4stroke hp Nissan stalls at idle

Kingtackle

Recruit
Joined
Mar 27, 2015
Messages
2
I think it has something to do with Idle portion of Carb. Can anyone point me to it's location. Tempted to pull one of those metal caps and play with pilot screw. The bottom jet in carb say's .35 and I can not see light through it such small hole cooper wire will not go through. Should I go ahead and drill this out bigger. Seen video of Honda and it was large enough hole to see through. Parts are cheap to replace and solid idle motor is important.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Welcome to Iboats,

Engine stalls at idle or at idle and load ? Probably your idle rpm is way down ? Adjust idle screw CW a bit and check. When was the last time tank, fuel line fuel filter and carb were serviced to impeccable clean cond ?

Happy Boating
 

Kingtackle

Recruit
Joined
Mar 27, 2015
Messages
2
No Idle speed did not help tried that. Carb was cleaned twice pretty spotless. The head of jets where you put screw driver on. They have a hole going through that portion right? Which controls idle speed circuit? Main jet?
 

pvanv

Admiral
Joined
Apr 20, 2008
Messages
6,500
Yes, your problem is likely varnishing in the slow-speed passages of the carb, but other factors, such as over-full oil can also show similar symptoms. What method was used to clean the carb? Did this problem just start? Do you always run the carb out at the end of each day?

The only Proper way to clean these carbs is by a complete disassembly (including jets and emulsion tube nozzle), followed by a 4-hour room-temperature soak of all non-rubber parts in real carb dip (available in 1-gallon cans at auto parts houses), and then a liberal and aggressive blow-out with generic carb spray. The spray alone in not adequate to dissolve the organic varnishing in the small passages.

Never ever insert any kind of wire through the jets or passages, as scratches can cause weird flow characteristics, turning the carb into scrap.

Always set the idle speed by tachometer, and verify that it's OK by warm idling both in and out of gear. If too slow, the motor will stall when engaging gear.

Not only is it illegal (in the US) to drill out the plug covering the idle mixture screw, they are set by instrument at the factory, and it is extremely difficult to improve on that, let alone get it as good as it was originally. If you richen the low-speed adjustment to cover up a varnishing condition, the mixture will be wrong at other speeds.

You must run the carb out at the end of every day to reduce varnishing.

The carbs for the MFS 4/5/6 are interchangeable, so if your carb is beyond cleaning (due to corrosion, etc), you can go with the carb for the MFS6A2, (as long as your boat can accept the 6 hp rating) for less than $200.
 

mf70

Cadet
Joined
Aug 7, 2015
Messages
14
...The only Proper way to clean these carbs is by a complete disassembly (including jets and emulsion tube nozzle), followed by a 4-hour room-temperature soak of all non-rubber parts in real carb dip (available in 1-gallon cans at auto parts houses), and then a liberal and aggressive blow-out with generic carb spray. The spray alone in not adequate to dissolve the organic varnishing in the small passages.
'''
Not only is it illegal (in the US) to drill out the plug covering the idle mixture screw, they are set by instrument at the factory, and it is extremely difficult to improve on that, let alone get it as good as it was originally.

Um, if you are planning on the four hour dip, remember that the pilot screw has an O-ring, so, law or no law, you probably should remove the pilot screw along with all the other rubber parts.
 
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