75 HP 4 stroke 2004 Mercury, stalls out

[UncleRay]

Hello to the forum. I've used the forum to help others and now find that I need some help with my motor. The engine had been running fine and a couple weeks later problems. Hard starting, floods, some times idles on only one or two cylinders, sneezes out the intake occasionally. Some times starts up ok and takes off onto plane but will very soon stall and stop running like the ignition was shut off and making a load "Blaaaaa" sound. Boat comes to a complete stop engine not running. It will start right away and idle, if I put into neutral right away when it stalls, the engine is still running at idle.
Here is what I have done so far and also with the help from the shop manual, drained the fuel tank and put in new gas, pulled the fuel pick up out of the tank and tested under vacuum ok, tested the fuel line from the tank through the primer bulb up to the fuel pump no leaks, fuel pump passed a vaccum and pressure test, new plugs, grounded the plugs and turned over showing good spark, pulled and cleaned the carbs found two partially plugged idle jets and one main jet, thermo auto enrichment tested ok hooked to a battery (dropped down when hot and 24.9 ohms when cold, checked cam timing alignments marks and top dead center (right on), compression check warm engine WOT 198psig #1, 201 #2, 195#3 and 192 #4, checked all wiring harness and plugs, water pump puts out a good stream at the tell tale. I have not checked the throttle position sensor yet.
While idling in the drive way it maybe a coincidence but when it was idling on only one cylinder I started tapping on the carbs and it immediatedly started hitting on more cylinders. Thought I was onto something but it still idles lousy and some times idles fine. Still doing the same thing when bringing up the rpm to 3 to 4000 it quits running making the big blaaaaa sound and stalls out with the engine not running. Some times blip the throttle and it runs like a million bucks and then a bit later stalls out again. Next time starting I can bring the rpm up to 4 to 5 and it will rung for a while just fine and then stall out again. Seems like back to square one and will continue to look for the problem. I will appreciate any advice where to look next. Thank you for taking the time to read and reply. Ray

 

[UncleRay]

Re: 75 HP 4 stroke 2004 Mercury, stalls out

Update;
Got back to sorting out the problem. Engine is running better in the driveway, idles ok when warmed up and will take throttle increases but can stall out when making quick increase in throttle as in a quick rev. It will rev right up and sometimes starts to rev and then stalls out. Things I've checked today are; timing is right about 10deg BTDC at 1000 to 1100rpm and 20 to 25 BTDC by 3000rpm. Hooked up each carb individually to the primer bulb. Drained out some gas and you can hear the fuel going into the bowl and then shutting off. All floats are working. When the carbs were apart two of the floats were set low and I raised them up a bit. All floats are near the max of .59" measured upside down which results in a lower fuel level in the bowl. May pull the carbs and raise them all. The inlet fuel line screens were clean when the carbs were cleaned. Tested the fuel pump by running a hose off the outlet back to the fuel tank. Pumping fuel just fine. There are lots of bubbles in the gas line. Noticed this earlier which is why I pulled the fuel pickup and checked it and the hose all the way up to the fuel pump. Light ends in the fuel vaporizing??? I don't get the bubbles if pumpiing fuel slowly with the primer bulb. Also disconnected, tightened and reconnected every electrical connection I could find including the master connections at the motor from the dash and controls. I have not gone over connections at the throttle/shift lever yet. Plan to put the boat in the water and see if it is running better. If it is still acting up I'll have to dig into the electronics testing and maybe pull the carbs again. Will update. Ray

 

[PaulF820]

Re: 75 HP 4 stroke 2004 Mercury, stalls out

Update;
Got back to sorting out the problem. Engine is running better in the driveway, idles ok when warmed up and will take throttle increases but can stall out when making quick increase in throttle as in a quick rev. It will rev right up and sometimes starts to rev and then stalls out. Things I've checked today are; timing is right about 10deg BTDC at 1000 to 1100rpm and 20 to 25 BTDC by 3000rpm. Hooked up each carb individually to the primer bulb. Drained out some gas and you can hear the fuel going into the bowl and then shutting off. All floats are working. When the carbs were apart two of the floats were set low and I raised them up a bit. All floats are near the max of .59" measured upside down which results in a lower fuel level in the bowl. May pull the carbs and raise them all. The inlet fuel line screens were clean when the carbs were cleaned. Tested the fuel pump by running a hose off the outlet back to the fuel tank. Pumping fuel just fine. There are lots of bubbles in the gas line. Noticed this earlier which is why I pulled the fuel pickup and checked it and the hose all the way up to the fuel pump. Light ends in the fuel vaporizing??? I don't get the bubbles if pumpiing fuel slowly with the primer bulb. Also disconnected, tightened and reconnected every electrical connection I could find including the master connections at the motor from the dash and controls. I have not gone over connections at the throttle/shift lever yet. Plan to put the boat in the water and see if it is running better. If it is still acting up I'll have to dig into the electronics testing and maybe pull the carbs again. Will update. Ray

Ray, did you ever solve this...I am having the same issue