Evinrude runs bad/back fires

[asch]

Hello everyone.

I have just got a 1970 evinrude 85 hp V4 (85093B) that runs bad when it gets warm.

When i start the engine i runs but after a while (10-15 min) it starts to go bad and back fire.
I have checked and adjusted the breakerpoints (ignition system IV) but just a small change to the better.
The spark is good, i have not tested the compression but i don't think it is bad.

How do you adjust the timing on this thing? or may it be a carburator problem?

I'm grateful for all help I can get

//Johan from Sweden

 

[Daviet]

Re: Evinrude runs bad/back fires

Is it backfiring through the exhaust or the carbs?

 

[boobie]

Re: Evinrude runs bad/back fires

Check your compression first, and then you may have an ignition prob when it warms up.

 

[asch]

Re: Evinrude runs bad/back fires

I have checked the compression today: Cyl1 7,5 cyl2 7 cyl3 7,5 cyl4 7,5 Bar

I have also tried to check the timing (see pictures), it seems to be a bit off maybe but i have no clue how to adjust it.

timing mark at idle

Timing mark at 2500rpm


Any good ideas are welcome

 

[asch]

Re: Evinrude runs bad/back fires

Is it backfiring through the exhaust or the carbs?

It is backfiring through th exhaust...
Some times it almost start going backwards.

 

[boobie]

Re: Evinrude runs bad/back fires

Your compressions results don't make any sense.

 

[asch]

Re: Evinrude runs bad/back fires

Your compressions results don't make any sense.

Compression is:

1 cylinder: 108 PSI
2 cylinder: 101 PSI
3 cylinder: 108 PSI
4 cylinder: 108 PSI

I hope that it makes more sense now.

 

[boobie]

Re: Evinrude runs bad/back fires

That makes more sense and it looks good. When it quits, what open air gap will the spark jump ?? You could also have probs in the dist cap.


Off the subject, do know what lefsa is ??

 

[Mas]

Re: Evinrude runs bad/back fires

Flywheel key sheared?

Mas

 

[boobie]

Re: Evinrude runs bad/back fires

On that mtr the flywheel key has nothing to do with the running.