75hp mercury 2 stroke issues

Heres what I got, ran great then just lost power by like 10 mph WOT, took it in and carbs cleaned and synced, new plugs, still.ran rough, took it back to the shop they replaced the cdi box, better but still wont open up, drain fuel and replace, new filter, better but still lacking, any help? I’m 1200 into this at a local shop and no fix

Have you tried using a different fuel tank and hose?

Hose yes, tank no.

Compression test?

Shop says it was ok, they also told me twice it was fixed and ready so who knows,I’m a few hours from the boat now ,I’ll do a few checks before returning to the shop again.

See if they can load test the coils. If you have a coil going out it could have affected the box, which got better you say, but not necessarily the issue especially if the coil isn’t handling high Rpms.

seems that I remember someone having similar problem, if I remember right it was a bad voltage regulator.

I would say Beast is on the right track here. Not sure what year your motor is but I know it was a common problem in the late 90s motors. I had a 1999 and when it went out, I had all the same symptoms.

Boats a 1995 I’m thinking its original motor

voltage regulator should be on the starboard side of the motor just ahead of the heads on the side of the block, If your boat has a tachometer, one of the signs that the regulator is bad is that it will either quit working of works erratically, I’m not sure if your boat has one or two regulators, if it has two just one may be bad.

I would be looking for another shop to work on your motor for sure.

A couple of easy cheap things for you to try. There is a short hose that runs from the block to the fuel pump. That is your impulse line. I’d replace it and also rebuild the fuel pump. I had a 75 Mariner and it acted the same.

Thanks guys ! I’m heading up to the camper Friday and do what I can as mentioned by your posts, if all else fails theres a few shops on lake Francis Case that I’ll talk to.

Replaced the voltage regulator and found a small leak in the fuel pump, good to go ,thanks every one for the help!!