F60 - adjustment of A/F screws

[Jason2tpa]

Something else I've been meaning to ask that is related to this thread. Is the "air adjusting screw" on my carb actually a screw that meters air or fuel? Because I'm a little confused.

I had read that if the mix screw on the carb is located on the side of the intake manifold it's a fuel adjusting screw, therefore it meters fuel. If the mix screw is located on the side of the air intake (silencer) it's an air adjusting screw, therefore it meters air.

I searched through some of my previous threads from a long time ago, thinking boscoe detailed for me the mikuni carb. Found it. Here is what boscoe wrote:

Some information from a Mikuni carburetor tuning book:

IDLE CIRCUIT (PILOT SYSTEM)
The idle circuit supplies fuel at idle speeds and has a major influence on fuel flow up to 1/4 throttle. There are three tunable parts in the idle circuit:
1) PILOT JET --- controls maximum fuel flow through the
idle circuit.
2) PILOT AIR JET--- controls the maximum amount of fuel that will flow through the pilot jet by allowing a higher (smaller air jet) or lower (large air jet) vacuum signal at the pilot jet.
3) PILOT SCREW --- controls how much fuel is allowed to enter the carburetor venturi.

The pilot screw is used to control idle mixture. Turn the screw out to richen the idle mixture. Turn it in to lean the mixture. The engine should have a smooth, steady idle with the screw between 1/4 and 3-1/2 turns out from fully bottomed (gently!).

So I believe the above information answer my question about whether or not the "air adjusting screw" meter fuel or air. According to the information boscoe provided from the mikuni carb tuning book, the "air adjusting screw" yamaha labels in the schematic actually meters fuel, not air. Why it's labeled as air adjusting screw, perhaps to confuse regular joe's like me?

[Jason2tpa]

Something else I've been meaning to ask that is related to this thread. Is the "air adjusting screw" on my carb actually a screw that meters air or fuel? Because I'm a little confused.

I had read that if the mix screw on the carb is located on the side of the intake manifold it's a fuel adjusting screw, therefore it meters fuel. If the mix screw is located on the side of the air intake (silencer) it's an air adjusting screw, therefore it meters air.

I searched through some of my previous threads from a long time ago, thinking boscoe detailed for me the mikuni carb. Found it. Here is what boscoe wrote:

Some information from a Mikuni carburetor tuning book:

IDLE CIRCUIT (PILOT SYSTEM)
The idle circuit supplies fuel at idle speeds and has a major influence on fuel flow up to 1/4 throttle. There are three tunable parts in the idle circuit:
1) PILOT JET --- controls maximum fuel flow through the
idle circuit.
2) PILOT AIR JET--- controls the maximum amount of fuel that will flow through the pilot jet by allowing a higher (smaller air jet) or lower (large air jet) vacuum signal at the pilot jet.
3) PILOT SCREW --- controls how much fuel is allowed to enter the carburetor venturi.

The pilot screw is used to control idle mixture. Turn the screw out to richen the idle mixture. Turn it in to lean the mixture. The engine should have a smooth, steady idle with the screw between 1/4 and 3-1/2 turns out from fully bottomed (gently!).

So I believe the above information answer my question about whether or not the "air adjusting screw" meter fuel or air. According to the information boscoe provided from the mikuni carb tuning book, the "air adjusting screw" yamaha labels in the schematic actually meters fuel, not air. Why it's labeled as air adjusting screw, perhaps to confuse regular joe's like me?

[boscoe99]

Boscoe must have a super duper engine schematic that details whether or not my engine intake has ability to attach vacuum hose......

Boscoe looked at the SM for your model. There is no mention of using a device to synchronize the carburetors. I don't think your carburetors have the fittings to which a device can be attached to measure intake manifold pressure.

[Jason2tpa]

Boscoe looked at the SM for your model. There is no mention of using a device to synchronize the carburetors. I don't think your carburetors have the fittings to which a device can be attached to measure intake manifold pressure.

I looked around the intake manifold for something that looked like where the vacuum tube could hook up. Red arrows pointing. The parts schematic says it's the check valve assy or nozzle, either one. There are a total of 4, each located in the area where you would hook up a vacuum. But I don't know. What do y'all think?

