2 stroke 40 HP outboard need help

I have a 2 stroke 40 HP outboard not sure what year it is. It idles fine but when yo get to about 3/4 throttle it starts to miss could the timing be out if it is how can i check it, any other opinions would be great thanks.

[dorf]

I'm guessing here and I'll bet that boats.net will respond, But ......2 to 1 carbs are clogged with the preticipate that ethonol leaves behind.

Drain the carb bowls, (maybe a dose of Sea Foam)(or similar stuff),clean the on board fuel filter or replace and get new fuel. Check the interior of your fuel lines and or replace.

Finally install a Yam 10 micron fuel filter and always use a fuel stabilizer year round.

Don't forget about new spark plugs also.

A Clymer manual will help tremendously.

Just my opinions but the above seem to work.

So you think its a fuel problem

[dorf]

It's hard to diagnosis from afar.

Checking fuel and draining carb bowls and cleaning fuel filters if haven't been done in awhile is the easiest.

Ok I took all 3 carbs off cleaned them all put all new fuel filters fuel line new gas still missing at 3/4 throttle

[dorf]

Shazam !!! That was fast....

How about plugs? and compression ?????

[reelnative]

pull them off again pull out all the jets and clean them really good, sometimes you need to run a tiny wire thru them to dislodge the gunk then use a good dose of carb cleaner and compressed air on them, it sounds like your high speed jet is clogged up, one last thing allways wear eye protection, if you are using the carb cleaner the right way you will see why you need the eye protection

took carbs off cleaned them cleaned jets still having same problem

High speed miss!

Don't mess around with cleaning old spark plugs. Do yourself a favor and invest in a brand new set every season. Also, check you plug wires and coil connections. Sometimes a high resistance due to poor connections can reek havoc on an outboard motor. I took my 25 hp mariner to a qualified dealer for a simple water pump impellar replacement. This required the removal of the starter and when they put things back together they left the main ground for all the engines electronic's loose. Fried my switchbox and rectifier.

Check all the electrical connections and pay especially close attention to the grounds on your motor, clean and use a good electrical grease on them. May help out. Sure can't hurt!

[boats.net]

What is the model number of motor and what is the rpm's when it starts to miss?

[saltyworks]

I had the same problem, it turned out to be a gasket on the fuel pump.

its missing around half throttle 3500 rpm model number 40ELK 6H4 L 404599

I took fuel pump apart looks good same with gasket any other suggestions

[dorf]

There are allot of issues here.

I believe I would invest in a compression gage and report back what your findings are....or....even....still a fuel problem.


Could be reeds or the ECU that controls spark etc, etc. or even synchronization and timing settings.

A Clymer book will help

Or best yet a professional marine mechanic.

Just my opinions though......

[boats.net]

Probably need to test pulsor coils and ignition componets to see if breaking down at high speeds.