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1975 Evinrude 85hp Low Compression!? Not Running

S

siduolocin

New member
Hi everyone, Me and my friends have a small speedboat that we love!!

Motor is not running no more :(

was running ok but took sometimes 5-20 seconds to start up always longer to start in water! then we started using start you bastard and that work great. But last time we took it out, we had to use start you bastard to get it started even on a warm the engine. now dose not start

first thing we did was run a compression on cold engine
95 PSI
95 PSI
95 PSI
100 PSI

Is this too low to get the engine started. we've recently changed the spark plugs and check there is fuel there is Spark most the time on crank up but we noticed one might be skipping a little bit. we are going to pull the flywheel off this weekend and check the points making sure it's 0.010"

so the question is there anything else we should look at or is the compression just too low to get this old girl running again

Cheers
Nick
Down Under
 

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First double check your primer solenoid and make sure it's working. Compression seems a little low, but even enough.

Looking at your pictures my first suspect would be poor electrical connections. Take a look at the snip I pulled from your image and zoomed in. The grounding wire for this coil looks to have a lot of corrosion where it connects to the coil and block. This can be a huge problem for generating proper spark. Remove and clean all these ground connections and cover them in dielectric grease.

corrosion.JPG
 
It has an adjustable choke solenoid ----But not a primer solenoid.-----If the compression tester is accurate the compression indicates problems !-----Remove bypass covers for inspection of pistons / rings.
 
We need a definitive spark test. Good 7/16" about 10mm jump, pull out all spark plugs to get a good cranking speed (as mentioned earlier), looks like some nasty coils here. Did you do compression with all plugs out, full battery, and choke off with throttle butterfly open? Head gaskets look ugly too, brother. This is one of my favorite outboards of all. I have owned lots of them 75's and 85's.
 
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Hi everyone, thank you for the help.

We also noticed the corrosion on the grounding points we removed all bolts and clean them but still we believe there is not enough Spark will run further tests in the next week to see the strength of the spark. The coils have seen their fair share too

There is a choke solenoid but we can manually pull it out if needed. which we've tried as well. We can smell fuel in all cylinders.

From videos I've seen on YouTube over these engines they tend to crank quite slow ask cranks very quick I'll post a video if I can with the spark as well.

I don't want to remove the bypass cover at this stage as we could break bolts and need new seals will do after other testings
 
Your motor should not crank slow. Get a different gauge and clean all the electrical connections to shiny brite. If the compression test fails a second.time you will have to inspect the rings. You do not need to have the throttle open for the compression test. You may even have to take the starter apart to clean it.
 
Your correct Mr. Scott, no need to have throttle open for a compression test, however....an open throttle will support more accurate results. On a 4 stroke, an open throttle is much more important, but I've only been repairing outboards and getting paid for it, for 50 years, so what do I know? I want to get as much air into the cylinders as possible. The 2 stroke will build to max compression by sucking air through the tiny butterfly opening or relief, however.........it will take more cranking. I have tried this, and here is an example. Test with 4 pulls on a 6 hp with throttle closed......get 65 psi. Then pull a few more times, till it tops out compression....80 psi. Now, release compression and start over with throttle open. You will have max compression at 4 or 5 pulls. The idea here is to minimize cranking and maximise compression. You can always do that extra cranking to build compression, but I prefer to minimize the amount I spin a motor, especially if the impeller is dry and I am pulling over a larger motor by hand.
 
Have some friends in Queensland, hope to visit next year, talk regularly on Skype. Alfred is a pig farmer, has over 300, but there is apparently not a good market there for pork. He keeps adding pigs, loves them. Is it true that you guys down there don't care much for pigs? Here in US we love it......but gotta try to keep away from the fat. When I was there in '96 seems beef is meat of choice. Love you guys, great people.
Looks like those coils are cracked. They may not arc externally, but could be partially shorting, or even arcing internally. I have run cracked coils, but not the best idea especially they could harm the power pack in time.
 
