Mercury 25 backfires out of exhaust

marinemike43 · #1 August 11th, 2009, 07:38 PM

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 · #2 August 11th, 2009, 11:48 PM

ck, spark plugs firing order, and fuel pump pressure

JB · #3 August 12th, 2009, 12:50 AM

Switch the spark plug wires back to the correct plugs.

marinemike43 · #4 August 12th, 2009, 07:27 AM

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 · #5 August 12th, 2009, 06:28 PM

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