The motor: Standard 1984 Johnson 9.9 hp motor. The extra 15 hp carb came off a 1979 Evinrude. The prop was an aluminum 9.5 X 10.
The boat: 15' aluminum Gregor v-hull modified into a bass boat. The boat with gear including myself weighed approximately 600 lbs during testing but that is a guess.
First test: I launched the boat in the river and idled out not knowing what to expect since I usually run a 30 hp Suzuki. I got out to deep enough water and opened it up. The boat took off fairly slow and for a moment I wasn't sure if the 9.9 was going to get it on plane. It took about 10 seconds but the bow was up and I was picking up speed eventually topping out at as high as 16 mph but the average speed was about 15.5 mph. I noticed the tilt pin was in the lowest position so I moved it to the third hole and redone the tests. With the outboard up a bit I could tell the boat picked up speed a little bit faster from the hole and ended up topping out at 17.6 mph but probably averaged around 17mph since the gps was fluctuating anytime the breeze blew. I tried other positions but the 3rd hole was the fastest.
I pulled the boat off to the side and swapped the 9.9 carb for the 15 carb. Took about 10 minutes and the conditions for everything was identical when I tested the 9.9.
I took off and the power difference was noticeable. I picked up speed alot faster and it just felt like I had more control of the boat with the extra HP.
I had the pin in the the 3rd hole and it the top speed fluctuated between 18-19 mph.
I moved the pin up to the 4th hole and was able to get the boat up to 20.2 mph. None of the other positions improved top end speed.
Top end speed only improved 2.5-3mph (not that great) but the most noticeable difference was the hole shot and handling. The 15hp took off and got up to speed with better handling characteristics unlike the 9.9 which struggled to get up to speed and maintain that speed when the breeze picked up.
I also had an old 30hp Tohatsu that I picked up for cheap that I tested real quick that day. It got up to a little over 25 mph quick but that was it.
I tested my mid 80's 30hp a while back with at least 200 more pounds of payload and it got up to 27 mph on the gps.
If someone had a 9.9 and was wanting to do a 15hp carb swap I would say its worth the approximate $150 it would cost to get one off ebay.
The boat: 15' aluminum Gregor v-hull modified into a bass boat. The boat with gear including myself weighed approximately 600 lbs during testing but that is a guess.
First test: I launched the boat in the river and idled out not knowing what to expect since I usually run a 30 hp Suzuki. I got out to deep enough water and opened it up. The boat took off fairly slow and for a moment I wasn't sure if the 9.9 was going to get it on plane. It took about 10 seconds but the bow was up and I was picking up speed eventually topping out at as high as 16 mph but the average speed was about 15.5 mph. I noticed the tilt pin was in the lowest position so I moved it to the third hole and redone the tests. With the outboard up a bit I could tell the boat picked up speed a little bit faster from the hole and ended up topping out at 17.6 mph but probably averaged around 17mph since the gps was fluctuating anytime the breeze blew. I tried other positions but the 3rd hole was the fastest.
I pulled the boat off to the side and swapped the 9.9 carb for the 15 carb. Took about 10 minutes and the conditions for everything was identical when I tested the 9.9.
I took off and the power difference was noticeable. I picked up speed alot faster and it just felt like I had more control of the boat with the extra HP.
I had the pin in the the 3rd hole and it the top speed fluctuated between 18-19 mph.
I moved the pin up to the 4th hole and was able to get the boat up to 20.2 mph. None of the other positions improved top end speed.
Top end speed only improved 2.5-3mph (not that great) but the most noticeable difference was the hole shot and handling. The 15hp took off and got up to speed with better handling characteristics unlike the 9.9 which struggled to get up to speed and maintain that speed when the breeze picked up.
I also had an old 30hp Tohatsu that I picked up for cheap that I tested real quick that day. It got up to a little over 25 mph quick but that was it.
I tested my mid 80's 30hp a while back with at least 200 more pounds of payload and it got up to 27 mph on the gps.
If someone had a 9.9 and was wanting to do a 15hp carb swap I would say its worth the approximate $150 it would cost to get one off ebay.
