Tohatsu outboard problems

I worked with tohatsu on the height of the mount. no difference. I measured it and it ended up only being about 1 and 1/4 inch lower than stock.

Got back with tohatsu yesterday and they are stumped. They think the boat is two big for the engine and that is why the rpms are running 1200 rpm under nominal . Nominal being according to them 5500 rpm. They are sending me free of charge a 6 pitch prop to test and see what that does. They agree that I am not getting 6hp at the prop if im not getting 5500 rpm but I can tell they want to say it is because the boat is to big/heavy.

I have a new theory. The engine cranks and runs fine if it is a given that it is supposed to vibrate like it does. It produces just a little less power at the prop than the old engine. everyone I have talked to including tohatsu says that 4 strokes run just a slight bit weaker than a comparable 2 stroke. What if this engine just ended up accidentally having the jets for a 4hp version instead of 6 hp version installed. there is no physical difference in the 4hp/5hp/6hp engines other than how the carb is jetted. It would be consistent with everything that has been said and observed.

Anyway that is where it stands right now. I was going to return the engine this week but tohatsu offering to send the prop got me to agree to test that and see what the results are.

So far

  • I am happy with the customer service from tohatsu USA and Vic who I have delt with there.
  • I am unhappy with as they have not responded to my last request for help at all.
  • Based on Jons (from forums) experience i think this engine is a great price/weight/power option for our boats.
  • The fuel economy on this engine is awesome. I am getting 6+ hours of runtime on 2.5 gallons of fuel at WOT.
  • I think my experience with this engine is probably atypical and that there is an issue with this specific engine.
  • Either it is jetted wrong
  • or something is wrong with the electronic ignition advance at the top end.

Jon on the forums speaks up for being friendly and helpful with his purchases. Actually here is a quote “I had great friendly service from them, both with the purchase of the outboard & the prop.” (I thought I would add this in just to be fair.)

I posted this back

“They were not friendly or unfriendly when I called them with the problem. I got them the information they asked for and then they dropped off the face of the earth. I have not badgered them so It is possible that in general they are not like this but just dropped the ball on this one. I have been working directly with tohatsu USA because I got a better vibe and response from them. If I return the engine it will be to and I guess I will find out if it was a fluke or what by how they respond. ”

 “I would recommend buying from if you purchase online. They are within a few dollars price wise and miles better with support/attitude. I had a list of several online merchants I had priced when looking for this engine and when I started to have problems I called their number by accident. we quickly sorted out that I hadn’t purchased from them but the service guy there was really friendly and spent some time giving me advice even after we found out they had not sold the engine to me. I mentioned to Vic at tohatsu how helpful they were to me even though they hadn’t sold me the engine and he said they were a good company and that he had worked with them before on stuff.”

131 comments to Tohatsu outboard problems

  • bill k

    i have a 90 hp t 2004 or so goes up to half power w and ten starts spazzing out until i lower throttle same with my sons 70 hp ????

  • Electronic ignition mabye/throttle advance.. otherwise maybe something is restricting fuel or air at that point and it isn’t getting enough of one or the other.

  • roy J studer

    2.5 4stroke had gas in oil check the fuel pump vacume hose found gas there the dieaframe had a crack in it order a new pump motor now works great

  • Lee

    Don’t listen to them Scott. That engine is the one that many Cape Dory 25 owners are using with no problem whatsoever. You can check CD25 specs at the Cape Dory site.

    It should push your boat with no problem.

    BTW I plan to be back down in that area this coming week. Maybe we can get together for a sail.


  • Bob Donaghe

    Did you ever get the issues with your Tohatsu resolved? I am considering an on-line purchase of a 4-stroke 18 hp Tohatsu, electric start (I may wait and purchase the new 20 hp model when they come out in February). It’s a replacement for a 2-stroke 15 hp Mercury that was stolen off my 20.5 foot jon boat.

    Like you I have a list of on-line vendors where I have checked prices, etc. Will these things run straight out of the shipping box or does a dealer have to adjust or tinker with them before you can put them on the water? Any advice you can give me would be appreciated. I have never purchased anything this expensive off the internet.

