Anyone here got the skills (or a person you'd recommend I talk to?) to help me through this? Here's the deal:

PROJECT: 1997 Mercury 40hp (2-stroke/4-cylinder)

SITUATION: Starts/runs well but after running a while (sometimes an hour or more) it begins to lose power at full throttle... It *feels* like a situation where you've forgotten to open the vent on your fuel tank, because it happens fairly dramatically, you're cruising at 4000 RPM, then it just drops down to 1500...

I'm suspecting an ignition issue, going to go through the coils tonight (they look good by inspection)... Next step is to look at the magnets/Stator under the flywheel...

I've got access to an impact wrench, but don't have a flywheel puller/etc... Can I go the next step here myself/with modest investment in tools? Or am I out of my depth? I have the Seloc guide and am reasonably handy, but am inexperienced so looking for sage wisdom!

Thx,

B

this maybe no help, but have done a youtube search on how to pull a flywheel?

there's quite abit of info and tutorials on YT.

Had to pull one off of my 225 Evinrude. They can be an absolute pain but I would guess that the smaller wheel should pull a little easier. Have a puller laying around if you want to borrow it. Other two things that come in handy- rubber mallet and a torch if it really won't move. Good luck.

Perhaps a little more troubleshooting might be in order before you consider removing the flywheel. I like to perform all possible minor troubleshooting before ripping into things to deeply.

Is your tank built in, or remote? If it is built in consider that many built in tanks have screen on the pickup tube which can clog. If you are using remote tanks have you tried changing tanks when the symptoms occur? Does it have an inline fuel filter? Many engines have a inline fuel filter under the hood, and some installations have a canister style filter mounted in the outboard well or, on the inside of the transom.


Good luck

try a different hose if you are using one. I had a hose with an inner liner that would suck shut slowly.

Typically it is not an ignition issue. Ignitions usually work or they don't. Loss of power as you describe sounds more fuel system related. Could be dirty carbs, plugged filter, or faulty tanks or venting. I would go through the fuel system completely before I ripped into the ignition system. A spark tester will tell you if the ignition system is working correctly or not. If the fuel system checks out, I would then start with a compression check of the motor and if that checks, then it would be onto the ignition.

Chuck S is a Merc guy, he might have some insight for you.

I would agree 100% with those who say try everything else first. Pulling off a fly wheel without knowing why or how sounds like a good way to end up with an engine laying around for parts. Outboards either run or they dont assuming fuel and basic stuff is taken care of.

Been there done that.

It sounds like it is going into "safe mode". My Yamaha was doing that. It ended up being the oil sensor. Might want to check those things first. There is a way to bypass those sensors. Contact a mechanic and ask about it. Does your alarm work?

All the feedback here is really helpful/appreciated...

The basics of the fuel system seem correct (new filters/etc) but I appreciate the "try igintion last" advice... I'll work thru that with more care... If I can reproduce the fault (which is not simple, I generally have to be on the water, it's hard to reproduce in the driveway) -- what suggestions do y'all have for testing the "fuel" theory -- squeeze bulb and see if that changes things? Obviously if I can get it to happen, then do a 'test' to indicate if we're fuel or ignition, i'll have made progress.

I'll read up on testing the alarm too, "safe mode" is an interesting theory as well!

FWIW, my endeavor into the ignition system was inspired by THIS THREAD

Another vote for a fuel delivery problem.

As simple as it sounds, squeezing the bulb when the problem is happening will tell you a lot. You should be able to tell if it is "normal" or empty (starved) for fuel and go from there. If you're lucky, you'll squeeze that bulb, feel the fuel go through it and the engine will pick right back up. At that point, I'd say you have some form of fuel blockage that should be easily fixed.

Another question I have is AFTER the event happens (dropping from 4000 RPM to 1500 RPM), can you shut the motor off, restart it, and immediately get it back to 4000? Or does the motor have to "sit for a while" before the restart and running it to 4000 RPM would even work?

my thought is (I am an old small engine mechanic) I suspect a fuel problem. Clean all the screens especially the one at the fuel pump and is there one in line? If so then replace it. Then check fuel tank and look at pickup tube in the tank. Does the fuel bulb go flat when running? if so then check the venting on the tank.

Ignition is electronic (99% sure of this) it works or it don't but if it gets hot it will shut down and when cooled it will allow a restart. Flywheel key could be possibly sheared or partially even, do not know if you can pull flywheel nut and inspect or if it is a 1/2 moon key and is hidden. Than can also somewhat do the symptom your having.

Just my $000.02 worth
GFN

I think u have a bad coil, u have one for each plug one of them is bad

That is a reasonable answer!
Run it till it happens. Then with a simple light cruciut tester probe the coil wires. Find which one isn't working. Then switch the power feeds to that coil. If the dead coil moves it's your chi box. If it stays the same it's the coil. I've had a box do that.once it's warm it would shut down a cyl. Like a coil will do.

Richard and I ran into a similar problem last fall, and we found a pinhole leak in the fuel line...at high RPMs as it was really sucking gas it would suck in enough air to kill the performance.

Changed out a $30 fuel line, problem solved.

Fish on...

Todd

You mean a timing light?

I did pull all the coils last night and inspection and testing (resistance) on the primary & secondary and they all are in-spec. Again the challenge is the failure is intermittent/when warm, and that's hard to get to in a driveway setting... I believe running at 3000+ RPMS on flush muffs is likely to do more harm than good, so I'm going to have to start visiting the lake a bunch...

When it's failed, it's not failed in the way I typically think of for fuel-starved. The RPMs just drop down in a step and stay there. It's not like it's going up/down/up/down as fuel supply surges... That's why I'm focused on ignition.