1983 Johnson 70 dies at full throttle

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
stoekd3
Posts: 11
Joined: Sun Dec 03, 2017 10:01 pm

1983 Johnson 70 dies at full throttle

Postby stoekd3 » Fri Jun 22, 2018 9:35 pm

I was taking my kids tubing, and the boat ran great for 10 to 15 minutes. Then while pulling them the 1983 Johnson 70 engine died at full throttle. The engine would start back up and then die again after three to fine minutes. I got her back to the dock and would start it with choke and it would run fine then put it in neutral and it would die.

Within the last two months, I have changed fuel lines, installed a new fuel tank, and put in a new thermostat. And I only run REC-90 gasoline.

My first guess [at the cause of the engine stopping at full throttle] was [a lack of] fuel supply, but having changed lines I wouldn't think this is the cause.

Could [the cause] be the carburetors need cleaning?

Or I guess it could be something with the fuel pump or fuel supply. Maybe bad diaphragm?

Thanks for any input

flymo
Posts: 130
Joined: Thu Oct 22, 2015 2:58 pm

Re: 1983 Johnson 70 dies at full throttle

Postby flymo » Sat Jun 23, 2018 5:07 am

Fuel pump is the most likely culprit. Carburetors are fine - it's not likely that all three got dirty between one run and the next. See if you can keep it going by pumping the fuel bulb. If that works, then the pump isn't pumping and you'll have figure out why. If it's the original pump, it could well be the diaphragm. Maybe you can find a rebuild kit.

stoekd3
Posts: 11
Joined: Sun Dec 03, 2017 10:01 pm

Re: 1983 Johnson 70 dies at full throttle

Postby stoekd3 » Sat Jun 23, 2018 12:26 pm

flymo wrote:Fuel pump is the most likely culprit. Carburetors are fine - it's not likely that all three got dirty between one run and the next. See if you can keep it going by pumping the fuel bulb. If that works, then the pump isn't pumping and you'll have figure out why. If it's the original pump, it could well be the diaphragm. Maybe you can find a rebuild kit.

Thanks I figure Ill put the muffs on and see if it has the same prob and will try pumping, I figure it has to be the pump --im looking online for a rebuild kit- thanks for your input!!

jimh
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Re: 1983 Johnson 70 dies at full throttle

Postby jimh » Sat Jun 23, 2018 12:59 pm

stoekd3 wrote:My first guess [at the cause of the engine stopping at full throttle] was [a lack of] fuel supply, but having changed lines I wouldn't think this is the cause.


There are many places in the fuel system where the flow of fuel could be obstructed:

—in the fuel tank, its filters, and its fittings;

—in the fuel lines, primer bulb, check valves, connections, and fittings;

—under the engine cowling in hoses, filters, screens, carburetor float valves, carburetor jets.

stoekd3
Posts: 11
Joined: Sun Dec 03, 2017 10:01 pm

Re: 1983 Johnson 70 dies at full throttle

Postby stoekd3 » Sat Jun 23, 2018 9:34 pm

jimh wrote:There are many places in the fuel system where the flow of fuel could be obstructed...


I agree I will check cowling hose and float valves: The fuel tank, water separator, the primer bulb and check values and fittings are all 3 months old. Its been running great until we started tubing/wakeboarding.

thx for the input will check tomorrow and update

stoekd3
Posts: 11
Joined: Sun Dec 03, 2017 10:01 pm

Re: 1983 Johnson 70 dies at full throttle

Postby stoekd3 » Mon Jun 25, 2018 1:36 pm

Update: Took out the [so far unidentified] boat today with my son so I could pump the [fuel] primer [bulb on the fuel hose to the 1983 Johnson outboard engine] while [my son was] driving.

[The 1983 Johnson 70 outboard engine] fired up first try and died after putting it in gear; tried to start engine again, and engine fired on the first try. We ran engine for three minutes while I was pumping the primer and engine died.

To gain speed seemed longer than normal—felt like a loss of power

The 1983 Johnson 70 fired up again, and we went back to the dock at low speed--didnt sound right but engine made it in. Tried to work on docking with my son and the 1983 Johnson 70 would turn off when he would go from forward to idle.

Do you have any thoughts [about the cause of these problems]?

I was thinking [the cause of these problems was a defect in the] diaphragm, but I'm not sure that is correct.