Mercury BlackMax 175Hp, difficult staring, and then bogging down.

[Robertse]

Hi All, I did a compression test and got readings 110, 125, 120, 115, 120, 125 which is average for a 2 stroke. The engine now has problems starting, and when and if it starts it also running on 4 cylinders intermitted. I have spark on all 6 cylinders, and sometimes at half throttle I hear/feel it running on all 6 cylinders and goes fast, then it will bog down and run slow on 4 cylinders. I think it maybe a fuel problem. The fuel bulb use pump to a hard status. But when I recently I took off the 3 * carburettors and cleaned whole unit including all the jets. I did not replace the needle and float within the carburettors and the looked and operated fine, I also cleaned the internals of the fuel pump as well, cleaned fuel filter which sits next to the fuel pump (within the engine), but it did not resolve the issue. The fuel tank (140 Litres/35 gallons) is under the floor and used about a 2.5-3 metres (9 feet) fuel hose. It is pumping fuel to the fuel pump and to the first carburettor , the second and third carburettor are daisy chained from the first and fuel pump.
I think the fuel hose may be too long, or I may need to replace the coils or power-pack? It still have the constant beep on start-up, but it is not overheating or low on oil.. Any comments will be appreciated.

 

[Chris1956]

What year is that motor? What is the color of the spark plugs? What spark plugs do you have in it? What kind of a beep does it have? Solid tone or intermittent?

A lot of those motors have an exhaust idle relief hose from the block thru the lower cowling. Make sure that is indeed sticking thru the cowling or exhaust can get sucked into the carbs, causing misfires.

You should run the engine at high speed and have someone pump the fuel primer bulb. If that fixes it, the issue is in fuel supply or fuel pump. If the primer bulb collapses, you have a restriction upstream of the primer bulb.

You might observe the spark plug wires for arcing to ground.

 

[Robertse]

What year is that motor? What is the color of the spark plugs? What spark plugs do you have in it? What kind of a beep does it have? Solid tone or intermittent?

A lot of those motors have an exhaust idle relief hose from the block thru the lower cowling. Make sure that is indeed sticking thru the cowling or exhaust can get sucked into the carbs, causing misfires.

You should run the engine at high speed and have someone pump the fuel primer bulb. If that fixes it, the issue is in fuel supply or fuel pump. If the primer bulb collapses, you have a restriction upstream of the primer bulb.

You might observe the spark plug wires for arcing to ground.

Hi Chris, thankyou for your reply. I think it is 1990-1992 model, there is not stickers or serial number. The Spark Plugs are silver model NGK Standard Spark Plug BU8H (they are clean and look new, should I replace them?) The beep is a very quick beep intermittent, miliseconds apart, like very quick constant beep, beep, beep, beep .....
Can you please explain further about the exhaust idle relief hose from the block thru the lower cowling? I have attached a photo of the engine.
One thing I noticed prior to cleaning the fuel pump, the primer bulb will pump to an hard position, however after I clean the carbs and fuel pump, I notice the primer bulb will not go hard no more, hence may the fuel pump is leaking within. I will pull the fuel pump off again and inspect or buy a kit for it?

 

[Dukedog]

looks ta be an '88 or very early '89 at best........ '89 went ta bucket cowls.. look here for a date stamp on tha block... probably won't be as clear as this one but is in tha same general area.. behind tha "bend" in tha timin' arm...

 

[Chris1956]

Look for a silver disc on top of the block. It should have the serial number.

My '93 has that exhaust idle relief tube, but I do not see it on your motor.

You might reconnect your overheat sensor, as I see the tan wire hanging loose. Of course, it may be the temp gauge sender wire, it is hard to tell. V6's often had both an overheat sensor on one head and the temp gauge sender on the other head.

Spark plug deposits should be brown, tan or black. White (sometimes greenish-white) spark plug deposits indicate overheat or lean running. Real clean spark plugs (like new) can indicate water in the cylinders.

Check the head bolts for proper torque. Sometimes they can work loose on the V6 motors.

A leaking fuel pump diaphragm allows raw fuel into the crankcase and can cause loading up and missing, especially at idle. Fuel pump kits are cheap and easy to install.

When servicing the carbs, it makes sense to install new gaskets, inlet needles and seats. Floats for the early V6 motors may not be replaceable or avail. Early V6 motors had fixed idle jets. On those, the carbs need to be squeaky clean and the float heights must be adjusted very accurately for the engine to run right. Later model had adjustable idle jets and those must be set, by trial and error (by ear) to allow smooth running and good acceleration.