    Thanks for your help.

  • Bob,
    No the issues were not resolved. I am still awaiting the results of a credit card dispute.
    The engine you are looking at is a two cylindar engine which power wise should perform a bit better than the one cylinder that I have. However going from a 2 stroke to a 4 stroke I would advise a 50% jump in power. so if you have a 15 hp 2 stroke you should look at a 20 to 25 hp 4 stroke to get comparable power.
    I have been doing a lot of testing and research and what the industry doesn’t want to say is that in practical application 4 stroke outboards do not produce as much power as the 2 stroke engines. In my case I have found that a 6 hp 4 stroke is comparable to a 4 hp 2 stroke. I have now tested other 6hp 4strokes and found them as a class to be under powered.

    A dealer won’t tell you this nor will the manufacture.. what they do is gently try to get you to buy a bigger engine without flat coming out and saying the comparable hp engine to what your replacing just isn’t as strong.

    After conversations with some mechanics I have found it is sort of a loose industry secret. Those with lots of experience that have had lots of boats and engines know this but you will not find from the manufactures or dealers anything in writing about it, nor will they tell you straight up that this is so.

    As to what you will need to do with the engine.. just add oil and break in the engine. you will have to run the engine for 10 hours in gradually increasing power increments over that 10 hours before using it at full power.

    After my experiences with I would not purchase an engine from an online dealer again. I would go to a local dealer that you can deal with and just use the online prices as a bargaining point to get a better deal. Trust me paying an extra 100 or 200 dollars locally would have been much better than what I went through (am still going through)

    If you do decide to buy on the internet then the only company I know of that I have been impressed with is
    they have tried to help me with my situation even though they didn’t sell me my engine.

  • brian

    I would have to disagree with the statements that a 4 stroke engine makes 50 % as much power as a 2 stroke engine. The true fact is the older 2 stroke engines were normally underrated example: a 90 hp merc would typically pump out 100 hp and that would be within the range allowable. The new 4 stroke engines are true rated hp. This was more noticeable when 4 strokes weighed more but now they are as light as the older 2 strokes. example: new Suzuki. HP is HP it does’nt matter if its 2 or 4 stroke. what matters is how much of it is reality and how much weight your moving around.Also 3 rd party boat tests do not show this to be true. Example: the Suzuki 4 strokes are now running with the E-Tec engines in performance.The new 90 Suzuki 4 stroke is actually lighter then the 2 stroke 90 Optimax Merc. Search videos on you tube and see real life performance. And always look for 3 rd party reviews on any manufacturer claims.

  • Brian,
    You are possibly correct in that there is a disreprency in how much HP different manufactures report for their engines. However the 6hp tohatsu engines do not in real life put out their rated HP. The reason I can authoritatively say this is that they will not run at the their rated rpm under any conditions or with any prop (stock prop all the way down to a super high thrust 5.99 pitch prop) on any boat from a dingy up unless in neutral. To reach rated HP they would have to run at the rated rpm. I have tested multiple engines and have tested them on everything from a dingy to a 23 ft sail boat on the water as well as static bollard pull tests. I tested for speed over the water and RPM as well as static thrust in lbs using a load cell rated accurate to +/- 1lb
    The results indicated that they engine was giving only about 4 to 4.5 hp of thrust. This was also borne out by the comparison to theoretical performance models. If you matched up the prop pitch and size against measured rpm in real life it confirmed that the engines were performing under manufacture claims. Maybe I shouldn’t say that a 4 stroke is less powerful than a two stroke for a given hp but that the manufacture is misrepresenting they actual power their engines develop based on their own claims.

