Help

[bstaten1]

I have a 2005 yamaha 40 hp 4 stroke. Just had carbs totally rebuilt, oil changed, oil filter, water pump, fuel filters, fuel/water seperator, New gas lines, lower unit drained and refilled, New spark plugs and wires, all of this done and a new prop added.

My problem is crazy. Went out saturday to the gulf drove boat almost 5 miles, ran flawlessly, shut off motor plenty of times and restarted without any issues.

Return to boat ramp at marina, put it in neutral and motor cut off. Unable to restart. Manually loaded boat.

Got home about an hour and thirty minutes, put water muffs on to flush lower unit and motor starts right up. This scenario has occured before.

Has any one had this issue before? My mechanic seems to be stumped on what is causing this to occur.

[99yam40]

We can only guess,
but maybe there is no spark when it will not run or it is flooded, or it is starving for fuel.

need to be checking things when it will not start.
so need to keep enough things on the boat when this happen so you can check

[TownsendsFJR1300]

When "it doesn't re-start", is it cranking / spinning over, just no start, or no crank at all?

Did you have to prime the fuel bulb for the re-start?

Sounds like it's loosing spark when it turns off by itself.

As noted above, more testing is necessary...

I would carry a known good spark plug and when the engine doesn't start, simply plug in the spare plug, ground it and crank to see if there's spark, rule that in or out...

I would also check for corrosion / tightness at all your electrical connections.

[bstaten1]

f40

When it does not start...yes it turns over no problem, yes sometime I will prime bulb a few times to tighten it up...however ifiam starting with warm-up lever I never touch bulb.

[bstaten1]

We can only guess,
but maybe there is no spark when it will not run or it is flooded, or it is starving for fuel.

need to be checking things when it will not start.
so need to keep enough things on the boat when this happen so you can check

So you saying it could be spark plugs- that were just changed? What would cause it to become flooded after simply running for a mile or two and then shutting it off? Excuse me for not having any mechanical sense- I am a RN and can save your life if needed but this kind of thing loses me...I just report it to my mechanic to view a different angle. After almost 2000.00 in repairs and problem still exists....well it's frustrating

[TownsendsFJR1300]

So you saying it could be spark plugs- that were just changed? What would cause it to become flooded after simply running for a mile or two and then shutting it off? Excuse me for not having any mechanical sense- I am a RN and can save your life if needed but this kind of thing loses me...I just report it to my mechanic to view a different angle. After almost 2000.00 in repairs and problem still exists....well it's frustrating

Not necessarily the spark plugs but everything else that makes spark... As well as the fuel system.

We're gathering info thru a computer screen, we're not hands on..

Testing when it acts up is what's needed...

Is your mechanic a Yamaha mechanic?

Did he hook up the engine to a lap top to check for any fault codes, etc?

After spending 2k for a fix that didn't fix it, I personally would find a certified Yamaha mechanic that's qualified. The very limited information we have makes a diagnosis almost impossible..

[99yam40]

The F40 has a fuel cooler I think that could cause excess fuel vapors to flood the motor if it was not cooling as it should. But that usually happens when run and shut off and then will not start. never heard of it shutting down a motor that was running.

you need to find out if there is spark/voltage to plugs or not when it will not start.
that eliminates some things, so you have an idea of what to chase

Checking to see if there is fuel in the carb bowls at least tells you the pump, tank,pick up tube,and lines are functioning to keep fuel to carbs.Fuel pressure test would be good also

then trying to figure out what is wrong with the carbs comes into play if everything else is good.

Just because carbs were cleaned dose not mean you did not contaminate them again with trash,water, or bad fuel.
and if so they need to be cleaned again

[rodbolt17]

the 05 F40 was a mercury .
it used unreliable Motorola electronics.
most likely a stator or pulser coil failure.
I would not rule out an ECU failure.
prestolite and Motorola basically killed the US market stuff.
Mitsubishi stuff just rarely fails.
you need to check for spark when it has failed.
over the years I learned to dread the merc Yamaha motors.

[bstaten1]

Thanks

Thank you all for your comments and suggestions. Its really appreciated. Will update when problem is discovered and fixed.