Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Please help with carb recipe - 455 GTO

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lrust:
Sent in the carb.  Have you had a chance to look at it yet?

Thanks,
Lowell

lrust:
Cliff,

Attached is the chassis dyno sheet from my engine with specs above as well as the QJet that you reworked.  I haven't changed any carb settings.  I has 69 secondary jets.

Engine specs are above except with 1.65 rocker arms.  Initial timing at 10 plus 20 of mechanical advance.  Ambient temp was about 90 degrees and car was at normal operating temperature.

Part throttle driving, my LM1 AFR meter reads about 14.5.  The attached sheet shows AFR of around 15 then transitioning into 13.xx as the power gets steeper.

Overall it seems lean (WOT and normal driving). 

I am interested in your comments on the transition at about 4,500 RPMs - it seems that the opening rate of the secondary choke pull off is too slow (I have not measured yet).  If so, it seems that my WOT jetting is ok if not a little lean, just needs to come in faster? 

I would be interested in your comments on this transition and other jetting recommendations.

Thanks,
Lowell

Cliff Ruggles:
I wouldn't worry about part throttle A/F as 14.5 is well within range.  It really depends on engine load and how the engine runs.  When an engine isn't happy at light part throttle they surge, lack power, and let you know about it.   I've seen some go well into the 15's at part throttle cruise and still be happy.  The engine combo and distributor tuning play a big role there as well.

The pull-off shouldn't be holding back the secondary airflaps till 4500rpm's.  Compress the pull-off and make sure it is fully open in about 2 seconds or slightly less.  Also make sure the airflaps and the linkage aren't binding anyplace and they open smoothly.

If all that looks fine, I'd try lightening up the spring tension slightly to bring them in a little sooner......Cliff

lrust:
Cliff,

I checked the diaphram and it closed in about a second and the linkages were all operated freely so I chose not to change anything.  Went to track yesterday for first time.

Launched cleanly in ~70F temps with good track prep.  Car ran best ever of:

60 - 1.615
1/8 7.24 / 95 mph
1/4 11.41 / 117

Second pass - all 5 OEM style lug nuts, trim ring and center cap exploded off the rim towards the wall on the driver side.  Fortunately no body or rim damage.  I replaced the studs and nuts and kept racing.  Got hotter during the day and track prep was worse.  Could only manage two more 11.6 ETs with tire spin.

Thanks again for the support.  I think my combo is doing well so far, need to work on suspension.

Lowell

Cliff Ruggles:
Yikes, good news that nothing was damaged and that you are running well, very respectable ET and MPH.

Traction is the key for good ET's for sure and you have no control over track prep, I run into that sort of thing all the time.....Cliff

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