1978 Evinrude 115HP Won't exceed 2800 RPM

[domint]

Hello, smart guys,
Y'all helped me a year ago - hopefully you can help me this time.
I have an Evinrude 115893 115 HP 1978 V4 outboard. It starts IMMEDIATELY when warm, and in 2 seconds when cold. GREAT motor on my 18ft Parker Center Console.

I was out Memorial Day and doing fine, pulling a tube, and suddenly the power dropped significantly. I fell off a plane, and "limped" home at 1/2 speed (even though the throttle was pinned down). An hour later, I limped out onto the lake, and then it kicked back in and behaved perfectly for another 20 minutes until I parked it. Now in my last 5 tries, it can't get up to power after that one last good spell. I didn't overheat (my overheat alarm works and did not go off) but it may have been warm under the load of that tube.

Compression is good : 125, 124, 125 and 125 psi. I bought a spark tester and realized I didn't know how to use it. But at idle with earmuffs on, I get good blue consistent spark which spans more than 1/2" of gap. The motor will start and run at idle with either the left 2 plugs unplugged or with the right 2 plugs unplugged.

When I'm on the water, momentarily choking it sometime seems to help, and sometimes seems to try to kill it. Inconclusive there.

This is a sweet motor that I stole for $500 and got a good year and a half out of it.. I think there's plenty more life in it.

Any ideas of what to test next? I have the manual, but I get lost reading through it, and I can't figure what to test next.

Thanks for any replies!

John

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

I forgot to mention, the timing at idle is perfect according to the manual. 5deg BTDC at idle and 28 deg BTDC at WOT (even though it limps at WOT now). I took the plugs out, and all 4 were wet after running for 5 minutes (maybe a function of just shutting them off. Looked OK to my uneducated eye, but maybe some black carbon, but not much, nothing dramatic.

Thanks,
John

 

[Daviet]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Fuel, spark and compression is what it takes to run. It sounds like the compression is OK. Spark should jump 7/16 inch. Fuel is a little harder to check. You could try squeezing the primer bulb when it acts up. If the carbs have not been serviced in a while, it might be time to overhaul.

Make sure you have the correct plugs and they are in good shape, maybe install new ones.

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Daviet,

Thanks for your reply.

The plugs have fewer than 10 hours on them and look fine. When I squeezed the bulb at WOT, it was already hard. Fuel/water separator (which I guess is also a filter?) is less than 10 hours old also. The fuel is 50:1 mix, done at the gas pump (1 pint of oil to 6 gallons of gas). All fresh within the last month.

I had the carbs as apart as they could get, and I did get some gunk out of the high speed ports (there were 4 of them). All 4 were probably 80% obstructed. Now they are clean and the three jets into the body that they feed are clean and flow well. Still won't get up to speed. Other than that, the carbs were clean - bowls, etc. I have trouble buying a fuel issue since it happened so suddenly.

I have replaced all my fuel hose with ethanol-resistant line, and the screen filter has always been clean as a whistle.

I tried to idle in the dark and saw no spark jumping. I read about that on one of these posts...

I'm just a shadetree mechanic, if that. (Worse yet, an engineer who likes to think he understands internal combustion...) I'm scratching my head.

John

 

[emdsapmgr]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Ignition components tend to fail when they heat up to normal operating temps. You can easily test for dropped spark (when it seems the hp is down) by checking each plugwire with an inductive timing light. Make sure the engine is warmed up and under load. The flashes in the light will indicate misfires, intermittents and non-firing plugwires.

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

EMD,

Thanks for your reply.

I have an inductive timing light, so I can do the test you describe. Do I understand you to say that I am looking for irregular timing light flashes off of each spark plug? And I guess I have to do this on the water, huh? Not with earmuffs and a garden hose?

I'll believe that this problem was heat-related to start, but now it does it on a cold engine, fresh from the dock. So, assuming we're barking up the right tree here, the theory is that the high heat caused a failure in a power pack or a coil or something?

John

PS - I hope the sapmgr in your name doesn't indicate that you are an SAP manager. I can't imagine a worser fate...

 

[emdsapmgr]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

When components start to get weak, they break down when hot. Later, they will break down when cold, too. You stress the engine the most when it is under load (like idling in gear at the dock.) Not a problem to check it on the trailer, though. You are looking for strong, steady, rhythmic flashes from your light. Anything else and you may have a problem. It could be a coil issue, but more likely the power pack, timer base or stator. All expensive items, so spending some effort to diagnose is worth your time. You are correct, I was a SAP mgr, in a prior career.

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

EMD,

Thanks for your reply again.

I was reading on the procedures for testing the timer base, etc. from the manual. It sounds like most of them happen with the engine off. I guess I'll try them tomorrow.

Right now, I'm leaning for a problem in the timer base. The problem seems to begin when I advance the throttle up to the point where the timing starts to advance. As soon as the timing ring thing (timer base?) starts to advance, the engine starts sucking wind...

