1983 Mercury Black Max 150hp Boggs under load???

[erubash]

Hello Fellow Enthusiasts-

Here's my Situtation..


Symptoms for Merc 150HP Blackmax- Boat starts on first turn, idles fine, but is very balky under load…will eventually plane out for about 30 secs then boggs down sometimes stalls but starts right back up again.

What I’ve done:
• Drained fuel tank
• Replaced all fuel lines going out of tank to motor
• Removed inline clear filter
• Installed a Moeller clear site water separating filter (Currently running 87 Octane with a 45:1 Ratio using Pennzoil Semi Synthetic 2 Cycle)
• All new plugs
• New water pump
• New Gear Lube
• Replaced 3 Ignition wires (Starboard Side)
• Replaced Idler Coil wires
• Has a new Stator already
• Cleaned Carbs
• Checked spark on all cylinders (OK)
• Did a compression check. 60psi exactly on all cylinders. Now I know this is low but it is a 1983 motor. I’m sure it might be the cause of my stalling problems but every time I’m on the water it runs better and better.

My question is how do I go about fixing the compression issue if that’s what It boils down to??? I know Yamaha makes a product you dump into the cylinder that is supposed to free up some valves or reeds or something are you familiar?

Any other troubleshooting thoughts?

[westexasrepublic]

buy a fuel pump kit dont use champion plugs, use BGK, and test your switch boxes as well as stator using a DVA meter

[erubash]

buy a fuel pump kit dont use champion plugs, use BGK, and test your switch boxes as well as stator using a DVA meter

Fuel Pump-Done
Switch Box-Done

Why not Champion Plugs? Dont have a DVA Meter but did measure AC(*1.4) on blue and Red wires. 170 on blue 55 on red.


Not sure what to do next!

Eric

[westexasrepublic]

i dont know why but these motors run way better on the oem NGK plugs. just do. those champ plugs are supposed to be equivalent but not from the 3 different Mariner motors Ive tried them on.

does your tach work properly? the tach not working right is a good sign your rectifier is bad.

[bajaunderground]

X3 on the NGK plugs (BU8H).

I noticed you "cleaned" carbs?! I would suggest a rebuild/rejet as well as replacing ALL fuel lines...also, the DVA meter will tell you lots, but a bad rectifier will not affect performance, just recharging and tach readings...

I'm not sure about your compression readings...they sound really low? Was the engine warm when testing? If they are you might want to consider a ring job? You might need to pull your heads and inspect cylinder walls? I'm not 100%, but I believe that's a chrome plated alum. block...if the chrome is compromised, you'll either need a need new block or a sleeve job. To me, if all cylinders are roughly the same, then it might be time for a rebuild, if done cold, do warm and report findings on here...someone with way more experience will chime in on it!

[CharlieB]

Ditto the NGK's

Bogging on acceleration is often a slightly lean idle

Dying soon after acceleration can be running out of fuel

First test, install a clear hose in place of the fuel line immediately after the fuel pump, run the motor and watch for any air bubbles passing thru, indicating air sucking into the system and NOT keeping all carbs filled.

If the motor starts, idles, and pulls up to rated speed, then compression is not an issue, suspect the quality of the gauge may not be the best and reads low.

Oh, a bad rectifier can have an effect on upper RPM, disconnect the yellow stator wires and retest performance, if all is well, replace the rectifier.

[erubash]

Hey Gang-

Thanks for the Replies. Just so were clear on the Symptoms. Last 3 times I had it in the water The Motor Boggs under load. It intermittenely gets up on plane but for no more than 15-20 Secs before it loses power and stalls.

Since then iv'e:
1- rebuilt the carbs
2- Tested switch box and found a faulty box and replaced it.
3-Re ran all ignition wires from both boxes to Coils

It started right up and seemed to idle a whole heck of a lot smoother than it was. I have yet to put it into the water to test but will do so this week and report back my findings. Thanks again for the replies.