Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

[JJS09]

So, I decided to go ahead and bump my 2009 5HP 4-stk Tohatsu upto a 6HP. And with my quick purchase finger I ended up ordering the 6HPA2 4-stk carb. The online dealer wont even discuss exchanging or taking the parts back, even though the order hasn't even arrived yet, anyway he say's these carbs are interchangeable and "should" work. So here is my questions.

1. Are they interchangeable?
2. If so what is the difference between the A2 & B engine models?
3. Am I better off ordering a 6HP "B" model carb? And use the A2 as a paper weight.
4. Anyone have recommended Jet part numbers to use for 5500 feet (live in Denver) for the "A2" or "B" version carbs?

Thanks In-Advance

 

[TOHATSU GURU]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

1) Yes
2) Different emission standard...You are much better off putting the A series carb on the B model.
3) No
4) Visit internetoutboards.com, look under Outboard Parts, then under High Altitude jet kits.

 

[JJS09]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

Thanks, I'll give the A2 a shot.

One other question will the 6,000 elevation jet set be functional at 5500? Or Am I better off with the 3,000 ft set?

Thanks again.

 

[TOHATSU GURU]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

You would use the 3000'.

 

[JJS09]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

So I completed the carb change out and here are the things I discovered with my motor so I thought I would share the information.

1. The #35 slow jet supplied in the 3,000 to 6,000 ft elevation jet kit from internet outboards didnt work for me. The engine would not idle, I had to stay above 2,000 rpms to keep the engine going.
2. So I reinstalled the factory #45 slow jet and motor would idle fine at 1200-1300 rpm range.
3. So faced with the issue of the slow jets, I contacted the local tohatsu service shop to inquiry about the main jet size and they recommended staying with the factory jets unless one plans on staying above 7,000 feet for an extended amount of time (1-2 day fishing trips were ok).
4. So I replaced the #68 main jet with the factory #75 main jet and took my 14 porta bota & Garmin GPS out for some test #'s (before & after numbers below).

5HP "B" Carb with 8 pitch prop (Loaded Boat weight - 600lbs):

Idle - 2.0 mph​

WOT - 9.0 mph​

5HP "B" Carb with 6 pitch prop (Loaded Boat weight - 600lbs):

Idle - 1.5 mph​

WOT - 10.1 mph​

6HP "A2" Carb with 6 pitch prop (Loaded Boat weight - 600lbs):

Idle - 1.5 mph @ 1200 rpm​

WOT - 10.9 mph @ 5800 rpm​

6HP "A2" Carb with 6 pitch prop (loaded Boat weight - 850lbs):

Idle - 1.4 mph @ 1200 rpm​

WOT - 8.5 mph @ 5,000 rpm​

Maybe at some point I will install the #68 main jet with a #38 slow jet and see how it performs but for now I am happy.

 

[vt17]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

So I completed the carb change out and here are the things I discovered with my motor so I thought I would share the information.

1. The #35 slow jet supplied in the 3,000 to 6,000 ft elevation jet kit from internet outboards didnt work for me. The engine would not idle, I had to stay above 2,000 rpms to keep the engine going.
2. So I reinstalled the factory #45 slow jet and motor would idle fine at 1200-1300 rpm range.
3. So faced with the issue of the slow jets, I contacted the local tohatsu service shop to inquiry about the main jet size and they recommended staying with the factory jets unless one plans on staying above 7,000 feet for an extended amount of time (1-2 day fishing trips were ok).
4. So I replaced the #68 main jet with the factory #75 main jet and took my 14 porta bota & Garmin GPS out for some test #'s (before & after numbers below).

5HP "B" Carb with 8 pitch prop (Loaded Boat weight - 600lbs):

Idle - 2.0 mph​

WOT - 9.0 mph​

5HP "B" Carb with 6 pitch prop (Loaded Boat weight - 600lbs):

Idle - 1.5 mph​

WOT - 10.1 mph​

6HP "A2" Carb with 6 pitch prop (Loaded Boat weight - 600lbs):

Idle - 1.5 mph @ 1200 rpm​

WOT - 10.9 mph @ 5800 rpm​

6HP "A2" Carb with 6 pitch prop (loaded Boat weight - 850lbs):

Idle - 1.4 mph @ 1200 rpm​

WOT - 8.5 mph @ 5,000 rpm​

Maybe at some point I will install the #68 main jet with a #38 slow jet and see how it performs but for now I am happy.

Great info for prop selection. Thanks!

Apologies resurrecting an old thread, but more of the same. Considering upgrading my 4HP to 6HP on my sailboat. My 4HP is 2004-2005 (not looking at it right now).

I see defender.com selling carbs for ~$100 ...are these decent or are they aftermarket and of lower quality than an original Tohatsu? Anyone know? They also sell A, B, and C carbs for the 6HP (as if they are not all interchangeable). It sounds like I should go with the A regardless of what my OB model is?

http://www.defender.com/product.jsp?path=-1|215570|1794283|1825671|1825674&id=1829684&cartId=3419177

 

[pvanv]

Re: Will a Tohatsu 6HP "A2" Carb work 5HP "B" Engine?

All the MFS 4/5/6 carbs will interchange. The difference re hp is in throat size; The differences in A, B, and C are emissions standards (The A2 carb will be a little more reliable and idle a little better). Re-jetting is ONLY for very high altitudes. We normally stock the carb for the 6A2, as it is the best performing, and unless a boat requires a smaller hp, the 6 hp output is usually greatly appreciated. So, you would order 3R4032001M CARBURETOR ASSY, MFS/NSF6A2, $116.52. They are available from any dealer, including me. Not sure of the source of that online dealer's stock (they are probably real Tohatsu parts). Most dealers (including me) will match price on identical units.