Boat not getting up to speed

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Mwilson18

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Nov 24, 2020
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I recently took my (new to me) bass boat out for its first maiden voyage. I’ve been fixing it up as a winter project and it has an 89’ 60hp Mercury 2stroke outboard.
As I opened her up to full throttle down the pond, I couldn’t help but notice that I was topping out at a painfully slow pace. My fishfinder speedometer said I was around 7 MPH. The boat is a 15’ long fiberglass Gemini bass boat, and weighs about 750lbs. I never expect to be flying down then water at 70 mph, but I should be topping out around at least 25 mph??
I checked to see if maybe my propeller hub was spun, and after making a mark on the hub and prop and taking it out for another ride, found that the prop isn’t slipping at all. Am I wrong in saying I should be going faster?
 
Faztbullet

Faztbullet

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yes....need to troubleshoot. Start with compression test followed by spark test of each cylinder.
 
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Mwilson18

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Faztbullet said:
yes....need to troubleshoot. Start with compression test followed by spark test of each cylinder.
Click to expand...
I have spark and good compression in all cylinders. I’ve checked my throttle cables as well and all linkages/controls are working fine.
 
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JDusza

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When looking at spark, be sure to look at spark plug output / performance, not just coil air gap performance. Coil may look fine on a tester but the plug may not be transmitting that energy. Don't assume the plug is working. Not that this has burned me before, ... NGK ...
Are coil to plug wires routed correctly? I recently opened up a 4 cylinder Force that was wired 1, 2, 4, 3. "Who was in here?"
If spark and compression check out, take a peek at timing linkage. When you throttle up, make sure you are advancing ignition timing along with opening the carburetor.
J
 
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Mwilson18

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Mwilson18 said:
I had it in a marine shop recently and my mechanic said he saw good compression in all cylinders. Unfortunately I don’t know any numbers:/
Click to expand...
JDusza said:
When looking at spark, be sure to look at spark plug output / performance, not just coil air gap performance. Coil may look fine on a tester but the plug may not be transmitting that energy. Don't assume the plug is working. Not that this has burned me before, ... NGK ...
Are coil to plug wires routed correctly? I recently opened up a 4 cylinder Force that was wired 1, 2, 4, 3. "Who was in here?"
If spark and compression check out, take a peek at timing linkage. When you throttle up, make sure you are advancing ignition timing along with opening the carburetor.
J
Click to expand...
Thank you for your response, I will check more tommorow on coil pack/spark. I did do a spark test with a tester and did see spark but as you noted, coil pack might not be giving enough power. I will look into that
 
M

Mwilson18

Seaman
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Nov 24, 2020
Messages
57
JDusza said:
When looking at spark, be sure to look at spark plug output / performance, not just coil air gap performance. Coil may look fine on a tester but the plug may not be transmitting that energy. Don't assume the plug is working. Not that this has burned me before, ... NGK ...
Are coil to plug wires routed correctly? I recently opened up a 4 cylinder Force that was wired 1, 2, 4, 3. "Who was in here?"
If spark and compression check out, take a peek at timing linkage. When you throttle up, make sure you are advancing ignition timing along with opening the carburetor.
J
Click to expand...
JDusza said:
When looking at spark, be sure to look at spark plug output / performance, not just coil air gap performance. Coil may look fine on a tester but the plug may not be transmitting that energy. Don't assume the plug is working. Not that this has burned me before, ... NGK ...
Are coil to plug wires routed correctly? I recently opened up a 4 cylinder Force that was wired 1, 2, 4, 3. "Who was in here?"
If spark and compression check out, take a peek at timing linkage. When you throttle up, make sure you are advancing ignition timing along with opening the carburetor.
J
Click to expand...
I did some more troubleshooting today. When running outboard, I found that by unplugging spark wire to cylinder 1, there was a minor audible difference to engine running but engine still ran. When unplugging cylinders 2 and 3 spark wires, the engine died immediately. I tested resistance on each of the spark plug wires and had 12,000 ohms on cylinder 2 and 3’s wires, while cylinder 1 wire had a resistance of 15,000 ohms. Could this be an indication of a bad/weak spark plug wire?
 
