Tohatsu M40D2 3C8 new to me

[Sea Rider]

OK, will work much better than current installed prop, report max wot rpm achieved. Just curious, looking at your last 2 posted pics see what seems there's a wooden shim placed between transom border and the under side of the swivel bracket.

If so, previous owner must have shimmed it up as could have been experiencing back water splashes due to engine siiting way low. Tohatsu engines sits bit lower compared to other engine brands in same S-L-XL sizes.

Happy Boating

 

[Vintin]

I will report back. What looks like a wood shim is the actual transom wood. A piece of aluminum channel is under the motor clamps leaving a bit of wood showing above. This is what you are seeing. The wood and aluminum hull have been reduced in height by about 1/2 inch. I wish it hadn't as I feel I'm still a bit low in the water. I get zero ventilation on hard turns and I like to set up a motor so it does ventilate just a slight bit on hard turns then drop it a very small amount. I am used to having an adjustable jack plate. I'm considering one for this boat and motor but it will make seven inches of set back and make steering rigging with cables a pain due to the narrow opening for the transom. Unfortunately the motor is bolted through the hull at its lowest setting in the motor mounting fixture making raising it just a little more complicated.

It looks like this motor has never had an overheat sensor. I plan on installing one and am trying to figure out how to wire it into the control box which looks to have an alarm built into it. I realize it also need wired into the motor ECM for better motor protection for forced lower motor rpm in overheated conditions.

Thanks again!

I wish you were here on site.

Dan

 

[Sea Rider]

Dan,

How did you determined having no prop aeration at close turns along no water splashes at back transom, was by ear while checking backwards from driving position ?

For me the only way to determine spot on at which lower leg is water flow passing by is by sole visual inspection, would be ideal if a boy or a light soul on board can check that for you while you are driving at full plane if you haven't checked it that way.



Raising OB till prop aerates or lowering it till lower leg produces water splashes up or over transom it´s a waste of precious boating time which most boaters here loves doing. A visual inspection is a much faster way to determine how much you need to raise or lower the OB on transom. If in need to add wooden shims, chop transom down to dial the SETHS cond it’s other story.

If prop doesn't aerate at close 360° turns as in pic nor have water splashes up transom your OB has all the lights flashing green and ready to go for a 13 pitch prop wot run.



As your OB is already sitting bolted on transom you definitely won't like unbolting it and playing with different heights. Bear in mind that each new height adjustment must be water tested again by same method. Could be a tedious long work, the good news is that only needs to be done once and forever and as the french say Voilá.

Happy Boating

 

[Vintin]

Sea Rider,
I'll attach a photo of the jack plate on my 1958 Feathercraft with its 1957 Johnson 35hp motor. I can get about 30mph out of this rig. Yes, I adjust up until I get ventilation on hard turns and then go down a bit. As I'm after top end and am not that interested in doing donuts in the water I usually have it set to just get a little ventilation on hard turns.

I've seen folks mount Go-Pro cameras on their transoms to get a video. I'd love to do that.

I was going over carb sync and timing settings today and did both. I also cleaned out the oil filter and the mixing valve and then purged the oil system of air. Also set up a good idle at 900rpm. I've never done three carbs before. It was great! I've got a hard copy of the service manual on it's way. For now I've got a huge pdf file I'm using here on the computer.

One question:
I set timing for 18° BTDC at full throttle.
I could not back idle timing back to 3° ATDC. Ended up about 0°.

When purging the oil system of air I was of course running on a 50/1 mixed tank. I disconnected the oil amount control lever and found a handy place it fit on the throttle fitting so I could run about 1k rpm but oil at a much higher rate. That hole in the throttle fitting must be there for that purpose yet I didn't seen it in the manual. The manual said to wire it to deliver more oil while purging.

I also found that I was not getting 100% full throttle. Just a minor adjustment. I've got to lube some moving parts!

 

[Sea Rider]

Any model boat, engine brand installation is unique. To each his own. If you perform a visual inspection no need to install a GO pro Camera on transom or outside of it.

Have tested with top water performance same recommended transom/engine height spot on flat calm to choppy and windy water conditions which are the most common ones that usually will encounter. Having nothing more to check tested making close circles as pure fun and discovered that prop grips very well with 0 aeration at that setting.

Was the engine found with incorrect carb and timing advance settings ? At full grip all carbs must be fully opened along 18º timing for the 40 and 20º for the 50. Have seen 40 HP OB's with altered timing advance set to 20º, bad idea as engine will work with much less fuel intake along more time advance, someone thought that converted his 40 into a 50, which ain't so. 2º + time advance will suit that 40 to run much better at higher altitudes but not at sea level..

