Mercury 150 Blackmax running rough

[krismik]

Hallo, I am living in the north of Germany and have a Problem with my 150 HP Blackmax.

Ideling and starting is good, but between 1000 1/min and about 2500 1/min in gear the engine is
running rough. Without load everything is smooth.
Compession is equal and within factory specifications.
It has a new stator, a new trigger, 2 new switch boxes and 6 new coils,
The rectifier is good, the sparks are new.
I cleaned the carbs several times, adjusted the float level, checked the jets....
Synchronized the carbs several times.
Checked the routing of the bleeding lines and the check valves.

Could this be a reed valve issue?
I noticed some of them, maybe 5 or 6 of the 60 have a little air gap to the housing.

Maybe someone can help me....

Christian

 

[aussieflash]

Re: Mercury 150 Blackmax running rough

Have you checked your timing is to spec?
Bad reeds usually mean bad idle.Check your gap specs on reeds if you have merc service manual.

 

[CharlieB]

Re: Mercury 150 Blackmax running rough

When there is a difference in smoothness between loaded and unloaded running, often the problem will be found in the small passages of the carbs, either idle fuel or idle air/emulsion tubes are still restricted and sometimes can be a real bear to get cleaned without actually running a very fine wire thru every passage, followed by a good solvent then compressed air.

 

[krismik]

Re: Mercury 150 Blackmax running rough

Thanks for the replies!
The timing is set to specs, also the trigger is moving the whole way.
Tomorrow I will look another time in the carbs to see if someting is restricted...

 

[krismik]

Re: Mercury 150 Blackmax running rough

I rebuilt several engines, but this one is really a beast.
I bent the reeds so that they completely close because they were uneven.
The most reeds were closing completely and some had a little clearance.
After that I went to the see for testing.
The rough running is still there, but has a little bit changed.
Than I read the manual - the reeds shall have a clearence of .51mm.
So I ordered a complete new original reed set with gaskets

I think it would be easier if the carbs would have seperate sync screws for
each carb.
My blackmax not even has mixture regulation screws.
The jets are all in the right size as printed in the manual.

I wonder why the nr 3 Cyl. has no bleeding line and why there are other
blackmaxes with no vent jet at nr 2 and nr 5 or nr 3 cyl - very strange.

At about 1800 rpm the engine smoothes out and runs like hell.
If you reach again the 1800 rpm going down the rough running begins.

My thought is that at 1800 rpm the reeds are constantly open so
that the different preload of the reeds take no effect anymore and the cyl
sync is there...

After 25 jears it is anyway a good idea to replace the reeds so the cannot be eaten

When I change the reed I will have a carefully look at the carbs if they are clogged in the little
channels.

Christian

 

[CharlieB]

Re: Mercury 150 Blackmax running rough

By 1800 the motor is completely off the idle circuit.

Your problem is still in the idle circuit of one or more carbs.

Be very carefule so as not to switch main jets between carbs as the factory has been known to stagger jetting on many of the V6's so just be sure that each jet goes back into its original position/carb.

Float height is also critical to idle mixture. Idle air passages must also be carefully cleaned.

 

[Mi duckdown]

Re: Mercury 150 Blackmax running rough

I use stiff mono/fishing line to make sure all carb passages are open.

 

[CharlieB]

Re: Mercury 150 Blackmax running rough

It is never a bad idea to check the basics, like a spark test and DVA testing of the trigger and stator.

A broken trigger wire can be abutted and fail in some positions and work seemingly fine in others as the timing lever moves the wires.

Spark and DVA testing should be done with the throttle cable disconnected so you can slowly move the timing lever from idle to WOT and back while testing to see if there is any change at any point in the wire movement.

A marginally weak low speed winding on the stator can cause a weak spark on three cyls and rough idle/poor acceleration until engine speed gets high enough that the high speed windings begin producing power.

Go ahead and do these tests just to be sure you do not have a hidden ignition problem.

Repost your findings.

 

[j_martin]

Re: Mercury 150 Blackmax running rough

The carbs are synchronized with the linkage. Be sure they all close tight and open at that same time.