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timguy said:
Your correct Mr. Scott, no need to have throttle open for a compression test, however....an open throttle will support more accurate results. On a 4 stroke, an open throttle is much more important, but I've only been repairing outboards and getting paid for it, for 50 years, so what do I know? I want to get as much air into the cylinders as possible. The 2 stroke will build to max compression by sucking air through the tiny butterfly opening or relief, however.........it will take more cranking. I have tried this, and here is an example. Test with 4 pulls on a 6 hp with throttle closed......get 65 psi. Then pull a few more times, till it tops out compression....80 psi. Now, release compression and start over with throttle open. You will have max compression at 4 or 5 pulls. The idea here is to minimize cranking and maximise compression. You can always do that extra cranking to build compression, but I prefer to minimize the amount I spin a motor, especially if the impeller is dry and I am pulling over a larger motor by hand.
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Maybe you should put a video up proving that. In my experience I have never had to have the throttle open for a 2 strk compression test. It has also never taken me more than 5 pulls. An 85 hp like that if the starter failed I would use my drill.
 
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u need to do a leak down test on the crankcase. their r 4 check valve on the intake manifold that u can remove & put a rubber tip air inflator & inject 15 psi with the piston just above the intake ports. if u hear the air escaping @ ur lower crank u have a bad seal. do this for each case.
 
fishhawk90 said:
u need to do a leak down test on the crankcase. their r 4 check valve on the intake manifold that u can remove & put a rubber tip air inflator & inject 15 psi with the piston just above the intake ports. if u hear the air escaping @ ur lower crank u have a bad seal. do this for each case.
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How is that going to work?
 
That's true Racer, but the correct and engineered concept for the 2 stroke is for exhaust flowing out and intake providing the "charge". I just am trying to get our viewers to do an "effective" compression test on ALL motors, this means an open throttle. It is a very good general rule. I'm not one to argue principle, based on personal technique, however......I base a possible diagnosis on a compression test with the accurate numbers. How many techs or viewers out there have looked at compression numbers and based their diagnosis on an improperly performed compression test? You shouldn't try to answer that, its like guessing how many marbles will fit in a toilet bowl. The answer is ALOT.
 
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But when the exhaust ports close the air in the cylinder is at atmospheric pressure.-------Does not matter where the air came from either the intake ports or the exhaust ports.------The crankcase is NOT a supercharger !!
 
It IS putting pressurized fuel/air mix into the cylinder as soon as the piston clears intake ports on fire stroke. So what do you call that, brother? Isn't the crankcase pressurized when piston is fired down? If it isn't, then what shoots in the charge? This pressure in the crankcase is also what triggers the fuel pump and/or in the case of pre 1960 OMC's.....it puts that pressure into the fuel tank to force fuel into the carb.
 
timguy said:
It IS putting pressurized fuel/air mix into the cylinder as soon as the piston clears intake ports on fire stroke. So what do you call that, brother? Isn't the crankcase pressurized when piston is fired down? If it isn't, then what shoots in the charge? This pressure in the crankcase is also what triggers the fuel pump and/or in the case of pre 1960 OMC's.....it puts that pressure into the fuel tank to force fuel into the carb.
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This argument seems to come up every so often.

FACT: The crankcase does compress the charge during the piston downstroke and yes that pressure pulse enters the intake ports when the piston clears the ports. BUT: The exhaust ports are also open at that time, so the intake pulse fills the cylinder and goes out the exhaust ports (called scavenging), resulting in cylinder pressure equal to the exhaust pressure---normally atmospheric pressure at cranking speed, unless the exhaust is somehow obstructed. A two-stroke depends on this fact in order to run.
 
timguy said:
It IS putting pressurized fuel/air mix into the cylinder as soon as the piston clears intake ports on fire stroke. So what do you call that, brother? Isn't the crankcase pressurized when piston is fired down? If it isn't, then what shoots in the charge? This pressure in the crankcase is also what triggers the fuel pump and/or in the case of pre 1960 OMC's.....it puts that pressure into the fuel tank to force fuel into the carb.
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Tim u are spot on abt everything expect for the pressure into fuel tank. The VRO has no control over the fuel as its passage is always open & fills the crab bowls when needed. The only relation to the vro & piston down stoke is a vacuum it draws from cylinder 4 that sucks the diaphragm to open the oil port.
 
