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Old 04-22-2019, 04:18 PM
jxhinoj
 
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750 DP jet sizes

Hello guys,

I was looking for a 650 dp instead i bought me a used 750 dp 4779-9. looks brand new i couldn't pass it up for $150 bucks. What jets sizes do you all recommend, to work with my combo below.

1968 350 over 30 2 bolt maine
RPM Edelbrock Aluminum cylinder heads 64cc chambers 185CC runners
Edelbrock head bolts 8550
Howards Cam 221/221 duration lift 470 108lsa
Howards lifters anti-pump
Comp Cam 1.52 roller tip rockers
Edelbrock head gasket .038
Edelbrock RPM Air gap
570 Street Avenger
Mallory dis. HEI
6L MSD box
1 5/8 headers with 3" flange with flowmasters/dumps
PA 700R4 transmission and 2200-2500 Hughes Stall Lock-up
373 POS. 10 bolt

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Old 04-22-2019, 05:33 PM
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Leave it with stock jetting and let performance and plug reading guide you to any needed changes. This is the same advice I give anyone when I rebuild a carb for them for use on a new combo when the carb isn't physically altered for more airflow(thinner blades, profiled throttle shafts, "HP" main body upgrade, milled off choke horn, polished venturi's, change out the boosters, etc).

Holley comes pretty close with the stock calibration on the traditional DP carbs like this.
Stock jetting for List # 4779-9 is 71 front, 80 rear. Based off your cam spec and engine size, I would say 6.5 to 8.5 on the front power valve. Rear doesn't have a power valve. It should have a 28 pump nozzle("squirter"/"shooter") front and 31 rear.

That's a pretty decent engine combo ...what's it in??
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Old 04-22-2019, 06:14 PM
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Thanks ericnova7, its in a 68 camaro RS. I will follow your advice 😁
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Old 04-22-2019, 09:36 PM
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Moving to Hotrodding Basics forum.
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Old 04-23-2019, 06:50 AM
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Thanks Crosley
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Old 04-23-2019, 10:48 AM
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You need to set this up with a transmission pressure gauge to insure the modulation on the 700R4 is in specification. Holley specifically warns in their specifications that the Double Pumper is not for use with overdrive automatics by that they mean, but don't say, the 700R4.

The issue is the throttle linkage position for what they call kick down is for manual kick down (passing gear) not for pressure modulation as in the TH350 which uses manifold vacuum for modulation and a throttle valve mechanical link for "passing gear" forced downshift. The 700R4 combined these functions into the mechanically linked TV connection therefore is sensitive to the amount of TV extension to throttle blade angle. The Holley TV hole on the DP carb's throttle bracket is not quite right for the modulation job in this regard.

Not that this isn't done (using the kick down for modulation with the 700R4) but given this transmissions sentivities to the TV set up it is a wise practice to test the generated pressures against book values. You want to meet or exceed these, falling short eats the band and clutches often suddenly, extending high just makes for harsh shifts.

Plenty of instructions are on the web for how to adjust the 700R4 TV cable and there are pressure spec's out there as well.

Compared to the cost of fixing the transmission if you get this wrong, jet sizes are the least of your worries. However, expect even an unmolested DP to exhibit rich on the street. But you'll have to test to find out so document where your starting from.


Bogie
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Old 04-23-2019, 11:12 AM
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Thanks for the info, i have burn a couple of transmissions back in my teenage days for the same reason That's the first thing i will check when installing the carb this week
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Old 04-23-2019, 11:53 AM
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There are linkage connection adapters made just for the purpose of connecting 700R4 and 200-4R overdrive TV cables to Holley and Edelbrock carbs.
That would be the very first thing you need.

https://www.holley.com/products/fuel...e/parts/20-121
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