Super stock crossram jetting for dual AFB chokeless 750s

[prostockstan]

as the vacuum catches up the rod will go down so your ok. When its out on the road is the only test. If its uder load with throttle wide open the needles will be up don't worry about that, then as you let off the gas and rpmm strarts coming down the rods will slowly go down. its all progressive with throttle and load. in the shop there is no load. wack the throttle they should go up let off they go down. Use the heaviest spring possible that allows the rod to stay down at idle without dancing.

 

[stage3]

as the vacuum catches up the rod will go down so your ok. When its out on the road is the only test. If its uder load with throttle wide open the needles will be up don't worry about that, then as you let off the gas and rpmm strarts coming down the rods will slowly go down. its all progressive with throttle and load. in the shop there is no load. wack the throttle they should go up let off they go down. Use the heaviest spring possible that allows the rod to stay down at idle without dancing.

in my shop..they start down..I crack open the throttle,,they go up..without any movement of the throttle blades..they go back down on there own..is this correct?.thanks..to lean it out some,,75-65 rods?without changing jets....

 

[prostockstan]

I think you should use rods .071x.047 or the .065 x .052s and juggle the jets. As i said if you just wick the throttle they will go up idle down when the motor is under load on the street the rods will stay up and allow full acceleration. But you must use the strongest spring that allows the rod to stay down at idle. This will allow the rods to go up quicker under full acceleration.

 

[prostockstan]

I don't get caught up about what it does when parked. You should be in gear at idle if its automatic when setting the springs up. I forgot to mention that. Sorry

 

[prostockstan]

When driving the car it's always in gear at a stop for automatics with a little drag from the convrter which affects idle vacuum. So always make sure you are in gear on automatics when setting up the rod spring tension.

 

[stage3]

I think you should use rods .071x.047 or the .065 x .052s and juggle the jets. As i said if you just wick the throttle they will go up idle down when the motor is under load on the street the rods will stay up and allow full acceleration. But you must use the strongest spring that allows the rod to stay down at idle. This will allow the rods to go up quicker under full acceleration.

my heads spinning on these rods..so...071-.047 will lean it out some because the .071 will at idle/part throttle allow less gas to flow?top number is idle lean out..larger equals leaner on both?i think...lol...

 

[prostockstan]

correct larger of either step is leaner smaller is richer.

 

[prostockstan]

correct larger of either step is leaner smaller is richer.

Once you understand it it's really easy to tune.

 

[prostockstan]

correct larger of either step is leaner smaller is richer.

The difference between .071 x.047 and .065 x.052 - if you notice the .065 is smaller than .071 but .052 is larger than .047 so the .065 will give more fuel at lower rpm and the .052 which is larger than the .047 will give less fuel on the top end versus the .071 x.047 rod. This allows you to tune to RPM where you might have an issue. Either rod will work but one will work better than the other you will notice the difference in throttle response and the sound of the motor. I hope this helps and remember to set the idle speed with the car in gear if automatic. Let me know, I'm curious to see which one works best in your motor combination. If you cant run the car on the street at this time just wait to do final jetting until it's on the road or your just wasting time and your motor. What sounds good in the shop is totally different once it's under load.

Stan

 

[stage3]

I think im going to drop down 2 points on all jets..i.e.,,107's to 105's etc..it is just a little fat..then I can go up or down with the rods well within the ball park..hopefully the last time I will have to pull the carbs off..easier to work on the bench than to take the tops off on the car..thanks for all the tips..

 

[lewtot184]

something I've noticed on edelbrock carbs is the high speed air bleeds are all over the place in sizes. I have one carb that is .033" on the primaries and one that is .90" (!!!!!!, this will never work.). this greatly effects the jetting. if using a pair of carbs make sure all the bleeds, idle and high speed, are the matched up.

 

[coloradodave]

Maybe this will help you understand the AFB metering systems and relationship between the jets and metering rods. All this applies to Carter and Weber AFBs other than some of the part numbers.
http://www.edelbrock.com/automotive/misc/tech-center/dl/carb-owners-manual.pdf

 

[prostockstan]

Maybe this will help you understand the AFB metering systems and relationship between the jets and metering rods. All this applies to Carter and Weber AFBs other than some of the part numbers.
http://www.edelbrock.com/automotive/misc/tech-center/dl/carb-owners-manual.pdf

View attachment 533281

This is information is for off the shelf Edelbrock carbs. Tuning the older AFBs especially the chokeless late 1960s Super Competition series to early 80 carbs have many differences. I agree that this guide is good for people that have no experience with these carbs. Notice the heading of the thread.

