31
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Mudsport96 on April 28, 2026, 06:12:06 PM »I would use the DP rods and tweak the hanger a little to lift them higher.
News:
We buy American, and use American Made parts for all of our exclusive Cliff's Carburetor parts and kits.
Recent Posts
32
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Zyen on April 28, 2026, 05:04:25 PM »i dont have a 'nice' assortment; DG, DR, DP and V, N, P, L. currently running richest i have.
the problem i see currently is i *think* the mains arent tuned properly yet. still working on that.
however, as this 4.3 will never open the 2nd door past ~40% and all the secondary rods are +/- 0.002" at that setting, i don't know how much difference that will make.
the problem i see currently is i *think* the mains arent tuned properly yet. still working on that.
however, as this 4.3 will never open the 2nd door past ~40% and all the secondary rods are +/- 0.002" at that setting, i don't know how much difference that will make.
33
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Mudsport96 on April 28, 2026, 03:54:27 AM »If i remember you had DG rods in it. They are a bit richer than the DRs. Could always try them again
34
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Mudsport96 on April 27, 2026, 04:33:22 PM »What secondary rods do you have available?
35
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Zyen on April 27, 2026, 03:34:23 PM »oops...i meant to say the 2nd air door spring was changed at same time i changed props.
36
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Zyen on April 27, 2026, 01:20:01 PM »next update. (had to heavily edit to make the 3500 char count...guess im just long-winded)
ebay seller claimed original 4.3l qjet. got it in last week. it has 71/41 mains with lightest spring and DG/P 2nds.
makes sense, as mine came off a 3.8l with 70/42 (not 43b; better magnification showed 42b).
changed to 70/39 for next test.
went out yesterday to get some data.
temp ~81°, 65-75%RH or so, winds 3-5kts, lake choppy...not idea for testing.
we put all all 4 props to get some readings, after cruising for ~20 minutes to warm everything up.
new phone, and havent thought about gps app, until i needed it...
tested in order below:
Prop Cruise Vacuum WOT RPM 2ND AIR SCREW WoT Vacuum (changed at same time as prop)
17 14" @ 3500 4400 1/2-5/8 turn < 1.5 (hard to get good read <1.5)
19 14" @ 3400 4300 3/4 turn ~ 1.5 - 2
21 9" @ 3500 4300 7/8 turn ~2.5
23 7" @ 3100 4100 3/4 turn ~1.5
i dont understand why wot is lower now...previous runs using the 17 would hit 4700 or so.
seems like im heading in the right direction in regards to jets. the 23p is way overpropped, so i think it's no longer a contender unless rpm come way up on others.
21 still 'feel' the best, but overpropped with current tune.
19 was (for the first time since i've had it) quite responsive.
17 felt like there was no load. from idle, hit wot and immediately jumped to 3800-3900 with bow way in the air. started popping thru intake so i didnt try that again. thinking about it, im sure with the 0.400" float dimension i was uncovering the main jets with that bow rise.
in all cases, plane time was ~3.4-3.5 seconds. seemed to pull about the same with all props; i couldn't tell a difference. will have to time 0-20 on mains to compare.
made couple more runs with 21 and 3/4 turn. cruise vacuum ~10" hg @ 3100.
still bog/lean...if hold wot > 3-4 seconds, it would backfire thru intake.
next step is richer main. i have 70,71,72,74.
downside is i cant (wont) do carb work on water or at (usually busy) ramp...so major tuning is at home on fridays, then the hour drive to the lake on saturday or sunday.
i am using the richest 2nd set i have, and it seems i still need more fuel. as this v6 cant open the 2nd air door more than ~40% and all the rods are +/- 0.002" at that range, the only way to get that richer is bending the hangar to pull rods up more. are there any other options?
thanks for the replies.
ebay seller claimed original 4.3l qjet. got it in last week. it has 71/41 mains with lightest spring and DG/P 2nds.
makes sense, as mine came off a 3.8l with 70/42 (not 43b; better magnification showed 42b).
changed to 70/39 for next test.
Primary metering rods aren't a big player when tuning a Marine carburetor...
so if i am understanding this, it is preferable to keep the 0.030" (+/- .002 or so) jet/rod difference and tune for best jet / response on mains?
...
If you can come up with a nice assortment of secondary rods and s decent range of hangers it will help with WOT testing to get the best results.
i dont have a 'nice' assortment; DG, DR, DP and V, N, P, L. currently running richest i have.
