Air Fuel Mixture

[Toulla]

2001 Yami F25 ELHZ. Took the motor in to a local mechanic to have the lower unit pressure and vacuum tested. It at ll checked out ok, however, this liitle motor never run SOOOOOOO sweet! Not even when it was new! So I asked the mechanic "What the heck did you do?" It never idled or run so smooth, Never!!!
His answer : Trade secret! Ok, I went on my way. Ah, but I kept going back every day asking the same question. After about a week and a couple of lunches he revealed his secret. He adjusted the air fuel mixture, or so he claimed. I took a long hard look on the curb. There is in ONLY one screw I can see and its the idle screw. So, back I went, and after a long conversation, he explained to me that he had to drill a seal off to get to the air fuel mixture setting screw. Ok I said, THANK YOU!!! for finally telling me. Anyway run the engine for a while. So smooth, so sweet, at idle in neutral and in gear . I mean the thing in gear at idle would be SOOOOO Smooooth like never before. And then I screwed thing up! Yes I did. I changed the fuel pump which caused the idle RPMS to increase substantially. So I turned the idle screw down to get down to 975 Rpm. Got the rpms down alright! but now the sweetness, smoothness and totally shake free operation at idle is gone!!!
Cant find the screw he messed with and I cant take the engine back to him because now the boat is in Florida. Loooong way from California. Please! does anyone know where the heck the mystery setting screw is???

[rodbolt17]

the idle screw is the one that contacts the throttle cam.
the air screw is about the center top aft of the carb.
he may have replaced the anti tamper seal.

[99yam40]

I believe being he was/is in Cal he was required to put the tamper resistant cover back, other states may require that of a tech also but not as strict.

Being all you did was change the fuel pump I do not see how that caused the increase of idle RPM.
Might need to get a Yamaha tech to have a look at it to see what you did to it to cause this

[Toulla]

Air fuel Mixture

Thank you both for your replies. I do appreciate them. just so happened the mechanic called to check on me and to see how the boat is doing in Florida. He told me to look for a top vertical flat head screw on top of the carb. I will. Thanks again!!!

[Toulla]

Air Fuel Mixture

Ok guys,
I know I am blind! but I though the glasses I have on my head took care of my blindness; or so I thought! Here is a photo of the carb on the engine. Where the heck is air fuel adjustment screw? How do I get to it.... It's driving me nuts!!!

[boscoe99]

I must be going blind also.

I don't see an EPA plug used on that model motor.

In fact, I don't see an adjustable idle mixture screw on that model either.

The service manual makes no mention of an idle mixture screw adjustment.

I do see a pilot outlet jet. I wonder if that is what he messed with!

[TownsendsFJR1300]

Just a note, if the idle raised substantially after changing out the pump, its very possible you have an air leak, leaness causing the idle to rise.

I would be checking into that..

Get that potential air leak fixed and you won't have to adjust the air screw..


BTW, what's with the chicken wire screen (in the first pic, blown up) over the air intake??

[greasyshaft]

Just a note, if the idle raised substantially after changing out the pump, its very possible you have an air leak, leaness causing the idle to rise.

I would be checking into that..

BTW, what's with the chicken wire screen (in the first pic, blown up) over the air intake??

It's to keep all that POOOWARR in.

[TownsendsFJR1300]

It's to keep all that POOOWARR in.

Kinda figured it was to keep the chickens OUT!

[greasyshaft]

it's an air filter with 0% efficiency!

[TownsendsFJR1300]

it's an air filter with 0% efficiency!

Actually, it does indeed have efficency. It'll keep birds out and prevent a potential "flame out"!

[Toulla]

Air Fuel Mixtyre

Indeed it is chicken wire guys. I am glad it attracted your attention. There use to be a stainless steel mesh in the intake assembly which came loose and I removed it. The chicken wire is a temporary fix till I come up with a better solution without having to replace the whole intake assembly. Any Ideas?
In the meantime it serves as a conversation starter

[TownsendsFJR1300]

Indeed it is chicken wire guys. I am glad it attracted your attention. There use to be a stainless steel mesh in the intake assembly which came loose and I removed it. The chicken wire is a temporary fix till I come up with a better solution without having to replace the whole intake assembly. Any Ideas?
In the meantime it serves as a conversation starter

Just BS'ing in the mean time. I would use a finer mesh as I'm sure the original mesh was considerably finer...

I would look for perhaps some steel mesh(about the same size as what came out) and if it doesn't fit comfortably snug after trimming, make some small "L" brackets out of aluminum and pop rivet it to the plastic intake and mesh.

Better yet, pop rivet the mesh direct to the intake.. Just make the mesh a little larger, bend the edge over (for a mounting surface) drill and pop rivet direct to the plastic.

It's all under the cowl anyway but will keep any flying critters from getting sucked in thru the cowl and into the intake..

BTW, were you able to re-check the fuel pump install for any air leaks?

[greasyshaft]

Well it wont stop the rats.

[TownsendsFJR1300]

Well it wont stop the rats.

Holy crap!!! Hungry lil critters!

Looks like they found a nice home!!