so this spring I decided to build a surface drive motor for my 1436 trakker jon. I used a 420cc 16hp clone motor. I spoke with Ron at Hill Marine and explained my setup and he suggested a 10x8 weedless prop. My original design I used a 3.7” centrifugal clutch for a b series cogged belt for my drive pulley and a 4.5” driven pulley. The clutch was set to engage at 1800rpm. My drive shaft is 30” long. The clutch worked relevantly good, but I would hear a slight grinding which I later found out was the clutch coming in and out of engagement. It also dawned on me that my math for the pulley gearing was wrong. My math would give me, with the original setup, roughly 2960 rpm at the driven pulley. I removed the clutch and swapped it out for 4.5” drive pulley and a 4” driven pulley. My math gives me 4050 rpm at the driven pulley. Which from my research is right in the appropriate rpm range, 3800-4200 rpm. My motor has the govenor still on, so my max rpm is 3600. Once I installed the new pulleys the motor spin up great and would push the boat out of the hole great, but then get bogged down and basically stall the motor from the resistance of the water. Probably because I have yet to come up with a way to trim the motor. I used a transom mount from an old johnson outboard. It has the preset spots for trimming the motor manually. Ive removed the motor for now and put back my 9.9 outboard to finish the remainder of duck season. Over the winter I plan on upgrading the exhaust, intake filter, removing the govenor, adding 18lb valve springs, adding a polycahin drive system, fabricating my own transom mount so I can add a 12vdc actuator with 6” lift so I can trim the motor. The motor has a 3amp charging system on it so I may not be able to use an electric trim, unless I can find a way to get it to an 18amp like the honda engines. A hand actuated trim may be the best route. I drive anywhere from 5 to 20 minutes in deeper water to get to the thicker weeds and vegetation where I hunt. Is a surface drive the right option for longer drive times in deeper water, or would a long tail be better fit? I like the surface drive because I dont always have to stand up to drive it. Ive also put a lot of time into this so I dont really want to abandon it. I feel the changes I want to make will be the right choice to improving and making this motor run properly. Sorry for the long post. Any suggestions would be a great help. Thanks in advance,

Mike

too confusing?

The engine pulley needs to be smaller then the drive pulley, try to get a 1.5-1 or so ratio. Ditch the centrifugal clutch it will just burn up at the wrong time anyhow.

i thought the larger pulley on top would spin the smaller pulley on the bottom faster? isnt that the theory? Why do you say small on top?

OK thanks. What size should I run? If I keep a 4" driven pulley and reduce it by 1.5 it would be roughly 2.6 or 2.5" for arguments sake. That would only give me about 2200 rpm at the prop. What would the ideal pulley size be or prop rpm?

It depends what prop you are spinning. You want your engine to run at your max governed speed at WOT, you need to play with ratio and prop to get you going.

I'm using a 10x8 hill marine weedless prop.