Once you get the primary side "dialed in" do NOT change anything there.....
understood.
went out yesterday to get some data.
temp ~81°, 65-75%RH or so, winds 3-5kts, lake choppy...not idea for testing.
we put all all 4 props to get some readings, after cruising for ~20 minutes to warm everything up.
new phone, and havent thought about gps app, until i needed it...
tested in order below:
Prop Cruise Vacuum WOT RPM 2ND AIR SCREW WoT Vacuum (changed at same time as prop)
17 14" @ 3500 4400 1/2-5/8 turn < 1.5 (hard to get good read <1.5)
19 14" @ 3400 4300 3/4 turn ~ 1.5 - 2
21 9" @ 3500 4300 7/8 turn ~2.5
23 7" @ 3100 4100 3/4 turn ~1.5
i dont understand why wot is lower now...previous runs using the 17 would hit 4700 or so.
seems like im heading in the right direction in regards to jets. the 23p is way overpropped, so i think it's no longer a contender unless rpm come way up on others.
21 still 'feel' the best, but overpropped with current tune.
19 was (for the first time since i've had it) quite responsive.
17 felt like there was no load. from idle, hit wot and immediately jumped to 3800-3900 with bow way in the air. started popping thru intake so i didnt try that again. thinking about it, im sure with the 0.400" float dimension i was uncovering the main jets with that bow rise.
in all cases, plane time was ~3.4-3.5 seconds. seemed to pull about the same with all props; i couldn't tell a difference. will have to time 0-20 on mains to compare.
made couple more runs with 21 and 3/4 turn. cruise vacuum ~10" hg @ 3100.
still bog/lean...if hold wot > 3-4 seconds, it would backfire thru intake.
next step is richer main. i have 70,71,72,74.
downside is i cant (wont) do carb work on water or at (usually busy) ramp...so major tuning is at home on fridays, then the hour drive to the lake on saturday or sunday.
i am using the richest 2nd set i have, and it seems i still need more fuel. as this v6 cant open the 2nd air door more than ~40% and all the rods are +/- 0.002" at that range, the only way to get that richer is bending the hangar to pull rods up more. are there any other options?
thanks for the replies.
37
For Sale / Wanted / Re: A few carbs for sale.
« Last post by 77cruiser on April 27, 2026, 05:53:18 AM »Pretty sure I do, I'll look later when I get home.
38
Diagnose a Quadrajet carburetor problem / Re: Quadrajet Throttle Body Swap - Will it work?
« Last post by Cliff Ruggles on April 27, 2026, 04:16:31 AM »The key to removing stuck APT screws is heat, patience and a custom made screwdriver that fits tight in the screw. It may take several "sessions" heating and applying penetrating oil but I'm close to 100 percent in getting them out.
I just removed one from a 1971 Olds couple of days ago that took three attempts to get it out. It actually starting moving a little back and forth on the first attempt, but I had to let it completely cool down and apply more oil, then do the process two more times before it would come out.
When swapping TB's on those units you are going to get much better results with a work APT system when it come time to dial in the tune on the primary side.....
I just removed one from a 1971 Olds couple of days ago that took three attempts to get it out. It actually starting moving a little back and forth on the first attempt, but I had to let it completely cool down and apply more oil, then do the process two more times before it would come out.
When swapping TB's on those units you are going to get much better results with a work APT system when it come time to dial in the tune on the primary side.....
39
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Cliff Ruggles on April 27, 2026, 04:10:37 AM »Primary metering rods aren't a big player when tuning a Marine carburetor. About the only time they are down is idle and light engine load. Any heavy/full throttle and they are going to be up on the .026" tips.
As for secondary metering rods they are the key player at WOT and full load. Secondary rods vary considerably is upper section diameter, taper, tip length and the included angle leading to the tips. So the hanger each rod is used with plays a role in fuel delivery.
If you can come up with a nice assortment of secondary rods and s decent range of hangers it will help with WOT testing to get the best results.
Once you get the primary side "dialed in" do NOT change anything there.....
As for secondary metering rods they are the key player at WOT and full load. Secondary rods vary considerably is upper section diameter, taper, tip length and the included angle leading to the tips. So the hanger each rod is used with plays a role in fuel delivery.
If you can come up with a nice assortment of secondary rods and s decent range of hangers it will help with WOT testing to get the best results.
Once you get the primary side "dialed in" do NOT change anything there.....
40
For Sale / Wanted / Re: A few carbs for sale.
« Last post by Captive8 on April 26, 2026, 06:35:13 PM »Just seeing this...if you still have the 17059253, I'll take it.