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The little daysailer I picked up had a late 70's Johnson 6HP seahorse, wouldn't run for shit. Put a carb kit in and it runs like a champ.

Also got a brand spanking new Honda 5HP, up at 9K feet it won't run for shit. Came down 2 sizes in main jet and it purrs, although it may only be putting out 3HP.

Now I'm working on a 50's Lincoln pipeliner, so old the electric is positive ground. The Marvel Schebler carb needs some love.

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God, Alfa made beautiful cars back in the day.

I had a succession of early-70's Fiat Spiders with similar styling and that fantastic 1600cc DOHC engine. At least it was fantastic until 1974, when they put all that (completely ineffective) smog control crap on it. 

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Carbs are diverse creatures.  The motorcycle CV carbs,  on one end, and the Rochester Quadrajet on the other.  Lots of people dumped their Q-jets for Holleys without realizing how very good a Q-jet is.

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Dad is likely an expert on carbs and ignition systems if he buys Craftsman power tools.

The background of 2 full tool chests bears this out.

It is how I got started as a young teenager trying to keep the old man's snowblower running so I did not have to shovel..

 

Good fundamentals in the video.  Nothing on power valves, primary vs secondary jets, etc.

Take a 1970s Rochester quadrajet apart, reassemble and get it to run correctly. You will be an expert by the end.

Fricking jets everywhere in that hollow carb body.

Still have my mercury filled carb sticks for synchronizing my 4 cylinder rice rocket.

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1 minute ago, Foreverslow said:

Take a 1970s Rochester quadrajet apart, reassemble and get it to run correctly. You will be an expert by the end.

Fricking jets everywhere in that hollow carb body.

That's why Q-Jets have their reputation.

If you knew what you were doing they were a very good carb - especially on the street. Holley's were better pure race carbs but not nearly as efficient on the street.

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4 hours ago, warbird said:

Carbs are diverse creatures.  The motorcycle CV carbs,  on one end, and the Rochester Quadrajet on the other.  Lots of people dumped their Q-jets for Holleys without realizing how very good a Q-jet is.

Kind if the same thing with Bing and DellOrto carbs for dirt bikes back in the day.  Once you got them "jetted" right and kept the floats clean, they were just as good as the Mukuni units the rice burners were using. 

Though I will say, putting a Mukuni on my Maico 490 made for easier starting.  And if you started one w/out a compression release.... anything helps. :wacko:

 

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So, now, can someone explain the carburetion on chainsaws, which to my admittedly limited knowledge, defy gravity and the known gas laws?

My experience when taking a large chainsaw in for some work involves either "there's a problem with the reeds!" or " it's old fuel, you need new fuel lines."

WTF are reeds in a carb and why do fuel lines now need to be replaced annually regardless of how meticulously you dose the fuel with all those damn ethanol and storage treatments?

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24 minutes ago, Willin' said:

So, now, can someone explain the carburetion on chainsaws, which to my admittedly limited knowledge, defy gravity and the known gas laws?

My experience when taking a large chainsaw in for some work involves either "there's a problem with the reeds!" or " it's old fuel, you need new fuel lines."

WTF are reeds in a carb and why do fuel lines now need to be replaced annually regardless of how meticulously you dose the fuel with all those damn ethanol and storage treatments?

$$$. Stihl etc. could make lines and parts that didn't dissolve in ethanol fuel, but they make more $$$ on the service and parts than they could by charging more in the first place. What I don't get is why some after market co. doesn't offer ethanol proof lines and carb parts.

 (I think "reeds" are jets)

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reeds are the"valves" in a two stroke. else on the compression stroke it would blow all the fuel mixture back at the carborator.

Remember the old man saying you needed a vacumn for a carb to work?

 

In order to open and close quickly, the reed valves have to be very flexible.

Chainsaws and 125cc motorcycles are run at WFO most the time.  That wears the reeds rapidly and they break.

Hey, you are saving a lot of weight by not having a cam, values, springs, keepers etc.

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So... reeds are basic flapper valves? And 2 stroke engines have no valves?

Good gawd, I'm but an egg.

 

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41 minutes ago, Foreverslow said:

reeds are the"valves" in a two stroke. else on the compression stroke it would blow all the fuel mixture back at the carborator.

Remember the old man saying you needed a vacumn for a carb to work?

 

In order to open and close quickly, the reed valves have to be very flexible.