[99yam40]

you do realize this thread is a bout a F60

[Jason2tpa]

you do realize this thread is a bout a F60

I sure do. It's also about using a carb tuner on a F60. This thread turned off the F60 coarse about half way down the page and has since been about carb tuners. Hence my continuation with most recent post. Panasonic asked for pics, now he's got one.

Feel free to chime in on whether or not what is pictured is where a carb tuner vacuum would hook up.

[panasonic]

What you pointed out in the pic Jason, I don't know what they are. But I bet someone else will...

[panasonic]

The black hoses in the picture are the oil injection lines. The Grey hoses you pointed out appear to be some kind of vacuum lines being that they are hooked up to intake manifold. But maybe they could be fuel over flow drain line as well? I am just guessing now.....

[rodbolt17]

on the pictured 2 stroke carb.
it has a fixed jet for air.
a fixed jet for fuel.
you can use the screw to simply allow more or less of the FIXED A/F mix into the intake.
yes Virginia it is that simple.

same as the F60.

however the F60 has ports on the intake to attach a vacuum test set to adjust the throttle plates correctly.

[exeter27]

As townsendsfjr1300 said, the screw allows more or less of the a/f mix into the intake. Because the intake already has air rushing through, it must be richer than stoichiometric (per boscoe99) - and then diluted by the existing intake air - resulting in the proper a/f ratio.

I simply opened mine (CCW) to allow this fixed (and rich) to allow more of this mix into the intake (as Rodbolt) says - and now my engine runs great.

So, I think that all - TownsendsFJR1300, boscoee99, and Rodbolt are - correct - that the jets fix the ratio, but it's a rich A/F that is metered by the "air screw" into the intake.

And yes, you need a way to hook into intake vacuum to use a Carbtune. Mine were designed into the F60. Other engines you would need to drill tap and tap a port - or just manually sync the carbs visually. It's not as accurate, but it may not need to be on engines with less carbs...

[99yam40]

I sure do. It's also about using a carb tuner on a F60. This thread turned off the F60 coarse about half way down the page and has since been about carb tuners. Hence my continuation with most recent post. Panasonic asked for pics, now he's got one.

Feel free to chime in on whether or not what is pictured is where a carb tuner vacuum would hook up.

How many people do you need to tell you that your motor does not have ports to use the vacuum tool?

[Jason2tpa]

1998 S115TLRW Yamaha Outboard INTAKE Diagram and Parts

Parts # 9(s) is a "check valve assembly" & # 10 simply a hose. It's function, IDK, but it's certainly NOT for syncing. You have 4, for each intake.

A vacuum port would be made into the casting with a covering of some sort.

As posted earlier, syncing is likely done by closing your shutters fully, then adjusting the linkage to fit exactly at that point. Then adjust the idle STOP screw

What does your SM state about syncing?

The carb time and sync is done exactly as you described. And there is no confusion or uncertainty on my end as to how this procedure is done.

The sole purpose of my questions about syncing my carbs is in relation to the OP's use of a carb tuner, and if this tool could be used with my carbs. If it could and I used it, would it indicate the carbs were out of sync despite me following the SM sync procedure? IDK. But it's worth the try if it's possible with my engine.

[Jason2tpa]

on the pictured 2 stroke carb.
it has a fixed jet for air.
a fixed jet for fuel.
you can use the screw to simply allow more or less of the FIXED A/F mix into the intake.
yes Virginia it is that simple.

same as the F60.

however the F60 has ports on the intake to attach a vacuum test set to adjust the throttle plates correctly.

Everything rodbolt indicated in black words above was never in question. However, his words I've highlighted in red is what I've been seeking to learn. Since he's worded that sentence as "however, the F60 has ports...." indicates to me my engine does not have ports on the intake to attach a vacuum test. This I take as confirmation. Appreciate all who chimed in with helpful thoughts.

[Jason2tpa]

How many people do you need to tell you that your motor does not have ports to use the vacuum tool?

Depending on the source, just 1. Everyone else either speculated to the possibility or didn't know. Rodbolt was the 1st to confirm.

[rodbolt17]

your F60 has 4 ports on the intake for a multi channel manometer to be attached.
it is that simple.
they are 6mmx1mm .