Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Need Tuning after dyno run

(1/5) > >>

leeklm:
Got the Pontiac 455 on the dyno today, and first run with my new 17059272.  I built this carb to specs under "recipe 2" in the book, including the drilling of idle bypass holes, which were not present, and only tested it in the garage on a stock low compression 400 just to be sure nothing major was wrong.  The carb seemed to run well during this minimal quick test.

On the dyno, the idle was a little rough, which could be smoothed out by applying a some choke.  During the pull, the engine was plenty lean and was not smooth.  I attached the dyno sheet if that helps regarding AF ratio, etc.  For comparrison, we picked up about 30hp & 30tq after bolting on a carb the dyno guy had.  Unfortunetly, we were running short on time to do much for adjustments.  Also attached is the dyno run with another qjet for comparisson.

One adjustment I made was to back the APT screw out to the max, which helped some at cruise rpm, but minimal.  Also, seemed like I really had to loosen the secondary flap, otherwise would not open.

Here are my carb & engine specs (all parts bought from Cliff)... Any thoughts or suggestions would be greatly appreciated!

Main Jet = 73
Main Rods = .021 - .039
Sec Rods = CE

462ci w/20" of vacuum
468/489 lift cam w/219 & 227 duration @.050   112 lobe

Shark Racer:
It looks like the secondary function is the culprit for the leanness; what have you set your air-valve spring tension to?

Going with off the shelf-stuff, it's a big leap to CC secondary rods, but that will certainly richen you up. You might hunt down a couple pairs of rods in the middle.

Cliff Ruggles:
We don't sell CE metering rods.

What primary metering rods are you using?

Did you modify the stop on the secondary airflap shaft linkage so the airflaps can open further?

I would also install solid secondary fuel nozzles if the factory ones are cross-drilled?

Did the idle mixture screws have any effect?

What size idle tubes, down channel and idle bypass air were used?.....Cliff

leeklm:
Thank you in advance Cliff for the help!  Here is additional info...

Secondary Rods are a set of Edelbrock CE that I had...  I did open the secondary flap restriction, added a stop screw, and adjusted opening according to book.

Primary rods = 44 (bought from Cliff :))  Measurements above are what I took from the fat & skinny part of rods

Idle Tubes = .036 (I think I installed these w/o changing when purchased in my kit)

Down Channel = .05

Idle bypass air, which I drilled into the baseplate passages = .098

I was not in the engine room when the tech made an initial adjustment of the idle screws.  It seemed to smooth the idle some, but still needed a little choke to smooth it out.  Unfortunetly, we did not have time to go back and make more adjustments.  At $70/hr, we had to keep things moving :)  I am tempted to spend another $300 for more fine tuning & experimenting at the dyno, but that also requires another day off of work, which is not always bad... Besides, I would probably get more results spending the $300 with Cliff :)

The secondary nozzles are cross-drilled.  Can these usually be extracted from another carb w/o damaging, or do you sell new?

Lee

Cliff Ruggles:
We sell new ones, insert a punch that just fits into them and work them in a circle, they will fall right out....Cliff

Navigation

[0] Message Index

[#] Next page