Will Carb change give me 5 hp out of my 4?

[Wee Hooker]

I've got a mid 90's Tohatsu built Mariner 4hp outboard that has seen little use but struggles to get my 13' tin pond boat up on plane.. I've found a carb from a cannibalized 5 hp Nissan (also Tohatsu) of similar vintage for cheap $. As I recall, olny the carb is needed to ekk out a bit more HP from my 4 but wanted to verify here before digging in.
Thanks
Dave

 

[Sea Rider]

If you're a heavy champ. don't think +1 HP will plane current 13 footer, too much hull drag to overcome fast, definitely will push it at a better fast displacement non planing speed than a 4. If carb is cheap go for it, swap and try, just cross your fingers to plane. Carb swap + prop maximization should work much better. Will need an induction tach for that.

Happy Boating

 

[Wee Hooker]

Thanks, FWIW, I know the 5 hp will help as I have tested the boat with a near identical 92' Tohatsu 5 hp as well. It doesn't leap up on plane like a 9.9 but has noticeably more power to get up over my bow wave. My 5 hp is clean and dedicated to a 17.5' Canoe that I run for fishing trips up north. IT's just too nice to leave on my pond boat (exposed to weather and inexperienced guests all summer long.) so I'd like to convert the 4 to a 5. I bought the carb $25 last night so will give it a try. Good point on the prop. I have a induction tach on my 30 I can borrow for that project.

 

[Sea Rider]

A 5 HP runs 4500-5500 rpm at WOT. Install induction tach, with engine sitting at 90° go for a wot spin you alone on flat calm no wind waters and check achieved max wot rpm, will know if in need of a prop maximization and by how much less pitch to raise wot rpm to at least middle or near max of its wot range. Post your findings just for the record.

Happy Boating

 

[pvanv]

Yes, the carb will work, and will help with 25% more hp, but as Luis said, you definitely need to dial in the best prop, as you are woefully underpowered.

 

[RichardBav]

Hello pvanv,

I am new to this site and have not figured out how to post a new thread but heard your are super helpful so here goes,,,,,,,,,,,, !

I have a new Tohatsu 6hp for my sailboat and need to lock the steering in a straight line. The friction screw just does not work, the motor ends up rotating. Is there a way I can lock the steering straight or is the engine faulty. Appreciate any help.

Thank you


Richard

 

[Sea Rider]

Welcome to Iboats,

The steering friction bolt was not meant to lock the engine to run straight, if you adjust extremely tight the bolt will end damaging the interior friction system. Could tie a tight rope at both ends of carrying handle to side of sailboat.

Happy Boating

 

[pvanv]

Hello pvanv,

I am new to this site and have not figured out how to post a new thread but heard your are super helpful so here goes,,,,,,,,,,,, !

I have a new Tohatsu 6hp for my sailboat and need to lock the steering in a straight line. The friction screw just does not work, the motor ends up rotating. Is there a way I can lock the steering straight or is the engine faulty. Appreciate any help.

Thank you


Richard

The steering friction is only for friction -- it is not a straight-ahead lock. If you overtighten it, you will damage it. But, Tohatsu does have: Steering Lock Kit for the 4 / 5 / 6hp 4-stroke models.
Kit allows motor to be locked into a fixed position to allow boat to be steered using the boat's rudder. Perfect for sailboaters that want to use their rudder to steer instead of the motor. Kit includes locking bracket, all necessary bolts, warning decals and installation instructions.
Caution: Once installed, the motor is locked in place and the tiller handle cannot be used to steer the boat unless kit is removed.
Fits 4hp, 5hp & 6hp 4-stroke "B" & "C" models
Part # 3GR625000M
List Price (MSRP): $22.05

Most dealers have some in stock; we do.

 

[Wee Hooker]

Thanks again. I have the carb now. Also have my tach and two different props. Hopefully I get time to get it all done now.

 

[RichardBav]

Hi Paul,

That is great news, thank you for your help with the info on the Motor lock, How can I reach you to order the correct part?

 

[pvanv]

PM Sent. email paul@obersheimersails.com

 

[Lund_bC]

i think i would try to put up on craigslist or other free classifieds that you would be willing to trade this 4hp for something like an 8hp motor, perhaps with a bit of cash (or not) you might get lucky and find a sailor or a fishermen that would like a smaller and lighter motor to move around easier, for instance i know i person right now with a 9.9 on their dinghy and they want to trade for a smaller motor,but of course we are to far but it's just saying that sometimes trades happen.

wanting to plane and just being on the edge like that is frustating,even if you get 5hp on a plane a little wind or extra weight and your not planing for sure.. that or accept not planning for now and enjoy put put around until you can get a bigger motor

It might take a year or more to find someone willing to trade but keep an ad up and in the meantime sure get that thing going as best you can and you might find your happy with it.

 

[Wee Hooker]

I don't really want a 75# 8 hp on there. ( I have a 60# 6 hp sitting in the basement now.) I need to drag the boat fully up the beach after each use so weight is an issue. I also don't want to stress the boat under power. I know it was likely rated for at least a 10 or 15 when new, but "new" was 40-50 years ago and she's seen a hard life in those years as she served as a work boat and tender at a salt water marina. .i.e She's been patched and welded a bi and has some corrosion in her frames. t. It's not that I can't afford a better boat or a bigger engine, it's just that I like this one.

All that said, I figured I'd follow up and report that I did the carb change and I've got more hp. The boat now climbs up on plane now at about 3/4 throttle and stays there. Just right for my needs. Thanks again to all who helped.