Mercury 150 Black Max

[Hoovy28]

I've had this boat 3 years now. Its always had trouble starting and idleing. I've paid big money to have it serviced and its reaped little results. Carbs have been re-built, new fuel pump/filter. It runs great when she's wide open, but I will fish for a bit and when I try to start back up it won't. I nearly drain my cranking battery every time. Could it be a fuel line problem?

Any feedback would be greatly appreciated, thanks!!

 

[Barnacle_Bill]

Re: Mercury 150 Black Max

What year is it?

 

[boudreux]

Re: Mercury 150 Black Max

I have an 88 blackmax 150 and had what sounds like the same problem. It would struggle cranking up and i would try so many times until the cranking battery was dead. I had mine taken in and it turned out to be a loose ground wire going to the stator. Tightened that up and its been cranking great. You may have a problem with the stator as well. I would go have that tested, it may be going out.

 

[lbfd48]

Re: Mercury 150 Black Max

Well, if its and early black max like mine 1978, it helps to trim the motor all the way down. That way the carbs are tilted back and the fuel flows into the motor easier. Mine wont start unless I do this.

 

[Hoovy28]

Re: Mercury 150 Black Max

Thanks for the feedback guys. It is an '89 so it might be the same problem. I've had it serviced and they said the starter was fine, but its a good possiblity that they're wrong!

 

[Hoovy28]

Re: Mercury 150 Black Max

Oh Stator.. Miss read that. That could definitely be the problem. Thanks

 

[Hoovy28]

Re: Mercury 150 Black Max

How pricey is a new Strator? And How difficult is it to repair for an amature mechanic?? thanks for the feedback

 

[sschefer]

Re: Mercury 150 Black Max

There are several things that can cause this.
1. Air leak in fuel line (common).
2. Bad float needle seats or needles.
3. Bad reeds.
4. Slow cranking speed.
5. Cracked coil(s).
6. Fouled plugs.
7. Bad head gasket(s).
8. Bad Stator
9. Bad ground.

Often it is just a corroded or inadequate ground in the ignition system causing a weak spark.
Air in the fuel line can be caused by a bad primer bulb or a bad clamp but in the later its usually accompanied by a visible leak (not always).

A leak down test will tell you about the condition of your reeds.

Fouled plugs can be analyzed.

Head gaskets can show up as one or more cylinders that have very little or no carbon buildup on the piston tops indicating water intrusion or you may have steam comming out your tell tale or prop.

A bad stator will can be accompanied by power loss or a rough idle.

Slow cranking speed can be checked with a tach and should be a minimum of 300 rpm.

Bad float seats or needles can accompanied by fuel spilling or spitting from the carbs.. Not always but sometimes.


Cracked coils can be either visually inspected or checked with a spark gap tester. They will likely produce a good spark at a 1/4" gap but will not hold up past 1/2" gap.

Hope that makes sense and helps.

 

[boudreux]

Re: Mercury 150 Black Max

Stator runs about $200-250. I tilt my motor all the way down as well. After i squeeze the bulb til its hard i squeeze it 2 more times to make sure fuel is in the carbs.

 

[Dukedog]

Re: Mercury 150 Black Max

What is your starting procedure? How do ya do it? Are you sure tha enrichmant valve is working? Do you keep tha motor trimmed ALL tha way down when your at idle? Most carb motors have their very own way of how they want ta be started. Could be as simple as idle timing if it does good everywhere except start/idle. Low side of tha stator is a good possibility.

"A leak down test will tell you about the condition of your reeds."
This just checks clyinder and ring condition. Won't tell ya nothin' bout tha reeds. Think ya talkin' bout checkin' pressure at tha bleed line fittings on tha reed plate..................

 

[sschefer]

Re: Mercury 150 Black Max

What is your starting procedure? How do ya do it? Are you sure tha enrichmant valve is working? Do you keep tha motor trimmed ALL tha way down when your at idle? Most carb motors have their very own way of how they want ta be started. Could be as simple as idle timing if it does good everywhere except start/idle. Low side of tha stator is a good possibility.

"A leak down test will tell you about the condition of your reeds."
This just checks clyinder and ring condition. Won't tell ya nothin' bout tha reeds. Think ya talkin' bout checkin' pressure at tha bleed line fittings on tha reed plate..................

Most people do a pressure test and look for 3-6 lbs of pressure. A full leakdown test is a little more difficult as it requires fabricating block off plates for the intake and exhaust and involves pulling the power head. It includes both presurization at 5lbs and then pulling a vacumm of 5lbs.

If done correctly it will tell you more about your engine than any compression test ever will.

Of all the problems listed, slow cranking speed is the most common culprit.

 

[Dukedog]

Re: Mercury 150 Black Max

You need to do a research on doin' a "leak down" on a V6 Merc..........Nothin' like your talkin' about.
Very simple with guage and a 100lbs of air.

