I'm going mad.
I'm trying to get my 50Hp running on more than 2 cylinders.
I have a 1998 Mariner 50Hp Bigfoot 4 Stroke, which internally is (was) in good condition.
I made the mistake of letting fuel sit in it for 6 months. Smelled more like furniture polish than petrol.
Bottom two cylinders refuse to fire at any rev. Which rules out the ignition modules because 1 and 3 are upper, 2 and 4 are lower.
So I have
- good compression
- flushes the lines out
- sprayed with carbie cleaner
- rebuilt the carbs three times, checked all the tiny little air holes are clear and lines are clear, floats are working, took out the jets, cleaned them all, made sure its all good
- put in a new fuel pump middle section (broke one of the damn bakelite outlets by looking at it for too long [seriously, bakelite? still?]. And I had to get the Yamaha component because Mariner dont sell the middle bit separately (they are the same engine). $122 in this country (Australia). $250 for the entire pump.
- swapped the upper and lower hoses on the fuel pump over to rule out fuel surging/starving (the fuel supply hoses are very convoluted on this model)
- sprayed the cylinders, cranked them out, left plugs out until clyinders are dry, swapped the plugs over, cranked again
- bled the float bowls to make sure they are getting juice. Broke one of the brass screws, paid $15 for a new one, then broke another so went for stainless instead.
- checked the spark (good to all 4)
- wound out the idler air screw in and out, no change
So, what am I doing wrong? What could I have missed?
It's got to be carburettor, right?
I just cant figure it out.

And the old fuel smelled like varnish

Rebuilt the carbies again, did some adjusting, running on number 4 now, but number 3 is sitll dead.
Has good compression, spark.
I used valve grinding paste and ear buds to clean the float seats.
So I'm thinking I need new floats and float valves.
This model also has two variants; adjustable pilot and non-adjustable.
Anyone know how to tell the difference?