Mercury Engine Stops

I have an older Mercury 150 hp Blk Max XR4 motor that had a previous owner.The PO had did some performance upgrades,pistons ,carburation etc, that really made this engine fly.Recently ,after a few fishing trips ,I`ve noticed that while idleing it will just STOP and wont start up immediately afterwards.!? When it does start it`s business as usual no loss of power that I can feel it gets up on plane and runs like a scalded dog.My Question is...is it time for a tune up and if so how often should I have one done?

48 views and not one response? Cmon guys does`nt anyone have a clue?

Carb Merc motors do not like being tilted up prior to restarting. Try pumping the primer bulb after lowering the motor. Also, plan to change the bulb and fuel line every few years as they are prone to breakdown caused by the crappy ethanol fuel we are forced to buy.

An annual tune-up by a skilled mechanic is advised. Not sure who in your area is qualified, but you can find good mechanics via this site.

I have an older carb motor and it runs great, but it is definitely harder to start than a fuel-injected motor.

Make sure you have the motor trimmed up to keep the exhaust ports above the waterline when idling.

had one doin' that several years ago... no pattern, jus ever so often... never failed ta restart and run a hole in tha wind.. always got 'em back to tha ramp... never found tha cause!!!

Power valves need serviced or replaced. They are one way valves in the bleed system to prevent puddling, that will cause the motor to load up, associated with early Merc carb motors.

Like Gary said check the bleed circuit check valves they could be stopped up or more likely wide open Does it smoke and chug before it dies. If the check valves are bad the fuel will just sit there in intake and drown the motor in fuel......OPTI

Not to hijack Fishbonz thread, But can the check valves in the fuel pump be cleaned and reused or is it best to buy whole new fuel pump kit ?, Reason i ask is i have a 19885 v6 175hp that i've had manyyear and this past year it started dieing on mejust like the op here said his were, I've replaced the fuel pump Diaphgragm twice in the past 15 years,
Engine ser.# is OA149036, thanks for any help.

lakeman new check valves come in the diaphragm kits. Yours being a 1985 would make me want to install carb kits w/new floats.

There is a diaphragm/gasket only kit and a complete kit with diaphragm, gaskets and check valves, fuel pump check valves are not available separately.

Bleed circuit check valves are available separately....

Is this kit recommended for the XR4 150 Merc??

I believe there were 2 different pumps used on that one, a square pump and a sort of rectangular one, I have the rectangular one and looked for the fuel pump check valves for a bit as I already had the diaphragm/gasket only kit. After no luck locating the kit with the valves locally and finding out they were not available separately I talked to mechanics and parts dept. at a couple service centers I was told they were not stocked cuz they never go bad and to reuse them and change the diaphragm and gaskets.....if still having problems check/change the bleed circuit check valves...

I rebuilt the pump yesterday reusing the check valves as I did years ago but haven't lake tested it yet. Pretty sure my bleed circuit check valves are original as they have black paint on them, sure wish I would have thought about them when I had the carbs off.....

Thank you for your response bronco71 What year and motor type do you have?

mine is the older 1980 Mercury 150 Black Max

Thanks again sir ! Let me know how your lake test turns out. That could just possibly be what my engine issue is.How much is the diaphragm/gasket only kit and where can I purchase one?

I actually had one that I bought years ago and never used. You can look up the part number for yours HERE and either buy from them or find it online, Amazon actually can get a lot of them to you fast....

Bass Pro in Grapevine (Mercury parts ans service in the back) has some of the diaphragm/gasket kits but didn't have the kit for mine with check valves. They may have yours without the valves.

Thanks a lot for this info! I`ll check it out

Nice, I think I am having this same problem. First start of the day is usually really good, but after idling around or some low RPM trolling, my engine feels like it loads up on gas and I have a hard time getting it going again.

The more times I stop, the worse it gets it seems.

The next day, fresh start with zero problems.

I'm gonna have to check this out. I'm hellbent on restoring my 150 Mariner Magnum III, which to my knowledge is the same engine as XR6, and very close to the Black Max.

I have a whole swath of maintenance to do this winter, I'm actually looking forward to it

identical other than paint!..

"black max" doesn't mean anything.. a "marketing" thing left over from many years ago....