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quadrajet jetting and primary rods?

Discussion in 'The Garage' started by Dunc03, Nov 22, 2003.

  1. Dunc03

    Dunc03 1/2 ton status

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    First off let me start with what i'm working on. I have a 86 blazer with a 4 barrel quadrajet off a stock 305, the one with the dual capacity pump. I have run the Dual capacity pump to a switch on the inside of the vehicle so I can operate it manually. I have installed a Gm crate 350 HO, the one with 330 hp.350 HO Engine specs
    I'm having problems with to lean of a mixture from a standing start and part throttle tip-ins in 4 gear. THe thing stumbles an then goes, sometime it dies out when its not warm or when I try to floor it. I've noticed that I don't have these problems as bad when the choke is on, thus a richer mixture. When I leave the dual cpacity pump off, richer mixture, i don't have the problem either, but this makes the mixture too rich at idle and it waste alot of gas. I tried adjusting the APT (adjustable part throttle), and this seems to help some until the tempature drops and then it starts the stumbles again. i have a pretty good idea that the jetting and primary configuration are too lean. I have .072 jets and .051 primary rods, i checked that out today. I have read that the difference in these two numbers needs to be close to .03 and I have only .021. I think this is causing the lean mixture off idle. I know that the transition from idle to part throttle requires the richest mixture, or at least thats what Doug Roe's book says. Anyways, the real question is, can anyone suggest a jetting and rod configuration that might help me out here, or do I have other problems. Also I have a feeling that the secondaries are lean also. I have the DP rods which have a minimum diameter of .0686. Is this going to be lean at full throttle, any suggestions. Thanks for the help in advance, and sorry for the long post, but i know you guys hate it when people don't give all the information. Here are the engine and cam specs again specs .
     
  2. R72K5

    R72K5 Banned

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    man, i wish i knew where i have all my URL shortcuts saved to for pages and sites that have Q jet modification and building info, probably have lost them because of past bad luck with HDD's dying

    hahve you searched on google.com for quadrajet performance or something like that yet ?

    you would be surprised what info sites/pages there are for these carbs nowadays

    on a side note, i have alot of parts carbs and parts, carter and roche Q jets, so if you are looking for any specific rod jets parts or anything then lemme know and im ight have them

    good luck
     
  3. mdm365

    mdm365 1/2 ton status

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    Try these links,Some good reading. links
     
  4. jms

    jms 1/2 ton status Author

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    I assume it's the carb with a solenoid controlling primary rod position, right? If not, have you considered changing the power piston spring?
     
  5. florida4x4

    florida4x4 1/2 ton status

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    post the carb number
     
  6. Dunc03

    Dunc03 1/2 ton status

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    The carb # is 17085292 and it also had these numbers by the part # 1206 HMJ. I'm not exactly sure what the second set of numbers are for. The carb is not a computer controlled carb, so it does have the power spring and valve assembly. I tried using a weaker spring, but it didn't work as well as the stock one. I think if anything i need a strong spring so the primary open sooner to give a richer mixture. I'm not sure what the spring rating on the spring is, and the most powerfull spring you can find from edelbrock is a 10 mmHg, which way to low for the amount of vacuum that I have. I have 19 mmHg vacuum at idle in park, and around 15- 16 mmHg when in drive. I know that the jetting and primarys must be a little on the lean side for two reasons. One, its and emissions carb, and two, it was calibrated for a stock 305 rather than a higher performance and higher compression 350. The power valve may also have some effect on the lean condition also, but i'm kind of at a loss for options since I don't know what spring tension I have right now. IF anybody wknow what spring rate they Rochester put in this thing, that would help out alot. Thanks for all the posts guys, and I hope that carb number helps out. /forums/images/graemlins/k5.gif
     
  7. florida4x4

    florida4x4 1/2 ton status

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    The first thing to do is verify the jet and rod is an original combo. I hoped to tell you the sizes but my book only lists them as a "package", PN 17110103. I did find that the number crosses over to 1985 5.7 with auto and a/c so you do have a 350 carb.
     

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