Mercury 25 backfires out of exhaust

[marinemike43]

Friend gave me a Mercury 25 hp he said it wont start,checked spark with spark tester and getting spark and has very good compression.

Sprayed some gas in carb and all it will do is backfire from exhaust.
Also sprayed a little directly in cylinder and done the same thing.

Anybody have any ideas what to check?

Have not hooked it to a tank yet

Thanks Mike

 

[radar7]

Re: Mercury 25 backfires out of exhaust

ck, spark plugs firing order, and fuel pump pressure

 

[JB]

Re: Mercury 25 backfires out of exhaust

Switch the spark plug wires back to the correct plugs.

 

[marinemike43]

Re: Mercury 25 backfires out of exhaust

Why would the longer lead go to the top plug and the short one go to the bottom?
Could someone have switched the pos wires going to the coils ?

Mike

 

[GritchGritch]

Re: Mercury 25 backfires out of exhaust

I had this exact problem with my 9.8 hp. The two wires from the swithbox to the trigger coils underneath the stator were connected backwards. Switched them and the motor fired right up.

John