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Weber 9770S carburetor CFM?


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Hey guys, so my 1994 Echelon is starting to run rough at 1000RPM and at top speed it feels like its sputtering. now I know there is tons of posts out there about this but my main question here is what the CFM is for the stock Webber 9770s carbs? Iv got the 350 Magnum tournament ski, stamp on the carb is "9770S 0363", but I can't find the CFM for this carb. 

Im looking at getting a Ebelbrock 1410. however i'm reading mixed reviews that this might be sized to big. 

(ive already "tuned" the carb, new cap and rotor, gaped the plugs out to 0.035 and set the timing correctly)

Any input will help! 

Thanks guys.

 

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The Edelbrock 1409 would probably be a better choice as a replacement for a small block engine.  The 1410 is normally used for big blocks.

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Michigan boarder

I've heard that the Eddie 1409 is the one to use as well, which would be 650cfm 

On the CFM, I replaced mine last summer in a conversion to electric choke and read anywhere from 650 to 750cfm, couldn't get a consistent answer from anywhere.  I did a rebuild swap and got the same OEM carb from here: https://flyingfishcarburetors.com/ for I think $350 shipped, and it works great.

I agree check the coil.  Have you pulled the new plugs and inspected them?

 

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An engine is basically an air pump.  I won't do all of the math here, but a 5.7L displacement engine has ~0.201 cubic feet of displacement.  At 5,000 RPM it would pump 0.201 * 5,000 / 2 = 503 cubic feet per minute.  Why divide by two?  It is a four-stroke engine, and only pumps half of the cylinders on each rotation.  Anyway, a 600 to 650 CFM carb is plenty to keep up with the air flow requirements of a normally aspirated 5.7L engine.  750 CFM is too much unless you plan to exceed 5,000 RPM on a regular basis.

If you suspect the carb, rebuild it before you replace it.  Even if you just take the top off and spray the throat and jets with a can of cleaner you will also get a chance to inspect the floats and look for debris.

I agree with the other suggestions.  If you don't know how old the plug wires are (or if you do know how old they are), they do degrade with age.  Consider changing them.  A timing light (remember those?) might also tell you if you have a misfire or other abnormal spark condition.

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Michigan boarder
57 minutes ago, justgary said:

An engine is basically an air pump.  I won't do all of the math here, but a 5.7L displacement engine has ~0.201 cubic feet of displacement.  At 5,000 RPM it would pump 0.201 * 5,000 / 2 = 503 cubic feet per minute.  Why divide by two?  It is a four-stroke engine, and only pumps half of the cylinders on each rotation.  Anyway, a 600 to 650 CFM carb is plenty to keep up with the air flow requirements of a normally aspirated 5.7L engine.  750 CFM is too much unless you plan to exceed 5,000 RPM on a regular basis.

 

That's a great breakdown of info!

 

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  • 2 weeks later...
On 8/31/2021 at 7:16 AM, Woodski said:

Before you do a carb swap consider replacing the coil.  Do the issues happen when cold, hot or always?

The accelerator pump is stuck when I accelerate the pump is not giving it the fuel. I removed the flame arrester boat out of the Kia looking in the carburetor add my friend punch the throttle the pump did not move no I did it on fuel into the carburetor

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On 8/31/2021 at 10:16 AM, justgary said:

An engine is basically an air pump.  I won't do all of the math here, but a 5.7L displacement engine has ~0.201 cubic feet of displacement.  At 5,000 RPM it would pump 0.201 * 5,000 / 2 = 503 cubic feet per minute.  Why divide by two?  It is a four-stroke engine, and only pumps half of the cylinders on each rotation.  Anyway, a 600 to 650 CFM carb is plenty to keep up with the air flow requirements of a normally aspirated 5.7L engine.  750 CFM is too much unless you plan to exceed 5,000 RPM on a regular basis.

If you suspect the carb, rebuild it before you replace it.  Even if you just take the top off and spray the throat and jets with a can of cleaner you will also get a chance to inspect the floats and look for debris.

I agree with the other suggestions.  If you don't know how old the plug wires are (or if you do know how old they are), they do degrade with age.  Consider changing them.  A timing light (remember those?) might also tell you if you have a misfire or other abnormal spark condition.

I bought the boat new , when I push the throttle down the accelerator pump does not move. So I’m not getting any squirting Into the carburetor.So by hitting the throttle hard I’m giving it more air than fuel. If I ease on the throttle stumbles a little at a third throttle once I pass that it’s fine. I’m thinking there’s a blockage after Accelerator pump that’s why it’s not moving. Have you ever rebuilt one of these carburetors if so how are how difficult is it.

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Sounds like debris in the accelerator pump circuit or defective part and also the issue.  Is the accel pump linkage moving the pump lever, front left of carb?  Is the rod that actuates the pump installed?  
These are easy carbs to rebuild.  You can follow any rebuild guide for a Carter AFB, Edelbrock 1409 / 1410 or Weber.  They are all similar / same.  Good luck.

Edited by Woodski
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