  • Charles Doerries

    I have a light displacement 26 ft. Sailboat that I had an old Johnson 8 hp SailMaster 2stroke on it… rebuilt it several times in 15 years. Put the 6hp ultralong shaft 4 stroke Tohatsu on 3 seasons back and have been well pleased. Rarely run at over 3/4 speed, cruse at 1/2 speed, great fuel economy, mush quieter then the 2 stroke, much less exhaust fumes, vibes not bad up to 3/4 speed. Easy to maintain. On the sailboat great. Drain or run the float bowl dry after each outing, run non-ethenol gas, and the carb won’t foul. If it does foul learn to clean the Idle jet, fast and easy job if understood.

    On a 10 ft zodiac the Tohatsu is a dud… the old 8 sailmaster ran the dingy well, came to a plane quickly and was smooth, not so with the Tohatsu 6. Match the motor to the job is what I take from my experience.

    The 6 ultra long shaft Tohatsu on my light 26 ft. sailboat is a big winner. Definitely a niche motor.

  • What boat do you have? displacement? and what speeds are you getting over the water at 1/2 throttle, 3/4 throttle, full throttle etc…

  • John

    I’m following this thread due to poor idling characteristics on our 2005 4hp Nissan/Tohatsu. It runs OK at 1/3 or higher and starts well but idles fast in neutral and idles weakly in frwd and reverse.

  • John,
    It sounds like your carburetor is becoming gunked up. Run a can of sea foam through a 6 gallon tank or fuel or through two 3 gallon tanks… Directions are on the can.. After about 10 to 15 hours or operation using the sea foam it should clean up and idle like a kitten purring. At least that was my experience. The only other thing to do is service the carb by taking it apart and cleaning and put it back together.. That is what the dealer will recommend.

  • John

    Thanks…… looks like you’ve found you calling in fielding Nissan/Tohatsu problems. I’m going to review the manual and see about servicing the carb because it would take me all summer to get 10 hours of operation. Cheers!

  • Bill

    I have a Tohatsu 4 cycle 6 hp.
    It starts perfectly, idles well, but does not run smoothly a more than moderate speeds. I have disassembled the carburetor several times, cleaned the jets in MEK, blown them out with compressed air . Every now and then, it will agree to run fast without missing for a short period of time, but then it goes back to it’s ways of missing at over 1/3 power.

    Gas is always fresh.
    A neighbor has a Tohatsu 9 that tohatsu swapped out his carburetor.
    Any ideas? Suggestions?

  • That is a new one on me.. I’m used to them starting to run rough at low rpms because of the carberator fouling. That sounds like a fuel supply issue or a air supply issue. I haven’t seen it on these engines before. I would consult with a good mechanic or a dealer. It might be in the fuel pump or maybe the choke? maybe a obstruction in the jets that lets enough fuel through until you hit a certain rpm? Wish I could give you more help .

  • Henry

    I have Tohatsu 15hp four stroke it is not running good at high speeds I Cleaned the carburetor and ran the same.I checked the ignition coil the resistance it was 7.9-8.2 is that the problem?

  • I don’t have the information on that engine. I would recommend calling a dealer and asking them. I would recommend the guys at they have bent over backwards to help me in the past.

  • The Tohatsus are usually a pretty solid engine for what they cost from what I’ve heard, should be worth persisting.

  • Russell

    Has anyone heard good things or bad things about the tohatsu 90 hp. Found one for sale but dont know much about them.. Thanks its a 2005 model

  • Maek

    I have a 40 hp 2stroke tahatsu
    Am I correct that it burns 50 to 1

  • I would give a quick call to a dealer or service center or the main tohatsu support line and ask. Anyone of the should be happy to answer that. Wish I could give you an answer but I am much more conversant with the under 10 hp engines than the larger ones.

  • Bill Vokac

    Bought a used Mac25 with an 8 HP Tahotsu engine– long shaft, electric start and generator . It was ultrareliable for 2-3 years and I loved how easy it started, idled smoothly and plenty of power.

    Then it started giving me starting problems. If it started at all, it ran very rough and died despite increasing throttle and or choking it.

    Have had a new carb kit installed by a local Tohitsu mechanic and it starts and dies — but I saw the mechanic start it in front of me when I picked it up — same hose, tank!

    Any ideas?