Make sure the enrichener is working properly or she will not choke up for cold starting.

I would think a beep beep of the warning system would be something to do with the oil injection system. Overheat is usually solid tone.

 

[Robertse]

Look for a silver disc on top of the block. It should have the serial number.

My '93 has that exhaust idle relief tube, but I do not see it on your motor.

You might reconnect your overheat sensor, as I see the tan wire hanging loose. Of course, it may be the temp gauge sender wire, it is hard to tell. V6's often had both an overheat sensor on one head and the temp gauge sender on the other head.

Spark plug deposits should be brown, tan or black. White (sometimes greenish-white) spark plug deposits indicate overheat or lean running. Real clean spark plugs (like new) can indicate water in the cylinders.

Check the head bolts for proper torque. Sometimes they can work loose on the V6 motors.

A leaking fuel pump diaphragm allows raw fuel into the crankcase and can cause loading up and missing, especially at idle. Fuel pump kits are cheap and easy to install.

When servicing the carbs, it makes sense to install new gaskets, inlet needles and seats. Floats for the early V6 motors may not be replaceable or avail. Early V6 motors had fixed idle jets. On those, the carbs need to be squeaky clean and the float heights must be adjusted very accurately for the engine to run right. Later model had adjustable idle jets and those must be set, by trial and error (by ear) to allow smooth running and good acceleration.

Make sure the enrichener is working properly or she will not choke up for cold starting.

I would think a beep beep of the warning system would be something to do with the oil injection system. Overheat is usually solid tone.

Hi Chris,
Sorry it was an old photo, the overheat sensor was connected some time ago.

The spark plugs are slight brown and some oil on the head of the spark plug.

The heads was pulled off, to check any passage ways was blocked. The heads was cleaned.

 

[Robertse]

Look for a silver disc on top of the block. It should have the serial number.

My '93 has that exhaust idle relief tube, but I do not see it on your motor.

You might reconnect your overheat sensor, as I see the tan wire hanging loose. Of course, it may be the temp gauge sender wire, it is hard to tell. V6's often had both an overheat sensor on one head and the temp gauge sender on the other head.

Spark plug deposits should be brown, tan or black. White (sometimes greenish-white) spark plug deposits indicate overheat or lean running. Real clean spark plugs (like new) can indicate water in the cylinders.

Check the head bolts for proper torque. Sometimes they can work loose on the V6 motors.

A leaking fuel pump diaphragm allows raw fuel into the crankcase and can cause loading up and missing, especially at idle. Fuel pump kits are cheap and easy to install.

When servicing the carbs, it makes sense to install new gaskets, inlet needles and seats. Floats for the early V6 motors may not be replaceable or avail. Early V6 motors had fixed idle jets. On those, the carbs need to be squeaky clean and the float heights must be adjusted very accurately for the engine to run right. Later model had adjustable idle jets and those must be set, by trial and error (by ear) to allow smooth running and good acceleration.

Make sure the enrichener is working properly or she will not choke up for cold starting.

I would think a beep beep of the warning system would be something to do with the oil injection system. Overheat is usually solid tone.

 

[Robertse]

Hi Chris,

I could not find serial number on top of the fly wheel.

Sorry it was an old photo, the overheat sensor was connected some time ago.

The spark plugs are slight brown and some oil on the head of the spark plug. Besides that, they are not rusted.

I have tested the suspect coils, I am getting a reading of 3000 ohms. So they are good. I cleaned all the ground connections, and check the wiring. I thinking of replacing the power pack.

The heads was pulled off, to check any blocked passage ways. The heads (water jackets) was cleaned. The head bolts are torque to 40Lbs

I re-examined the Fuel Pump, and realised the rear single strip gasket was not connected correctly and was rip. I re-applied it and added gasket maker. I also ordered a new Fuel Pump and awaiting delivery.

When I pull off the Carbs, I realised they were in the wrong order. The air hose was not connect to the bottom and did not reach, so I swapped the bottom to the top carb position.

In relation to the beeping, I always make sure the internal oil tank is full, and took of the oil cap with the sensor and turn it upside down, and also temp discounted the cable to the sensor. But the beeping will not go away.

Thanks in advance.

Hi Chris,

I could not find serial number on top of the fly wheel.

