1977 Evinrude 140 HP Bubble Back runs fine on hose but not in lake

[MaPaHa]

My '77 Evinrude 140 HP Bubble Back will run fine on a water hose attachment but wont hardly start and idle on the lake (it cranks over fine). If you trim it out high it will start and you can get it going but it has a severe loss of power taking off. Once it gets planed out it runs OK.

As I see it the main difference is the back pressure of the water against the exhaust.

I've got to get it on the water or in a barrel to re-create the problem and the first thing I'm going to do is a spark test along with a timing light around each wire as I'm testing that cylinder. I believe I'm going to find a weak or random spark. If I do, would this make since why it wont run in the water but OK on a hose?

I think this motor has two power packs (one for each side) but I haven't looked at it in a while. I fired it up on a hose and some friends took it out and had trouble. Is there any common problems with the ignition system on this model? I've got a slightly older 85 HP (parts only) with the same looking ignition modules so I was thinking about swapping one out if the spark test fails.

I had erratic spark problems with my '96 175 HP Johnson with nearly the same symptoms, but also dying, and changed the single ignition module and all 6 coil packs and it fixed it.

Thanks for any help on this one

 

[henleyhale]

What speed do you idle at on the muffs?

 

[MaPaHa]

I don't recall exactly but it seem a little fast from the sound. I haven't used this boat in over a year and didn't remember having any trouble with it so I just fired it up to make sure the battery was charged and that it would run. It cranked right off and sounded good maybe a little fast but I didn't pay attention to it. Now that I think about it I may have run a spark test on it and thought there was a problem. I was fighting two motors with similar problems and got them mixed up I think.

I just picked up on your comment about idling faster on the hose than water on the other thread similar to mine. I'd say it would be about right but I'll check it and see.

 

[emdsapmgr]

That engine will seem to run just fine, when sitting on the trailer. It will appear to run ok with only 2 or 3 cyls firing. You really can't tell. You need all 4 cyls firing when the prop is buried under 20" of water and it's in forward gear. You can do a simple test to check for spark when the engine is running: the cyl drop test. Pull one spark plug wire of a cyl. See if the engine rpms slow somewhat. That's normal. Re-attach that wire, then go onto the next cyl. Any cyl that has no rpm drop may not be firing. Also, when running, you can use an inductive timing light to check for spark on each plugwire at the plug. The flashes from the gun will show intermittents, non-firing, weak firing. Best to test for ignition problems after the engine has completely warmed up. That engine has one power pack.

 

[MaPaHa]

Thanks for the input. I'll try the spark test, cylinder drop test and the timing light test one at a time. My trouble at this point is that I'll have to drive a bit to get to the boat rather than working on it at my shop.

If the tests point towards ignition issues, what are the possibilities (probabilities) other than the ignition module? I'll probably rob the ignition module off the 85 HP and take it with me and was considering buying a module from my local Evinrude dealer and having it on hand if the used one works. I don't think I would trust the used one long term. Is there any other parts I should rob off the 85 before I make the trip? Is there a "most likely" cause for bad-weak-erratic spark on this model? I usually don't toss parts at something unless there's a good reason but with the travel involved I need to take as much as I can with me.

 

[emdsapmgr]

What year is the 85 hp? 1977 or older?

 

[SparkieBoat]

follow the instructions in my sig below.

 

[MaPaHa]

Yes, the 85 is an older but I'm not sure how much older.

Thanks for the troubleshooting guide.

I'll re-post what I find out.

 

[emdsapmgr]

The 77 85 hp and older use the same single power pack. It is was a 78, it uses the newer dual packs. You should be ok.

 

[racerone]

They all " bark " and spin on a hose.------To the untrained ear they sound just fine.---------Do a compression test on that motor.