Fishhawk, just explaining how the old 2 line tanks work I love 'em. Got about 40 of them here in my shop and sheds.
Mr.,Scott, I will do another test and have my son figure how to do an accurate clip on it.
Mr. Gator, will research what you say and come to a conclusion, thanks.
You guys are all awesome.
 
fishhawk90 said:
Tim u are spot on abt everything expect for the pressure into fuel tank. The VRO has no control over the fuel as its passage is always open & fills the crab bowls when needed. The only relation to the vro & piston down stoke is a vacuum it draws from cylinder 4 that sucks the diaphragm to open the oil port.
That is not at all how a Vro works. All fuel pumps have some sort of check valves in them to prevent fuel from running backwards. Since the VRO is the fuel AND THE oil pump it cannot just be an open line to the carbs. Since it is both pumps and mixes on the fuel side of it. It has to have a way to prevent mixed fuel from running backwards to the tank. So no it is not just an open line to the carbs. The VRO is also an air motor so the pressure and Vacuum do not directly effect the diaphragm like a standard pump. It also does not ever stop pumping because as long as the motor.is.running it is pumping.
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Check this out, it is a very well done CGI annimated explaination covering the 3 most common types of 2 strokes. It shows loop charging, which of course utilizes ports almost directly across from each other and a flat top piston. You will notice how ineffective that any 2 stroke design would accommodate the imput of air from the exhaust side. Also notice the go cart has an "expansion chamber" exhaust. This optimizes exhaust pressure, sequentially timed based on chamber retention, by calculating cylinder displacement and other factors. What does this accomplish? It provides just enough backpressure, at the exact moment, to enhance the performance of the 2 strokes. Megaphones have also been used to expedite exhaust removal, but in theory and more importantly when considering performance, they are mostly ineffective when compared with "expansion chambers". The design of exhaust will vary based on loop charged, or standard 2 strokes. The design of multiple cylinder 2 strokes in an outboard application is very limiting when considering exhaust mods. What we have is a poor platform of performance when exploring possible, practical, exhaust configurations. In a perfect situation, the outboard should have a separate expansion chamber for each cylinder and the exhaust should not meet between cylinders.

https://youtu.be/Z6YC3I54so4
 
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To be honest with u guys i think the vro system was a bad design by Johnson, reason is my engine blew seals & worn out crank rings twice because of lack of oil in the mixture by the vro.
 
Now, don't argue anymore, friends........ole' timguy did his homework for you. If you know what it takes to do an animation, this one would take 1 excellent man, or woman, about 800 hours.
Fishhawk, you are right.....engineers work to create things to operate within limited parameters, but as life would have it......unconsidered variables might ultimately present them as "fools".
 
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If you suspect low compression is causing the problem, it might be interesting to temporarily run it at a 25 to 1 fuel/oil ratio and see if there is any change.
 
fishhawk90 said:
To be honest with u guys i think the vro system was a bad design by Johnson, reason is my engine blew seals & worn out crank rings twice because of lack of oil in the mixture by the vro.
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Highly doubtful the VRO caused blown seals. Lack of oil will cause a scored piston and or crank. What are crank rings. Sounds like something VROs get blamed for and do not cause. People who work on that system know its a good system. People who do not know anything about them tend to blame them for everything.
 
Those would be the crankcase sealing rings.-----6 metal rings that fit on the crankshaft.------Look like big piston rings.-----Separate the 4 crankcases.
 
that's right. my guess the bottom 2 cases is where the issue is. cylinder 1&2 is at the top separated by the crank center bearing from cylinder 3&4 @ the bottom. on the piston downstoke u will have abt 60psi in that case, any leak into the neighboring case & it will throw compression so off that all other cylinders will be effected. If it was just one case leaking through crank seal or between the halves it will still run. a proper leak down test on each case & cylinder heads will point u to the problem.
 
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