Merc 40 hp tracker dies after running full throttle

[killemall1983]

So i have an incredibly frustrating problem.
I have a mercury 40hp 2 stroke.
When i test it at home it starts instantly.
On the water it starts instantly the first time.
I ran it full throttle to my fishing spot. ran great, ran 25mph the whole way.
parked and fished for a bit. started up again instantly.
Then i went to another spot, fished for a bit. then it wouldnt start on its own and i had to run the throttle to get it to start.
Then it wouldnt idle. if i backed off the throttle at all, it would die. i couldnt put it in neutral.

Heres the kicker. i have another boat with a johnson 55hp. it does the IDENTICAL thing. 100% identical. starts instantly. runs about 2-3 starts then wont start or wont hold idle.
Is there something about running the throttle or stopping the boat that im missing to avoid this? how could 2 entirely different boats have the idencial problem? its super frustrating and i cant even fish because they both do the same exact thing.

 

[Mad Dog 2]

So i have an incredibly frustrating problem.
I have a mercury 40hp 2 stroke.
When i test it at home it starts instantly.
On the water it starts instantly the first time.
I ran it full throttle to my fishing spot. ran great, ran 25mph the whole way.
parked and fished for a bit. started up again instantly.
Then i went to another spot, fished for a bit. then it wouldnt start on its own and i had to run the throttle to get it to start.
Then it wouldnt idle. if i backed off the throttle at all, it would die. i couldnt put it in neutral.

Heres the kicker. i have another boat with a johnson 55hp. it does the IDENTICAL thing. 100% identical. starts instantly. runs about 2-3 starts then wont start or wont hold idle.
Is there something about running the throttle or stopping the boat that im missing to avoid this? how could 2 entirely different boats have the idencial problem? its super frustrating and i cant even fish because they both do the same exact thing.

Water in fuel? Drain fuel filters into a glass jar and let it sit see if water separates out.
You could have a fine mesh screen on the pick up tube in the tank that gets clogged after running a while?
I work for a marine contractor most of the O/B problems were water in the fuel.
I liked to drain the carburetor’s, get a fresh tank with fresh gas (ethanol free), flush the fuel line (with the hand primer) with fresh gas and try running the O/B again. If the problem goes away then the previously used fuel tank is probably the problem.

When a crew went to a new job site I tried to provide a new fuel line assembly as a spare as a back up.

 

[killemall1983]

Water in fuel? Drain fuel filters into a glass jar and let it sit see if water separates out.
You could have a fine mesh screen on the pick up tube in the tank that gets clogged after running a while?
I work for a marine contractor most of the O/B problems were water in the fuel.
I liked to drain the carburetor’s, get a fresh tank with fresh gas (ethanol free), flush the fuel line (with the hand primer) with fresh gas and try running the O/B again. If the problem goes away then the previously used fuel tank is probably the problem.

When a crew went to a new job site I tried to provide a new fuel line assembly as a spare as a back up.

I dont think its likely. this happens with 3 different gas tanks. 1 of which works fine on my 4 stroke merc.

 

[killemall1983]

Also something to add,
both boats run fine if i never go full throttle at all. if i just leave it at trolling speed the whole time, it runs perfectly fine all day.

 

[cyclops222]

Head gasket starts leaks after WOT long runs.
WOT .....kills engines.

 

[racerone]

Any pictures / model # / serial # of this tracker?----- Is there a head gasket on this 2 stroke 40 HP ?-----Why would full throttle " kill " an engine ?

 

[cyclops222]

Does WOT running reduce the time between breakdowns ?
Probably cooking the ignition system parts.

 

[killemall1983]

Does WOT running reduce the time between breakdowns ?
Probably cooking the ignition system parts.

what is WOT? i have never heard that term before.

 

[killemall1983]

Head gasket starts leaks after WOT long runs.
WOT .....kills engines.

what do you consider a "long" run? this is maybe 5 minutes of driving

 

[racerone]

Motor can run a WOT ( wide open throttle ) all day long.-----These 2 strokes can handle it with no immediate issues.

 

[cyclops222]

2 different engines. Both driven the same way. At WOT speed.
You have your reason. Why both engines have the same problem.
WOT is wide open throttle. Also called full speed.

 

[Mad Dog 2]

2 different engines. Both driven the same way. At WOT speed.
You have your reason. Why both engines have the same problem.
WOT is wide open throttle. Also called full speed.

I would prioritize a engine and troubleshoot it as a individual problem.
But you need to focus and fix one O/B at a time.
In a orderly manner swap fuel systems, drain the carb, fresh fuel, run on a portable tank, compression test, follow troubleshooting chart in outboard engine manual……..
(I just cleaned a carb on a small Honda I did not think it should need, starts right up now. It would not start, not firing but a whiff on either it would fire. So I knew the problem was fuel related.) Use either with restraint especially on 2 strokes no oil/lubrication in either. 2 stroke engines need oil to lubricant the cylinders walls to prevent scaring and engine damage.

 

[killemall1983]

2 different engines. Both driven the same way. At WOT speed.
You have your reason. Why both engines have the same problem.
WOT is wide open throttle. Also called full speed.

That isnt a reason. why would both engines, designed to run at high rpm/ full throttle, not work purelyl because of that? Full throttle does not cause damage.

 

[killemall1983]

so literally nobody has a single real reason? the only reason on the entire internet is because i used it full throttle?

 

[racerone]

The internet cannot see , hear or touch your engines.----Difficult to trouble shoot from 1654 miles away.

 

[airshot]

Need make, model and real compression numbers before and after the engine fails. When you come off of a wot run, do you shut off the engine or let it run at idle for a little while before shutting it off ?? Get a spark gap tester and check spark before then again when the engine acts up. When the motor acts up, have you tried pumping the squeeze ball to pump more fuel to the carb ? I would still check your fuel for water, easy to get bad fuel today right from the gas station!!

 

[airshot]

so literally nobody has a single real reason? the only reason on the entire internet is because i used it full throttle?

Need some test results otherwise just guessing.....

 

[chrisgt]

Is this the same as the mid-90's through early 2000's mariner/merc? If so those don't have headgaskets (at least the 2 cyl version doesn't), they're really simple engines.

Do you have grey fuel hose with the inner plastic liner? The liner comes loose and randomly stops the flow of fuel killing the engine. If you have grey fuel hose throw it all in the trash and see if new hose solves the issue.

 

[airshot]

That isnt a reason. why would both engines, designed to run at high rpm/ full throttle, not work purelyl because of that? Full throttle does not cause damage.

Unless there is another issue where running at wot makes the problem worse !! Your issue could be a number of different problems, only carefully precise testing will solve the problem. Often things like yours could be more than one issue....we can guess all day long, but actual answers take tests...