Pontoon Repower from 2 to 4 stroke

[retriever]

I have a 1976 Flote Boat that I am looking to repower from a '76 Johnson 85hp to an '02ish Yamaha 90hp 4 stroke. My wife and I run a business from the pontoon that requires us to idle in coves for up to 3 hours at a time. We ran into issues with fouling out plugs and having to change them every time we would shut down at the gas dock or any other time during the day. And while trying to "blow out" the motor to avoid fouled plugs we would smoke out the entire cove and still have fouled plugs. This is why we started looking at 4 strokes. I have been told however, that a motor such as the 90hp will "rip the transom right off the boat". Anyone out there with experience in repowering old pontoons and does it sound like this guy knows what he is talking about? I like what the 4 strokes offer and don't have to worry about service as I have a deal with a mechanic for free service in exchange for some advertisement on our rig. Any advise or words or wisdom are greatly appreciated as I am completely in the dark on this one.

 

[MinUph]

Re: Pontoon Repower from 2 to 4 stroke

I'm no wrench but a 1976 85 HP Johnson must weigh 20 times what a 02ish Yamaha 90 does. And the 5 extra HP can't make that much of a difference. I'd just be sure the transom is solid as it should be for your 85 anyway and go for it. Ya know there are always naysayers for whatever you want to do. Talk to your wrench about it.

 

[Tony T.]

Re: Pontoon Repower from 2 to 4 stroke

First what size pontoon are we talking about? and what does the data plate attached to the pontoon recommend for max hp? As a example I have a 1995 21ft Suntracker and according to the data plate on mine 90hp max is recommended. The motor I have is a 75hp Mariner, but it is a 2 stroke engine. Rip the transom right off the boat, is he referring to weight, high torque, ? I not aware of that from a 4 stroke, but I have never owned one. Maybe someone will chime in that's more knowledgeable with the 4 strokes.

Tony

 

[Rancherlee]

Re: Pontoon Repower from 2 to 4 stroke

Well the F90 is heavier by 50# or so an puts out 10-15 more HP so I don't think it's TOO much more for it. The downside is I think the 02' 90 is still carbed but I may be wrong. Then again I did bend my 75hp rated transom with a 359# 70hp 4 stroke, old 70-75hp engines were in the 250# range. If your looking at used 4 strokes a Suzuki DF70/Johnson 70 EFI four stroke would be a gem as they swing 14" props and have steep gears which are great for a pontoon. At idle/trolling I get 3-4hours out of a gallon of gas. Mercury/Yamaha 60hp Big foot engines are also nice. As for new 90s, the Suzuki DF90a lean burn and Evinrude 90 etec are both sweetheart motors if you have dealer support in the area.

 

[Davem3]

Re: Pontoon Repower from 2 to 4 stroke

it is all about weight and torque............ new 4 strokes weigh more then the older 2 stroke counterparts.......

perfect example is my boat ............. rated for a 15HP motor, in '87 a 15HP weighed in at 77 pounds, my new 9.8 weighs 88 pounds a addition of 11 pounds, so to compensate i now use a 3 gallon tank, instead of a 6 gallon, cutting 24 pounds off the boat............

holeshots now, OMG forgetaboutit, it is insane............

 

[steelespike]

Re: Pontoon Repower from 2 to 4 stroke

You might look for a Evindude Etec direct injection 2 stroke, exceeds CARB standards. Designated service boats on lake Tahoe
Where all outboards that don't meet CARB standards are banned A 20" 90 hp is 320 the 60 hp is 240.
These have fewer, less complicated service intervals, hole shot to spare

 

[retriever]

Re: Pontoon Repower from 2 to 4 stroke

The boat is 24' and rated for power up to 115hp. The mechanic that made the claim about the 4 stroke ripping off the transom said it was due to both, too much torque compared to the 2 stroke on the boat as well as the extra weight. He said he would be hesitant to install any 4 stroke over 50hp on the boat. At this point the 2 stroke gets the boat up to approx 15mph and that is acceptable for what we are doing but I would never turn away the chance to gain more speed at cruise. The quicker I can get from cove to cove means that much more money I can make.

 

[WaterDR]

Re: Pontoon Repower from 2 to 4 stroke

I think it is sometimes cheaper to buy a different pontoon then to re-power.

 

[Fleetwin]

Re: Pontoon Repower from 2 to 4 stroke

Your 85 Johnson is powerhead rated so it's really about a 75-80 HP at the prop.

The Yamaha is prop rated so it really is a 90.

What is the boat rated for?

How does the boat sit in the water now? The Johnson 85 weighed in at about 310#. Give or take 10#.

 

[retriever]

Re: Pontoon Repower from 2 to 4 stroke

I agree sometimes it IS cheaper to buy a different boat than repower which is what we have ended up doing. Once we looked at the cost to reinforce the motor pod, difference for a smaller motor and all other options for the current boat the mechanic that was going to install and maintain the 90hp yamaha decided to throw in the boat it was mounted on for a few hundred more to get us back on the water. The "new" boat is much more boat than our current model and I think we will be much happier with this set-up.

Thanks for all your input and help. I greatly appreciate the amount of wisdom that can be found on this forum.

 

[Bamaman1]

Re: Pontoon Repower from 2 to 4 stroke

2 strokes have much more torque than a 4 stroke of the same horsepower. And they'll run circles around 4 strokes coming off an idle.

The 4 strokes' advantage is in smoothness, they're quiet and get better fuel mileage in most cases. 4 strokes will generally last longer if properly maintained. 4 strokes have gotten to where they're about the same top end speed as 2 strokes, but they also get pretty loud at high rpm's.