Merc Blackmax V2000 1978 Compression

[Scooby42]

Hello everyone. I just inherited a 1975 Glastron V173 Bayflite with a 1978 Merc 200hp V6. I love the style of this boat although it does need a rebuild of the transom and sole. I’m performing a compression test to determine the health of the old beast and make a decision whether this is a project I want to take on or not.

Heres my first numbers.

Starboard bank
Top 90psi
mid 95
bottom 91

Port Bank
top 81
mid 79
bottom 70

I know you the cylinders need to be within 10% of each other. Is this 10% per bank? Or over all cylinders. It seems I might have an issue in the port bank. I also am unsure how to open the throttle on it while keeping it in neutral. I’ve been doing the test with all the plugs removed and the shifter up front in neutral.

I’m super new to outboard work but have done extensive engine repairs to cars and am familiar with the basics. I feel like I need verification that I’m doing it right though. It’s a great forum site and I’ve already learned tons from reading it. Thanks everyone.

Ryan

 

[racerone]

Throttle does NOT need to be open to get a good compression test on that 2 stroke motor.

 

[Scooby42]

Okay awesome and thanks for the reply. Good to know I’m doing it correctly. What’s your opinion on the readings? Should I squirt some 2stroke oil in and try again? See if it changes?

 

[racerone]

Those compression values are NOT encouraging.----Try another gauge.

 

[Scott Danforth]

10% across all cylinders.

Those numbers are all low, indicating a rebuild is in your future

 

[tommarvin]

You should buy a boat with four stroke EFI if your boating budget is enough.
Life is short, and days on the water are shorter/priceless, dont pay good money for a life time of boating problems.
Carbs suck, there like Harley Davidsons, dont start that well, never really idle that well sound like there about to die all the time, there loud ,love the sound, never really run well for long.
The concept, dont buy carbs if you have the money for four stroke EFI>

 

[achris]

You should buy a boat with four stroke EFI if your boating budget is enough.
Life is short, and days on the water are shorter/priceless, dont pay good money for a life time of boating problems.
Carbs suck, there like Harley Davidsons, dont start that well, never really idle that well sound like there about to die all the time, there loud ,love the sound, never really run well for long.
The concept, dont buy carbs if you have the money for four stroke EFI>

What a load of twong!
I guess that means for the 100 years before injection, no engine was right (in your opinion).

Now, I'm all for electronics, but if an engine was designed for and has carbs, there's no good reason on this planet why it can't be made to run well and reliably.... And 4 strokes are maintenance intensive and heavy. Ask anyone who's pulled a 25hp 2 stroke off and put a 25hp 4 stroke on the back end of a boat.

As for the compressions, yes, those figures are 'rebuild time' numbers. But, the first thing I would do is verify you gauge, or use another. A 'wet' test, with oil in the cylinders is also a good check.

Chris...........

 

[Faztbullet]

That the first generation non finger ported chrome bore block...Save your time and money and find a newer 1989 and up 200hp to put on it. That motor only had about 170hp.....