johnson 55 dies after running full throttle

[killemall1983]

ive searched dozens of forums and groups and not a single person can give me even the slightest answer.
this motor will start very fast. it will stay running forever in neutral. even at low speeds it runs fine, UNTIL i drive it full throttle.
once i drive it full throttle, and put it back in neutral it will die. then it wont start again unless i full choke it a few times then punch the throttle. once its been driven full throttle, it will never start the first time or run at low speeds again that entire day.
if i never use full throttle, like one lake where its no wake lake, it runs fine all day zero problems.
And the kicker is i have another boat, a tracker with a merc 40 that does the 100% identical thing

 

[racerone]

Is this a 3 cylinder 1968 / 69 model ?----A 79 2 cylinder ?----Model # must be posted.

 

[killemall1983]

Is this a 3 cylinder 1968 / 69 model ?----A 79 2 cylinder ?----Model # must be posted.

It's the 79 2 cyl

 

[racerone]

Test run with another hose and tank.----Perhaps install a new diaphragm in the fuel pump.-----And motors need a new water pump impeller about every 5 years.

 

[killemall1983]

Test run with another hose and tank.----Perhaps install a new diaphragm in the fuel pump.-----And motors need a new water pump impeller about every 5 years.

I've used different tanks on both with the same result

 

[racerone]

Does spark jump a gap of 3/8" or more on both leads?---And post the actual compression test values here.---What elevation are you running at ?

 

[killemall1983]

Does spark jump a gap of 3/8" or more on both leads?---And post the actual compression test values here.---What elevation are you running at ?

I haven't tested compression.
Ive ran it at 5000 ft to 7000 ft here

 

[racerone]

At those elevations you may need to change carburetor jets.----Consult you local friendly shop.----They may have experience / know exactly what to do , to solve this issue.

 

[killemall1983]

At those elevations you may need to change carburetor jets.----Consult you local friendly shop.----They may have experience / know exactly what to do , to solve this issue.

That's why I'm asking here. Mm only has a few boat mechanics on the entire state and maor are over 2 hours from me. The only one close to me charges 3x normal price

 

[racerone]

I am at 600' elevation.

 

[racerone]

You may need to adjust idle stop screw to prevent the stalling.

 

[killemall1983]

You may need to adjust idle stop screw to prevent the stalling.

But why does it idle fine at very first start? And nobody can show me how it where do adjust that

 

[racerone]

Sorry----I can not see , touch or hear your motor.----Trouble shooting must be done by you.