Mercury 4HP to 6HP Carb Conversion

[Oldspool]

Hello Folks! 1st post

I have a 2006 4hp Mercury 4 stroke of which I need to replace the carb. In doing some research on the forums I found out that Tohatsu parts of this era are compatible with Mercs (the Merc is a Tohatsu powerhead as I understand). I figured this was a good time to upgrade to a 6hp carb, and thought since the Tohatsu was less expensive I would go with that. There are 2 different Carbs listed on the 6HP parts diagram.

My Question is: Which one of the 2 will be compatible with my 4HP Mercury? The 3AUA model or the 3R4A model.

Thanks in advance!

My Merc motor Info
-Yr: 2006
-Ser # OR128972
-Model: ME4M 4ST
-Made in Japan

 

[jimmbo]

Welcome to iboats

What is your reason for changing the carb instead of rebuilding? If you think you are magically going to have a six horse engine, you might be in for a disappointment. The engines share the same displacement, however there may be other differences, such as; Camshaft, heads, intake manifolds may also be different.

 

[Oldspool]

Thanks for the welcome Jimmbo.

Engine was running really rich, low WOT RPM and would not idle down. Used quicksilver fuel system treatment/cleaner (didn't help) and tried to do a thorough cleaning. I even bought new jets and main nozzle to replace the old clogged ones. However, main nozzle is under the main jet and I think the previous owner tried to remove the main jet and broke the ears off it so no luck trying to remove it easily. Had to resort to an extractor bit which not only destroyed the jet but beat up the threads pretty bad too. Figured at that point the internal passages were probably pretty clogged too and a straight up replacement was my best bet, and why not try to pick up 2 more HP in the process?

I did some research on on this forum before posting my question and came across this post:
http://forums.iboats.com/forum/engi...rds/160493-tohatsu-4hp-parts-to-make-it-a-6hp

User Tohatsu Guru says (about halfway down) that to jump the 4HP to 6HP on these motors the entire carb is necessary, not just re-jetting I guess the internal passages are a larger diameter as well.

The Icing on the cake is:
Tohatsu 6HP carb = $110
Merc 4hp Carb= $214

I may attempt to helicoil the threads for the 4hp carb but at this point I'm considering it "pooched"