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Currently my boat motor has an annoying problem.

It actually started at the end of last season.
If I throttle back quickly from anything over 3000rpm to below 1500 the motor will quit.
This can get annoying, particularly when tubing, sking ect.

I can be @ 5k and back down quickly to 3k with no issue.
2500 to idle no issue.
When it quits , it starts back up easily.

The motor always starts easily.
Throttles up smoothly, no bogging down
Idles smoothly for hrs on end (trolling), runs full bore smoothly ,

The motor is a 1999/2000 Evinrude, 40hp 4strk.
The plugs have been changed,
I'm assuming its likely ignition related.

Any ideas were to look?

Dartee, It sounds like a fuel delivery problem. I believe that is a carburetor model and it sounds like the fuel bowl may be emptying as you throttle down suddenly. It may be time for a rebuild of the carb.
....Larry

Sorry Larry, she's an EFI
The reason I'm thinking electrical is when it quits its like turning off the key. No indication of being fuel starved.

You might also try checking all connections for the fuel line at the tank, engine, also electrical connections on the motor itself.
...Larry

Do you do alot of trolling??????


Efi models will have the idle air controlled by a valve or slide etc if this started last year was it at the beginning of the season or half way through or at the end????

Who does winterisation?????

There should be someway of monitoring IAC valve and see if it is working properly????If this gets sticky it can change the calibration of air at idle especially when throttled down quickly......

Does it have a water separating filter and is that replaced yearly????

Send me a pm with model ###

I have the same problem with my 1985 Johnson 2 stoke. It revs and coughs revs and coughs. i replaces the fuel line and bulb, ran a can of Johnson engine tune through it and installed new plugs this spring. It runs better but still does the same but not as bad.

Mark

mikemicropterus wrote: Do you do alot of trolling??????


Efi models will have the idle air controlled by a valve or slide etc if this started last year was it at the beginning of the season or half way through or at the end????

Who does winterisation?????

There should be someway of monitoring IAC valve and see if it is working properly????If this gets sticky it can change the calibration of air at idle especially when throttled down quickly......

Does it have a water separating filter and is that replaced yearly????

Send me a pm with model ###

Hi Mike

Yes lots of trolling.
I'd say it may have started mid season or closer to the end (I cant remember 100%)
Winterizing done by me... Lube, oil , filter, fog, stabilizer, crank oil, plugs in spring ect.

If by water separation filter you mean the fuel filter at the back RH side...nope.

PM sent with the model #

I had this same problem with my Evinrude 15 HP 2-Stroke. I changed the spark plugs, and used a gap 0.010 smaller than specified (0.030 instead of 0.040), and the problem went away.

Try some Sea Foam Motor Treatment for Small Engine Applications. It can be purchased at any NAPA store. I’ve included the Sea Foam website.

It Stabilizes fuel, Cleans carburetor, Cleans carbon, Removes moisture, Assures fast starts, Frees sticky rings, Restores power, Upper cylinder lube, Smooths rough idle


http://www.seafoamsales.com/motorTuneUp.htm

Good luck