Mercury Black Max 150 XR2 Running Rough!

[ShaneC]

I want to start by saying I have read the thread "Black Max 150 has me baffled" and I think I have a different problem, but man, what a bunch of good info in that thread.

I can start my engine (starts very easy) and idles good. I usually let it warm up to about 1/2 way between hot and cold. When I go to WOT the boat takes off as expected then seems to really jump up (in RPM) right before it planes out and will run great. ~62 MPH. This behavior is not consistent though. Other times when I dump to WOT it will run at ~3900 RPMs and is real rough. When this happens I can take it out of gear and I still have the same results - rough running and only about 3900 RPMs.

When the rough running condition is present I can smell alot of fuel and motor seems to really be smoking. It also seems I can always reproduce the problem if I get into the throttle very slowly.

When the problem is not present, it always seems that out of hole the motor has almost like a click or surge that allows the RPMs to jump up.

When the problem does exist, I get around it by several attempts at dumping to WOT till I get that click and RPMs jump.

Just ordered the Seloc book as this engine is very intimidating currently.. My first thought after reading some of the online Seloc material is possibly the Fuel Enigizer is hanging up... Any advice would be appreciated.

Shane

 

[Windykid]

Re: Mercury Black Max 150 XR2 Running Rough!

sounds like a sticking float needle. Causing a flooding condition. You can shut it down when this happens and check the plugs for fouling.

 

[ShaneC]

Re: Mercury Black Max 150 XR2 Running Rough!

Will the fouled plugs be a sympton of the float needle sticking or just another thing to check.. It has a new set of plugs installed.. Is a sticking float needle hard to correct?

Shane

 

[studlymandingo]

Re: Mercury Black Max 150 XR2 Running Rough!

If that is indeed the issue, then you will need to pull the carbs; you might as well clean them while they are off.

It is not too difficult a procedure to do this.​

 

[ShaneC]

Re: Mercury Black Max 150 XR2 Running Rough!

I looked at the Carb Kit from iboats but it seems to be only a gasket kit. The Seloc manual says to replace the inlet needle & seat which is not part of the kit from iboats. I found this part on another site (ishopmarine.com).

The previous owner told me he always ran SeaFoam in this boat. I have not put any in since I bought it. I wonder if prolong use of the fuel additive caused some build up or maybe I just need to add some..

I think I am going to eliminate the fuel enricher circuit the next time I have it out.. This seems simple enough to do and would save a lot of work if this turns out to be the culprit.

Shane

 

[j_martin]

Re: Mercury Black Max 150 XR2 Running Rough!

My best guess is the high speed charge coil in the stator. It looks like it's getting fuel, but not firing above a certain RPM.

A stuck float needle won't let it idle. A leaking float needle won't let it idle.
A leaking float needle won't be noticed at high speed. They basically stand open at WOT anyway.

hope it helps
John

 

[ShaneC]

Re: Mercury Black Max 150 XR2 Running Rough!

My best guess is the high speed charge coil in the stator. It looks like it's getting fuel, but not firing above a certain RPM.

A stuck float needle won't let it idle. A leaking float needle won't let it idle.
A leaking float needle won't be noticed at high speed. They basically stand open at WOT anyway.

hope it helps
John

Thanks John,

Now would the high speed charge coil produce a intermitten result like what I am experiencing?

I pulled the plugs this past week and the top ones were covered in deposits and the plugs got cleaner as I went down the engine.. the bottom set being the cleanest but yet still dirty. So I have cleaned those and bought another set for back up.

A buddy of mine told me to try the Seafoam first. Cheap and may save me a lot of headaches.. Can't hurt so I am going to give it a try this week..

SC

 

[j_martin]

Re: Mercury Black Max 150 XR2 Running Rough!

Seafoam can't hurt. It's just rough on the neighbors. I usually put a can of sea foam in about a galon and a half of fuel in a pony tank, and run it on the cuffs until gone or it almost quits. Let it sit for a few hours, then take it out and run it. Will be rough till the sea foam clears, and might even kill a plug or 2. Be prepared. Cleans the carbon out and spreads it all over the neighborhood as smoke.

