air mixture screw

[clintbeastwood]

I know manual says not to drill but what about o-ring on a/f screw? Not good to be soaking that. I think its a CYA for manufacturer to tell you not to drill plug so All Gore doesent get on them!! The screw can be reset. Just curious about o-ring.

 

[pvanv]

Re: air mixture screw

What make/model/serial?

 

[clintbeastwood]

Re: air mixture screw

2004 nissan 9.8 4stroke (nsf9.8a2?)

 

[pvanv]

Re: air mixture screw

Don't drill it out. Yes, it is a violation of Federal law (though I've never heard of anyone being arrested/prosecuted for it)
If you have "too lean" issues, completely disassemble the carb (including jets and emulsion tube nozzle), and give all non-rubber parts a 4-hour soak in real carb dip. Then a liberal spary-out with generic carb spray. Then reassemble carefully, paying attention to float height. The 9.8 has a plastic, "non-adjustable" float, so if it's significantly off parallel with the casting when inverted, either replace it, or... Carefully, Gently, adjust the lever arm, using a little heat and Great Care.

The mixture screw is factory-set by instrument, and is 100% perfect when it leaves the factory, so changing that adjustment might possibly "band-aid" your idle for a while, masking varnishing in the low-speed/idle circuits, but changing the adjustment can lead to real problems later on... especially if someone subsequently does clean the carb correctly.

BTW, year is unimportant for servicing Tohatsu/Nissan outboards. The precise model (NSF9.8A2) and serial are the critical servicing identifiers.

 

[clintbeastwood]

Re: air mixture screw

Thanks Paul yeah mine was drilled by PO and in cleaning it I noticed the o-ring on a/f screw looked puffy. I got to thinking the soak has to be harsh on o-rings in non drilled carbs. In the motorcycle industry(I know we talking boats) if its not drilled and removed before soaking its not properly clean? Anyway just curious thanks for the info.

 

[clintbeastwood]

Re: air mixture screw

Outboards are very similar to metric motorcycles but also very different, especially when you dont work on them everyday.

 

[pvanv]

Re: air mixture screw

It's difficult to reset the screw as well as it was done at the factory. You need a good-running motor, fresh fuel, an impeccably clean carb, patience, a very good ear, a great shop tach, etc., etc. If the welch plug is in place, the o-ring only serves as a restriction so the screw doesn't vibrate out of adjustment, so no big deal. OTOH, if it's already been disassembled, you should be OK by counting the turns to bottom, and keeping that setting. Most amateurs set them way too rich, causing fouled plugs, loss of fuel economy, etc.

 

[Bosun's mate 1st class]

Re: air mixture screw

just eavesdropping on your threads...you were referencing o-rings and carb cleaner.. The last time I cleaned my Honda 75 hp carbs...I cleaned everything, without segragating anything made from rubber. Could this be a reason why I'm having (I think) carb problems now.
Been blaming the problems on ethanol and rubber fuel hoses, diaphragms in pumps, etc. creating carb blockages.

 

[TOHATSU GURU]

Re: air mixture screw

Yep. Ethanol is almost always not the cause of anything other than water absorption into fuel.

 

[pvanv]

Re: air mixture screw

Yep. And that absorption can lead to corrosion, etc. But in general, one still needs to follow the rules. If you dip rubber in carb cleaner, expect issues later.