Mariner magnum 40hp 91 drops dead on forward

" Hi, I've got a Mariner M

" Hi, I've got a Mariner Magnum 40hp 1991 that goes perfect in a bin at a serviceman but dies when you forward it bolted at the boat.

They have tuned the carburators and the ignition, replaced the CDI-box and the gearhouse is working properly. I cant get it going however I try faster gas-giving.

Shortly before this problem occured the motor lost appx 25% of its top speed (22 to 15 knots)Anyone who have any ideas about this??

Thanks in advance !!
Staffan Tornqvist "

" Staffan... check your compre

" Staffan... check your compression first, make sure all cylinders are even and above 100lbs. If that checks out then you might consider a reed valve problem. You might also look into the stator as mercury has a problem with black stators. "

" Thank you, I forgot to menti

" Thank you, I forgot to mention compression check is done and new plugs are fitted. Do you have any idea how I can get a diagnosis of the reed valve ??

Staffan "

" Staffan... The reed valves a

" Staffan... The reed valves are located on your crankshaft so they are very difficult to visually inspect properly. WHAT i do is run each piston [ 1 at a time] to the far end of the cyl. Then blow smoke in the cyl. in the spark plug whole and look to see if smoke comes out the carb. IT SHOULD,T. If it does than a reed may be lifted or broken. Note... it helps to have the throttle wide open to allow the smoke to travel through the carb. If the reed valves are your problem the powerhead ha to come apart for repair. Let me kmow how you make out DJ. "