idle mixture screw

[paul conti]

I am working on a 2010 Tohatsu MSF20c. Is the idle mixture screw behind the large brass plug on the carburetor. I know your not suppose to adjust it but I am cleaning the carb and want to remove it clean. I have tried to find a parts break down but can't seem to locate one that explains the mixture screw.

 

[pvanv]

Yes. If you want to pull the pilot screw for dunking in carb dip (the only way to really clean these), pull the plug (may need to carefully drill it out), and then count the turns as you turn the screw in until it seats gently; then remove the screw. When reassembling, reset the screw the same number of turns.

 

[TOHATSU GURU]

Keep in mind that it is a Federal crime to remove that plug as it violates EPA regulations.

 

[km1125]

Keep in mind that it is a Federal crime to remove that plug as it violates EPA regulations.

Sure about that? Got a link?

I believe those EPA regs are for the MANUFACTURER of the engine, not the operator. There are SOME states that don't allow you to make modifications to the manufacturer configuration, but most apply to the parts (i.e. if it is equipped with a catalytic converter). I have not seen those vehicle laws apply to boats, but in some places they might.

 

[TOHATSU GURU]

I'm real sure. It is a violation for ANYONE to alter the emissions of any product that has a use approval based on an emission level. Now, does anyone really care? No, they don't. Are the Feds going to show up at your house at 3 AM, bust in your door and hall you away? No, they aren't. But, should you touch it. No, you shouldn't. Forget the legal reason. The real reason you shouldn't touch it is that you will probably not get it back to the correct setting. IE You will probably set it too rich or to lean. I have no faith in individuals, little faith in back yard mechanics, modest confidence in certified technicians and I believe that master technicians are rank amateurs with arm patches, etc.

There really is no reason to get in there. Drop the carb in an ultrasonic cleaner. If that doesn't get it clean just buy a new one like Tohatsu wants you to.

 

[pvanv]

Personally, I use an ultrasonic with carb cleaner dip in it, and heated. After 6 hours of that I've never had a carb that didn't come clean when the crud is then blasted out with aerosol generic acetone-type spray.

 

[km1125]

I'm real sure. It is a violation for ANYONE to alter the emissions of any product that has a use approval based on an emission level. Now, does anyone really care? No, they don't. Are the Feds going to show up at your house at 3 AM, bust in your door and hall you away? No, they aren't. But, should you touch it. No, you shouldn't. Forget the legal reason. The real reason you shouldn't touch it is that you will probably not get it back to the correct setting. IE You will probably set it too rich or to lean. I have no faith in individuals, little faith in back yard mechanics, modest confidence in certified technicians and I believe that master technicians are rank amateurs with arm patches, etc.

There really is no reason to get in there. Drop the carb in an ultrasonic cleaner. If that doesn't get it clean just buy a new one like Tohatsu wants you to.

It's just not true. The Federal EPA regulations are for manufacture and sale, not for use. There might be some STATE regulations that they put on usage, but I'd suspect only CA would have those.

The mixture screw functionality hasn't changed in over 75 years. These carbs aren't any different than those that have been built over those timeframes and are very easy to get correct.

 

[pvanv]

It's just not true. The Federal EPA regulations are for manufacture and sale, not for use. There might be some STATE regulations that they put on usage, but I'd suspect only CA would have those.

The mixture screw functionality hasn't changed in over 75 years. These carbs aren't any different than those that have been built over those timeframes and are very easy to get correct.

Almost true. These are high-efficiency carbs, with very narrow and very long passages to get the fuel into an air/fuel emulsion. They run super-lean. Minor changes to the pilot screw can have a big effect, and are very very difficult to set by ear. They are set by instrument at the factory. A very good shop tach is needed if you want to readjust one.

 

[Sea Rider]

All outboard factories located at sea level adjust their carbs mixture screw to achieve top smooth idle operation at that given height. There will be an issue if idle setting needs to be adjusted for high altitude boating in order for engine to achieve a smooth idle.

Idle operation compared to any other throttle setting has such low momentarily use use that find funny being mandatory regulated when there are way more harmfull forms to contaminate air, water.

Happy boating

 

[km1125]

Almost true. These are high-efficiency carbs, with very narrow and very long passages to get the fuel into an air/fuel emulsion. They run super-lean. Minor changes to the pilot screw can have a big effect, and are very very difficult to set by ear. They are set by instrument at the factory. A very good shop tach is needed if you want to readjust one.

I would agree if you are trying to set exactly to factory specs. As a dealer or a certified shop that can be important. However, the factory has to run them as lean as possible so they can pass HC emissions to be able to sell them. Running them a tad richer in real life would not be an issue and could improve low speed operation.

 

[TOHATSU GURU]

You can visit the EPA website for the actual wording. It's definitely against the Federal rules and regulations. The Feds required the mixture screw to be sealed to pass the manufacturer requirements....By opening it up and adjusting it you would be in violation of Federal regulations against "tampering"