Mariner 90 HP 4 Stroke.

[abc]

Old carburettor version. Appears to be missing on one and running unbelievably rough.
I think this is a carburettor problem, has any one else had similar problems.
Had carbs set up before Xmas, was ok for a short time but now not usable.

abc

[9D280]

Welcome to ribnet!

How much of a step change was it between OK & running like a bag of nails, and does it run like that both at idle and open throttle?

Thought process -
idle only, probbaly got crud in the idle jets.
wot (well, > about 2.5K), main jet probably blocked.

Assuming it's at all throttle positions, pull all 3 spark plugs - are any particularly wet & manky? if so you may have to adjust or worst case replace the float or the valve it closes. on the offending carb, however.....

Another thing to do (on grounds that it's an easy test and costs nothing) might be to swap your spark plugs & leads (or coils if they are the sealed units wuith short HT leads) around & see if the problem follows either the plug or the HT lead / coil. I've had 2 plugs die on me in almost as many years.

[outboardtech]

\abc when you say the carbs were setup . were these done with the vacuum gauges or someone standing next too it and trying to adjust all four cylinders . just asking as this will DEFINETLY MAKE THAT OUTBOARD run rough if not done properly , what the compressions like , has an ignition spark check been done ? cheers