2004 90 2 stroke pilot screws

[bhumphrey]

Are the pilot screws located under a brass plug on this unit? If so, can I drill a small hole and extract brass plug to access screws?
Thanks

[throrope]

I have the exact motor. It's a workhorse, but old technology. Per Yamaha, it's compatible with ethanol fuels, but IMHO they updated the materials only. From experience, these carbs are still better suited to fossil fuels and the alcohol mixes forced upon us at the loss of livestock feed has a short shelf life and requires more smarts to burn (i.e. fuel injection).

The little brass plugs you see cap strait passages inside the carburetor to create elbows. Not something to mess with.

I had ours apart numerous times. Last season I dropped a cylinder and resigned myself to an expensive ignition job. Rudy Marine in Wilmington DE did a professional job of rebuilding all three carburetors and now it runs like a Swiss watch. An old salt there advised pulling the fuel quick connect after every trip and running it dry. Their committed young buck made sure before I departed that old ethanol fuel will gum up anything. My issue was a tank full of old gas. Stabilizer or not, until I corrected that issue with a new tank sized for the trips I take and new lines to the disconnect, all the rebuilding could not put humpty dumpty back together.

To give you a usable answer, I suggest buying Yamaha's service manual from their online sight. YAMAHA MANUAL STORE Appears expensive until you use it for the first time.

[99yam40]

I have no idea if your motor has the EPA mandated anti mess with covers over your pilot screws or not.

But from what the previous post said I do not agree with trying to run all the fuel out of the carbs , as you cannot do it.
the top carbs will run out 1st and then then some cylinders are lean or with out fuel and oil while motor is still running.

And you can not get the motor to suck all of the fuel out of the bowls, leaving some in the bottom of bowl to evaporate much sooner than a full bowl and leaves gunk in the bottom anyway.

Service manual is a must if you plan on working on the motor yourself.

treat fuel and run often or drain bowls with drain screws if laying up for long

[bhumphrey]

Thanks for the info

I use fuel stabilizer and have been running Shell V Power (premium) fuel that does not have ethanol as an octane booster. I have the Seloc Manual in paper form and the Yamaha Manual in PDF on a laptop. The Seloc & Yamaha manuals discuss the adjustment procedures but don't say anything about the brass plugs. From the info / pictures I have I believe these plugs are there to prevent the tinkerer from turning screws. Very similiar to the plastic idle mixture limit caps they used to put on car carburetors in the late 70's which most of us would break off so you could richen up the idle mixture and get a decent idle.

When I get back to the camp in a week or so I will give it a go and let you know how it works out.

Brian

[boscoe99]

Yes, the pilot screws (idle mixture adjustment) have an anti-tamper cover over them. Barely drill through the cover. Then use a pick to pry the cover out of the bore that it is pressed into.

Lightly turn the screws completely in without forcing them at the end. Count the number of turns it takes. Write this in your SM for reference.

Ethanol leans out the mixture. Sometimes it helps to richen the idle mixture somewhat. Sometimes it helps to install larger jets. Both idle mixture and main jets.

[rodbolt17]

I use a 1/8th dril bit and drill a hole in the center of the plug.
then thread in a #10 self tapping screw and use my side cutters to pop them out.
from there they go into the round file.

you can use the carb pilot screw settngs from a slightly older NON EPA carb.

each carb has a bowl drain screw,why bother attempting to run them dry.
loosen each screw,wait 10 min and retighten said screw.
as the pilot fuel jet is about 1/2" off the bottom of the bowl there is no way to run them dry.

[throrope]

Sorry, I thought you were talking about the tiny brass plugs on the body.

Yea, like rodbolt sez, the screws are under the caps. Mine came without from the prior owner who's marina tinkered until all was wrong instead of cleaning them. Rudy Marine straightened all after I ran some bad gas and replaced the plugs. Since it runs fine, I'll leave as is.

Thanks rodbolt, next time after running dry, I'll open the drain screws to see what's left. If any, I'll go that route instead. I expect they won't seize and break if used somewhat regularly.