Nissan 4hp conversion to 6hp

[Igyjastabay]

I have a nissan 4hp 4stroke. Can i replace this carb with lets say a 2010 tohatsu 6hp carb? Will it fit. I was under the assumption that they were all the same from year to year.

 

[Sea Rider]

Both sizes share same timing advance and same CC, so a carb swap should upgrade your current 4 into a 6 HP.

Happy Boating

 

[pvanv]

I have a nissan 4hp 4stroke. Can i replace this carb with lets say a 2010 tohatsu 6hp carb? Will it fit. I was under the assumption that they were all the same from year to year.

Yes. BTW year is irrelevant; Model/serial is what you need. Order and install

3R4032001M

CARBURETOR ASSY, MFS/NSF6A2

$116.52

 

[Igyjastabay]

Hi guys, installed the 6hp tahotsu carb on my 4hp nissan. Now it is burning oil and smoking. As i accelerate the engine will "lull" and backfire. I adjusted the idle screw to no avail. Was there something i needed to do to the new carb before installation? Thanks for your help.

 

[pvanv]

You have something else wrong; the carbs are 100% interchangeable.
The idle stop screw is only to adjust idle RPM. Too slow and the motor will stall going into gear; too fast and the motor will slam going into gear.
If you have drilled out the pilot screw plug and changed that setting, you are sure to have issues until it is reset to the correct mixture.
If you got a used carb that has been "modified" by a so-called "mechanic", all bets are off.
Smoking could be either overfilled oil, or running way too rich... or possibly a bad head gasket.

 

[Igyjastabay]

Hello and thanks for your imput. I have a 1999 nissan 4hp 4stroke that up untill the carb switch ran perfectly. I put in the 3r4032001, but noticed you recommended the
3R4032001m. Is there a difference? I bought the carb new down the street at a marina. Also how do i adjust the fuel mixture.

 

[pvanv]

The correct way to identify your motor (any Tohatsu/Nissan outboard) is by model/serial, not year. You probably have an NSF4A, or possibly 4A2.

Your part number is incomplete; the parts are identical.

The mixture is not adjustable by ordinary means. When you say that you "adjusted" the "idle screw", exactly what adjustment did you do to which screw? I would only expect to make a minor idle speed adjustment to confirm that you are in specs. You do need a good shop tach to set that idle properly. If at very high altitudes, there is a different high-altitude jet kit available, but only for very high altitudes.

Do you have the insulator and both base gaskets between the carb and intake? Are the gaskets installed properly (the carb throat hole is NOT in the center, and they only go one way.) Did you use new gaskets, or were the originals in good shape? Are the bolts torqued properly?

If the carb was installed properly, then... You either got a bad carb (doubtful if it's a factory-new unit, as they are tested at the factory), or have a different problem.

OR... if you laid the motor down on the wrong side, and motor oil migrated into the carb (mixing with fuel)... that could be your culprit. If so, drain the bowl, refill with fresh fuel, and everything will be OK.

If in doubt, take the 10 minutes to re-install the original carb. That will tell you a lot. If you did get a bummer, have the dealer replace it.

 

[Igyjastabay]

Pvanv, Thanks for sharing your knowledge about this issue. I put the original 4hp carb back on and it runs normal like it should. So this makes me think the 6hp carb I bought is a bad one. You said they test them first, I am wondering If I shouldn't try taking apart the new carb and clean it abit. I think I will take the part back. thanks again.

 

[pvanv]

Since you confirmed a bad carb, I would have it replaced by the dealer.