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36 votes

Symptoms of Lean or Rich carb settings on a motorcycle

Lean and Rich Symptoms in Motorcycle Carburetors In your post you indicate that some of the symptoms you have read are contradictory. I will try and clarify between the two conditions and attempt to ...
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11 votes
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What's the meaning of a "lean" vs "rich" air fuel mixture

I do not know the etymology of these words or the history of their use in the context of air-fuel ratios, although their dictionary definitions (lean [adj.], rich, too bad I don't have an OED ...
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7 votes

What's the meaning of a "lean" vs "rich" air fuel mixture

A lean air/fuel mixture is when there is more air than required to burn the fuel. A rich mixture is when there is too little air for the given quantity of fuel. The ideal mixture, where there is ...
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  • 1,086
5 votes

Can a permanently stoich or lean running engine ruin a catalytic converter?

A lean burn won't necessarily ruin your catalytic converter. What it may do long before that happens (depending on how lean you're running) is burn the exhaust valves, piston crowns and overheat your ...
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4 votes

How much leaner can you responsibly run an old engine?

I wouldn't go too far with it, for risk of pinking, which could damage your pistons - plus, as I'm sure you well know, the Triumph slant 4 isn't exactly known for it's cooling abilities! You'll ...
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3 votes
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2009 Aprilia RSV1000 - Piggy Back ECU, Should I get one?

Background The 2009 Aprilia Tuono has a writeable ECU but you need the appropriate equipment from Aprilia in order to perform the task. AFAIK there are no aftermarket tools to replace the ECU ...
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3 votes

Strange surging and like it's going to stall, hesitant whilst idling

Just because the OBD says it's an O2 sensor, doesn't necessarily make it so. Some diagnostic codes are pretty simple & to-the-point. But, the logic baked into the computer also has rules like "...
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2 votes

Motorcycle V-Twin CV carbs riding poorly on 1/4-3/4 throttle after carb rebuild

The symptoms you describe (hesitant, low power, running hot) point to a lean condition. It sounds like you may have set the floats too low, I'd set the floats back to where they were and see if that ...
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2 votes

Spark Plug Deposits

Depending on the mileage on these plugs, I'd suggest there's absolutely nothing wrong with the way your engine is running. These plugs look to be in great shape. The small amount of deposits on the ...
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2 votes

Fuel Trim Readings

@Fred Wilson's comment is right on the money, high, positive long term fuel trims at idle that reduce at higher engine speeds indicate the presence of higher-than-normal unmetered air. The fact that ...
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1 vote
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How can I diagnose if my engine is running lean or rich?

If your car is running rich you should have a strong smell of gasoline from your car. Have you considered using an air/fuel ratio gauge? Personally, I prefer to see the exact number. I have the air/...
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  • 26
1 vote

Engine lean issues

From the data we have so far (thanks for supplying the second set of traces OP!) I'm leaning towards the Mass Air Flow (MAF) sensor being the culprit. Looking at the initial traces the air flow ...
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  • 9,674
1 vote

Help on diagnosing positive Long term fuel trim

+- 5% for LTFT is ordinary. +- 15% is more concerning but still not detrimental. If you see +-30% then you should worry. That said, the smaller the problem the harder it is going to be finding it. ...
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1 vote

Is there a chemical limitation to the mixture an engine can maintain?

You can't go any leaner than injecting no fuel whatsoever. This may sound dumb but actually an engine will continue to spin for a few firing cycles without fuel. Some engines are able to actually ...
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1 vote

Can a permanently stoich or lean running engine ruin a catalytic converter?

What damages the catalytic converter is the heat of reacting unburned fuel. So a lean or stoichiometric mixture should do no damage at all.
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1 vote

What's the meaning of a "lean" vs "rich" air fuel mixture

Ideal air fuel mixture (ratio) is 14.7:1. That is 14.7 parts of air ignites with 1 part of fuel. This will archive the best fuel economy and lowest emissions. This figure is also known as Lambda 1. ...
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