80's 150HP black max problem (won't run when shifted)

[rjcamel2355]

Hey folks, I have an early 80's blackmax 150HP (I believe it's an XR2), all the usual tricks haven't worked.
1. Cleaned carburetors, double and triple checked.
2. Compression (cheap china gauge) is 85-95PSI on every cylinder
3. New water pump, new lower unit oil
4. New switch box (Had no fire on 1,3 and 5) *It now has spark jumps 7/16"+ on all 6 plugs

Engine runs fine on the hose, starts easy and idles great, shifts in and out of gear, and revs on a hose.
1. Engine idles high when put in the water dies when shifted into gear (forward or reverse)
2. #3 spark plug is black after running (Double checked compression, and spark, both are good), triple checked the carburetor.
3. All other plugs look normal, not black, not fouled.
4. Tons of white smoke when lower is submerged and running.
5. Engine will rev in neutral (in the water), but shift into gear and it will die, bumping up idle does not help.

Any ideas? Thinking a possible powerhead gasket, with the white smoke and not wanting to run with the lower submerged (load on engine).

 

[Chris1956]

Gee, White smoke is usually steam. If water is getting into the cylinders, usually the spark plugs look brand new, as they tend to get steam cleaned.

You can remove the spark plugs and crank the motor in a tub of water. Now hold a rag over each spark plug hole and look for droplets on the rag. That would be water.

 

[rjcamel2355]

Gee, White smoke is usually steam. If water is getting into the cylinders, usually the spark plugs look brand new, as they tend to get steam cleaned.

You can remove the spark plugs and crank the motor in a tub of water. Now hold a rag over each spark plug hole and look for droplets on the rag. That would be water.

Hey Chris, appreciate the reply.

Smoke is very white, I know these motors smoke, but this ain't the normal 2 stroke light blue smoke.

I'm under the assumption it's steam as well. Odd that the compression is "good" but water getting into the cylinders. Plugs 1,2,4,5,6 all look the same, #5 is as dark as coal. I was assuming possibly a bad coil, but sparks great across all 6.

I've been through both the bowl side, and the idle (top plate side) of the carbs, with cleaner, and wire through each orfice, everything is clean and checks out.

 

[Chris1956]

Water can get into the cylinders from the exhaust water jacket, and the compression can be just fine. It may be able to get into the cylinders from other places including block cracks, but I am not too familiar with the Merc V6 engines. The exhaust covers on my merc IL 6 engines leaked and water was sucked into some of the cylinders, so I have some (lousy) experiece with this issue.

You will see some steam from that motor on a cool day, but it should not be too much.

 

[cmw1]

Not to hijack this thread just a quick question....are the carbs supposed to open all the way when at wot with the boat off or is that vacuum controlled?

 

[rjcamel2355]

Not to hijack this thread just a quick question....are the carbs supposed to open all the way when at wot with the boat off or is that vacuum controlled?

(ON AN OUTBOARD)

Carbs are mechanically controlled, when you move the throttle handle all the way forward, the carbs should open fully, boat on, or off does not matter. If they're not opening fully you'll need to do a link and synch

 

[cmw1]

(ON AN OUTBOARD)

Carbs are mechanically controlled, when you move the throttle handle all the way forward, the carbs should open fully, boat on, or off does not matter. If they're not opening fully you'll need to do a link and synch

i know how a traditional carb works like on anything other than a boat. push handle, carb opens. i push my handle and the carbs are cracked just slightly....can you share a pic of what its supposed to look like at wot? my boat seems to have good power its not like its running super sluggish or anything.

 

[NooBoarder]

I'm having a similar issue, what can you do if this is the case? Anything at all?

Water can get into the cylinders from the exhaust water jacket, and the compression can be just fine. It may be able to get into the cylinders from other places including block cracks, but I am not too familiar with the Merc V6 engines. The exhaust covers on my merc IL 6 engines leaked and water was sucked into some of the cylinders, so I have some (lousy) experiece with this issue.

You will see some steam from that motor on a cool day, but it should not be too much.

 

[Chris1956]

Noo, start your own thread with engine year, HP and make, along with symptoms. i.e. How do you know water is getting into the engine?