Yamaha built Mariner 40hp, 2 stroke...stalling under a load

[The Milkman]

OK guys...I need some help here. I have a 40hp, 2 stroke Mariner...but the motor was built by Yamaha ('82 or '83). When this problem started, the boat ran great down the lake for about 5 miles...then started to slow down until it just bogged out. Very hard to restart...got it started...ran about a mile, then bogged out. Got the boat home and when I put it in the water, it'll start right up, using my "throttle only" button on my shifter/throttle remote. I don't have a tach, but I'd say it's doing about 2000-2500 RPM's when doing that.

Then, when I drop the throttle back down to idle, it runs rough, sounds like it's missing, etc. Put it in gear, and it just bogs down and stalls.

Here's what I've done, as I was sure I had a fuel/carb delivery problem:[*]New Attwood, self venting, fuel tank - makes no difference if the cap is on or off, so it's not a venting problem[*]Brand new primer bulb and hose[*]Rebuilt both carbs with carb kits...used carb cleaner and compressed air. When I turn the carb upside down (off of the boat) and blow through a fuel hose, no air comes through, so I know the needle is setting...air comes out when I turn the carb right side up[*]New fuel hose from the carbs, going back to the fuel inlet (where the primer bulb hose connects)[*]Rebuilt the fuel pump with new gaskets and diaphragms (didn't change out the check valves, but they look to be good)[*]Checked the fuel filter to make sure there was no blockage/debris

The only thing I haven't done is replace the connector on the end of the primer bulb line, nor did I replace the connector on the outboard, where the fuel tank line connects to.

I was certain it was a fuel delivery problem, but now I don't really think that's what it is...I don't know much about Reeds, etc...hoping it's not that.

I have also:
- Checked compression - approx 125 psi in both cylinders
- Put in TWO new sets of spark plugs to make sure that wasn't an issue...has a strong blue spark on the spark plug when I ground them to the block and turn the motor over.
- Performed a Linc and Sync, per my Seloc manual...twice...to make sure I did it right. I suppose it's possible that the manual is wrong, but everything else in the manual is pretty spot on, and the photos in the linc and sync section are accurate.

I'm kind of at a loss here and am on the verge of taking it to a shop. I really don't want to spend that money, but I may have to. Any other ideas?? I haven't changed the spark plug wires, and haven't really checked anything with the ignition system to make sure that's all working properly.

I'm open to any ideas at this point...REALLY!! When making suggestions...remember...the problem was kind of intermittent and erradic at the beginning, but now it's constant. The motor is doing the EXACT same thing as it was doing prior to doing all of the things that I mentioned above, so I think the carb/fuel pump/spark plugs/compression/timing/primer bulb/fuel tank, etc are out, as possibilities

[boats.net]

Need to check spark at time engine dies.

[alan mariner 40]

re staling under load

hi guys , i had similar problem i did the same as you rebuilt carbs etc , the few things or combination of things i found cured mine was 1 ) i had a new fuel tank and line so thats ok i thought but NO it had a air leak as the manufactured crimping of the fuel line was poor check ALL pipes 2 ) was the trigger /pulser coil under the flywheel was braking down under load , it was ok when going slow/medium speed but failed when i opened to WOT it couldnt produce the correct amount of spark/current so the speed dropped and it stalled and 3 ) was remove your carbs undo your float chambers one at a time turn upside down the float should be horizontal with the casting where the float bowl screws into if it is not bend the tags on the float until it is this will allow more fuel into the chamber my floats werent horizontal so i bent my tags so they were (both to match ) i reassembled it and straight away my idle was faster which alllowed me to lower the idle speed by the idle screws this prevented cutting out on idle (remember a engine needs 3 thing to work fuel , air and spark hope this helps Alan

[alan mariner 40]

when a coil brakes down it usually is inntermitent so it works fine one minute then it plays up the next whenever it wants or when you ask it to work hard ie at WOT etc and its great in neutrel reving it sound great beefy etc but that is NOT under load , load is when it has to work under demand / force to make prop push the boat and it cant cope so it cuts out , il try to explain , there are 3 guys each has a weight to lift, ones a strong man ,ones a middle strength guy , and the 3rds a wimp each have a weight they can lift, heres the thing the middle strength guy can lift his own weight AND the wimps but NOT the strongmans so as long as hes only asked to lift the lighter weights alls good but when hes asked to do more and lift the strongmans weight he cant cope its to much for him and he brakes down under load (the weights represent the increase of speed / load /demand /effort required of it whatever you want to call it , and the 3 men represent the coil as a whole )