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The service manual clearly states that primary jets are larger than secondary jets in the 3507S WCFB on supercharged 289s. Jets can of course be swapped, resized, drilled as a means of modifying performance. Avanti jets were number-stamped with size, such as 120 and 104, and can also be size-checked with calibration sets.

I’m hoping to get a quick confirmation of the original size numbers for the 63 Avanti R-2 primary and secondary jets, and any recent updates to jet sizing in relation to today’s (less than stellar) typical fuel. Hope I’m not opening a can of worms gone through many times before, but while rebuilding my carb I find the larger jets are in the secondaries, opposite from the service manual.

Thanks for anything you can add.

 

John H.

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Sorry - yes Carter, WCFB sticks in my mind when I look at one of these 😉 Thanks for the info!

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Got what I need on steps leaner or richer from Bob's site. Good resource. AFB, AFB, AFB.....

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If anybody is interested, the rest of the story is that all of the jets and metering rods have been changed in our R-2, in addition to being installed with the jets in opposite locations. Jon Myer is sending the stock parts and I will spend some time checking performance.

Probably not the first Carter put together backwards.

 

J

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If one is going to all that work, suggest adding a direct reading O2 meter to confirm the jetting is optimum for your use, altitude and temperature.

Of course, on an R2, it can never be optimum.  The jetting which would give the best MPG at cruise would be terminally lean at WOT under boost.  The jetting which will give max power and be safe under boost will be too rich at cruise.  Knowing where it is now is the first step to getting it right.

Also, confirm the correct intake manifold gaskets are being used.  The R2 gaskets restrict the exhaust heat crossover.  Personally, I block the passage completely with thin stainless steel plates.

jack vines

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If you live below 3000ft. altitude, I have had great luck with this jet combination. (as a starting point....your results may vary)

Out of the Edelbrock 600cfm zip kit......098 primary jets. 74-47 metering rods. Orange 4 in" Hg step up springs. Use .095 secondary jets.

Edited by brad
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On 1/9/2021 at 12:10 PM, PackardV8 said:

If one is going to all that work, suggest adding a direct reading O2 meter to confirm the jetting is optimum for your use, altitude and temperature.

Of course, on an R2, it can never be optimum.  The jetting which would give the best MPG at cruise would be terminally lean at WOT under boost.  The jetting which will give max power and be safe under boost will be too rich at cruise.  Knowing where it is now is the first step to getting it right.

Also, confirm the correct intake manifold gaskets are being used.  The R2 gaskets restrict the exhaust heat crossover.  Personally, I block the passage completely with thin stainless steel plates.

jack vines

Thanks Jack. Some good thoughts - and I will check those intake gaskets! J

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On 1/9/2021 at 8:02 PM, brad said:

If you live below 3000ft. altitude, I have had great luck with this jet combination. (as a starting point....your results may vary)

Out of the Edelbrock 600cfm zip kit......098 primary jets. 74-47 metering rods. Orange 4 in" Hg step up springs. Use .095 secondary jets.

Brad - “ your results may vary”- LOL! Appreciate this starting point very much, though! J

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