Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
bry593:
Carb Assy Tip - Spray your gaskets with Aerosol Silicone Lubricant. This will help prevent sticking and ripping when disassembling for multiple tuning changes.
I have disassembled this carb at least 10 times and still using all three gaskets: airhorn, throttle plate and manifold.
Cliff Ruggles:
I breezed back over the thread and noticed a few common denominators with not having a big enough camshaft in an engine based on the CID and static compression ratio, or the LSA is a little too tight, etc.
Some run-on after shut down.
Pinging in certain conditions without a lot of timing.
Making a LOT of vacuum at idle.
Difficulty tuning the idle system.
Not a deal breaker but for sure this engine would have loved about 10-15 degrees more seat timing, duration @ .050" and pushed out of a wider LSA.....IMHO
I tune couple of Saturdays a month and ran into a very similar scenario with a 454 "LS5" engine last summer.
Long story but it follows yours pretty close. The short version is that I did the OEM carb for it based on the owner supplying me specs that the engine was built to "stock".
This was a "high end" restoration so the carb was restored and built to stock specs with the only change being the addition of an external APT screw and slightly smaller primary metering rods.
The engine didn't run for chit from day one and of course the carb guy was getting ALL the blame from the engine builder. After at least a year of correspondence and trying to help out I simply had the owner bring the car here so I could see what was going on.
Immediately when he fired it up and backed it off the trailer I knew the engine was off someplace. I very quickly found out that the timing was retarded pretty far, it had pretty high cranking pressure, and idling very smooth and making a butt-ton of vacuum despite not much initial timing.
Any attempts to increase initial timing resulted in "bucking" the starter pretty hard when it was hot and ping right off idle and at heavy/WOT.
I tried few things with the distributor and timing and it didn't like any of it, but taking away timing everyplace helped some.
So I went to the owner and asked him once again what the engine specs were? I told him that there was no way this was a stock or even close to stock cam in the engine. So he contacted the engine builder via his cell phone and had him send a copy of the cam card.
Turns out the engine "builder" and "guru" had Howards supply the cam. It was supposed to be a "modern" version of the original LS5 camshaft but turns out it had about 30-40 degrees LESS seat timing and ground on a much tighter LSA. The .050" numbers were close but even slightly less than the factory camshaft.
We were pretty much done at that point. I recommended removing the cam and tossing it down over the hill and making a better selection since the engine had pretty close to the stock compression ratio up near 10.75 to 1.
Of course that went over like a fart in Church and the owner ended up leaving with the car and not overly happy about it. I did "de-tune" the carb to help out some as it had WAY too much idle fuel since the engine was making up near 20" vacuum if you put any timing in it.
So more or less a "crutch" fix for a fundamental issue not really related to the carburetor or distributor.
As for your set-up I think it can be effectively tuned to correct all the issues. I personally believe that the real fix is to install a bigger camshaft in it on a wider LSA.......FWIW......Cliff
bry593:
I have unintentionally installed an A/F alarm to the truck. What is that you ask? Well, I had my mufflers changed from short to long last Friday, and one has a loose baffle. Any slight backfire will vibrate like a snare drum.
This morning I fired it up with one pump on the throttle. At first I heard some snare drum, but it faded within a few seconds and smoothed out at 1400 rpm. The next step on the choke, same thing with a bit of drum followed by quiet. By the time it hit warm idle, no backfires and smooth.
A slight drum during transition, but is gone instantly.
Cruise seems good, no drum noises from the muffler.
Acceleration gets a bit rattly at higher rpms, but I suppose that's just due to a more powerful exhaust pulse.
Tomorrow, a replacement muffler will be installed and I plan to run it through all four barrels. Right now it is just too embarrassing sounding with the loose baffle to open her up.
tayto:
it's interesting how the exhaust note can change as the tune gets better. i built a Qjet for a friend of mine for his 80 firebird a few years ago. he had (at the time) owned the car for 12+ years, never really ran right, but did run. One of cliff's kits, some major straightening of the air horn & main body, major tune up and fixing an exhaust leak it had had for sometime. the note totally changed from idle to part throttle and wot.
bry593:
Yes, I noticed a substantial decrease in exhaust noise going from the 800cfm 170 to a 750cfm 70 series. However I assume it was due to the calibration. The 70 series was calibrated to a '71 350 and had the IABP plugged to work on a 305.
How did you straighten the main body (zinc die casting) of a quadrajet? The two front corners are typically mashed due to an overzealous mechanic. I've heard that you can bolt the body solidly to a thick piece of steel plate, bake it in the oven at ?F for awhile, loosen and re-tighten the screws, then repeat the process. After ? cycles, let it cool while bolted to the plate and voila, the corners magically return to almost flat. Not sure how this works exactly, but that's what I heard.
Of course I also heard that you might as well toss that mashed quad body in the scrap pile.
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