40 hp evinrude bad miss cold, sometimes ok warm

[tomnort]

I recently bought a '91 40 hp Evinrude VRO on a pontoon. Ran perfect for several weeks until suddenly started badly misfiring at speed, wouldn't rev over 2000. Intermittent, but mostly won't rev when cold. Starts missing about 1800 or so. Somtimes will go briefly up to 3000 or so, then stumble. It's a bad, dropped cylinder stutter. If fully warm, sometimes (not always) revs normally, runs perfectly. I've taken to sneaking revs up to see if I can sneak thru the 2000 barrier. Have eliminated plugs, fuel filter, fuel line, bulb, tank, have cleaned out high speed jets, have been running Sea Foam, etc. thru it plus premium gas. I'm now looking at coil or maybe stator, thinking a crack or something closes when warm. Any wisdom or ideas on this? Lotta people stumped on this.

 

[Daviet]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Use a timing light and check both plug wires and see if you have spark on both cylinders.

 

[tomnort]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Since my timing light was last used 20 years ago (I'm still looking), I disconnected plugs to see which one was dropping. In neutral they were much the same, but under load, the top cylinder pulls past 3000 with no miss and the bottom one stutters past 2000. Below 1500, all is well with both connected.

 

[tomnort]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

OK, found my timing light, checked the lower cylinder which seemed to be dropping. Got good spark until it stuttered, then spark went away. Threw a new coil at it to eliminate that, made no difference. Will try the timing light with each plug disconnected to if anything jumps out. Then maybe new plug wires (cheap and easy). After that, I'm out of Schlitz; maybe look at stator, though several mechanics doubt it.

 

[Daviet]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Instead of throwing parts at it, get the factory manual and use the trouble shooting section to check out your engine. There are several components to your ign system that can cause your problem. Will probably save you some money and aggravation in the long run.

 

[fireman57]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

physically swap the coils and retest to see if the problem follows that coil. The new coils are packaged so that you have to put them together yourself and it can sometimes be a pain to get the wire centered on the post in them and the coil for the plug centered in the wire. They also sometimes back out of the coil unless you get them "screwed" all the way in. Take a piece of wire and measure the depth in the coil and make sure your wire is in that far. I fought one for a while on a 35 a few years back.

 

[Exotic4x4]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

My 70 HP is doing the same even after swapping coils try your kill switch circuit if not that try powerpack

 

[tomnort]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Coli is a single sealed unit - no assembly required. The aftermarket manual isn't much help here (don't have the factory one, I'll try to find one). Did another run with timing light; loss of spark goes with sputtering, but not consistent. Tried the upper (good?) cylinder alone, run good, then the lower (bad?) cylinder alone, cut out at 2000. Then I tried the upper again, and it quit at 2000 also (what the..!).

Most consistent result is roll along for a half hour, stop and chat with someone for 5 minutes (engine on or off), then resume, and it usually runs perfect for the duration.Someone here suggested lift pump (part of the $350. VRO pump), but it still smells electrical based on the timing light. I'm going to try to find someone who can gauge it up and go for a ride. Good suggestion on the kill circuit - I'll check it out. Has a rhythmic quality when it cuts out - bumps up and down 1 or 2 times a second.

 

[Rick.]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Your kill circuit would drop spark to both plugs not just one. I'm not certain how myself, but you need to trouble shoot the CDI components. Best of luck. Rick.

 

[tomnort]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Well. I think I have it surrounded. Had mostly looked in the manual for fuel issues. Closely reading the ignition section, I find my motor has a system called S.L.O.W., for Speed Limiting Overheat Warning. Basically a rev limiter that holds speed to about... are you ready?... 2000 rpm. This fits all my symptoms. Now just need to walk through tests to see if it's the temp sensor or ignition control. Will post final results when I sort it out. Thanks for the leads - pointed me in the right direction (I hope).

 

[tomnort]

Re: 40 hp evinrude bad miss cold, sometimes ok warm

Disconnected the temp sensor, ran like a champ for 30 seconds, than back to bouncing off 2000 rpm. Acted slightly differently, but same stuff. Now will go after checking the wire, then ignition module.