Logo
FULL SITE MENU

1975 Johnson 85 hp No power under load?! Please help!!!!

J

JDBOXER02

Member
Ok so I have a 1975 Johnson 85hp with a 13 1/2" 20p prop on a 1984 Stratos 179 Fiberglass bass boat. I pulled the Evinrude 140hp off because of a bad cylinder. So here's a little background of what I know, and the issues I'm having.

Compression check results:
Cylinder 1: 105psi
Cylinder 2: 110psi
Cylinder 3: 100psi
Cylinder 4: 108psi
Compression test done with all plugs removed and fully charged battery.

Spark test results:
All 4 cylinders have a strong Blue spark with a loud "snap" when tested at a 7/16" gap.

Fuel tank has been cleaned thoroughly and all fuel lines replaced, as well as having fresh fuel.
Both carbs have been completely rebuilt. Idle and high speed jets were removed and all pathways cleaned thoroughly and blown out with compressed air.

Motor starts easily and runs good on muffs and in water. But when I try to run at WOT I get a top speed of about 3-5mph and the rpms are definitely not at 5800 rpms. Not sure of actual rpms because I do not have a tach. I'm having an issue with one of the cylinders and cannot figure it out. The motor has an intermittent "miss". Sounds kinda like this when running.....Baaaaaaaaaaaadadaaaaaadaaaaadaaaaaadadadaaaaaaaadaaaaadaaaaaa etc. (I think you get what I'm saying) So what I decided to do was pull the plug wires off one at a time while the motor was running and see which cylinder had the least or no effect when removed. The results of that "test" was that cylinders 1,2,and 4 all made a significant change in the way the motor ran, but cylinder 3 made absolutely no difference at all. The only difference when I remove or connect the spark plug on cylinder 3 is the tone of the exhaust. The way the motor runs isn't improved or worsened when the plug wire is connected or removed. I checked to verify that it is sparking when connected to the plug, and it definitely is. That cylinder has good compression, spark, fuel, and air but doesn't seem to be contributing to the performance of the motor. Also did a decarb on the engine and when spraying Sea foam into the side of the bottom carb for that cylinder there was no change in the way it ran but the motor would bog as I sprayed into the carbs for the other cylinders. I'm lost on this and not sure what to do next.
Also the Port side head is getting too hot. I had it hooked to the muffs and pulled the tubing off both heads that runs to the thermostat/vernatherm housing and had water flowing freely from both heads. Can the vernatherm cause the port side to not flow while allowing the starboard head to flow like it should?
The last issue I noticed was that the motor runs good when trimmed up but as soon as I lower it down and it tilts past being level(actually leans backwards) it instantly runs worse?! Not sure what is causing that. Please, Somebody help me figure this thing out. I'm very mechanically inclined, it's what I do for a living(Industrial Maint. Tech), but I'm fairly new to the world of outboards. Thanks in advance for any and all advice and suggestions.
 
I thought the same about the prop being too much for this motor with the load it has to push. I failed to mention that I have pulled the inspection cover off of all the cylinders and inspected each one of them. No scoring and rings all look good. I figured that since the compression is good on all cylinders, i wouldn't be having this problem, but here I am. Is it possible for this cylinder to be firing out of time? I'm not sure if it's even possible for one cylinder to fire out of time if the rest are correct. I'm at a loss on this one.
 
You sound like you are sharp with this stuff.....
If you think #3 is firing out of time, simply mark TDC for #3 on the flywheel, and put a timing light on it to see.
At idle it should flash at or near TDC, at speed it will flash somewhere before TDC.....depends on RPM and your particular motor spec.

While there, double check for free operation and full movement of the timerbase under the flywheel. No sticking, linkages moving the TB thru
it's range, etc.
 
Reed valve problem ??------------Do this test.--------At full throttle out on the lake , look into the carburetor bores.------------Use a STRONG flashlight and compare fuel coming up the main nozzle.
 
Last edited:
Finally, a couple of tests that I can try that I haven't already done. I brain farted on the timing for #3, wasnt sure that b it was even possible to have happen but as soon as i read ur reply, daselbee, i did the ol' palm to the face routine. Sorry for the late reply, I work nights and was sleeping during the day. I'm off for the next three days so I will get these tests done as soon as possible and I will post the results. Thanks to both of you for all of your help so far.
 
Racerone, I considered a possible reed valve problem too but as I'm new to outboards I'm. Unsure of how to test for that problem. I'll do the WOT test but the cylinder not functioning is happening throughout the entire rpm range. Even if I spray something directly into the carb that should go into that cylinder, it makes no difference. Yet the plug is completely soaked, like the other 3.
 
While you have your timing light out, crank her up at night, and point the timing light right in front of the carb throat, individually for each cylinder.
You will see dancing droplets of fuel, or you are supposed to anyway. They will be suspended in air due to the strobe of the timing light.

So, compare each carb throat. Hopefully you will see all 4 the same. If so, the reeds for #3 are OK.
If #3 has excessive blow out of fuel droplets by examination with the timing light, then possibly reeds.
The thing that is pointing me away from reed problem is the fuel soaked plug.
 