A stuck needle is possible, but on that engine there are 6 needles, one for each cylinder. With more than one cylinder affected, it's unlikely.

If you have a whole bunch of wrong (aftermarket) needles in the carbs and also have a high fuel pressure situation (over 6 lbs) it could affect more than one hole.

If the engine uses a choke plate system for starting enrichment, all 6 cylinders could be affected by a malfunction. If it is an enricher valve setup, the top 2 cylinders would be unaffected.

The varied plug fouling deal sounds like your engine is overcooled. What is the water pressure at idle, 2000, 4000, and WOT? Do you have a strong cool pee stream on the cuffs? (should be 140* if strong, maybe cooler if weak, both being normal) If there were too much water flow, the top of the engine would be the coolest because of the routing of the water. It goes in at the top, down the block, and back up the heads. Some is metered into the exhaust, and the poppit dumps some more into the exhaust at over 12 psi or so. It's all designed so the temp can be more or less regulated by the t-stats.

If you, or a previous owner has been convinced to discard the t-stats, or gut the poppit, you've found your problem. They don't run worth chit cold. Those things are for engines tricked out to burn 25 gph or so of fuel in a drag race.

It still looks like an intermittent failure (could just be a scuffed wire) in the stator, or one switchbox crapping out. There are 2 stator wires going to each switch box. One charges the CDI caps at low speed, and the other at high speed. A flakey ground on the stator could do this, also.

hope it helps
John

 

[ShaneC]

Re: Mercury Black Max 150 XR2 Running Rough!

The SeaFoam seem to clear up my problem. Put in 12oz. in 12 gallons of fuel and took it out to the lake with a spare set up plugs (just in case). I didn't have alot of black smoke. The boat had experienced the problem when I first started running the seafoam through it. After I finally got the boat to run normal it shot up the lake with no problems. I slowed down to almost a stop and then dumped the throttle and it came right out of the hole again. I fished for about hour and half and then started the boat again and it ran perfectly the rest of the night. I am not going to call it a complete success till I take it out for another successful trip.

I did notice something else that has bothered since I bought the boat. The temperature gauge only reads C ----- H . When at idle or running down the lake the gauge will creep up to Hot. The only time it will really drop is if I have the boat neutral and rev the engine. I can get it to drop down to the halfway mark. The pee stream seems to be strong and I have not heard any audiable alerts but I am concerned the boat may be running hot. Does this sound like it is time to replace the impeller? I am thinking dropping the lower unit would be a pain....

Thanks,

Shane

 

[studlymandingo]

Re: Mercury Black Max 150 XR2 Running Rough!

If it is running on the hot side, then I would definitely replace the impeller and the thermostats.​

 

[Bigprairie1]

Re: Mercury Black Max 150 XR2 Running Rough!

....ok, I'm no expert on this motor but there might be something else to check out.
If your linkage is at all connected to ,or even near touching, the choke linkage and you pull anything of those plates even slightly closed on your carbs...youre going to run rich and poorly. Any motor will behave this way...car, boat......internal combustion motor that isn't fuel injected.
You mentioned when you quickly WOT it you don't have the problem so there might be a linkage problem going on.
I'd check it out and make sure you didn't have any accidental carb-choke/plate restrictions that you didn't know about.
Maybe go for a run with the cowling off and make sure this isn't occurring.
Good luck.

 

[j_martin]

Re: Mercury Black Max 150 XR2 Running Rough!

Unless you have real numbers for temperature, don't get your shorts in a knot about it.

Mercs like to run a little warm. Also, they will usually run pretty cool in neutral. That's all because of the design of the water circuits. Quite a bit of water bypasses the t-stats, and at idle the engine just isn't producing enough heat to keep it hot. The pee stream will fall off quite a bit if the stats are working and it still will be cool. If you rev it up out of gear, it still isn't burning much fuel, or making much heat, but the poppet valve will open and it likely will get downright cold.

In other words, you're probably OK.

Feel the pee stream when it's idling and the gauge seems high. If it doesn't downright burn you, it's OK.

hope it helps
John