Chainsaws and 125cc motorcycles are run at WFO most the time.  That wears the reeds rapidly and they break.

Hey, you are saving a lot of weight by not having a cam, values, springs, keepers etc.

Shall we discuss 2 stroke tuned exhaust with the class?

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3 hours ago, El Mariachi said:

Just a frickin bitch to dial in correctly.....

 

 

I built a stout Buick 455 for my son years ago. IIRC 9.4-9.6:1 cr. 3angle valve job and port clean up, 280 intake/290 exhuast cam with 0.450n lift, 0.060 over (the block had seen dirt track time with it's original 7.8:1 Cr, go figure :) ). We put it into a '67 Riviera.  Having two complete engines, I of course chose then wrong Q--jet and the new motor ran "good enough?" and pulled pretty good in a 5400lbs car (dope slap). Son dropped the motor intro an 80 ish Cutlass a few years later and hired (Case of Busch, go figure) a Q-jet guy who promptly grabbed the other (leftover) carb, did some baseline spring and plunger changes, mounted it, played with it a couple of hours and left. Son said "day and night" hardly applied.  That 80 ish Cutlass with ladder bars and bigger tires in stock wheel wells, a floppy hood ornament, Landau top (remember those :) ,   became a wheel stander.  The sad part of this soliloquoy is we dumped the old Riviera 430 not realizing it was a true hot rod motor right up there with the   Chev L78 327 motor.

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55 minutes ago, Foreverslow said:

reeds are the"valves" in a two stroke. else on the compression stroke it would blow all the fuel mixture back at the carborator.

Remember the old man saying you needed a vacumn for a carb to work?

 

In order to open and close quickly, the reed valves have to be very flexible.

Chainsaws and 125cc motorcycles are run at WFO most the time.  That wears the reeds rapidly and they break.

Hey, you are saving a lot of weight by not having a cam, values, springs, keepers etc.

Reeds are nice but before reed there was "Piston Port" :ph34r:

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7 hours ago, SloopJonB said:

What's a carburetor?

Is it related to a watch?

It was used in the past to equally distribute carbon byproducts in the combustion chamber of internal combustion engines.

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57 minutes ago, Foreverslow said:

reeds are the"valves" in a two stroke. else on the compression stroke it would blow all the fuel mixture back at the carborator.

Remember the old man saying you needed a vacumn for a carb to work?

 

In order to open and close quickly, the reed valves have to be very flexible.

Chainsaws and 125cc motorcycles are run at WFO most the time.  That wears the reeds rapidly and they break.

Hey, you are saving a lot of weight by not having a cam, values, springs, keepers etc.

There is also the "Rotary Disc" .  I had a Can Am 175 TnT that was a efff'n rocket with that rotary disc Rotax engine. 

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6 hours ago, warbird said:

Carbs are diverse creatures.  The motorcycle CV carbs,  on one end, and the Rochester Quadrajet on the other.  Lots of people dumped their Q-jets for Holleys without realizing how very good a Q-jet is.

tech

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2 hours ago, Willin' said:

So, now, can someone explain the carburetion on chainsaws, which to my admittedly limited knowledge, defy gravity and the known gas laws?

My experience when taking a large chainsaw in for some work involves either "there's a problem with the reeds!" or " it's old fuel, you need new fuel lines."

WTF are reeds in a carb and why do fuel lines now need to be replaced annually regardless of how meticulously you dose the fuel with all those damn ethanol and storage treatments?

Chainsaws and cheap lawnmowers have a little diaphram pump in the carb that uses intake positive/negative impulses to pump fuel to the float bowl. (see video for float bowl explanation) :D

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6 hours ago, Willin' said:

So... reeds are basic flapper valves?

Just like the flaps in a Whale Gusher 10 pump - the simplest form of one way valve.

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17 hours ago, SloopJonB said:

Just like the flaps in a Whale Gusher 10 pump - the simplest form of one way valve.

And to think all of this started right in my backyard as a kid...  Eyvind Boyesen  was a regular racer in District 6

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1 hour ago, Ventucky Red said:
On 7/2/2021 at 7:07 PM, bmiller said:

Shall we discuss 2 stroke tuned exhaust with the class?

I'll take Mitch Payton for $200 Alex....

 

55 minutes ago, cyclone said:

Actually Walter Kaaden

Ille tacke ressonance waves foire $200 Alex.                              :)

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