  • How long since the mechanic started it? was there time for water to condense in the tank between him and you starting it? if he looked at it and started it and then it wouldn’t start correctly I would take it back and show him what it is doing. The only other thing to look at, is did you have it the correct side up when you transported it. You are only supposed to have them laying on one specific side.. forget which one but it says this side up on engine. If you lay it down on the other side then oil from the crank case can get in the carb and spark plugs. If this is the case take the plugs out and clean them and try cranking it again. If you can get it running for a few minutes it should flush any oil out of the carb as fuel flows through. maybe clean the plugs again after it is running and the carb is working. All the oil being burned as it flushes through the cylinders will partially foul them again. I’ve done this before and it does run rough at first. made me more careful about what side up to transport the engine.

  • Blair

    There is a reason why buying outboards on-line is less expensive than buying from your local dealer – customer service. it is so easy to sell an outboard in a box without a proper PDI, etc. for cheaper – because you don’t have to employ mechanics and service representatives to address any issues you may run across. I am sure there are lots of outboards sold online that never have any issues but you are taking a risk to be one of the few who do experience issues when you try to save a few bucks instead of visiting your dealer. I manage a Nissan/Tohatsu dealership and though I can testify to the quality of the outboards, we will always service the customers who buy local versus the ones who buy online.

  • Gary

    Been thinking about Tohatsu 9.8 hp engine still puzzled if these are good engines,with all the hype about vibration ..rough idle..true h.p. will be installing on wide 14ft john boat any suggestions thanks

  • The 9.8 will run very smooth. It is a two cylinder engine and is a much smoother running engine than the one cylinder 4, 5 and 6 hp models.

  • Hi Scott
    I am a photographer and work a lot on rivers. I have a 3.5m Quin-trex traveller alluminium boat that allows me to travel and launch with ease.

    I had a 15hp l/shaft Yamaha 2 stroke engine on in (Stolen now) and have been looking at a TOHATSU 15hp to replace it.

    Readong your articles I am concerned as to how much power will be delivered to the props against my Yamaha.

    I am also concerned of physical weight differences bettween the two engines but still lookong for information

    Hope you can help

    John Irinside


  • John,
    Sorry it’s taken so long to reply. For some reason I didn’t notice your post hit the moderation que last month.

    I’m not personally familiar with the 15hp models. However it would be 2 cylinder so would run pretty smooth and have decent fuel consumption. You will have to decide on the weight issue, 4 stroke is heavier though not as bad as it used to be. I think at between idle and about 1/3 throttle you will like the low noise of the 4 stroke. If you are taking pictures of wild life it will be nice to have a quite engine. At anything over half throttle though I have not noticed a lot of reduction in noise in my 6hp model compared to my old 4 hp 2 stroke. Power is an issue. I’m not sure if the difference in power is as pronounced in the 2 cylinder engines compared to the one cylinder engines but with the smaller one cylinder ones it is about 25%. My 6hp 4 stroke performs about the same as a 4hp 2 stroke in the top end. In the bottom end I got more torque out of the 4 stroke. So for low speed manoeuvring or responsiveness at low rpms the boat felt more powerful.

    If you have already read the whole article and comment threads you will see the details about all this.

    Wish I had some personal experience with that engine and could help you with it.

  • Carl Lovisolo

    Good afternoon! I was searching for information on a new 4HP Tohatsu (Mercury) I recently purchased and found this site. Got mor info from this site than Googeling the past few days. Maybe you guys could assist.

    4HP Merc 12′ PortaBoat. My maximum attainable speed is 5MPH with me (240lb) Motor, 55LB Minkota Elect. My throttle max’s out at half throttle and half to full nothing!

    Any ideas on helping me get a little more speed would be greatly appreciated.



