Late 80s mariner carb adjustment

I've got a late 80s mariner 75 hp on my house boat.
The shop cleaned the carbs right before I had to put the motor on and pull the boat 2 hours away.
They told me I may have to make some slight adjustments. I out the boat in the water and when I start it it has a back fire to it. Seems as if it's back firing into the crankcase? Doing some other reading it looks like this is due to the carbs not being adjusted correctly.
Can someone explain how to adjust the carbs, a few pictures would be helpful?
Boats in the lake, takes a permit to haul it. The guy at the marina it's docked at only works on Johnson and Evinrude.
Any help would be appreciated.

Carb adjustments are universal, so that guy should be able to do it. Sounds like the idle mixtures are way off (too lean). Try a half turnout on each.

Jeff

Thanks for the reply,
the problem is the guy won't work on anything but Johnson and Evinrude not that he can't.

Air/fuel mix screw settings are 1 & 1/2 turns outwards from soft stop .... also make sure your spark plug boots are on there real good.

That 1 1/2 turns is just to get the motor running. It needs to be fine tuned. Can't you find some older guy who knows how to adjust a carb?

Jeff