Faztbullet

Faztbullet

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Check compression ...again, test spark on that cylinder, must jump a minimum 3/8 air gap
 
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Mwilson18

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Nov 24, 2020
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57
I have an interesting find. I did a compression test myself and what I found was the 1st cylinder has 120 psi while the bottom two cylinders both have 140 psi. I would imagine this would explain why the engine doesn’t die when I pull the top cylinder spark plug, and would also explain for the loss of power? How would I go about troubleshooting this indifference in compression?
 
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Chris1956

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The top cylinder has enough compression to allow the engine to run normally. That is not your problem.

Spark must jump a 3/8 air gap. Are you sure about the resistance of those spark plug wires? That seems like very excessive resistance.
 
lprizman

lprizman

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Year of motor the HP has losses hp.....be sure fuel is mixed correctly....

Age of boat....has gained lbs over time

And your underpowered to start.

Repower to get close to your expectations.....like a 90 HP....I had one on my bass boat....Procraft 18 - 40+ mph

All the Best!!!
Lance
 
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Mwilson18

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Chris1956 said:
The top cylinder has enough compression to allow the engine to run normally. That is not your problem.

Spark must jump a 3/8 air gap. Are you sure about the resistance of those spark plug wires? That seems like very excessive resistance.
Click to expand...
Okay, I suppose I could switch the top spark plug wire with one of the “good” ones and see if that makes a difference on that cylinder?
 
Sea Rider

Sea Rider

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Mwilson18 said:
I recently took my (new to me) bass boat out for its first maiden voyage. I’ve been fixing it up as a winter project and it has an 89’ 60hp Mercury 2stroke outboard.
As I opened her up to full throttle down the pond, I couldn’t help but notice that I was topping out at a painfully slow pace. My fishfinder speedometer said I was around 7 MPH. The boat is a 15’ long fiberglass Gemini bass boat, and weighs about 750lbs. I never expect to be flying down then water at 70 mph, but I should be topping out around at least 25 mph?? Am I wrong in saying I should be going faster?
Click to expand...

Once the motor is running strong report how loaded do you usually go boting with, max wot rpm achieved at full throttle on flat calm water cond. Ideally the motor should rev middle to max of its wot rpm range factory stated. Need to prop right that combo with a tach to get the max out of it...

Happy Boating​
 
M

Mwilson18

Seaman
Joined
Nov 24, 2020
Messages
57
lprizman said:
Year of motor the HP has losses hp.....be sure fuel is mixed correctly....

Age of boat....has gained lbs over time

And your underpowered to start.

Repower to get close to your expectations.....like a 90 HP....I had one on my bass boat....Procraft 18 - 40+ mph

All the Best!!!
Lance
Click to expand...
Hi Lance, thanks for the response. I have considered upgrading to something with higher HP…
 
Sea Rider

Sea Rider

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That 60 HP motor is way sick to run at just 7 MPH. For instance my 450 Mtr Rib with a max load of 1,100 Lbs powered with a 2 stroke Tohatsu L shaft 18 HP runs 22 Knots/hour. Motor height, trim, correct deck load distribution accounts also for a crappy speed.That size combo powered with a healthy 60 HP well propped should fly nonstop to Mars...

Happy Boating​
 
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Mwilson18

Seaman
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Nov 24, 2020
Messages
57
I’ve now ruled out that I have sufficient spark in all 3 cylinders (more than a 3/8 air gap), compression has checked out, and my throttle linkage appears to be visually fine. I am now leaning more toward my timing advance. I am not sure what a normal setting is on this, I will have to look in my outboard manual. It appears that as I shift into forward, my timing advance linkage moves toward the spark stop and once I’m fully in gear it bottoms out onto the spark stop. Thus, when I throttle up, the linkage doesn’t move at all. Is this normal?
 
lprizman

lprizman

Chief Petty Officer
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Messages
440
How is the hub....is it spinning and the prop not so much? Under load.....
 
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