Problem starting 1993 75hp mercury outboard, starts and runs fine at home???

Question

I have only had the boat for 2 weeks and really happy with the engine as it runs very well 43mph on 15.5ft fletcher! Starts straight away at home warm or cold but it seems to me that as soon as its fully tilted up and travelled to sea ( only 20mins from when it was last started! ) it takes forever to fire up? ( probably 10-15 mins ) Once running in the sea its very reliable and has no problems all day long! I have pumped the fuel ball til it goes hard and do an 8 count on the choke, sometimes no choke too, still won't go? I cleaned the plugs, run it on high octane unleaded made sure it would start at home and on the second attempt it went. DOES ANYONE KNOW WHATS HAPPENING??

Answer 1

at home on the muffs, there's no load on the engine.  when you submerge the lower unit, there's backpressure on the underwater exhaust.

Look at the back of the motor, just under the powerhead, there are two holes, the "exhaust relief ports".  Those are there to relieve some of the pressure, to facilitate starting.  If those holes are submerged, it'll be way harder to start.

If you've cranked the engine at home and let it warm up, then it'll be warm when you get to the ramp and choking will just flood it.

Do you have a manual that specifies high octane fuel?  If not, note that higher octane than than the motor was designed for will just result in a less complete burn, more unburned fuel in the exhaust, carbon build-up in the cylinders, yada yada yada.