1977 evinrude 6hp loses power

[rlbovell]

The motor started ok but after a short time running at full revs it just slows down to very slow revs for no reason.
Have overhauled the carb and fuel pump and checked there is no vacuum in fuel tank but problem continued
Strangely it did not happen in reverse or when motor is not engaged in drive,
Has anybody got any ideas what the problem is?
Rob from Perth Western Australia

 

[hardwater fisherman]

Have you checked that you have good spark on both cylinders?

 

[rlbovell]

Thank you for the quick response Hardwater.
The spark appears ok in both cylinders as the motor runs very well out of gear or in reverse just not when in forward gear.
I can only test the spark visually as i do not possess a meter,
Rob

 

[hardwater fisherman]

You can do a drop test. Start the motor and using insulated pliers pull off on spark plug wire at a time if it dies then you know its only running on one cylinder. It will start and idle well with spark on one cylinder.

 

[rlbovell]

HF Thank you once again.I will go down to the river a test as you have suggested.
Rob

 

[boobie]

Do a cylinder drop test on it to see if it's running on both cylinders.

 

[rlbovell]

Thank you Boobie I will do the test shortly and report back as to the outcome
Rob

 

[rlbovell]

Boobie its Rob here but I am also in the same forum with the same ID I tried to delete this post but without success. See above posts

 

[rlbovell]

HF I did the drop test and clearly its the top cylinder which does not work.
Changing over the spark plugs produced the same results
Any ideas how to progress the repair
Regards Rob

 

[rlbovell]

Did the drop test and the top cylinder does not work.
changing the spark plugs over produced the same result
What can I do now to get to fix the problem.
Regards

Rob

 

[hardwater fisherman]

Switch the ignition coils from top to bottom and bottom to top. If the top cylinder fires then you have a bad coil. If not the coil maybe your powerpack is bad.

 

[racerone]

Model # of the motor is ?

 

[Tim Frank]

Make sure that the top cylinder has compression.

 

[GA_Boater]

Both topics have been merged to a single.

 

[rlbovell]

The motor is a 6704m Evinrude
Did not swap over the ignition coils (mainly because it appeared too complicated) but tested the spark from the lead to the top (faulty) cylinder.The spark connected over 15mm and showed well when connected to the spark plug.
Going to buy a compression tester because I really dont know where to go next with this non working cylinder..
Can it be a fuel problem or is it likely to be rings etc

Regards Rob
And thank you all for assisting so far

 

[racerone]

Could be something stuck in a reed valve.---Has the waterpump impeller been replaced recently ?-----May just be as simple as the head gasket blown so carry on with a compression test.

 

[Tim Frank]

The motor started ok but after a short time running at full revs it just slows down to very slow revs for no reason.
Have overhauled the carb and fuel pump and checked there is no vacuum in fuel tank but problem continued
Strangely it did not happen in reverse or when motor is not engaged in drive,
Has anybody got any ideas what the problem is?
Rob from Perth Western Australia

Just to refresh/clarify.....

Will it still start and run fine THEN after a short time fall off ~ or ~ was that event the start of the problem and now it only runs on one cylinder at all times?

 

[racerone]

Motors will sound just fine in nuetral , even running on one cylinder.----In reverse there is less load on the prop because of exhaust bubbles and blade shape.

 

[rlbovell]

Tim Frank
The EVENT was the start of the problem and now it runs on one cylinder.Just purchased a compression test meter and will report back shortly
Rob

Raceone
The waterpump impeller was recently replaced.I am just about to do a compression test and will report back.

Rob

 

[rlbovell]

Undertook the compression test
Top cylinder (which does not work) 90 psi
Bottom cylinder (which works ok) 87 psi

Are these levels satisfactory?
If the levels are ok what do i check next to find out why the top cylinder does not work.
Where do I find the reed valves.

Thanking you

Rob