My Mariner 150 will fire right up on the muffs and while unloading. Runs great wide open and will idle all day long, but as soon as I kill it, dang thing won't hardly crank.I usually have to choke or raise my fast idle lever all the way and eventually it will start, but when it does I get alot of smoke. Then it runs fine but like I said as soon as I kill it gives me trouble. It doesnt matter if I run it for 15 minutes or thirty. If I kill it, it's hard to start. As long I as keep it running I don't have any problems.Today I went to load up, docked the boat backed my truck down to the ramp took me 5-10mins to get it to start. Got it loaded on the trailer figured I would see what it would do so I hit the key and it fired right up out of the water. Of course I killed it as soon as it busted off. Any recommendations?? With all the smoke when it finally cranks it's almost like it's flooding out

Could be carbs
Faulty ignition packs
Trigger
Stator
Ignition coils.

Look for any corroded wires, crack housings on coils.

carb, efi?

If carb:
As mentioned about, check for good spark at cranking. Make sure your battery is healthy and turning that motor fast enough to get a good spark.

Needle seat issue in carbuertor causing flooding? Or bad float or floats? Carb rebuild could cure it, Again already mentioned.

Possible hole in fuel pump diaphragm allowing excess fuel into crankcase?

Faulty primer/choke solenoid? Not very familiar with Merc�s, so not sure what kind of enriching system they have?

If EFI:

I�m not smart enough for that....

agree with above for a carb motor.. mainly fuel pump thingy.. anything 'lectric would show when its runnin'...

that year efi squirts two injectors every time you hit tha start circuit..... not controlled by "push tha key"..

It is a carb motor

If it is push to choke, check the solenoid hooked to the fuel lines. It should click and allow fuel to flow into the carbs.

It clicks like it's working. Is it possible to be stuck open allow fuel into my carbs?

Yep, stuck or not sealing off. Pull the primer lines off and pump your bulb, see if fuel comes out. If it has a manual lever, make sure it is completely in the �run� position.

if it "clicks" every time ya push on it then its not stuck.. it has to open and close ta make it "click"....

Is your primer bulb leaking down, could be a bad check valve.

Mercury/mariner carb engines do have a cold starting procedure. It is a pain and if mine sit for over 10 minutes I had to use the starting procedure..

In a nutshell it is-
Pump the ball
Engage throttle only
Choke for 5 seconds
Start the motor