But I'll confirm with tests and post results.

John

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Assuming it's the stator or the timer base or the sensor, should I just replace them all while I have it apart? Are all these parts likely to be weak with age? Will my replacements parts be "new"? Or just as weak? Would I be wasting money on something that doesn't need fixing?

 

[emdsapmgr]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Before you get into replacing everything, you should be sure you are actually losing spark and which plugs are affected by spark loss. The power pack is a likely culprit and some investigation there can be worthwhile. The nice thing about your engine is that it has two power packs which can be interchanged to validate spark capabilites of the ignition sytem between the two heads.

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

EMD,

Thanks for your reply. I tested the "charge coil" which I guess is the stator coil. It reads 300 ohms, but the book says it should read 560 _/- 75 ohms. The manual says replace it, but I'm not sure 300 ohms is wrong - I see 2 different stators online, a 10 Amp for power Tilt and Trim and a 6 amp for manual tilt and trim. I have manual T&T, so I should have a 6 amp stator. And 300 ohms is about 6/10 of 560.

Am I thinking correctly? Does my stator need replacing?

I'm about to head out to the water to tinker some more, try some spark tests at WOT, different fuel, etc.

 

[emdsapmgr]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

My 77 manual says 630 ohms +- 75, so you are looking at the right figure for your 78 model. Did you get an infinity reading on both coils? I am not a fan of condemning based upon ohm readings and prefer to check voltage outputs myself. Unfortunatley, your year service manual does not indicate a votage output test for your year. (usually later models have peak-reading voltage tests: usually 150 volts or higher.)

 

[domint]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

EMD,
Thanks for your continued interest and help.

A buddy and I played hookie from work and went out on the lake today with this boat, and (I think) we got it figured out.

The timing was good at idle and WOT, the spark jumped a 1/2" gap tester at idle and WOT on all 4 cylinders, blue sparks, mo missing, nothing.

My buddy used the manual choke to apply a different level of choke-itude while we were at 2800 RPM and WOT, and it planed up and went to 5000 RPM! Thinking I had bad gas in my main, under-the-deck 60 gallon tank, I filled my 6 gallon reserve spare tank with fresh gas, new oil, and it went back to the same problem (2800 RPM).

Turns out that the quick disconnect on the fuel line (that connects the fuel line to the motor itself) was kinda sorta flaky loose sometimes, and it was breaking the vacuum in the fuel system. Sometimes it would "catch" and the boat would run fine, then we could turn and the fitting would change position slightly, make the line lose vacuum and fall off the plane. The reserve tank did the same thing with a different line and quick disconnect, but I remember that I bought them both aftermarket from WalMart on the same day. Once we had that figured out, we could reproduce the problem at will, and fix it at will. We ran the boat dry out of gas intentionally, and went back to the ramp on the reserve tank.

So guess what part I'll be ordering tomorrow!

I really appreciate your advice and help on this one.

Stay upright and dry!

John

 

[Sandmedic]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Thank you for the idea.. We just got our engine back form the shop, had it rejetted, carbs all redone, new gasket heads, plugs... the works.. took it out twice for less than an hour.. amybe 1.5 and she ran fine.. Today took all the kids out for one last run of the season and it did the exact same thing yours did.. running great then all of a sudden I cant get it past 3000 RPM WOT.. AND she kepts flooding..I was reading your post and then i remembered, we changed half of the fuel line( the side that goes into the engine) out last night to make it longer and i was worried the clamp wasnt tight enough and it would leak.. Ill change it back to the old one in the Am and give it a shot..

 

[jayyyy]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Don't forget about the fuel pump. They wear out especially with todays fuel. I had a johnson 115 that had similar symptoms your describing, turned out to be the fuel pump.

 

[Sandmedic]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Thaks! Got it coevered. right before we took it into the shop i replace it becasue the check valve inside had gone bad, so its brand new. We were having flodding and stalling issues and swapped out the fuel lines ( for shorter, newer ones).. Will give it a shot tomorrow and see if new lines fix our issues...

 

[emdsapmgr]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

Consider another alternative. Remove the hose barb from the engine end of the fuel hose. Remove the hose barb in the lower cowling and it's hose to the fuel pump. Run the fuel tank hose end into the cowling where the old hose barb used to be. Connect the fuel hose end directly to the hose barb on the fuel pump. End of issues with the fuel connectors. Make sure you use a sweeping bend inside the cowling so the fuel hose does not kink.

 

[Haffiman]

Re: 1978 Evinrude 115HP Won't exceed 2800 RPM

How are your spark plug wires?
On that engine they must be clamped properly tight to the cylinder head.
If any of the wires gets to close to the lower cowling latches, the cylinder(s) will drop out!
If your problem reoccur, try running without the cowling.