Can find all the adjustments on page 2-27 in the 3-4 cylinder Service Manual :

Place advancer arm (3) in the minimum speed position (throttle fully closed) and adjust low speed side stopper (5) so ignition timing matches the following spec : ATDC 3 º + -1º

If adjusted or remained adjusted to 0º idle rpm will be found a tad higher in which case need to lower it a bit to factory specs. All my engines are adjusted to 0º, achieves a faster throttle grip response and acceleration due less accelerator travel from ATDC fact specs compared to keeping factory specs unaltered. Should apply same for remote control installations.

All moving an sliding mechanisms needs to be well lubed/oiled where required for a smooth throttle operation throughout the whole throttle range. If the 40 HP lower leg has a third water intake right under middle AV plate don't need to install a heat alarm as it's near impossible for all 3 water intakes to be clogged at same time and that's from personal water experience

When will the new 13 pitch prop arrive ? Don't forget to light grease the whole prop shaft before installing the new prop and torque nut tight to specs.

Happy Boating

 

[Vintin]

When will the new 13 pitch prop arrive ? Don't forget to light grease the whole prop shaft before installing the new prop and torque nut tight to specs.

Happy Boating

Thanks again for all of the advice. I just returned from a week of boating with the new 13" prop. Here is a link to where I bought it on Ebay: https://cgi.ebay.com/ws/eBayISAPI.dl...=1856488098001

Max RPM achieved was in the 5,100 to 5,200 range.

I believe my motor is a bit deep in the water and there are some minor hull improvements yet to be made that will increase speed and efficiency. This should result in a little hight motor rpm.

I'm still thinking I need to go to a 12" pitch.

Here is a link to a prop I find interesting and looks to be made by the same company.
https://www.ebay.com/itm/Aluminum-O...m=292726857167&_trksid=p2047675.c100012.m1985

Attached is a photo taken last week. I was keeping up with a 50hp short shaft OMC on an identical hull and was slight faster than a 48hp OMC on the same hull. Neither of these other boats have tilt/trim so I do have an advantage there. As my Tohatsu is a 40hp I'm quite happy. I have a 40hp OMC 1998 short shaft that performs identically to my 40hp Tohatsu on the same hull and it also has tilt/trim.

We are the ship with the red bottom. We were cruising the Tennessee River with 23 other Feather Craft ships that day. Ample opportunity to get up beside each other and give it a go. I was the only Tohatsu there and there was one Merc 1962 45hp. The Tohatsu ran and performed well but I want more! :lol:

 

[Sea Rider]

Hello Dan,

Recapitulating :

So a 13 pitch rendered 5100-5200 wot revs as loaded. Still 600 wot revs from max 5800 factory stated.

If going for a 12 pitch prop you're after increasing current hole shot or increasing top end speed ? Playing with different prop barnds while maintaining same pitch will cause to dial different wot rpm ranges. Personally preffer to play with OEM props or same prop brand, that's props with same diam and different pitch.

Congrats, a astonishing picture..

Happy Boating

 

[Vintin]

Hello Dan,

Recapitulating :

So a 13 pitch rendered 5100-5200 wot revs as loaded. Still 600 wot revs from max 5800 factory stated.

If going for a 12 pitch prop you're after increasing current hole shot or increasing top end speed ? Playing with different prop barnds while maintaining same pitch will cause to dial different wot rpm ranges. Personally preffer to play with OEM props or same prop brand, that's props with same diam and different pitch.

Congrats, a astonishing picture..

Happy Boating

The new 12 inch pitch prop is here. It is made by the same company at the 13 inch pitch prop described above.

I'm after top end and plan on going with a stainless prop eventually. I'd imagine 12 would give me a slightly better hole shot than 13 inch and that would be good, too. Mostly I want to run the motor with the prop that is best for the motor.

If you have a link to a factory Tohatsu prop you think I ought to try please post it up.

Thanks for the kind comment on the photo. I believe we had 23 Feather Craft boats on that trip. I was tied for second fastest at 33mph. 43 Feather Craft ships at our latest get together.

Thanks,

Dan

 

[Sea Rider]

Dan,

If you already have a 12 pitch prop, try it out, just for the record report max achieved wot run as loaded to check what's the wot rpm difference going from a 13 to a 12 pitch prop. Tohatsu OEM props usually can rev as much as + 500 rpm going per one less pitch on light to medium light applications. Your combo for me would be rated as a light one.

One less pitch will increase max wot rpm, by how much isn't known, a wot test will determine that, should increase lightly top en speed too.

If all other 50 HP powered boats haven't gone through a OB-transom height optimization along a prop maximization, with a 12 pitch prop you should pass from being second to first place in hole shot and speed as well. If that happens don't tell the other boaters what you've done, keep it as a secret... LOL!!