 

[j_martin]

Re: Mercury 150 Black Max

You need to do a research on doin' a "leak down" on a V6 Merc..........Nothin' like your talkin' about.
Very simple with guage and a 100lbs of air.

And I can't see it telling you anything about the reeds. Luckily the reeds in a V6 are reasonably easy to inspect visually. Easy enough so if you're getting into the carbs, you'd be foolish not to go there (reed inspection) for one more gasket.

I think sheffer is confused with water jacket pressure testing, looking for pinholes in the casting. Way overblown for this project so far.

 

[sschefer]

Re: Mercury 150 Black Max

And I can't see it telling you anything about the reeds. Luckily the reeds in a V6 are reasonably easy to inspect visually. Easy enough so if you're getting into the carbs, you'd be foolish not to go there (reed inspection) for one more gasket.

I think sheffer is confused with water jacket pressure testing, looking for pinholes in the casting. Way overblown for this project so far.

Yeah your right maybe I should buy a V-6 and learn about them a little more.

 

[Dukedog]

Re: Mercury 150 Black Max

No need ta get your panties in a bunch. Makes no difference if ya built ONE or a thousand, Theres always something different thats gonna come ta light. Thanks ta tha Merc/Mariner team...................

 

[sschefer]

Re: Mercury 150 Black Max

No need ta get your panties in a bunch. Makes no difference if ya built ONE or a thousand, Theres always something different thats gonna come ta light. Thanks ta tha Merc/Mariner team...................

Duke dog, lighten up... I was jokin ya.. I just picked up a bridgeport and have a 150 2.5 on the bench now. Just having fun and spending the money I used to spend on beer and smokes.

 

[Hoovy28]

Re: Mercury 150 Black Max

There are several things that can cause this.
1. Air leak in fuel line (common).
2. Bad float needle seats or needles.
3. Bad reeds.
4. Slow cranking speed.
5. Cracked coil(s).
6. Fouled plugs.
7. Bad head gasket(s).
8. Bad Stator
9. Bad ground.

Often it is just a corroded or inadequate ground in the ignition system causing a weak spark.
Air in the fuel line can be caused by a bad primer bulb or a bad clamp but in the later its usually accompanied by a visible leak (not always).

A leak down test will tell you about the condition of your reeds.

Fouled plugs can be analyzed.

Head gaskets can show up as one or more cylinders that have very little or no carbon buildup on the piston tops indicating water intrusion or you may have steam comming out your tell tale or prop.

A bad stator will can be accompanied by power loss or a rough idle.

Slow cranking speed can be checked with a tach and should be a minimum of 300 rpm.

Bad float seats or needles can accompanied by fuel spilling or spitting from the carbs.. Not always but sometimes.


Cracked coils can be either visually inspected or checked with a spark gap tester. They will likely produce a good spark at a 1/4" gap but will not hold up past 1/2" gap.

Hope that makes sense and helps.

Great Info man thanks alot. I looked over my fuel line assembly- pretty good and have no visible leaks/holes. Spark plugs are 2 years old at most w/ very little hours on engine. Because of the response to my problem (greatly appreciated) I'll give you more detalil. The boat runs great outside of a slow idle to moderate idle. Runs great going fast. But ANYTHING under a stationary idle to slow idle (i.e. parking in a marina) the engine will DIE. VERY frustrating!! Thanks for the help

 

[Hoovy28]

Re: Mercury 150 Black Max

Most people do a pressure test and look for 3-6 lbs of pressure. A full leakdown test is a little more difficult as it requires fabricating block off plates for the intake and exhaust and involves pulling the power head. It includes both presurization at 5lbs and then pulling a vacumm of 5lbs.

If done correctly it will tell you more about your engine than any compression test ever will.

Of all the problems listed, slow cranking speed is the most common culprit.

How do you fix Cranking Speed??

 

[Dukedog]

Re: Mercury 150 Black Max

Good battery/ starter. If tha motor starts then "crankin' speed" can be taken out of tha problem. If all your fuel lines, filter, carburators and tank are good (you need ta know this for a fact) you need ta look at idle timing/throttle settings first (easiest) since it does everything right as soon as you get off idle. If it has a idle stabilizer on take it off and throw it away then reset idle timing. If that doesn't work then you can go into tha stuff thats a little more involved. Reeds, bleed lines and check valves would probably be next. Do you have a Manual? If not get one, your gonna need it.........

 

[sschefer]

Re: Mercury 150 Black Max

How do you fix Cranking Speed??

You first need a tach that can accurately read cranking speed. Good timing lights can be purchased that have tachs built into them. If your cranking speed is less than 300 RPM or if your engine seems to crank slow then increase it's proabably time to either rebuild or replace your starter. Rebuild kits can save you a lot of money and starters can usually be rebuilt many times.

The engine needs to turn over at around 300-350 rpm to produce adequate voltage and compression to start the engine easily. Notice that I said easily and didn't say an engine wouldn't start.