tohatsu 4 hp -2strok caburetor question

[carlos bairo]

hi....i have a tohtsu 4hp 2 strok with only 15 hr work in it. i will like to find if cold be ok to making it a 5 hp changing the
carburetor for a big one of 5 hp, and how much extra power i ll have ,the situation is that i can t fit a heavy motor on my tender .,the weight of 2 stroke tohatsu M4c and M5b are the same . any advice welcome

 

[pvanv]

Re: tohatsu 4 hp -2strok caburetor question

The M4C is not available in North America, so we can't obtain parts specifically by that application. However, the M4 and M5 are identical blocks, so you should be fine using the carb for the M5 on your M4. I suspect, but do not know for certain, whether the ignition advance curves are the same. If they are (Tohatsu Japan can confirm -- I would contact them), all you would need to go to 5 hp would be the carb... but the M4 may just have the throttle limited by a narrow carb base gasket, or butterfly plate blocking... so it's possible that all you need is a different gasket or to reset the sync. Since I can't get the M4 parts list to compare, you will need to confirm with Japan: Sales&Service/Tohatsu Outboard Motors

 

[TOHATSU GURU]

Re: tohatsu 4 hp -2strok caburetor question

It's the same engine so the difference is just in the carb.

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

thanks guy s for your advice, i will contact Tohatsu.

 

[pvanv]

Re: tohatsu 4 hp -2strok caburetor question

It's the same engine so the difference is just in the carb.

Or does the 4 hp model use a limited "restrictor plate" carb gasket?

 

[TOHATSU GURU]

Re: tohatsu 4 hp -2strok caburetor question

Nope, everything's the same except the carb.

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

hi buy s ,i did contact the dealer about better performance ,the only way is to fit a small propeller , $140 AuD .the carb are bout the same/
but is not sure if i ll get more speed the propeller i have is 7.8x8.pitch i not sure to make the change/

 

[Sea Rider]

Re: tohatsu 4 hp -2strok caburetor question

The 4 HP carb has smaller main and slow jet plugs along restricted fuel passages compared to a 5 HP carb, no carb restrictor plate whatsoever. 4 HP is a F-52C and 5 HP is 78 BC model. Tohatsu is not a Company that cheers buyers into making engine modifications specially under warranty.

Being both engines same CC will beniefit by having a 5 HP carb instead. Don't assume will fly you to Mars, but engine will have better power to overall transport same weight better than with a a 4 HP on same boat. Latter can play with prop pitch if needed, will need to install an induction tach to test under wot preferably with you alone.

Happy Boating

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

sea rider . thanks for the advice,that will be the way,replace the carb,but ,the garanty won' t cover the motor.
so i have to ply with a small prop,that will be no problem ,.the prop that cam with the motor from dealer as new 7.8x8.0-is for engine 5B-D.S.L.UL -the specified one for 4C- are 7.8x7.0 out of stock ,in Sydney ,so by the time i ll get better performance with this motor ,i ll better buy a new one ,will save a lot of dollars

 

[pvanv]

Re: tohatsu 4 hp -2strok caburetor question

Carlos,
Luis is quite correct: The carb swap will indeed add 25% more output. Also: You cannot guess about props. You MUST test in actual conditions, with a good tach.

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

Paul.thanks .swap the carb will cancel the guaranty ,engine have only 2 hr work, the idea to fit a small prop cam from the Australian National Distributor in Sydney with the advice to fit a 393B64512-1 part number prop ,it won ' affect my guaranty ,
i think that i ll cannot guess to do any modification . better i ll look for other option that will be safe and cheap like change the engine

 

[Sea Rider]

Re: tohatsu 4 hp -2strok caburetor question

Carlos,

The only way to know for sure how is your actual prop performing is going for a wot (wide open throttle) spin with you alone and check max achieved rpm, then check if inside min and max safe working parameters stated for you 4C engine which are 4500-5500, same for the 5 HP model. Then go from there if wanting to optimize engine/boat performance with different prop. 25% more outputwhile pushing makes a difference. As the saying goes : Better is having it and.. you already know the answer...

