Tohatsu 2004 40hp question?

[james082273]

Hi Everyone!

I'll have had this motor 3 years in December. Overall it has been great, starts awesome and typically runs smooth and quiet.

It has always had a problem at trolling speeds where it seems to drop a cylinder and shake or vibrate really bad.

Also possibly related it will foul a plug when run at around 3000rpm possibly a little lower speeds. Hard to tell since I do not have a tach but it is just enough to keep the boat on plane. It typically will give a "banging/popping" sound until I speed up slightly just with old plugs. With brand new plugs it does not do that.

The issues have been easily lived with but I would like to do what I can to fix. Any suggestions on where to start? I know it is something that it left the factory with....possible bad carb sync, float level, weak ignition, etc...

Thanks in advance!

 

[james082273]

Re: Tohatsu 2004 40hp question?

BTW when I said "old" plugs I meant 4 or 5 days on the water.......

I only use NGK plud too.

 

[TOHATSU GURU]

Re: Tohatsu 2004 40hp question?

I would look really hard at the carburetors. Since the engine is fine with new plugs it's more likely that it is loading up over time from being too rich than from an ignition problem.

 

[Herra Raana # 1]

Re: Tohatsu 2004 40hp question?

What model 40 hp. 3 or 2 cylinders?

 

[james082273]

Re: Tohatsu 2004 40hp question?

It is the 3cyl / 3 carb 40D version.

I was thinking carb issue as well, good place to start anyway. Any one know if the float level can be incorrect on this model or is it even adjustable?

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

The problem with this engine is that the idle speed mixture is to lean compared to middlerange RPM, I have got one engine to run extremly well with boyesen reeds and richening the low speed (bigger idle speed jets) can be found when removing the floatbowl cup under the rubberplug. Leems like some Tohatsus run well from the factory and others don´t.

 

[james082273]

Re: Tohatsu 2004 40hp question?

Thanks Motion Line. I was afraid someone was going to say something like that!

It does make sense as my idle mixture screws have zero affect on how the engine runs. Where on earth did you order the jets from?

I may consider the boy reeds as well. I installed them on a 9.9 rude and they worked really well.

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

James,
you can´t get them from anywhere, you have to make them by yourself, or I could drill them for you , needs special equipment which is not for sale.

 

[deejaycee_2000]

Re: Tohatsu 2004 40hp question?

hey motion, do you modify tohatsu motors?

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

DJC 2000,
Tohatsus are real quality products but sometimes the guys insist on modifying them.
Didn´t you know almost all guys in Sibbo are hard tuners, you can start looking here, no Tohatsus though but stay tuned, Mod TOHATSU 50 and TOHATSU 90 comin´up;

http://gumboracingteam.com/grt/index.php?lang=EN&p=Home

 

[deejaycee_2000]

Re: Tohatsu 2004 40hp question?

I know that is why I am asking you .... I've modified 50hp and 90hp ... was just wondering how many times you have had crank snapping issues? I have about 25 tohatsu motors in my workshop in pieces beyond repair ... nice racer ... i like ... what speed do you get out of it?

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

DJC,

The crank can be a problem if you are reving the engine, on M 40 C the crank has broken sometimes and the flywheel came flying like an UFO. No problems with the 30 hp. engine. The 40-50 3 cyl had loose fittings on the older engines newones are OK, the 90 hp. might twist the crank if pistons are seized.
This is an old 40 hp. crank but can be improved by welding the fittings.

 

[deejaycee_2000]

Re: Tohatsu 2004 40hp question?

I am so glad you cleared this one up for me ...... I hope ziemann and TOHATSU GURU is reading this ..... we've tried welding the fittings, but then it adds quite a bit of weight and a real effort to try and balance it again ..... we've done all kind of mods to 40hp, 50hp and 90hp ... and at the end it all boils down to the crank ...

 

[TOHATSU GURU]

Re: Tohatsu 2004 40hp question?

Nothing new here. Just some some known racing adaptations that you need to make if you are going to exceed the top RPM on any multipiece crankshaft. I'm not sure why this fallacy about Tohatsu crankshafts keeps being brought up. As long as you operate the engine in the recommended RPM ranges you will not have a problem with a crankshaft turning out of spec. ONLY using a Tohatsu in racing applications will twist crankshafts or if you have a catastrophic high speed stop. I don't profess to know everything in the world about Tohatsu's...But, what you can do to an engine for racing applications is not something that should be recommended for consumers to do to their pleasure engines. Let me know when you get to something I don't know.

 

[TOHATSU GURU]

Re: Tohatsu 2004 40hp question?

Back to the 40 D...You can check the float level by flipping a carb upside down and making sure the float is level. Anything in the fuel system or electrical system can cause a miss, but the carburetors are the culprit 90% of the time. I would urge you to have a dealer check it out. There is no substitute for experience when diagnosing what is wrong with your outboard. Your local dealer should have that experience.

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

Still on cranks, what bothers me is that you can´t race most engines without doing mods to the crank and according to U.I.M. rules it has to be in stock condition, conclusion, the world organisation forces people to cheat or quit racing, I prefer the later.

Floats, ...who has ever tampered with the levels, if it is in factory shape (horizonal level upside down) probably OK, I have seen quite a few 40-50 engines with wrong idle jets. The reason for this according to the factory is in the fuel not the engine itself. Running todays leaned fuel can cause this problem.

 

[MOTION LINE]

Re: Tohatsu 2004 40hp question?

I have to tell you all one funny thing that really made my day, some 20 years ago when I was tuning an M 40 C engine for competition use and tested different exhaust tubes (there were at least 5 different versions from the factory),
all tubes were pretty close until you gave them a closer look, but on one tube there was a stamped marking TOHATU not TOHATSU as on all the others, the Tohatu tube was one of the neglected ones, all parts were ordered from the factory, seems like one mold was made on a monday, but continues....my good friend who is the importer of theese engines showed me proudly one of his old tohatsus 2 hp. I do not know the year but I guess end of the 60ies, on the plate where you find the serial it was marked TOHATSU MORTOR.
Maybe this same guy worked on different compartments who knows???

 

[james082273]

Re: Tohatsu 2004 40hp question?

Motion, you have PM.....

 

[TOHATSU GURU]

Re: Tohatsu 2004 40hp question?

Out of the hundreds of 40 D's and 50 D's I've sold in the last 15 years we have never had a case of having the wrong jets in it. But, it could happen and I'll take your word for it. In fact it would be likely that if you saw one you would see several because the same guy at the factory that did one would do a production run's worth.

As to 40 C tubes...Beats me. The only time we sold 40 C tubes was to racers in Sport C so they could "polish" everything down to the spec...If there was one. We used to supply Terry Rinker with stuff while he was racing 40 C's and he could polish the gearcase down enough to pick 2 mph before he did anything else. Just bringing everthing to the best possible spec was enough for him to set world records.

 

[james082273]

Re: Tohatsu 2004 40hp question?

Hey Elvin,

I don't think the jets are wrong per say. They are likely all the same. Problem is the spec jet maybe too lean for the altitude and oxygen rich gasoline I buy here in Dallas. I really don't know but it does make sense.

Any suggestions are welcomed. I have a factory service manual on the way. I am not a professional ob mechanic but I have done my fair share of engine overhauls and carb rebuilds. Working with the fact that this issue was present from day one it seems it would have to be something related to an adjustment (float, sync, etc.), not likely to be anything clogged in the carb. Anything is possible I guess.