  • Carl,
    I would be willing to bet that the motor isn’t making its rated rpm and that you are not getting full hp at the prop. You can try to fight that battle with the dealer and mercury but I had no luck. They shut me down when it came time to talk rated performance with actually performance. I have a feeling all these tohatsu/nissan/mercury engines don’t perform to spec. To maximize your performance you need to just go to the super high thrust 5.99 pitch prop. It will allow your engine to turn more rpm and get you a little closer to rated hp. It won’t get you all the way there but I know with the 6hp engine that I was using on my 3500 lb sailboat that it helped. That engine is identical to yours in the motor other than the carb. Your carb is jetted differently so that you produce less hp. The other difference is that I had a super long shaft compared to your short shaft. You can get a tach and measure your rpm on the engine at full throttle. To get the full hp it needs to be pushing 6000 rpm. I think you will find you are getting somewhere around 4000 to 4300 rpm at a guess. I have put my 6hp engine on a dingy and though I got a bit better speed than your reporting I still couldn’t get better than about mid to low 4000 rpms.

    If you have read the entire article and comments you should have a good feel for everything I have done in testing these engines. I would love for someone else to tilt at the dealer/manufacture windmill and see if they get a different response than me. They were very helpful up to the point I started questioning their posted performance numbers compared to numbers I was getting based on measured stats in the real world.

  • Carl Lovisolo

    Greatly appreciate the information Scott. I have to call the dealer today. They were looking into the 1/2 throttle issue and are supposed to have a response for me. Considering the motor is brand new with one test drive if they can’t resolve the issue I’ll be back at the dealer Monday with motor in hand. We’ll either be upgrading or returning the motor.

    Any idea where I can get a 5.99 pitch prop?

    Thank you and all the other posters for all the great info.

  • Here is a link to the prop at Internet outboards down in florida. This prop will fit your motor.
    They didn’t sell me my engine but when I was going through the fight with the dealer that sold me the engine and Tohatsu as the manufacture they actually tried to help me and offered a lot of information and even sent me this prop for free to try and help resolve the problem. I was pretty amazed at their level of help when they hadn’t even sold me the engine. I would recommend doing business with them anyday based on their help.

  • Carl Lovisolo

    Thanks Scott! Did you notice any performance difference with the new prop? I’ll keep you updated as to how the dealer and Mercury/Tohatsu handle the issue. I’ve been in Law Enforcement for 30 years. I’m pretty well versed on customer complaints. LOL! We’ll see how they handle that if they don’t help me.

    I’m going to look into that prop. I’m probably going to order one just to have on hand to replace the stock once I’ve exhausted all avenues to get this engine up to par.

  • Carl,
    Yes it was a major performance enhancer on my boat. It didn’t get the engine to full rpm to make its rated rpm but it brought it up almost 20% over where it had been with the stock prop.

  • Carl Lovisolo

    I sent a email to the company last night and had a response back today (Sunday). Now that’s customer service. The motor is at the dealer at the moment. I’ll find out what they have to say on Monday! If I don’t get anywhere there I’ll be upgrading the carb to the 6HP model with a new prop.

    They responded quickly stating that the 5.9999 pitch is to heavy for my application but made other recommendations.

    Greatly appreciate the info. It’s may save me alot of bickering with the dealer.

    Thanks again


  • Jim O'Toole

    I have a 2003 Tohatsu 4 stroke 4HP engine I’ve been using on my Hunter 216. I bought the engine new and each year have had more frequent problems with engine foaling caused by ethanol. This summer I spent most of the season with the engine in the shop having the carb cleaned and serviced. A new problem has developed where the engine will run for maybe 10 minutes and then stop at which point I cannot get it to start. I’ve tried hot start and that doesn’t work either. I’ve noticed that the fuel line leaving the pump is dry and after priming with the bulb on the fuel tank and cranking the engine it still is dry. I’ve got a new fuel filter and a rebuilt carb and I’ve lost most of my sailing season. Any thoughts will be helpful. PS I’m not mechanically inclined so I’m at the mercy of the mechanics with this. They all blame the ethanol which I know is a major problem. Looking forward to comments. Jim O’T

  • Jim,
    It sounds as if there is a problem in the fuel pump.. I haven’t had an issue there yet so don’t know a lot about the fuel pump or replacing it. I would think it would be pretty simple. I would call your mechanic and describe it to him and ask him what you can do.. or give a dealer a call and ask. If all they tell you to do is bring it in, try to call someone else first that might give you some simple troubleshooting steps to take before having to pay someone to work on it.

