week for cruising around or running to fishing spots.

 

[racerone]

Last effort to help.----You say when you operate the manual pump nothing changes.----That suggests to me that the fuel pump on the motor is working just fine.----Perhaps test run with another hose and tank.----Fuel pumps are easy tio inspect and repair.-----I would never buy a new one !!

 

[saltchuckmatt]

the VRO has been disconnected for years by previous owner. Since i bought it 5 years ago its ran great and I've been mixing 50.1 in the tank.

the last 3 years it has been in the water all spring summer and fall. Basically ice out to almost freezing. and runs weekley or some times multiple times a week for cruising around or running to fishing spots.

What do the spark plugs look like after the no start happens?

 

[flyingscott]

Good luck with your motor.

 

[oldboat1]

Check and monitor operating temp. Look for 130-140F at the top of the head. 160 is overheating. May be due for a new impeller.

New fuel filter may be restricting flow. Try operating without the filter.

 

[saltchuckmatt]

the VRO has been disconnected for years by previous owner. Since i bought it 5 years ago its ran great and I've been mixing 50.1 in the tank.

the last 3 years it has been in the water all spring summer and fall. Basically ice out to almost freezing. and runs weekley or some times multiple times a week for cruising around or running to fishing spots.

Just throwing this out there. VRO, most people back when I had one anyway would just plug off the oil line and then run 50 to 1 in the tank. In fact omc included the plug. People are now installing regular pumps because they are much cheaper and because they don't trust the vro's. What I don't know, and maybe these guys do know if pumping the primer ball to test fuel pressure still works in the vro fuel pump.
Watch this video and I think if I was pondering a fuel pump problem, this is what I would do. Also, I'm assuming that that has not been done already.

 

[flyingscott]

Check and monitor operating temp. Look for 130-140F at the top of the head. 160 is overheating. May be due for a new impeller.

New fuel filter may be restricting flow. Try operating without the filter.

How do you have a 130-140 degree temp with a 143 degree thermostat? How is 160 overheating?
Definitely good luck with your motor.