Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Dreaded nozzle drip 17056200

(1/7) > >>

68rs/ss:
Looking for possible solution for new engine/carb. This is fresh 396 BBC and reconditioned using cliff's parts and recommendations.
Engine is 9.5 CR using closed chamber heads, with mild bowel cleanup and good flowing valves. Cam is Crower with 224intake, 232 exhaust, .542 lift intake, .514 exhaust. Lobes are at 112 degrees.
using Q-jet RPM and headers.
This is fresh engine and is on test stand for break-in and carb adjustments before putting in car.

After initial break-in, can not get it to idle down. Primary throttle blades are open too much causing idle drip. Does not run smooth with blades turned down to stop drip. Mixture screws have little effect. Pretty sure no vacuum leaks as all the ports are plugged. Initial timing is roughly 8 degrees.

Carb is as follows.
Jets:79
primary rods: #46 tapered from cliff
Upper Idle air bleed:.070
Lower idle air bleed: .059
Idle tube: .038
Idle down Channel: .053
Mixture screws: .090
Idle by-pass air: .110
Float was set a little high so lowered it to 1/4"
Needle and seat vacuum tested and held for hours.

Looking through cliffs book, seems like the idle down, mixture passages and lower idle air bleeds are all a little small compared to some of the recipes.

Where should I look to cure this?
Thanks.
Phil

Cliff Ruggles:
Your carburetor "recipe" should be adequate for what you are doing.  Before making any carburetor changes get the idle speed as low as you can and gently "tip-in" the choke flap or place your hand over the choke housing area and see if the engine speeds up and smooths out.

I would also try more initial timing.  Your compression ratio is pretty "low" for the CID and camshaft specs so it's going to enjoy more timing at idle speed.

Do both of those things before adding any more idle fuel......Cliff

68rs/ss:
OK, I will put it back together for another try. It did smooth out with more timing and it did run better when I put my hand over the carb.
It's a little discouraging hearing the cam is not the best choice for the application. I sent my engine and car details to "cam guy" at company and that's what was recommended.
Do you have any recommendations? Hate to do a cam change, but I do want this to run without any issues. Better to do it now before it goes in car. You've been very helpful in the past.
Phil

Cliff Ruggles:
You simply don't have enough compression IF you are needing to add a lot of timing and fuel at idle speed for the cam being used. 

Doesn't always make it a bad choice, but from what I've seen with these things if you find your engine wanting a lot of timing at idle, and you aren't making a lot of vacuum without adding a bunch of timing, the cam choice isn't optimal.

Sadly I see a LOT of this sort of thing these days.  Started back when someone (who needed to go very quickly back to their day job and stay the hell off the Forums) came up with some proverbial "brick wall" of 9.5 to 1 compression for these engines if you want to burn pump gas in them.

That statement alone is probably the most inaccurate statement ever made related to these engines......FWIW and IMHO.

Anyhow, next time it's up and running do a vacuum reading at 700-750 RPM with 8 degrees timing.  Increase it to 10, 12, 14 and keep going till it's pretty happy, and take a vacuum reading at each point. 

Once you reach your "happy spot" shut the engine down, let it sit 3-5 minutes and see if it "bucks" the starter on a hot restart........post the results.......Cliff

Kenth:
You might try the 1965 Impala High Performance vacuum advance (STANDARD MOTOR PRODUCTS VC181) and use full manifold vacuum at idle.
Starts @ 5-7 in/hg and have 16° @ 11-13 in/hg.

This will make a stronger "pull" thru the idle ciruit due to bigger difference between atmospheric pressure and vacuum beneath the trottle blades.

Navigation

[0] Message Index

[#] Next page