Depending on year, MerCruisers had mechanical or electric fuel pumps. What do you have?
They normally do not have primer bulbs.
a 3.0 carbed motor will have a mechanical fuel pump.
Did full tune up so thought a good idea. Gas in tank maybe at 4in above bottom maybe pickup tube is higher. Never let it go below a 1/4. Going to fill up today and see if that helps. Im thinking fuel pump is pretty tough so maybe the carb if it primes but stalls?
I rebuikt the carb 3 years ago and it solved this same issue.. i had a clear inline filer so i could see low to no flow
Lets back up -
3 yrs ago carb rebuild running well?
Did a tune up ? What was done during tune up? Timing set correctly - some require being in base mode?
this year as a preventative measure decided to empty fuel tank? Would not stay running after that?
Then you installed primer bulb?
When you start it is choke closing and throttle advanced? Is this a TKS carb?
I would take the primer bulb out as it doesnt need to be there and is not rated for install in side a compartment. This would eliminate any issue that it may cause with the pump or if installed backwards Would think 4" is enough fuel unless you are on a hill.
remove fuel line from carb , ground / disable ignition, crank the engine and see if you get fuel up to the carb (put a small container on end of fuel line. if fuel is not present would look for a leak on up stream side of fuel pump where it is sucking air, take off antisiphon valve make sure it opens. Pull the dip tube and see if there is chit clogging it may have an internal screen.
if you have fuel would tap on top of float bowl where needle and seat is sometimes sitting they can get stuck, especially if cheap carb parts were used. Hook fuel line back up try adjusting mix screw(s) out. see if fuel is being pushed out accelerator pump nozzle when throttle is stabbed.
Just need to figure out if it is fuel starved, and where supply or carb. This assumes spark is good. Wouldn't hurt to verify spark strength with cheap gap tester first. I learned this the hard way on a OB , went through fuel pump rebuilt carb, new points ... all to find out the hard starting was due to weak spark as both coils ohm'ed out of spec. If you took a plug out you would see a spark but it wasn't strong enough. New Coils was the root cause
