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Is any gauge/tool to check if the A/F mixture on a F80 with carburettors is correct? (nor to lean or to rich) besides have a look on spark plugs
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An O2 sensor would have to be connected to each exhaust port to accurately measure the air/fuel ratios for each cylinder. There are no such ports on any Yamaha that I am familiar with.
Some four stroke EFI motors have an O2 sensor port to measure A/F ratio but have never seen one on a carbureted motor.
Now if one were to measure the A/F ratio, how it would be known what is too lean versus too rich? Yamaha does not provide any A/F specifications.
I have instrumented three Yamaha's to see what the A/F ratios looked like. An F70, an F150 and the new I4 F200. The results might surprise you. -
What you mean? The motors run to rich or to lean? Suzuki seems to use some lean burn tech.Originally posted by boscoe99 View Post
How did you provide you tests?Comment
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It is interesting to me that Suzuki uses what they refer to as "lean burn" technology. What does this mean? Lean compared to what? Is it lean compared to the stoichiometric air/fuel ratio or is it lean compared to some previous A/F ratio used in earlier model motors?Originally posted by allaboard View Post
Yamaha training in the US seems to think their motor runs at stoichiometric, and evens says so in some of their manuals. The motors that I tested indicate they run much, much richer than that. Which stands to reason since for driveability issues most piston motors are operated on the rich side of stoichiometric. Not to mention that for detonation preventative measures it is favorable to run on the rich side.Comment
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my thought is that just after reliability the 2nd concern when purchasing a outboard is fuel comsumption.
If those models run much rich than stoichiometric that will not increase a lot the fuel comsumption?
what should be the benefits? (probably just the engineers at Yamaha have the answer)
my limited knowledge says that if we run to lean we may have a overheating problem but if we run to rich we will spend much more gas than would be necessary ( at least with carburettor models, is my guess)
I want the A/F mixture better as possible on my F80 and besides have a look on spark plugs yamaha could have other way to check this (seems not)Comment
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Best power comes from a richer mixture than stoichiometric.
A richer mixture than stoichiometric provides some protection from detonation.
A richer mixture than stoichiometric provides for better throttle response and driveability.
In a carbureted motor the only way I know to play with the air/fuel mixture is to swap jets and inspect the plugs. That can get expensive if Yamaha jets are used. It will be time consuming no matter where you get the jets from.
An F80 has four damn carburetors. Each with two different jets. One is an idle jet and the other is the main jet. Think of how many possibilities of various jet sizes that you can test and how expensive that will be. If you start going to a smaller jet size to save money, what happens to the health of the motor if the smaller main jet gets a bit clogged and causes a leaner air/fuel mixture. Could have no effect best case or could damage the motor worst case.
Is it just reduced fuel consumption that you are after?Last edited by boscoe99; 01-02-2014, 04:29 PM.Comment
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And I understand that many carbed outboards have slightly different sized jets on different carbs on the same motor....another variable to consider. There must be some outboard manufacturer happy "comfort zone" regarding fuel/air mixtures giving reasonable fuel economy and still protecting the engine from dangerously lean mixture....which can burn pistons....I am willing to read the color of my plugs center electrode insulator and trust that regarding mixture...Comment
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That should be close as possible of stoichiometric.Originally posted by allaboard View Post
After your comments in doubt sounds better run rich than lean.Comment
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Rich mixtures can burn more fuel, foul plugs, make carbon on rings and ports, make smoke....but lean can really damage a motor, burn pistons, etc....Comment
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as the motor,for the US market, had to pass EPA emissions. would it be to hard to simply assemble it correctly and surprise, it works.
there is no setting for the A/F mixture screws as they came covered with a plug to prevent tampering.
this is a US EPA thing not a Yamaha thing.
typically AFTER syncing the shutters I set the idle speed to the specified RPM then adjust each screw to obtain the highest vacuum and still maintain a smooth idle.Comment
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Nice to have your opinion
My mechanic tuned the A/F with 4 turns out on each carburettor what I tought to be to much
When had a look on manual parts found that in Brazil??? (BRA) or whatever that means? The jets are larger than on others places/applications
Look at the pic.
EX: on F100 the main jet recomended is #125 but for BRA is #140
The slow jets are #42 and for BRA #48
Any special reason for this? fuel?Comment
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Four turns out on the pilot/slow jet would appear to be too much. The specification for a US F80 motor is 2.5 (plus or minus .5) turns out from lightly seated. If you start with what you say is a larger pilot jet, and richen the idle mixture by 4 turns instead of 2.5 turns, your motor is going to run much richer at idle than a US motor will.Originally posted by allaboard View Post
As Rod noted, we here in the US have to contend with the Environmental Protection Police. They are making US spec motors run much leaner than motors that are sold for use outside of the US. Sometimes they then run so poorly that folks want/have to adjust the idle mixture or change jet sizes. The EPA tries to prevent this by making Yamaha install a tamper resistant plug. Fortunately, it is easy to remove the damn thing and adjust the motor as needed to get it to run right.
In Brazil don't you guys use a high percentage of ethanol in your gasoline? Gasoline contaminated with ethanol will result in a leaner mixture. Maybe this is why the jets used in Brazil spec motors are larger than the jets that are used in US spec motors, to try and counter the effects of ethanol. That and maybe the fact that we have the EPA forcing our jets to be on the small side.
On a political note, the number one threat to the US environment is too many people. What is the EPA doing to address the number one threat to the US environment? Not a damn thing.
Where you finding a parts catalog that addresses Brazilian models? Is this available online somewhere?Comment
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from what I read brazil does use a high percentage of E in the gas.
I read some years ago that no new cars would be imported into Brazil unless they would run on 100% Ethanol.
yet Brazil doesn't have to burn its food for ethanol.
4 turns out isn't out of the normal range, however I use a 4 channel manometer to sync and adjust.Comment
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If Yam specifies a max of 3 and a min of 2 turns (2.5 plus or minus .5) how is it that 4 isn't out of the normal range?
Now I am not saying that 4 turns sometimes might not be needed to get a motor to idle correctly but that is because the damn things run too lean in the first place. With some F40's it can take more than an idle mixture adjustment setting change, such as bigger idle mixture jets.
Allaboard, are you in Brazil? If so, do you have access to an owner's manual for a Brazil model and what does it say about the use of ethanol in the gasoline? In the US it is maximum of 10%. I am guessing that it might be more for a Brazilian model.Comment
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See comments in red. I learn something new all of the time. Hopefully, anyway.Originally posted by allaboard View PostComment
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