gmmeyerIII

1973 bone stock motor
Car has had high idle issues since i got it. never felt like it really ran well
i have good oil pressure, good voltage, dont burn oil and motor is actually pretty quite
i have been through the gambit
So lets start with what's new. some is new due to a mild restoration
New Fuel Lines front to rear and fuel filter
Distributor completely refurbished by Northwest Florida Distributor Service this month. top bushing came out and stuck on shaft when i tried to disassemble.
New Coil this week
new spark plugs couple weeks ago
Adjusted Valve lash this week
New vacuum lines two months
Intake manifold new install this week.
Carb rebuilt by Lars about 4 years ago, quadrajet, not original to car. we peices one together out of two carbs
fuel pump looks relatively new, ive owned car for 4.5 years.
car has only seen 2500 miles in that time

Timing set accordingly
Dwell set at 30, fluctuated 29.9 to 30.1 occasionally
vacuum is at 20 and holds steady. head lights work flawlessly after complete rehab
With no vacuum advance and carb plugged at advance connection, set initial at 12
remove one spring, bring to 36 before 2750 rpm with adjustments to distributor.
install new spring, timing at idle is at 22 degrees, connect vacuum, idle at 1000 rpm timing at 36 degrees
running with two silver springs from mr gasket as i could not get to 36 degrees otherwise.
i cannot adjust idle now as idle screw is all the way out.
carb fuel and air are at 2.5 turns out currently
car will run like this but fall completely flat at 3000 to 3500 rpm if mashed, can slowly persuade that way, but will start popping & sputtering.
one thing i cannot get is my secondaries to even start to pop open while revving in driveway.
im really starting to believe this carb is my issue.
idle will still fluctuate at times as well.

anyone have any others thoughts.

I also confirmed TDC on harmonic balancer is correct

naramlee

trash clogging the internal filters, starving for fuel OR trash in the needle /seats blocking fuel

those are vacuum secondaries? They wont open untill your airspeed reaches a certain velocity under load, reving in neutral wont open them

lars

Sounds like a fuel starvation issue, but the high idle is indicative of a vacuum leak, which will lean out the carb and cause problems. You cannot get the secondaries to open while "winging" the throttle in neutral - there's not enough airflow to open them in neutral, so what you're doing is an invalid and irrelevant test of secondary operation. If you suspect the carb, send it back and I'll re-test it. All carbs are tested extensively to assure correct operation. Part of my test procedure and acceptance is to verify that the engine can be "killed" by backing out the idle screw. If you are idling at 1000 with the screw backed out, you either have a faulty divorced choke keeping the idle on the fast idle cam, or you have a vacuum leak. Popping at elevated rpm and "falling on its face" is a sign of fuel starvation or vacuum leak.

No, the Q-Jet does not have vacuum secondaries. It is a mechanical secondary carb with a secondary airvalve. This is not a vacuum secondary carb.

Lars

gmmeyerIII

Lars
i almost agree in fuel starvation. the vacuum leak i guess is a possibility, but i i have changed all hoses under hood including headlights actuators and so on.
just pulled intake thinking there could possibly be a leak despite not being able to source one.
would vacuum leak explain high timing when setting? that's the other thing that really threw me for a loop.

jb78L-82

As LARS stated:

Quadrajet carburetors have mechanical secondary throttle plates operated by a progressive linkage; the primaries open before the secondaries, and use on-demand air valve plates above the secondary throttle plates. The air valves are connected by a cam and linkage to the secondary fuel metering rods. As the airflow increases through the secondary bores, the air valves are pushed down, rotating a cam that lifts the secondary metering rods. The secondary rods are tapered in a similar fashion to the primary metering rods, effectively increasing the size of the fuel metering holes as the rods are lifted and delivering more fuel. Therefore, the position of the air valve will control both fuel and air flow through the secondary venturis, even if the secondary throttle plates are fully opened. Thus the Quadrajet acts like a vacuum-secondary carburetor and only delivers more fuel as it is needed.[[i]citation needed]

lars

Vacuum leak has no effect on timing. You should be able to set the timing to any setting regardless of any issues with carb or induction (timing affects carb, but carb does not affect timing). Why is your timing "high when setting?" You should be able to set the timing to any spec you desire.
If the throttle plates are completely closed, the engine will die regardless of timing or any other issues, since the engine cannot idle without air. If the air is not going by the throttle plates (because they're closed), the air has to be coming from some other place other than through the carb. That source is a vacuum leak. The engine cannot idle if the throttles are fully closed unless air is leaking into the manifold from another source. Make sure your throttle cable is not holding the throttle open. Again, if in doubt, send the carb back and I'll re-do the entire test procedure and setup for the cost of the postage.

Lars

OldCarBum

Blue73Shark

gmmeyerIII

I have vacuum gauge, stated above im holding at 20 steady at idle with a small gain through rpm

Jebbysan

Go around with the engine at idle and use a propane torch (unlit) to 'sniff' out any potential vacuum leaks. The idle will change if it pulls in unburnt propane.
You need to fix the idle problem first. Are any of the pulloffs or linkages casing the blades not to shut? With the curb idle screw all the way out....are the blades shut?
Your explanation of how you did the timing confuses me as you are saying you are pulling more timing after the springs are installed. With a spring removed....you should see full advance WAY before 2750 rpm.
What is the story on the Q-jet? Was it run on the car before? Did it sit for a long period of time with pump gas in it?

Jebby

jackson

Folks ... who else backs up their work so well?

And, in this instance, after some 4 years

gmmeyerIII

Jebby,
I guess i should have mentioned as well, any start is rough, cold or hot. when hot takes a minute to get to correct idle speed, when cold its a rough start
i disconnected choke and accelerator cable to check for binding. curb idle does not allow blades to shut when screwed all the way out.
car idles well when without advanced timing, when i hook up advance canister my idle jumps dramatically and pulls in all timing it seems.
Q-jet has been on car for past four years, sat for last 4 months due to much needed rocker channel rear suspension rehab. car gets driven regularly before that. at least once a month or more for enjoyment purposes
it pulls more timing with vacuum advance hooked up. it raises my idle about 2000rpm

gmmeyerIII

agreed, im not going to let Lars pay for shipping though if i take him up on offer.
im not sure i even want to stick with the q-jet. its not original to car, which doesn't have all that much meaning anyway.

Jebbysan

Remove it and send it to him.......let him run it on his test engine....that will confirm or eliminate the unit.....I fear it may have gummed up components inside.
Unless you plan on mods like cam and or heads......leave the Q-jet on it....you will not find a better fuel mixer.

Jebby

lars

Even if it's gummed up or has some issues after 4 years of service, I'll "refresh" it, fix it, and check it out for you for the cost of the postage to assure it's running right.
If the throttles are not closing completely with the idle screw backed out and throttle cable disconnected, there is a problem.

Lars

gmmeyerIII

Lars,
sending you a pm

gmmeyerIII

well guess im not.
i will send carb out this week. i have will have my personal contact info in it and i will shoot you an email from our last correspondence.
Thanks Lars!

lars

It's in the PM here now, and I just checked my e-mail and I do not have anything from you.

Lars

7t9l82

Yank the distributor and send that to Lars too. I think that distributor may have issues too.

lars

My distributor machine is out of service, so I can no longer assist with distributor testing and setup. If I can get it repaired at a cost that makes sense I'll let everyone know. In the meantime, Gene has the carb on its way to me, and I'll give it a good test, checkout, and evaluation to see if it's the cause of the problems. With Gene's permission, I'll post up test results and progress in this thread along with some photos.

Lars