70hp 1981 - motor out of power, I'm out of ideas

Hi there,
I need some help with my Evinrude 70 hp 1981 (3 cyl) E70ELCIM.
I have owned this engine for many years and it used to ran like a real champ. But last year it started to give me some headache.

Problem description:
It simply does not have the power it use to! It is struggling to get on plane and feels sluggish in the "lower/middle register". Very noticeable when under load.
With only me in the boat it does run pretty decent, but with just one extra person you notice the hesitation right away. It will plane, but not fast enough to have some fun When it finally do plane it runs good, max rpm 5600'ish.
It definitely can't pull up a water-skier or not even a tube.. Which used to be no problem at all.
Doesn't help with pumping the primer bulb or using the choke while trying to accelerate.

So far I have done/checked these things (not in order):
New plugs: Champion L77JC4
New fuel.
New fuel lines.
New primer bulb (it stays hard).
Tank vent open.
Carbs completely disassembled and cleaned (with ultra sonic) blown out with compressed air then rebuild with carb-kits.
Rebuild fuel pump with kit.
New impeller.
New thermostat.

Compression test gave these:
Cyl 1: 120psi
Cyl 2: 123psi
Cyl 3: 118psi

WOT Timing advance seems to be at 16deg with the timing light (not 100% if it is correctly measured as the pointer was taken of by previous owner, I put it back and positioned it as good as I could).

Reed valves looked ok visually when looking when the carbs where of, but I'm absolutely not qualified as a judge of that. Also blew them out with the air compressor.

The motor starts real quick, and it always has! Idling rpm is ok.

The problem seems to be with the lowest cylinder (no 3).
When I spraying premixed gas directly in to the carb no3 it picks up the rpm and the engine seems to run smother (when idling on muffs).
When I do it to the other two carbs the engine almost stalls. Therefor I suspect cyl 3 going lean/starving...or something.
Also when I "choke" the carb no 3 with my hand I feel suction but engine does not respond any different (no change in rpm). When I do it on the other two carbs it (again) almost stalls...

To rule out the carb for cyl no 3 I switched carbs for cyl 1 and cyl 3, but the problem did NOT follow! Still the same result when spraying premixed gas.
Cyl no 3 is still the one that has a problem!

Power pack? Coils? Reeds?

As the motor picks up rpm when I spray premixed gas in the carb for cyl no 3 guess that it has a spark and therefor maybe the ignition can be ruled out??
Also notice that the problem cylinder is the one with the lowest compression value (if that can give you any hint..)?

If someone more knowledgeable can give some new idea or point me in a direction I will be more than happy!
Sorry for the long post, but I guess if you would to have a chance to help me you'll need as much info as possible

Please advise fellow boaters!
Best reg// Ryon13

Re: 70hp 1981 - motor out of power, I'm out of ideas

Hi
You seem to have narrowed it down well.
Have you tried spraying around the bottom crankcase to see if the seals gone near the bottom?
Any small hoses on that bottom carb or bottom cylinder that may have perished and leaking air in?

Re: 70hp 1981 - motor out of power, I'm out of ideas

Do a GOOD Decarb on it and see what happens.

Re: 70hp 1981 - motor out of power, I'm out of ideas

boobie said:

Do a GOOD Decarb on it and see what happens.

Click to expand...

Thanks for the reply, but how would a GOOD decarb be done then?
I took them COMPLETLY apart and cleaned all metal parts with ultra sonic, 60 deg C for 3h.
After that I used a toothbrush and brushed them with some cleaning product. Then compressed air through all chanels and openings/orifice. They can't be any cleaner.
Rebuild with carb kits including new floats.

Also by swiching the carbs and problem didn't follow I think that a carb fault is ruled out?

@Bosunsmate
Thanks. No I havn't done that. Are you referring to the gasket for the cylinder head? I will spray it next time I'll get to the boat.
With holes or cracks in the cylinder wouldn't the compression test show much lower values?

I have gone through a hole bunch of threads and post about this kind of problem but nothing seems to but the last nail in the coffin...
Thanks again:joyous:

Re: 70hp 1981 - motor out of power, I'm out of ideas

The crankcase seal is what i mean, where the two halves join, around the middle of motor, a small leak there can lean it out.
Yes holes in head would reduce compression, some motors have small hoses called bypass lines going to the carbs and aft, your motor might not have them if so, one less thing to rule out.
You could try running it for like 10 seconds with the bottom spark plug lead grounded to the block. Then remove the bottom plug and check its getting fuel
Also look for any excess fuel dropping down and out of leg

Re: 70hp 1981 - motor out of power, I'm out of ideas

I tore one of these down that had a shredded lower seal due to the bottom ball bearing coming undone. It also had a freshly rebuilt lower carb. And a brand new bottom coil. And a brand new power pack. My guess was tha someone was chasing the bottom cylinder issue and never found it. No bottom seal, no run on bottom cylinder.

Re: 70hp 1981 - motor out of power, I'm out of ideas

Bosunsmate said:

Have you tried spraying around the bottom crankcase to see if the seals gone near the bottom?

Click to expand...

I went to the boat today with hope of finding a leaking seal or something that makes it run lean..

But the thing is, I may have to revise my earlier statement that cylinder no 3 runs smother when I spray gas directly in the carb. The cylinder no 3 does not respond to any extra fuel, and it does not respond when being choked.

Bosunsmate said:

You could try running it for like 10 seconds with the bottom spark plug lead grounded to the block. Then remove the bottom plug and check its getting fuel

Click to expand...

I did that now, and I'm pretty sure that it is getting the needed fuel... So it might be the ignition anyway
Did not see any excess fuel dropping down and out of leg (not really sure where you meant...leg=section that holds the drive shaft?) but I could see some dark stuff coming out of the propeller/exhaust and on to the grass beneath, that might be unburned fuel?

Thank you so much for your input

I did one other quick test before I had to go home; with engine idling on muffs and by using a timing light I tested if power was being delivered to the plugs.
All three spark plug leads made the light flash continuously and it looked equall on all three..?
But dont know if that simple test is enough?
I guess I might have to by me a spark tester to verifiy a really sufficient spark...

Could a weak spark give these kinds of symptoms?
I mean; can one cylinder be "dead" at low rpm then wake up at higher rpm and the error be weak spark??
If that is the case where or what is the first thing to look for?

@chinewalker
Thanks for the info! It sounds like a real big deal to fix... Hope that's not the case for my engine, fingers crossed:joyous:

Re: 70hp 1981 - motor out of power, I'm out of ideas

Thats good its pointing away away from being the bottom carb/vacuum as its quite a job to get the lower seal changed. Its easy if the motor has had the powerhead off recently but normally you have years of binding/ oxidation to contend with.

You should mark top dead centre for each cylinder on the flywheel. Number 1 cylinder will be marked on there currently. Then use your timing light to check all sparking is done at the same time in regards to top dead centre on each cylinder.
A failing powerpack can often do regular spark but until you show where its happening on the flywheel you cant tell if its actually happening at an inappropriate time.
Run it at night and look for any shorting out too.
Yep spark tester would be useful too