Happy Boating

 

[Vintin]

This afternoon I got a chance to try out the 11.6 X 12" pitch prop. The max speed was 30 mph and I believe I was up against the rev limiter at 6,000 rpm. This is Vs 32 mph at 5,200 rpm with the 13 inch prop. It seems I need something in the middle. I am surprised that I saw an 800 rpm increase and a reduction in speed. The props I'm using are made by Polastorm and I don't know much about them other than they seem to be built well and the motor has low vibration. The prop specs are etched into the props. What I'm seeing should not be expected by the specs the manufacturer is supplying as there seems to be more difference in practical use. I have some hull improvements to make and I'd like to get the motor about an inch higher. It may be these changes bring up rpms and making the 13" prop the best choice. I put the 13" pitch back on and will use the 12" pitch when I have 4 in the boat or when I have to tow another boat a long distance.

 

[Sea Rider]

Welcome back Vintin,

So with a 12 pitch achieved 5200 rpm and 32 MPH and with a 12 one achieved 6000 rpmand 32 MPH. The less pitch you go after, the higher the revs that will rev up along max MPH slight decrease.

Would advise not to rise the engine, leave it for water flow to skim right under small upper plate where possible, raising the engine from where now sits will increase wot rpm, reduce max MPH speed a bit as there will be less water bed height for prop to get the max thrust.

If wanting middle response between both props send to a prop shop the 13 pitch and have it repitched to 12.5 or the 12 pitch to 12.5. Should gain, lose +,. 400 wot revs going for any of both ways. Have you realized that with a 12 pitch the hole shot is way faster than with the 13 one.

Another prime example that one less pitch will never gain + 200 wot revs if going per the idiotic rule of thumb...

To get the max out of the combo assume that is run with 2 up as the last posted pic, the engine is trimmed to sit at 90 deg and water flow is passing right/close to upper plate, right ? If yes on all 3, stay there.

Once ideal transom/engine height is dialed, it's only a matter to play with prop pitches. repitching must be done when1 full pitch is too much and only need to play with 1/2". Most times those sizes are very hard to get or even be market available.

BTW, don't do anything to the hull, just have it clean, mirror like, shinny cond to slide efficiently on water. Engine height optimization along a correct prop maximization is the way to go.

Happy Boating

 

[Vintin]

Sea Rider I have three issues with the hull. 1) A self bailing drain that adds resistance. I will replace this with a flush patched hull drain. 2) I have a rough patch job that was done by a previous owner. Pop rivets and a surface patch. This will be replaced by a flush patch. 3) The Feather Craft has tabs on the back about an inch long. It is not a smooth transition from the hull to the tabs with about 3/8" of difference. This area will be filled with glovit and sanded smooth.

I also have a few leaking rivets.

The water is not passing below the largest cavitation plate. It is slicing the water telling me the I'm still a little bit deep. Maybe an inch.

Thanks!

 

[Sea Rider]

Vintin,

When you sort out all described hull issues and hull is flat if that's what you're aiming for. If that's a bolt-on transom OB, lower it a bit for water flow at speed to skim right under or as close as possible to small upper plate. OB will have better prop thrust, prop will bite better due to having more water bed height while achieved over revving will decrease some.

Is it mandatory to have rear tabs installed, have you tried running the combo as usually used ? Assume that were added to plane the combo faster, right ?

In my personal experience rigging many Tohatsu HP-OB's in different hull types if :

-Deck weight is evenly distributed.
-OB sits at 90 deg, has a agile fast throttle response.
-Water flow skims right under upper plate.
-OB has undergone a prop maximization, that's propped right to run at max wot rpm range or bit over it if in pursuit to attain a faster hole, shot there's no need to install trim tabs nor doel fins. The combo will literally jump on plane at 3/4 throttle.

Happy Boating

 

[Vintin]

SeaRider thanks for all of the tips. The tabs are a part of the boat hull and were installed factory. They are only about one inch wide and you can see how long in the attached photo. The hull has a 'rocker' in the last four inches of the hull and the tabs are installed about 3/8 higher than the bottom of the hull. I plan on making this whole area smooth to reduce drag. This kind of tab is found on many of the Feather Craft boats.

I tried the 'smart tabs' on another feather craft but ended up not liking them. Everything I did slowed the boat down. Through proper trim and boat weight balance I was able to eliminate purposing and achieve a good top end.

I don't have any problem at all jumping up on plane. The hull only weighs about 320 lbs and with 175 lbs plus my 200 lbs. the package presents a pretty light load to the motor.

I have another prop on the way to be tested.

Thanks.