Bear in mind that's Mission Impossible to test without installing a induction tach. Australian dealer is doing wrong recommending to change prop, he doesn't know for sure your general boat weight, size, etc to recommend a blind swap.

You won't tell the physical difference between both carbs, the differences are well hiden inside carb, so not an issue with warranty. Those 4 and 5 horses are very reliable and almost bullet proof if well cared and maintained. Paul could give a precise real cost. Personally would invest on a new carb and achieve 25% more power/torque rather than on a new prop that will only give less or more RPM at wot. + 25% Torque and max wot RPM is the way to go.

Happy Boating

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

Sea Rider, you give me a good idea,i ll find the cost of a carb in Australia.and then i ll contact Paul for a cost with fright to Sydney.

The dealer and the distributor in Sydney don't give a dam about, i find that the prop is no the one in the owner's manual that's recommended .Luis,for your information, i have a Walker bay R I D 3.2 dingy so the ideal weight 5-6 hp max. do you think i need an extra fuel inlet with the 5 hp carb?
thanks Amigo for your advice.

 

[pvanv]

Re: tohatsu 4 hp -2strok caburetor question

Carlos,

The carb is 369032002M CARBURETOR ASSY, 5B/5BS, $182.18. I have a WB RID (rigid dinghy with added tube kit) as well... use it as the dink for my sailboat. The 5 will definitely push it better (I run a Tohatsu 6). Also check transom jack height. The WB dinks were designed for 15" shaft, but modern motors are almost 2" longer. You may need to raise the motor on the transom for best rigging.

 

[Sea Rider]

Re: tohatsu 4 hp -2strok caburetor question

Carlos,

Investing on a new carb is wiser that selling actual 4C and buying a brand new 5B. About fuel inlet, that model has a internal and external tank that swaps both by menas of an internal fuel ****, no need to add anything if swaping carbs. Can you manage to plane yout WB with you alone ? If swaping cafbs will need to get an induction tach, better if it's an hour/tach.

Check Hardline, piece of cake with wipped cream to install. Besides reading rpm at any throttle range will know instantly metered worked hours for preventive/corrective state of the art maintenances.

If that sib doesn't plane with you alone lightly loaded, just achieves fast displacement speeds, not an issue if engine sits a bit lower on transom as the water splash produced at back lower tail should be minimum.

Happy Boating

 

[TOHATSU GURU]

Re: tohatsu 4 hp -2strok caburetor question

Buy the 5 hp carb from a different dealer than the one that would ever do warranty service...No one will know the difference as the carbs look the same

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

Paul,,thanks .i have the price for the carb-in Sydney today $216.25.AUSD.so i order the part's from other dealer with the number you give me ,i think that the price is on the range compare with yours plus fright, it will be around the same .
nice to have people like you and Luis in the forum.
Carlos

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

thanks ,mate.. you open my mind .i ll change the carb right a way
Carlos

 

[carlos bairo]

Re: tohatsu 4 hp -2strok caburetor question

Luis gracias.for all you wise help,guys like me will be lost at the hand's of (shark's)dealers and distributors .
i order today the carb with the number part that Paul posted to me,i think that you advice is the best way to dealing with the motor.
i ll change the carb myself ,hope is not a complicate job to do ,but i ll really value your opinion,
regarding the induction tach i ll take to a marine mechanic to do the job,
thanks amigo
Carlos

 

[Sea Rider]

Re: tohatsu 4 hp -2strok caburetor question

Carlos,

Nada que agradecer, that's what the forums are for. Did not answer if you can manage to plane that sib lightly loaded with you alone ? About induction tach, must be installed outside engine cowl for the wot test to check max achieved rpm, ideal 5000-5500 rpm.

Happy Boating