Needle Valve in Tohatsu 4hp 4-stroke OB

Louiis

Recruit
Joined
Jul 23, 2007
Messages
3
I have a 2005 Tohatsu 4hp 4-stroke outboard. I have recently had idle issues in that the warm engine idle speed drops very low at idle, the engine chugs a bit and back-coughs and stalls. New plug installed, new clean fuel in exterior tank, and it still happens. I have adjusted the idle speed screw, but that either puts it at a too high an idle speed or I get the same same problem if I try to then reduce the idle screw down to an acceptable rpm, as after 15 seconds or so at idle (warm/hot engine), it will start to slow, chug, back-cough through flame arrestor and stall. Engine has been flawless until recently.

I am a do it yourselfer, I assume I need to adjust the fuel-air mixture in the carburator. Can someone tell me how I can 1) find the needle valve on the carb to do this; 2) how best to adjust it? I assume that the adjustment should be done on a warm/hot engine while at idle. Somebody must have a quick thought as to what they would do.

Any thoughts or direction will be greatly appreciated.


Louiis
 

TOHATSU GURU

Admiral
Joined
Jul 22, 2004
Messages
6,164
Re: Needle Valve in Tohatsu 4hp 4-stroke OB

There is no adjustment on the carb other than idle speed as the air circuit is fixed. You likely have a dirty carb.
 

Louiis

Recruit
Joined
Jul 23, 2007
Messages
3
Re: Needle Valve in Tohatsu 4hp 4-stroke OB

Elvin
InternetOutboards

I appreciate your quick response. Is there a decent way of cleaning out such a carb w/o total disassembly, such as spraying a compound like Gumout into the air intake where the flame arrestor screen is located? How about adding a fuel additive to the tank, would that take the "gum" out of the carb?


I've heard that some folks run a tank of 93+ octane gas through their engine or add a high octane additive to the OB tank to get a cleaner, hotter burn. Thoughts?

Although not recommended, wouldn't blocking half to 3/4 of the water intake screen permit the engine to run a little hotter for awhile so that the gum you said is building up inside the carburator can burn off from a cleaner, hotter burning engine?
Thoughts?
 

TOHATSU GURU

Admiral
Joined
Jul 22, 2004
Messages
6,164
Re: Needle Valve in Tohatsu 4hp 4-stroke OB

No, the only way to clean the carb is to take it apart and soak it in carb cleaner. Addititives act as a preventive, but are usually to weak to solve an existing problem. Increasing engine temp would have zero effect on the carb...Unless you got the engine so hot that you could crack the block, only then could you get enough heat transference to help the carb:) Wrong way to solve that problem. You are right about the higher octane providing a better burn, but it will not help the carb.
 

Louiis

Recruit
Joined
Jul 23, 2007
Messages
3
Re: Needle Valve in Tohatsu 4hp 4-stroke OB

Elvin:

You Da'h man! Thank you. Is it difficult to disassemble and soak the carb unit on this outboard? I can forsee zillions of pieces coming apart as soon as I unbolt the carb. Any tips?
 
Top