Learn me something..

Scrubcadet10

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Got a question on Carburetors in general.
New carbs run leaner, than say, "old" Carbs to cut back on emissions supposedly. So, why don't these new leaned carb engines surge, if surging is a symptom of a lean running condition.
Is it that just more fuel is restricted in a dirty carburetor than a leaner carburetor with what i presume would be smaller jets?
 

bertsmobile1

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Old carbs ran a touch on the rich side of perfect
New carbs run just on the lean side of perfect.
Old carbs will run happily with slightly blocked jets or slightly low float levels,
New carbs won't.
The flow jet on your flat twin, once set up will run reliably for a decade, till the fuel pump eventually packs it in.
The new carbs require a strip & rebuild ever few seasons .
The carbs on some of my 60's mowers have not been touched for over 5 years & they live out in the weather 99% of the time .
Depending upon what fuel you are running, the engine will run fine on almost any air:fuel ratio from 16:1 through to 12:1 .
But if it has been jetted to 14.5:1 to start with it takes very little to lean the mix past the 16:1 limit.
We used to jet around 13:1 but now days that is considered too rich.
 

slomo

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Lean is mean = more HP. Fat mixtures are sluggish and carbon up the head and valves.

Every used and abused mower I've bought, pull the head and strike black gold. Carbon sandwich all around. Valves weigh double from all the carbon LOL.

slomo
 

bertsmobile1

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Poetic license is one thing
Dramatic license is another
but the volume of carbon equivalent to the weight of the valve would make a cylinder of carbon about 2" long ?
 

slomo

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Poetic license is one thing
Dramatic license is another
but the volume of carbon equivalent to the weight of the valve would make a cylinder of carbon about 2" long ?
Do you have it in Troy ounces too? Bet you are sitting around having your morning coffee and out of thin air calculated it all up. Corrected for sea level and Covid-19 on the fly LOL :) Only you Bert. (y)

Bet it would be accurate as heck too. LOL

slomo
 

StarTech

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It is note that some newer carburetors do surge at startup until the engien are fully warmed up... Some here even need slight fine tuning of the jet sizes as the surging never completely goes away. But don't tell anyone that I have those micro bits. My personal mower is on the lean side too as there is very very little carbon in the cylinder. Just pulled the head a couple weeks ago for another problem and while I was in there I did a valve job.
 

bertsmobile1

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Do you have it in Troy ounces too? Bet you are sitting around having your morning coffee and out of thin air calculated it all up. Corrected for sea level and Covid-19 on the fly LOL :) Only you Bert. (y)

Bet it would be accurate as heck too. LOL

slomo
Foundry Metallurgist in a previous life.
Used a lot of carbon anodes, carbon crucibles & carbon chlorine pumps .
Then there were carbon reductions in the lab for assay rather than a cyanide reduction for some specific recoveries .
To be pedantic, I did say about 2" and that implies +/- 0.5" ( 1/2 the stated precision )
However I did not take into account the compactness of the deposited carbon which would be somewhere better than 60% but less than 90%.
Sorry, but I could just not let that one go to the keeper without having a swing at it .
 
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