Often this engine likes the throttle valve pick up cam adjusted so the carbs open up after the timing is advanced a bit. They idle plenty rich so they'll tend to load up if the carbs open too early. Set the pickup cam gap a bit more open, or the timing a little further along the throttle lever movement. Play with it, there's a sweet spot there somewhere.

If it idles, the reed valves are fine. Above idle the engine pressures will slap them shut if there's anything left of them at all.

hope it helps
John

 

[krismik]

Re: Mercury 150 Blackmax running rough

Almost the complete ignition is new. Stator, trigger, switchboxes, coils.
Today I replaced the reed valves. Now I have the right air gap at the reeds and
can be shure that the enigne will not eat them in the near future.
I discovered the tiny holes at the top of the carbs underneath the top cover steelplate.
Maybe two of them where blocked.
I cleaned the carbs with denture cleaner and compressed air.
Mounted new gaskets
Tomorrow we will see....

 

[j_martin]

Re: Mercury 150 Blackmax running rough

Well, did it run or sink?

 

[krismik]

Re: Mercury 150 Blackmax running rough

because of the strage jetting of the V6 mercs I removed the vent jets of cyl 2 and 5 as it should be in some other configurations.
On the water with nearly cold engine it ran fine at 1200 rpm at first. Then getting hotter the rough running was there, maybe worse.
My blackmax should have 078 vent jets at all cylinders 048 idle and 080 main jets, as it has...
I gave the pickup cam a litte more gap with no results. Its running better with the cam almost laying on as the manual says.
I ordered a new head gasket because its leaking a little bit at the outside, but I don t think thats the problem.
As I ran the engine with carb cleaner under load at my test tank some weeks ago all pistons and sparks were completely clean but cyl 3.
Nr 3 was black and the spark too.
At cyl 3 there is no bleeding line and there is also no valve at the reed block housing at cyl 6...
I think one cyl is 4 stroking in that shaking running condition because of a rich mixture.
But my 078 vent jets are on the small side compared to the others.
Maybe there is one tiny bore in the carb that I didnt see?
I noticed the bores at top of the butterfly valve.
Are there others I should pay attention on?

Unfortunately I have no comparison to other blackmaxes, maybe a little 4 stroking in that particular rpm area is normal???

Christian

 

[j_martin]

Re: Mercury 150 Blackmax running rough

I just typed a huge response and lost it. I'll try again.

Black Max just means big and black. Without further information on your engine it's impossible to know if it's been molested or not. Useful info at this time would model, (maybe misleading, it's just decals on the cowl) serial number, and numbers off the carburetors. Would also help if you know if the reeds are vertical or horizontal.

Jets are dependent on the carbs. That's why the numbers off the carbs are important. Also carbs, though similar in looks, can be widely variable, so if you don't know for sure, check the numbers on all 3 carbs to see if they are similar. They will be slightly different for 1,2,and 3, but should be in the same family, and the numbering would make what the position is obvious. It's also perfectly normal for jetting to vary from carb to carb on the same engine, and for 1 bleed line to be missing in the configuration.

I wouldn't worry about the head gasket right now if you have good compression. It should be replaced, but is probably not part of the problem.

At this point the main problem is misfire on #3. If you rig a timing light on it and take it for a ride, the light should blink at all times. If it goes out when the engine misbehaves, it's a spark problem. Possible causes are #3 coil, wire from switchbox to #3 coil. #3 high tension wire, or switchbox. All the above problems can be moved by swapping parts around for trouble shooting purposes. Trigger and stator are unlikely to cause a 1 cylinder misfire.

Each engine and boat setup is subject to some compromises. Most big V6 installs set for top speed will be overloaded when the boat is climbing out of the hole. Normally that's just a second or so, but if you try to run at that attitude, you'll have problems.

hope it helps
John

 

[krismik]

Re: Mercury 150 Blackmax running rough

Thanks for the response John,
the engine number is B3498.. so it should be from 1988 i think.
The carbs are numbered 1374-5424-C.
Top says WH A, middle WH B and bottom WH A ??
The block numer says it is a 150 hp Block, identical with XR2.
The flywhell cover says 150 HP.
The reed blocks are vertical mounted.

