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Skipper
Posts: 12
Registered: ‎05-31-2015
Accepted Solution

1980 70hp Top Speed Problem

[ Edited ]

Hi!

 

This is my first time posting so bare with me.

 

1992 Thundercraft 17ft Bowrider

 

I purchased a boat last week off a friend of mine, it has a 1980 70hp Evinrude Model#E70ELCSA. He had owned it for 2 years and always ran well and was able to achieve 55-60KPH. This year he thought it may be a good idea to run a tank of fuel with seafoam to clean out the carbs. Obviously ran a little rougher but was still able to achieve his top end power.

 

After I purchased it i noticed a small problem with its idle, so we made the appropriate adjustment and now idles perfect. But still can only achieve about 30-40KPH on the water under perfect conditions. It just feels like its not getting enough juice to go Wide open. It is also sluggish out of the hole.

 

Due to the specs I've looked up engine is designed to operate around 5800RPM at WOT

I currently can't exceed 4100 at very best or less

 

Other than the lack of power at the top end, engine runs like a dream. What could we be missing?

 

Things we have tried.

 

New NGK spark plugs

Remove and clean all 3 carbs.

Fresh tank of fuel 50:1 mix using Amsoil Synthetic

All 3 Coil packs were replaced last year

 

 

Thanks in Advance!!!!

Admiral
Posts: 6,140
Registered: ‎07-14-2011

Re: 1980 70hp Top Speed Problem

[ Edited ]

 We arre talking about a 35 year old engine here, so anything is possible.

 

You may want to switch to the factory recommended Champion QL77JC4 plugs gapped to .030"

 

The ignition system should be strong enough to spark across a 7/16"  gap at cranking speed

 

check compression for all cylinders to be within 15% of each other

 

inspect the throttle arm to spark advance plate (timer base) link and be sure the plate rotates smoothly in conjunction with the movement of the throttle arm.

 

All three throttle plates have to be closed at ilde and open fully at WOT. Remove the air silencer to inspect. The three throttle plates should be completely horizontal.

 

Check fuel pressure at all speeds.

 

Remove and inspect each high speed jet from the carb float bowls and compare the sizes with the one in the parts book.

 

Replace the nozzle well gasket and float bowl gasket in each carb as any air leakage around the nozzle well leans out the fuel flow and loses power.

 

Refer to the service manual for proper synchronization of the linkage adjustments,timing and throttle pickup, and the high speed timing.

 

The engine may need a 15" propeller to push a 17" runabout to acheive the proper rpms - 5000-5500

***************


"There is never just one thing wrong with a boat";
                                                 -- Travis McGee, main character in a book series by John D. McDonald


***************
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. If you elect to do it yourself, be sure to use caution, common sense, and to observe all safety procedures in the vicinity of gasoline, moving engine parts, high temperature components, heavy items, and electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation or a technique, enlist the services of a factory trained technician.
Skipper
Posts: 12
Registered: ‎05-31-2015

Re: 1980 70hp Top Speed Problem

Thank you for the response. I will check all the above.
Now that I have had time to think about it, I never tried swapping the old plugs back in to see if it ran WOT normally again or not, that would without question rule out the plugs being the problem or not. (I'm an amateur) Smiley Happy

Do you happen to know what the prop specs are for this engine?
Skipper
Posts: 12
Registered: ‎05-31-2015

Re: 1980 70hp Top Speed Problem

Ok.....
So here is my update
I replaced plugs with OEM spec
Installed new power pack
Double checked coils-all good
Installed new timer base
Verified fuel-all good
Verified wires-all good

Still not getting spark on Cyl #1
It occasionally will kick in and then go out again.

I am at a loss as to what this issue could be. If you guys could help me out I would be very greatful!
Skipper
Posts: 12
Registered: ‎05-31-2015

Re: 1980 70hp Top Speed Problem

Forgot to mention compression is 125,127,130
When the cylinder kicks in I've got full power until it kicks out again
Captain
Posts: 30
Registered: ‎06-09-2015

Re: 1980 70hp Top Speed Problem

I would double check wires again, start the engine at night or in a dark garage and look for spark jumping out of the wires. Or you could just touch the wire when running but I don't recommend that, it will give a real good shock if wire is bad. I found bad wires on my old 70 evinrude this way and just had a wire on my 12 year old Mercury 50 go bad and was jumping out of spark plug boot.
Skipper
Posts: 12
Registered: ‎05-31-2015

Re: 1980 70hp Top Speed Problem

When I pull the wire off there is no drop in rpm like the other two. I have tried swapping wires from another cylinder still no change. I've tried another spark plug as well, no change.
Skipper
Posts: 12
Registered: ‎05-31-2015

Re: 1980 70hp Top Speed Problem

Not sure if it's related, but when I pulled the plug off #3 I got a good shock.... But the cylinder is firing
Admiral
Posts: 6,140
Registered: ‎07-14-2011

Re: 1980 70hp Top Speed Problem

[ Edited ]

To see if it is an ignition problem, first make sure that the system is in good enough shape to jump a 7/16" air gap at cranking speed.  For a running test, use a clip-on timing light on #1 and monitor its flashes as the motor operates. See if the timing light flashes disappear when the cylinder no long fires.

 

If it does this at low speeds, watch the timing marks on the flywheel to see if they jump around or if another cylinder is firing at the wrong time occasionally.

***************


"There is never just one thing wrong with a boat";
                                                 -- Travis McGee, main character in a book series by John D. McDonald


***************
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. If you elect to do it yourself, be sure to use caution, common sense, and to observe all safety procedures in the vicinity of gasoline, moving engine parts, high temperature components, heavy items, and electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation or a technique, enlist the services of a factory trained technician.
Captain
Posts: 30
Registered: ‎06-09-2015

Re: 1980 70hp Top Speed Problem

Have you tried swapping the coil that did not drop rpm to another cylinder and see if condition stays or moves to the different cylinder?