Factory Dual Quad jetting/tuning

[62 Dart Convertible]

I restored my 3258/3259 combination a while ago and the jets/step-up rods were badly pitted with corrosion and needed replacing. I found they were unavailable, so I did the calculations to find the closest equivalent combinations in the Edelbrock range. I'm yet to fit an AFR meter to fine tune but on the road/plug reading it seems OK..

Is the staggering of the jetting between rear and front carbs done purely to correct uneven distribution of the manifold, to suit the progressive throttle linkage or because there are emulsifiers, venturi or air bleed differences between 3258 and 3259? I wonder if I will require primary jetting changes with my planned addition of a PCV valve?

Those with real experience, please chime in.

 

[dvw]

Front jets are larger because the metering rod takes up part of the area of the jet. The steps in the metering rod richen the mixture under load as the rod rises upward. Any jetting changes right to left would be for manifold discrepancies.
Doug

 

[62 Dart Convertible]

Front jets are larger because the metering rod takes up part of the area of the jet. The steps in the metering rod richen the mixture under load as the rod rises upward. Any jetting changes right to left would be for manifold discrepancies.
Doug

Hey Doug. I understand how rods/jets work. Staggering on these is front and rear carb have different primary jets/rods (same on both sides in each carb tho).

 

[lewtot184]

I just looked at an old jetting spec for the factory inline carbs. looks like 3 step rods for the back carb which is typical Chrysler driver/fuel economy stuff. measure all of the high speed air bleeds and carefully look at the emulsion tubes. if everything is symmetrical then that's how I would jet for that manifold. something tells me though symmetrical may not be the case with the big secondary jetting differences.

 

[62MAX]

Frank,
I didn't have to change any jetting on the 3258/59 on my 440 with a PCV valve.The original 62 300H jetting was adequate for what I was looking for.I think I have a extra set of correct rods,I'll check today and make sure.if I still have them,you can have them if you want.Also,I have at least,probably more than 50 + sets of rods each,both two and three step,if you want something specific I probably have it.I have the complete Carter spec sheet for these carbs,it covers "everything"all part numbers,all adjustments and all jet and rod specifications,here is first page,I'll have to scan the other two.Here is a complete rod and jet spec sheet just in case you may need it.

 

[lewtot184]

62max is the man! bill, sending you a pm.

 

[62 Dart Convertible]

Frank,
I didn't have to change any jetting on the 3258/59 on my 440 with a PCV valve.The original 62 300H jetting was adequate for what I was looking for.I think I have a extra set of correct rods,I'll check today and make sure.if I still have them,you can have them if you want.Also,I have at least,probably more than 50 + sets of rods each,both two and three step,if you want something specific I probably have it.I have the complete Carter spec sheet for these carbs,it covers "everything"all part numbers,all adjustments and all jet and rod specifications,here is first page,I'll have to scan the other two.Here is a complete rod and jet spec sheet just in case you may need it.

Hi Bill, and thanks so much for your help.
Great news on PCV. Did you plumb it in to rear port on manifold? (Mine will be free when I lose brake booster.)
The Carter Rod/Jet chart I have already, but I don't think I've seen the Carter Spec sheets before.

 

[62 Dart Convertible]

I just looked at an old jetting spec for the factory inline carbs. looks like 3 step rods for the back carb which is typical Chrysler driver/fuel economy stuff. measure all of the high speed air bleeds and carefully look at the emulsion tubes. if everything is symmetrical then that's how I would jet for that manifold. something tells me though symmetrical may not be the case with the big secondary jetting differences.

I'm pretty certain that my rods are 2 step... the jetting sure is different from carb to carb on both prim and sec, hence why I'm wondering if due to other internal differences in carbs or poor distribution?

 

[lewtot184]

the front vs back jetting differences make me think air bleed differences. all manifolds have issues of some sort but some need jet staggering to work. that manifold is rather simple as compared to a dual plane and this makes me think look at the air bleeds first.

 

[miller]

Wouldn't that chart only apply if your running the 'stock' cam?
If not, differences.

 

[62MAX]

I'm pretty certain that my rods are 2 step... the jetting sure is different from carb to carb on both prim and sec, hence why I'm wondering if due to other internal differences in carbs or poor distribution?

Frank,
Here are the other two sheets of specification,should give you everything you need.

 

[62 Dart Convertible]

Frank,
Here are the other two sheets of specification,should give you everything you need.

Cheers Bill!

So is your PCV plumbed in to the vac port at rear of intake?

makes me think look at the air bleeds first.

Agreed, but my carbs are intact, and I am "looking" by way of specs/part nos..

 

[62MAX]

Frank,my PCV valve is Max Wedge,plumbed to rear intake port.

 

[62 Dart Convertible]

Frank,my PCV valve is Max Wedge,plumbed to rear intake port.

Great, thanks Bill!

 

[1962polara]

Frank this is the manifold fitting ,the smaller port is for the heater vacuum.I know you run a brake booster so you'd need twin large +small?I have seen this with different combinations on eBay before.

 

[miller]

Frank this is the manifold fitting ,the smaller port is for the heater vacuum.

I have the single PVC port fitting on the rear of my manifold. Heater vacuum is hooked up using the port off the rear carb.
Same difference, isn't it?

 

[62MAX]

I have the single PVC port fitting on the rear of my manifold. Heater vacuum is hooked up using the port off the rear carb.
Same difference, isn't it?

The rear port on the carb would be at least twice the size as the intended port for the heater control,would this give the same amount of vacuum the control or does it matter?

 

[miller]

Dual 600cfm Eddys, on a stock crossram. No. For heater vacuum, to the normal vacuum small port at the front (base), of the rear carb.
Already checked things, heater controls work fine. PVC to rear fitting on the manifold.
Only reason is, finding, and the cost of that two port fitting pictured.

 

[62 Dart Convertible]

Frank this is the manifold fitting ,the smaller port is for the heater vacuum.I know you run a brake booster so you'd need twin large +small?I have seen this with different combinations on eBay before.

View attachment 539584

That's the exact fitting I have, in the rear of my manifold, and since the brake booster is being removed (as the MW exh manifolds are going on), the 3/8" port is avail.

Miller - there are no ports off my rear carb (pre PCV.)

 

[Darter6]

Miller, Thanks for that info. I have to plumb my heater vac to my crossram with hopes that the carb port would be ok. See, this is why this site is so great.Learn something new everyday.