oddball

Crazy question, I know, but I'm just shooting in the dark.

Anyone have a known-good qjet that I could use for an afternoon? I'm about ready to pull my hair out getting a decent idle on my 403 and want to make sure I'm not totally crazy.


For reference, it's a 403 with the KB flat tops, Edelbrock heads, measured 10:1 comp, Lunati 60803 cam, Performer RPM intake, with a TH350 sitting in a '72 Supreme. I have multiple carbs, all 704X25X's. Been through three main bodies, two throttle plates, two air horns. I've used several different size air bypass (modified throttle plate for set screws), modified idle tubes, drilled out air bleeds and down tubes.... Drivability is fine, but idle is terrible. To get idle in drive at 750 requires neutral around 1200. Timing is at 24deg initial + vacuum on manifold. Anything less and it won't idle at all. Ignition is a Pertronix Ignitor III with a MSD Blaster 2 coil.

Rickman48

Did you set the idle at the highest vacuum point with a vacuum guage?
Could be that minor, or a bad base gasket.

gearheads78

Possibly not enough converter?

oldcutlass

My thoughts exactly, 24* BTDC sounds a bit extreme. Have you tried ported vacuum?

oddball

Ebrock heads + 227/233 cam + small block = tons of advance. Just ask Octania!

It pulls about 14" of vacuum at idle, around 20 to 25 at cruise. It just dies if I switch to ported vacuum on the can. Set by watching the vacuum gauge and a tach. It's easy to tell when it's off - half a turn either way and it starts stumbling like crazy.

Checked for leaks with starter fluid, and all is well. I know because several times it wasn't!

Could probably use more converter. This one is around 2k stall? Maybe 2500? Can't recall. Of course, I *did* have it idling well at one point. I just didn't bother to take good enough notes to get back to that point.

oddball

Solved!

You know that saying, "90% of all carb problems are ignition problems"? Well, it's true again.
I *thought* I had my new dizzy working properly (Ignitor III billet w/ Blaster 2 coil) - at least it finally showed consistent spark via the timing light. Put the old Ignitor I back in, and idle is vastly improved.
Yeesh.