1989 40hp tohatsu issue

[oxbeast1210]

I received a small boat in a trade with a 40 hp tohatsu 1989 model
the motor idles fine and runs to about half throttle but anything past half throttle doesn't increase speed the boat is going. It almost sounds like is gargling or wanting to cut out past half throttle.

m40c is the model
Things I have replaced::::

compression is 140 in both cylinder
*replaced all fuel lines
*new fuel and oil
*new plugs
*new fuel water separator
*had carb rebuilt and cleaned out
* new spark plugs
* new fuel pump
*new water pump

more details we took the boat out today for some trouble shooting.
boat fired right up idled great and ran at lower speeds just fine .
my friend check to see if the motor was firing at higher speed and it was.
My friend then decided to mess with the choke a little first it just died when
he pulled the choke.He tried it one more time but pulled it slower he got it just
right and the boat picked up great and ran like it should for a good while until
he stopped and tried to do it again. We weren't able to get it running right the
rest of the day. What do you all suggest I check or do next? Im guessing since
pulling the choke got it running right it must be a fuel issue of some sort?
if you need any more information just ask
thank you

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

I will be grateful for any advice or suggestions.
thank you

 

[pvanv]

Re: 1989 40hp tohatsu issue

No shortcuts on this one. Using your Factory service manual as a guide: Pull the carb, disassemble and verify that it is spotless; also verify float height. Verify link (sync) to confirm ignition advance curve. Also run the ignition tests to make sure you aren't having an issue there. At what RPM is the motor limiting?

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Is the air butterfly getting kind of stuck when placing choke back in ? If so clean well with carb spray and lube with oil drops 4 sides of butterfly shaft.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Pvanv Im having hard time finding the manual ill get with my local dealer and see if he can help.
Sea rider i have not noticed the air buttery sticking I will check later today when we take it out to troubleshoot again.

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Today i replaced the fuel filter and had the carb cleaned again.

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Sea rider i have not noticed the air buttery sticking I will check later today when we take it out to troubleshoot again.

Must remove air cover silencer round lid, check if with sticky issues on butterfly when pulling/pushing choke knob.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Thanks sea rider,
I just noticed when looking at the parts diagram that mine is missing the silencer?..
Im going to troubleshoot on the water in about ten min wish me luck. Since messing with the choke got it running fine does that mean its more then likely a fuel issue? Also does the fuel/air screw effect idle only or top end too?
thanks manual should help me just need to get my hands on one

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

HMM so after taking it out today still had the same issue. I decided to try and give it a little choke . that made it get on plane nicely!
Since the silencer was missing i decided to cover the plastic intake hole and it took off and ran great every time I covered it..
I'm going to order the silencer cover and see what happens

 

[pvanv]

Re: 1989 40hp tohatsu issue

Sounds like you are running lean. What method was used to "clean" the carb? (is the float/needle sticking shut?) Did you verify the entire fuel system, from the tank pickup all the way through the fuel pump and carb? A little air getting sucked in could cause your symptoms.

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

I talked to a tohatsu dealer and he said the missing silencer cover sometimes can cause to much air to get in he says if i order the missing part the motor will be fine.
345-02415-0 COVER, AIR SILENCER is the part my motor is missing

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Yep, what you need is the front round lid, cover air silencer : 345024150M. Just for the record, report back when installed and tested, will be good to know if this stupid missing part can screw an entire engine down...

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Yep, what you need is the front round lid, cover air silencer : 345024150M. Just for the record, report back when installed and tested, will be good to know if this stupid missing part can screw an entire engine down...

Happy Boating

the cover solved my problem pretty crazy to think
that it could make such a difference . does anyone know what
pitch prop i should be running its pretrt slugfiah to get on plane unles
some one moves to the bow..

current pitch is 11 1/3 doesnt sound to be near full rpm ill install
my tiny tack to test . boat is 14 ft center console load is 12 gallon gas tank
2 battey and two adult males plus fishing gear..

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Incredible how the cover air silencer solved the problem. If you want that combo to plane fast, set trim angle at proper hole and move passengers up front to level boat on water once on plane. Install a induction tach full throttle to wot with at least 1 person siting at bow. Check if inside 5200-5800 min/max rpm factory stated for that engine, your wot reading will determine if under or over proped, a prop that slightly passes middle parameters would be ideal, nice hole shot and speed.

Happy Boating

 

[pvanv]

Re: 1989 40hp tohatsu issue

I talked to a tohatsu dealer and he said the missing silencer cover sometimes can cause to much air to get in he says if i order the missing part the motor will be fine.
345-02415-0 COVER, AIR SILENCER is the part my motor is missing

Yes, that older 40's will run too lean without the complete air silencer.

 

[pvanv]

Re: 1989 40hp tohatsu issue

the cover solved my problem pretty crazy to think
that it could male such a difference . does anyone know what
pitch prop i should be running its pretrt slugfiah to get on plane unles
some one moves to the bow..

current pitch is 11 1/3 doesnt sound to be near full rpm ill install
my tiny tack to test . boat is 14 ft center console load is 12 gallon gas tank
2 battey and two adult males plus fishing gear..

See if you can move the fuel tank (75 pounds, ya know!) and batteries (maybe 50 pounds each) forward (thereby moving about 200 pounds) to balance better during hole shot. Confirm correct jack height and trim. Check WOT RPM with tach.

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Yes I kinda figured that there was to much weight in the back But there isn't any room to move anything towards the front I will take it out this weekend with a tach hooked up to see where I am at
thank you

 

[Sea Rider]

Re: 1989 40hp tohatsu issue

Post whatever rpm tach reads at wot, to have an idea if under or over proped with your current prop.

Happy Boating

 

[oxbeast1210]

Re: 1989 40hp tohatsu issue

Couldn't resist and took it out today at WOT the tach read 5500 rpm.
It required my wife to sit on the bow once it gets going it runs pretty quick just takes forever to get there..
its weird though cause the bow never rises it stays pretty much level with the water but adding wight up there still helps it get going..

One other thing that I think is strange the trim is set on the 3rd hole from the transom I figured since the extra
weight on the bow helps it get on plane that if I put it down one hole closer towards the transom that it would
help with my issue. It actually made my problem worse it took even longer to get up....Im going to set it to the 4th
hole from the transom to see what happens. my theory is that where it is set right now the bow is digging in too much.

thank you for the help

 

[pvanv]

Re: 1989 40hp tohatsu issue

Also check the jack height. Typically, the anti-ventilation plate of the LU should be within 1 inch of the bottom of the boat. When at speed, the plate should ride slightly submerged. A motor that is too deep will drag more, making for a slower launch.