 

[prostockstan]

There is also some good information for older Federal Mogul AFB guides on the net.
Stan

 

[stage3]

well,,I guess im going to .104's,,looks like they r only ava in 3 step increments..101-104-107 and so on..and of course my 2 carter strip kits..1 .104 is missing!...I saw the edelbrock instruction manual also...basicly its thinner is richer,,and lite springs = more gas in quicker..

 

[miller]

This thread screams...sticky!

 

[stage3]

There is also some good information for older Federal Mogul AFB guides on the net.
Stan

heres an update..after running it..several cylinders were dropping off.after checking the plug wires..5 of them had burn thru issues..fouled those plugs out..the others show a little blackness but were still o.k...i think its running better than I thought with the jetting and rods/springs..ceramic wires will be here tomorrow..changed all the plugs,,gaps at .040..msd7al2..and will test again..and that was with titanium fabric sleeves..

 

[coloradodave]

This is information is for off the shelf Edelbrock carbs. Tuning the older AFBs especially the chokeless late 1960s Super Competition series to early 80 carbs have many differences. I agree that this guide is good for people that have no experience with these carbs. Notice the heading of the thread.

FYI, I was referring the member to the manual to get an idea of the relationship between the jets and metering rods and how changing either one affects the mixture, which also applies to the Carter Super Comp carburetors of old.
I keep seeing references to staggered jetting. The specs given were for WOT for the Chrysler super stock cars. Is that what your ride is going to be used for? If so, the sizes and manifold modifications in the Direct Connection manual will be applicable; however, if the car is street driven, those numbers will have very little relevance. A wide band dual reading A/F ratio gauge with a sensor for each bank if running a crossram will help get the jetting spot on.

 

[prostockstan]

FYI, I was referring the member to the manual to get an idea of the relationship between the jets and metering rods and how changing either one affects the mixture, which also applies to the Carter Super Comp carburetors of old.
I keep seeing references to staggered jetting. The specs given were for WOT for the Chrysler super stock cars. Is that what your ride is going to be used for? If so, the sizes and manifold modifications in the Direct Connection manual will be applicable; however, if the car is street driven, those numbers will have very little relevance. A wide band dual reading A/F ratio gauge with a sensor for each bank if running a crossram will help get the jetting spot on.

We used straight jetting across the board when we first ran the car on the street. The crossram we are running is an A&A 440 not the max wedge one. When we ran the car we used a heat gun to check cylinder temps and they were all over the place. I then spoke with Dan Dvorak who has won more races with this set-up than anyone. I took his kind advice and put the staggered jetting in only on the mains not the metering rod side. I then checked the cylinder temps with a heat gun and I was amazed how they evened up much better. This car is driven mostly on the street but is 90% superstock. It is smooth and under full throttle doesn"t miss a beat. The way the fuel is distributed through the open plenum is the reason for the staggered jetting. The staggered jetting is for the crossram set-ups only. I'm not an expert but I can definitely tell you it made a big difference on this crossram set up. The final jetting for the 512 ci. was .107 primary jets, .095 throttle side mains, .089 on choke side mains and the blue step-up springs. The carbs are 4762S AFB super competition series 750s. Finding your correct jetting for each combination is all over the board and it will take a lot of time and patients. We almost got to the point of ripping off the crossram set-up and going with a hi-rise intake and 4bbl. but that would have taken away from the classic look we were after. I'm happy as hell we didn't take it off. It runs perfect now. I know we sacrificed a little power with the crossram set-up versus the 4bbl and hi-rise set-up but with 512ci and tons of torque who cares about a little loss.

stan

 

[prostockstan]

well,,I guess im going to .104's,,looks like they r only ava in 3 step increments..101-104-107 and so on..and of course my 2 carter strip kits..1 .104 is missing!...I saw the edelbrock instruction manual also...basicly its thinner is richer,,and lite springs = more gas in quicker..

When the vacuum drops the lighter spring will will not be as fast at raising the rod out of the jet than the stronger spring will. The strongest spring you can run with rod completely down at idle in gear is what you want.

Stan