Well I just did the timing light on cylinder 3 and it's dead on. Also chcked the carb throat for each cylinder and they all have a fairly equal amount of fuel coming from the tiny holes in front of the butterfly valve. So I assume there's no reed issue either.
 
I will pose a question. Could very low crankcase compression cause this non-contributing #3 cyl to behave dead, but still allow a fuel soaked plug?
Anybody want to speculate?
 
I wish u were right about it not telling me anything, dasalbee. First inspection showed no scoring on the side of the piston or in the small arwa of the cylinder wall that can be seen from the small inspection area.upon further investigation I unfortunately discovered that 1/3 of the top piston ring was missing. It happened to be on the side of the piston that I couldn't see and still had spring to it when I pressed it in to make sure it wasn't stuck. When I noticed that there was at least a small amount of the ring missing, I pulled the head. Then I discovered how much of the ring was actually missing. Weird thing about it, there is only one spot on thetop side of the cylinder(towards flywheel) that is scored. And it's not so bad that a light hone wouldn't take care of it. The bottom ring is still completely intact. Also discovered a LOT of water is getting into cylinder#3. I'm still curious how I vould get a good compression reading with a broken ring and a leaking head gasket?! While checking the head and head gasket for damage, to determine the cause of the water leak, I discovered the remains of the piston ring. It is embedded into the flat surface of the head, about 1/4" from the inside metal ring of the head gasket. How did I still have "good" compression?
 
Well! So great...you found a serious problem. I too wonder why the compression testing on that cylinder was OK.

LOOKS LIKE A REBUILD IS in your near future.

Good luck with it.
 
I'll be finding a replacement motor. A 1975 Johnson 85hp is not worth rebuilding, in my opinion. I still have the 1980 Evinrude 140 that was on this boat when I bought it. It too had a broken ring and scoring (According to the marine mechanic shop) and it still had 123-125psi on 3 cylinders and 100psi on the one with bad rings. They said it was no good and would need rebuilt. If I decide to rebuild one, it'll be the 140, but I think I can find a replacement motor for a good price if I keep my eyes open. Thanks for all the help Dasalbee!
 
Post # 2 suggested pulling the bypass cover and that was not a joke.----That is a low effort , low money spent technique.
 
Sorry Racerone, maybe I was unclear in my responses in both post #3 and post #13?! I stated that I had pulled the inspection covers for all the cylinders but failed to mention it prior to ur suggestion. They were pulled and checked last Monday and the motor has only idled in the driveway during a decarb since then. The first time I pulled them I saw no issues, no scoring, rings were all intact, and everything appeared fine. Which I expected based on the compression results. The second time I pulled the cover, earlier this evening, I just barely caught a glimpse of what looked like a possible gap in the very top edge of the groove for the top piston ring. That's when I pulled the head and discovered that there was infact a piece of the top ring missing, and there was still only one small spot on the cylinder wall that was scored and it couldn't be seen by removing the bypass cover. I'm still at a loss as to why I had good compression though?! Oh and whwn I removed the bypass cover I instantly noticed milky water in the cylinder, which would explain it not contributing while running. But how is water getting in, a ring is partially missing, and compression still checks good?! Prior to removing the bypass cover, during the initial compression check, I got a reading of 101psi. So I squirted sone oil in the cylinder to see if the compression would come up, indicating a broken ring or piston issue, and the compression stayed exactly the same. How do I still have good compression?!
 
Racer, why didn't you flag that 101 low compression earlier?
I personally thought it was OK, since they were all within 10% of each other....
But now 18 posts later, 101 is not OK.

I assume you know this due to the age of the motor...that they were higher in compression back in '75....but I missed that.

So....?????
 
If they should all be up at 140 or so, then the concept that the motor is worn out and has low crankcase compression is probable.
 
My advise here is based on some 40 years ( not 40 minutes ) of observing the behaviour of a compression test guage.----------Knowing the behavior of motors with the " pressure back rings ) and having owners anwering seemingly dumb questions.----Such as how long have you owned it ?---What happened ?---Did this happen suddenly ?--------How do you operate this motor?----do you understand the importance of the correct prop ? etc , etc.
 
Ok I'll reword it. Why do I have a cylinder that is still checking out to be within the 10% variance allowed between cylinder compressions, when that cylinder has so many issues and the other cylinders are all free of damage?
 
Although they may all be worn but the are free of damage. Since this motor is no good to me I went ahead and pulled the other head to inspect it. I was curious if there was something else I missed that was allowing them to all check out within tolerance but have only 1 cylinder that was damaged. The other 3 cylinders look great. The rings are in great shape and so are the pistons and walls. I haven't checked the bore to see if they are worn or out of round but they all look great except #3.
 
So basically what ur saying is that doing a compression check will only tell u if u definitely have a bad cylinder. If it reads low then ur SOL. But if it reads good (120psi) or even within the 10% variance, it only meanse that u MIGHT have a good cylinder. Correct? Like I said, I'm new to the world of outboards and I want to make sure I don't buy another motor and end up in the same spot. Every motor for sale lists the compression readings for each cylinder, but apparently that doesn't matter. So what do I need to verify on a motor if that motor isn't on a boat and can't be run at the lake? I have a bore scope now, bought it today. I'm hoping it will be a useful tool in determining the condition of the engines I go and look at.
 
Back
Top