Nissan NSF8A3 low end carb adjustment???

[Traxion]

My '09 8hp Nissan 4s has always had sort of a dead spot from right off idle till it picks up speed. I've got a Trollmaster on the motor and can advance the throttle quite a bit from fast idle till it picks up speed. I've read that many of the Merc guys with the same motor are removing a welch plug that covers a low end adjustment screw. Some say it's set for emissions purposes. Is this the case? There is a welch plug on the side of the carb but I have not messed with it. I'd like to tinker a bit with it because I use the motor as a kicker and the dead spot leaves me between speeds at times. Any help is appreciated!

 

[pvanv]

Re: Nissan NSF8A3 low end carb adjustment???

If you have a flat spot at tip-in (coming to transition from idle), you are probably too lean there. Yes, there is a pilot screw, but the EPA requires that it be "sealed" from access by the general public. The pilot is set by instrument at the factory, so in theory, it was correct when the motor was shipped.

While it is indeed possible to drill out the brass plug that covers the screw, it is in fact illegal (but I have never heard of anyone being charged with a crime for removing it), and adjusting it could cause more problems than it solves. Care in removing the plug is paramount; if your drill strikes the screw head, you risk damaging the screw, or destroying the seat in the carb. If you end up setting it too rich, you will foul plugs, and will use too much fuel.

Usually, a carb removal and complete disassembly, followed by a proper 4-hour soak cleaning of the carb (in real carb dip), followed by a blow-out of all passages, will remove the varnishing that typically plagues the transition passages. Keep in mind that not running the carb dry at the end of the day, and allowing fuel to evaporate from the carb -- even for only a week, early on in the life of the motor, may have caused the problem. If so, that problem will persist "forever" until the passages are properly cleaned.

That said, it is possible that the pilot was not set perfectly at the factory, or that a bit of machining sprew was inadvertently allowed into one of the passages. If considering that adjustment, start with a proper cleaning first. If the problem persists, and you want to attempt pilot adjustment, you will need a very good ear, a razor-accurate shop tach, and the boat will need to be in the water. Then follow the standard procedures for adjusting any pilot to maximum warm idle RPM (starting at the number of turns that it was originally set to), while also adjusting the idle stop to stay in idle speed specs. Finally, richen the screw about 1/16th to 1/8th of a turn beyond that "perfect" setting to allow for warm-up and tip-in performance.

 

[Traxion]

Re: Nissan NSF8A3 low end carb adjustment???

Outstanding info. I'll do a super soak of the carb, then go from there. I've heard so many guys that have done this with their Merc/Tohatsu Pro Kickers that I question that factory setup a bit. But, we'll give things a good cleaning and go from there.

I've messed with a ton of welch plugs before, if you've ever messed with old snowmobiles with Tillotson and Walboro carburetors you know what I mean!!!!

Thanks for the info, it is greatly appreciated!

 

[TOHATSU GURU]

Re: Nissan NSF8A3 low end carb adjustment???

The factory set up is perfect. The problem is that there are a lot of people, including outboard techs, that have no idea of how to correctly clean a carburetor. Usually a Billy-Bob will spray some can of carburetor cleaner, made from magic beans, into the carb body. That stuff is so weak that it cannot dissolve the offending particles of X. Then they assume that the setting is off or that they need to get into that area to clean it. Like Paul said, it just a matter of cleaning by soaking rather than tinkering.