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Hello experts,
I'm a newbie to the Johnson forum as I just purchased my first Johnson motor two weeks ago. As the subject states, I bought a used and in great condition 2004 Johnson 150 2 Stroke Saltwater Edition, serial no 5045178. I've only had mercury's so far and am recently coming from a 1983 Mercury 150 Blackmax. I replaced my Merc with the Johnson on my 1986 Starcraft Mariner 220V.
During the first water test with the mechanic, I couldn't have been happier in the first 15 minutes. She fired right up and purred quietly while we idled past the no wake zone. Also, there was very, very little boat vibration. Needless to say, a night-day comparison with my old mercury to this point. Hole-shot put a big grin on my face as I couldn't believe the difference. We (the mechanic and I) came up on plane very quickly.
Then, my disappointment starts. We reached 5500 RPMs at WOT but were only going 33mph based on the GPS from my Lowrance Gen 2. I could tell a big difference without looking at the graph. My old mercury would reach 43 depending on load and conditions, and I promise that is not just dock talk. I even asked the mechanic if I had the throttle wide open, and he said yes. However, I did notice that the motor looked like it was sitting very low in the water.
Let's fast forward a week. Over the last 5 days, the mechanic has made many prop and motor height adjustments, and he feels that it is properly setup. However, the top end speed only increased 3mph to 36. I got the disappointing news this morning and am doing another lake test this afternoon. One theory that the mechanic has is that the gear ratios are different between my old Merc and the Johnson, and this is the reason why the holeshot has dramatically improved but top end speed is lower. I'm not mechanically sound to disprove this theory, but I'm not buying it. My old Merc's HP is rated at the powerhead and the Johnson should be rated at the prop. Roughly speaking, the Johnson should have about 20 HP more at the prop than the Merc.
I'm out of ideas because logic tells me that the Johnson should out-perform the Merc in all areas given that it's 21 years newer. Here are a few additional points to make:
- A manual jack plate was installed due to the longer shaft of the Johnson.
- Compression is 125 across all cylinders.
- Engine is in great mechanical and electrical condition.
- I had pre-mixed gas in the tank, and the Johnson is oil-injected, so it's running double oil. However, the mechanic has confirmed that no spark plugs are fouled.
Any suggestions are very much appreciate. Also, are there any specific questions I should be asking. I will get the prop size and pitch later today.
Thanks a bunch!
Josh
I'm a newbie to the Johnson forum as I just purchased my first Johnson motor two weeks ago. As the subject states, I bought a used and in great condition 2004 Johnson 150 2 Stroke Saltwater Edition, serial no 5045178. I've only had mercury's so far and am recently coming from a 1983 Mercury 150 Blackmax. I replaced my Merc with the Johnson on my 1986 Starcraft Mariner 220V.
During the first water test with the mechanic, I couldn't have been happier in the first 15 minutes. She fired right up and purred quietly while we idled past the no wake zone. Also, there was very, very little boat vibration. Needless to say, a night-day comparison with my old mercury to this point. Hole-shot put a big grin on my face as I couldn't believe the difference. We (the mechanic and I) came up on plane very quickly.
Then, my disappointment starts. We reached 5500 RPMs at WOT but were only going 33mph based on the GPS from my Lowrance Gen 2. I could tell a big difference without looking at the graph. My old mercury would reach 43 depending on load and conditions, and I promise that is not just dock talk. I even asked the mechanic if I had the throttle wide open, and he said yes. However, I did notice that the motor looked like it was sitting very low in the water.
Let's fast forward a week. Over the last 5 days, the mechanic has made many prop and motor height adjustments, and he feels that it is properly setup. However, the top end speed only increased 3mph to 36. I got the disappointing news this morning and am doing another lake test this afternoon. One theory that the mechanic has is that the gear ratios are different between my old Merc and the Johnson, and this is the reason why the holeshot has dramatically improved but top end speed is lower. I'm not mechanically sound to disprove this theory, but I'm not buying it. My old Merc's HP is rated at the powerhead and the Johnson should be rated at the prop. Roughly speaking, the Johnson should have about 20 HP more at the prop than the Merc.
I'm out of ideas because logic tells me that the Johnson should out-perform the Merc in all areas given that it's 21 years newer. Here are a few additional points to make:
- A manual jack plate was installed due to the longer shaft of the Johnson.
- Compression is 125 across all cylinders.
- Engine is in great mechanical and electrical condition.
- I had pre-mixed gas in the tank, and the Johnson is oil-injected, so it's running double oil. However, the mechanic has confirmed that no spark plugs are fouled.
Any suggestions are very much appreciate. Also, are there any specific questions I should be asking. I will get the prop size and pitch later today.
Thanks a bunch!
Josh
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