Put together a Briggs/Evinrude outboard, have some questions

Hello all, I have a 10 ft Starcraft aluminum V hull that I have been working on for the upcoming fishing season. I just put together a Frankenstein outboard, it's an Evinrude lower unit (1968 6hp) and on top is a 6.5 hp Briggs and Stratton pressure washer engine. We took it out for a water test yesterday evening and the engine ran well and moved the boat but it needs some improvements. The water pump on the Evinrude still works and was spraying me a little during the test run. I am thinking I can attach a hose to the water pump tube and run it out the back to divert the water. Good idea or no? Also, I was only getting 7mph top speed. The top speed didn't change from 1 person in the boat to 2 people in it. I could not get the boat to plane either. I watched a bunch of videos of people with the factory Briggs 5 hp outboards and their engines seem to plane out no problem on similar boats to mine. Here's one of them: https://www.youtube.com/watch?v=71cH1v88vQE&t=6s So I'm thinking I might need a different pitch prop. What do you all think?

Well..first off the Briggs turns at what..3600 rpm. Maybe 5500rpm or so for the rude..so..

As for the pump still working..can't ya remove it..don't need it for anything except a water cooled exhaust..


I suppose ya could divert the exhaust onto the mid and use that water for cooling the exhaust..sure would be quieter..
Remember also if ya get it pitched correctly the drivetrain will need to stand up to the added torque of transmitting 6hp at almost half the rpm.

Lastly..looks as though that briggs outboard is a designed as unit and not a conversion..

Sinkingfast said:

Well..first off the Briggs turns at what..3600 rpm. Maybe 5500rpm or so for the rude..so..

As for the pump still working..can't ya remove it..don't need it for anything except a water cooled exhaust..


I suppose ya could divert the exhaust onto the mid and use that water for cooling the exhaust..sure would be quieter..
Remember also if ya get it pitched correctly the drivetrain will need to stand up to the added torque of transmitting 6hp at almost half the rpm.

Click to expand...

I'm aware of the rpm difference, I was just a bit disappointed at the performance. I'm not expecting miracles but if I could get it to plane I would be happy. I saw a video where a guy swapped out props to a bit higher and got a couple mph better on a similar setup to mine. I also noticed that the Briggs factory outboards have a 3 blade prop so maybe that is part of my problem too. As far as the water tube goes, I would like to leave the lower end intact. That's why I kind of had the idea to just divert the water out the back with a tube.

bikerider said:

Sinkingfast said:

Well..first off the Briggs turns at what..3600 rpm. Maybe 5500rpm or so for the rude..so..

As for the pump still working..can't ya remove it..don't need it for anything except a water cooled exhaust..


I suppose ya could divert the exhaust onto the mid and use that water for cooling the exhaust..sure would be quieter..
Remember also if ya get it pitched correctly the drivetrain will need to stand up to the added torque of transmitting 6hp at almost half the rpm.

Click to expand...

I'm aware of the rpm difference, I was just a bit disappointed at the performance. I'm not expecting miracles but if I could get it to plane I would be happy. I saw a video where a guy swapped out props to a bit higher and got a couple mph better on a similar setup to mine. I also noticed that the Briggs factory outboards have a 3 blade prop so maybe that is part of my problem too. As far as the water tube goes, I would like to leave the lower end intact. That's why I kind of had the idea to just divert the water out the back with a tube.

Click to expand...

Alright...here is an idea for that water...many Yamaha pwc's scoop some water from the pump and shoot it up in the air to help with visibility. Maybe shoot it up and back like the Yamis...

Prop turning 35% slower...don't be disappointed..

Sinkingfast said:

bikerider said:

Sinkingfast said:

Well..first off the Briggs turns at what..3600 rpm. Maybe 5500rpm or so for the rude..so..

As for the pump still working..can't ya remove it..don't need it for anything except a water cooled exhaust..


I suppose ya could divert the exhaust onto the mid and use that water for cooling the exhaust..sure would be quieter..
Remember also if ya get it pitched correctly the drivetrain will need to stand up to the added torque of transmitting 6hp at almost half the rpm.

Click to expand...

I'm aware of the rpm difference, I was just a bit disappointed at the performance. I'm not expecting miracles but if I could get it to plane I would be happy. I saw a video where a guy swapped out props to a bit higher and got a couple mph better on a similar setup to mine. I also noticed that the Briggs factory outboards have a 3 blade prop so maybe that is part of my problem too. As far as the water tube goes, I would like to leave the lower end intact. That's why I kind of had the idea to just divert the water out the back with a tube.

Click to expand...

Alright...here is an idea for that water...many Yamaha pwc's scoop some water from the pump and shoot it up in the air to help with visibility. Maybe shoot it up and back like the Yamis...

Prop turning 35% slower...don't be disappointed..

Click to expand...

Now that would be something to see haha. :lol: A family member had a Yamaha ski with that feature many years ago.

Keep in mind a v hull probably has less weight in the front than a flat bottom. Have you tried adding weight to the front?

I guess I am not sure if spending money on a prop is worthwhile. Small conventional outboard like that don't cost very much but I realize budgets are not universal. I have not seen anyone running a Briggs engine other than long tail mud motor kits.

My two pesos....filter for your comfort level.

Remove pump impellor as stated above. It consumes hp.

Remove govenor from your engine. You will get extra rpm. If propped right you will not overev the motor.

Call PowerTec props and get you the right prop for this application. What ever they recommend just go with it. They do this for a living.

After those mods move on to finding the correct engine mounting height. Don't pay attention to internet engineers on this one. Let the boat tell you what it wants. Move the engine up in 1/2" increments until the speed falls off and then go back to the setting with the most speed.

All of these mods are reversible if you go back to a water cooled engine.

Have fun.
Rob


Sent from my SAMSUNG-SM-G900A using Tapatalk

thedude said:

Keep in mind a v hull probably has less weight in the front than a flat bottom. Have you tried adding weight to the front?

I guess I am not sure if spending money on a prop is worthwhile. Small conventional outboard like that don't cost very much but I realize budgets are not universal. I have not seen anyone running a Briggs engine other than long tail mud motor kits.

Click to expand...

I had two of us in the boat on the test run with the other person all the way in front and it did level the boat out a lot better than with just myself driving it. The top speed wasn't really changing with differing amounts of people in the boat. That's kind of what made me consider a different prop with more pitch.

Pappy said:

Don't do anything with the water tube. Simply remove the impeller from the pump and plug the impeller end of the tube. End of issue.
Others have already touched on the RPM difference.
On a 10' boat do not expect much. I would rather see this engine on a wider, longer, flat bottom and you may have or see better performance with the larger planing surface. There were not a lot of choices in propellers for the 6hp.

Click to expand...

I will watch some videos and give it a shot. Thanks for your input.

Ebug said:

My two pesos....filter for your comfort level.

Remove pump impellor as stated above. It consumes hp.

Remove govenor from your engine. You will get extra rpm. If propped right you will not overev the motor.

Call PowerTec props and get you the right prop for this application. What ever they recommend just go with it. They do this for a living.

After those mods move on to finding the correct engine mounting height. Don't pay attention to internet engineers on this one. Let the boat tell you what it wants. Move the engine up in 1/2" increments until the speed falls off and then go back to the setting with the most speed.

All of these mods are reversible if you go back to a water cooled engine.

Have fun.
Rob


Sent from my SAMSUNG-SM-G900A using Tapatalk

Click to expand...

Those all sound like good ideas to me. Thanks for the recommendation. I think after some experimenting I will get it dialed in.