Christian

 

[j_martin]

Re: Mercury 150 Blackmax running rough

I can't find the part number anywhere.
Usually we go by the WH number. Usually the WH is followed by a stamped number, yours is likely 40
Serial number is on the clamp leg of the motor. That would help, but WH40 carbs go about '88 150's.

Still thinking yer having an electrical problem on #3.

If someone put WH41 carbs on it from an XR4, the main jets are way too big. Like I said, jetting goes with the carb model.

 

[krismik]

Re: Mercury 150 Blackmax running rough

I don`t think it?s an electrical problem. Stator is new, Trigger is new, both CDI?s are new, all Coils are new.
As I said when I remove the nr 2 and nr 5 vent jet, the engine runs much better till it gets warm.
Yesterday I wanted to flush the engine with fresh water. At starting white smoke came out of the exhaust and one cyl
was missing for a few seconds.

 

[j_martin]

Re: Mercury 150 Blackmax running rough

I don`t think it?s an electrical problem. Stator is new, Trigger is new, both CDI?s are new, all Coils are new.
As I said when I remove the nr 2 and nr 5 vent jet, the engine runs much better till it gets warm.
Yesterday I wanted to flush the engine with fresh water. At starting white smoke came out of the exhaust and one cyl
was missing for a few seconds.

I make my living in logical analysis. Look at what you just wrote.
A factoid that may help; We all have bought new bad parts.
The white smoke is unburned fuel. If the miss was fuel related it would either not be there at all, or be black as in half burned because of too much fuel.
The stator and trigger are not suspect. They seldom cause a single cylinder failure.
The switchboxes can be swapped to see if the bug moves.
The other parts it could be are
The coil
The secondary wire on the coil
the plug itself
the wire from the switchbox to the coil.
The ground wire on the coil.
A shunt on the switchbox signal to the coil. The oil alert connects to one cylinder. It's usually #2, but it can be moved to any one.

And the one that is hardest to find.
One of the many connections you just confessed to working on.

hope it helps
John

 

[krismik]

Re: Mercury 150 Blackmax running rough

I replaced one of the ground connectors. Tested the resitance to ground. removed the oxide from the nuts etc...
I also do not think that one cyl is completely not fireing. Its more an issue of
4 stroking, fireing only every second time. There also is a reaction on each cyl if I unplug
the spark plugs when the engine is in the rough running condition.
And I can not hear any difference in rpm drop.
So I think it is only a slight difference of one ore more mixtures comming out of the carbs.
Rejetting the vent jets of the problem carbs would maybe solve the problem.
In two weeks I will do a test drive to find out if tand how he engine reacts on changing the
vent jet sizes. I think I will try this with a little hose that I can block or open.
Changing the vent jets on the water is difficult without losing them.
Now I will go to kreete into the sun for two weeks

Christian

 

[j_martin]

Re: Mercury 150 Blackmax running rough

"Four stroking" is a misfire. If it's caused by rich mix, it'll smoke black. If it's electrical, it's usually white. The one black spark plug indicates misfiring on that plug.

Now on the jetting issue. Until you have identified which WH carbs you have on the engine, (ie WH40, WH41, WH41A) etc, you have no idea what the stock jetting is. I suspect there is a lightly stamped number between the WH and the A that you stated are on the carbs before. B doesn't make sense. The part number you stated I can't find anywhere.

Running lean on a cylinder in this high performance 2 cycle engine that relies on fuel for cooling is a sure way to melt down a piston. If you don't even know what carbs you have, you are risking that kind of damage by experimenting without knowledge.

The troubled cylinder is the one with the different plug. It might be something as simple as a missed gasket under the intake seat for that carb. A sunk float is also possible. Usually such troubles will blacken a plug. I still think it's electrical on #3.

I refuse, however, to argue with you any further.