    If I was still using my beneteau F235 I think I would get one of the torqueedo motors and just go electric. Small engines just seem to have a lot of issues nowdays due to the fuel. Lets all say thank you Uncle Sam 🙁

  • They generally are pretty quick to help on the simple stuff.

  • Jim O'Toole

    Hey Scott
    Appreciate the feedback. I have given some thought to going electric but I haven’t been able to convince myself its the best way. Do you have a resource site for the torqueedo motors? Or are we just talking about trowling motors?


  • i dont have any links off hand for the torqeedo but that is what I am talking about. I have heard really good things about the newer more powerful units from them. I would have on now if they weren’t so pricey…. but they seem to have good reported power and fairly long run times. I think for a 25ft and under sailboat they would give really good service. I haven’t done any web searches on the thought in the last 6 or 7 months so there might be more out there on them now.

  • Jim O'Toole

    Thanks for the info. I’ll do some research and see what I can find now that my sailing season is over I’ve got some time. I get back to you when I resolve this issue. Thanks again.

    Jim O’T

  • geoffrey mc innes


  • sounds like something sticking in the carb letting more fuel through…

    run some carb cleaner/fuel conditioner through the carb. I use a product called Seafoam here in the US.. one can to a 6 gallon tank of fuel on my small outboard and the carb will hum afterwards.
    Other than that I would check with a dealer.

  • geoffrey mcinnes

    thanks for your info scott ,i have tried a dealer ,nothing found i will try the fuel cleaner ,trouble is i have a 150 ltr tank i will let u know later on how i get on thanks geoffrey

  • Jim Briscoe

    I have a 50hp tohatsu 2 stroke that will not shift into forward gear. It will shift into reverse and neutral. Engine runs great. had a mechanic look at it and he adjusted the shift linkage. I ran it for 30 min. all was good then when I tried to put it back in forward same issue returned. Can the linkage slip due to vibration? or could it be something else? Any help appreciated.

  • Jim,
    I just don’t have enough experience with the larger engines to give good advice on that. I would believe that vibration could do that if stuff isn’t tightened correctly.

    I would take it back to the mechanic and make him fix it again at his cost though. If the fix only lasted 30 minutes he obviously didn’t do something right.

  • Andrew

    Tohatsu msf 25Hp.Thje impeller blade is same where in the cooling pasage,kloged water flow and cant find it.I did presure the water pasage no flow,did back presure from thermostat side no flow to water pump direction.Any sugestion haw to solve this?

  • Larry Kellogg

    I cleaned carb on 25 hp Tohatsu and put in new float valve, but it still floods at prime and fuel comes out of carb. Have run some sea foam through it, but not for extended time as it won’t run long. Very low hours on motor, but sat for extended time.

  • Jocabo

    I have worked on quite a few 4/5/6 Tohatsu and Suzuki 4 strokes that will not run upto full revs,quite common on these engines when they get a few hours on them, the trick is to remove tha anti tamper plug from the idle jet adjustment and get or drill out the main jet to the next size up, you can then reset the idle and get rid of flat spots and the engine wil run up to full revs under power. The main diffrence between 4/5/6 hp engines is the jet sizes in the carb and the CDI unit that limits the revs of the engines. I have use a CDI unit from a Tohatsu 5hp two stroke on a Mercury/Tohatsu 4 hp 4 stroke and the 4hp engine will then rev upto the same revs as the 6hp version of this engine.
    Len England.

  • Jocabo

    I should have said that by removing the anti tamper plug from the carbs of these engines it will also allow you to remove the idle adjustment needle and let you make a better job of cleaning the carb, but before you remove the needle gentle turn it in (clockwise) and count the number of turns till it bottoms out, normally 1 1/3 to 2 turns, but do be gentle.

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