Sorry it was an old photo, the overheat sensor was connected some time ago.

The spark plugs are slight brown and some oil on the head of the spark plug. Besides that, they are not rusted.

I have tested the suspect coils, I am getting a reading of 3000 ohms. So they are good. I cleaned all the ground connections, and check the wiring. I thinking of replacing the power pack.

The heads was pulled off, to check any blocked passage ways. The heads (water jackets) was cleaned. The head bolts are torque to 40Lbs

I re-examined the Fuel Pump, and realised the rear single strip gasket was not connected correctly and was rip. I re-applied it and added gasket maker. I also ordered a new Fuel Pump and awaiting delivery.

When I pull off the Carbs, I realised they were in the wrong order. The air hose was not connect to the bottom and did not reach, so I swapped the bottom to the top carb position.

In relation to the beeping, I always make sure the internal oil tank is full, and took of the oil cap with the sensor and turn it upside down, and also temp discounted the cable to the sensor. But the beeping will not go away.

Thanks in advance.

 

[Robertse]

Hi Chris,

I could not find serial number on top of the fly wheel.

Sorry it was an old photo, the overheat sensor was connected some time ago.

The spark plugs are slight brown and some oil on the head of the spark plug. Besides that, they are not rusted.

I have tested the suspect coils, I am getting a reading of 3000 ohms. So they are good. I cleaned all the ground connections, and check the wiring. I thinking of replacing the power pack.

The heads was pulled off, to check any blocked passage ways. The heads (water jackets) was cleaned. The head bolts are torque to 40Lbs

I re-examined the Fuel Pump, and realised the rear single strip gasket was not connected correctly and was rip. I re-applied it and added gasket maker. I also ordered a new Fuel Pump and awaiting delivery.

When I pull off the Carbs, I realised they were in the wrong order. The air hose was not connect to the bottom and did not reach, so I swapped the bottom to the top carb position.

In relation to the beeping, I always make sure the internal oil tank is full, and took of the oil cap with the sensor and turn it upside down, and also temp discounted the cable to the sensor. But the beeping will not go away.

Thanks in advance.

I found the year it was made, it is 1988. Recently it overheated again and this time scored one of the bores, see the attached image. I yet to do another compression test after this happen.

 

[jimmbo]

On the 3rd you reported "I did a compression test and got readings 110, 125, 120, 115, 120, 125 which is average for a 2 stroke"
5 days later... " Recently it overheated again and this time scored one of the bores, see the attached image. I yet to do another compression test after this happen."

Regardless, of what another Compression Test shows for Numbers, the Cylinder is Scored, and the Numbers will get worse

 

[racerone]

Motor must come apart for repairs.

 

[dingbat]

My 1989, 175HP BM was a "chrome bore".
This motor looks to have chrome bores as well

 

[Robertse]

On the 3rd you reported "I did a compression test and got readings 110, 125, 120, 115, 120, 125 which is average for a 2 stroke"
5 days later... " Recently it overheated again and this time scored one of the bores, see the attached image. I yet to do another compression test after this happen."

Regardless, of what another Compression Test shows for Numbers, the Cylinder is Scored, and the Numbers will get worse

Thanks for the reply, I another recent compression test and I got 110 in that scored cylinder/piston.

 

[Dukedog]

My 1989, 175HP BM was a "chrome bore".
This motor looks to have chrome bores as well

All 2.4 175's were chrome... used tha 200 block half.. thats why they ran really good... "most" could stay with any 200.. tha horizontal front on tha 200 made a slight difference with top end.

 

[jimmbo]

Merc got the Extra Displacement by removing the Iron Sleeves from the 2 liter Block, and chroming the Bores. Pre 82, that displacement was for the 200 and 225, then in 82 when Merc started Prop Rating their bigger Outboards, the 2.4 black was used for the 175 and 200. Removal of the Iron Sleeves, resulted in a lighter Engine

 

[Dukedog]

Merc got the Extra Displacement by removing the Iron Sleeves from the 2 liter Block, and chroming the Bores. Pre 82, that displacement was for the 200 and 225, then in 82 when Merc started Prop Rating their bigger Outboards, the 2.4 black was used for the 175 and 200. Removal of the Iron Sleeves, resulted in a lighter Engine

pretty sure tha blocks are of different castings.... porting is way different plus tha 2.0 in first original casting is with tha sleeves in it.. thats one of tha reasons they are so tough.. has "99.9%" fewer interface problems....