Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: 17058263 on April 12, 2012, 08:32:24 PM
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Ok does any one know the stock 301 jetting pontiac. I tried 72 jet with 52p rod had o power went to 43k rod 72 apt now has power will break the tirers loose. Also i do not run a egr or cat. Timeing 15 intial.any help would be great
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The carburetor number for a 1978 Pontiac 301 is: 17058272. Jets and rods for that carb are:
72 jets, 51 rods. The stock rods and jets for the 17058263 are: jets 70, rods 39. That carb is listed for a 1978 Pontiac 400 c.i. engine. Hope this helps billy 2
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Im using a , 79 301 carb. number 17059272 with.065 air bleeds. It was lean and mpg did not improve by leaning it out. So i went back to 43k also tried custom 44 rods. :) it runs good with the richer rods. Also with the 52p rods the throttle responce wasent that great. On line the manual 301 has 72 jet and 44rod. Just want some mpg
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There is no power difference using "K" or "P" metering rods at heavy and full throttle, as the tip size on either one is .026".
Used in .072" main jets, the 52P rods would allow .042-.052" of the upper section in the jet at light throttle cruising.
Using 43K rods you have a range of .039"-.043" in the jets cruising or any other high vacuum situation.
If using .072" main jets, you will have a broader range of control with the APT with our custom .044" metering rods, as the upper section tapers all the way down to .026", and is .044" at the greatest diameter with the APT fully seated.
Some tips on tuning. Choose the jet size first, based on heavy throttle power/performance without using the secondaries. Climb some steep grades at heavy throttle on the primary side only and change jets until you have the best power.
Install a set of tapered metering rods just over .030" difference than the jets size. For .072" main jets, .044" metering rods would be perfect.
Adjust the APT at apprx 3.5 turns up from seated, or use the "tip-in" method described in our book.
Do some extensive driving at light part throttle, and fine tune the APT screw for best transition off idle, light throttle power, and fuel economy. This may take several tankfuls of fuel to find the ideal setting(s).
Rarely does going really lean with the APT screw delivery best fuel economy, or power, unless you are driving strictly at freeway speeds on flat roads with very light load. More often than not, richer settings yield the best fuel overall fuel economy as the throttle angle will be lower for most driving situations.
Don't forget about the vacuum advance, it is equally as important as the carb setting(s) to find the best fuel economy. Lean mixtures need more lead time (advance timing at light part throttle) to be effective. You may have to add more timing in conjunction with leaning up the APT screw to see improved results......Cliff
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Well last year i had the 44custom rods and 72 jet and it faild smog at 23000 rpm co was to high so i went to a 70 jet and it past. And aso got 21mpg at that time. Also what jet would be good for a 49p rod. And trust me o power with 52p rods and it ran hot plugs wear bone white. But had a tan color on the rim of the plug. Total timing is 38.
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I took out my plugs and all are black. So I put in a 49k rod with a 73 jet will post how it works
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And trust me o power with 52p rods and it ran hot plugs wear bone white. But had a tan color on the rim of the plug. Total timing is 38.
With the APT at full height, a 52P metering rod would be around .042" in the jets, or very close to the 43K rod at a lower APT height in the same jet.
Are you running the APT thru it full range of adjustment with these jet and metering rod changes?
Also our 44 full tapered rods would have given you a broader range of adjustment that than the 43K rods in the same jets.
Increasing jet size is going to have it using more fuel, no other changes. If it ran OK a while back with .070" main jets in it, install our full tapered rods with those jets and raise the APT till it runs the best at part throttle.
Also, make sure that you are using new jets with these changes, and that they are the correct jets, designed for Q-jet carburetors.......Cliff
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Ok took it on the highway 40 miles each way got 18mpg. I adjusted my vacuum advance to 20 from 16 that made differnce took less throtle on cruise. Apt 2.5 did use the 4bbl to pass a honda kick right in at 50 and shifed at 4400.. 5 gall for 92 miles . With 73 jet 49 k rod . Ch seconday rod. L hanger.