Confirm these specs, please. Cadillac 500

[Marx3]

I have a 17056230 on a stock 500.
I recently rebuild the carb and modified the main system with great results.
On the idle circuit I shot a bit over the target.
.097 bypass
.058 DCR
.037
.090 mixture screw holes.
With this set I couldn't bring the idle lower than 8-900, unless I backed down the timing a lot.
I finally realized the idle circuit was way too generous.

Here is the new setup:
.051 bypass
.046 DCR
.036 tubes
.090 holes.
Needless to say, I can now bring the idle down as much as I want until I kill the engine, but I am swing erratical idle.
For example: engine is idling at 600 and I blip the throttle, revving it to 2500-3000 rpm for a split second.
Coming back down to idle, the engine tends to want to settle a different rpm than before.
Than I back down the idle and flip the throttle again. Coming down now, the idle is too low suddenly.
The car needs brake work, so I chat take it for a spin and get some realistic action from the the carb.
These adjustments are made in a warm greenhouse. At the end I had the air horn off and confirmed the idle was boiling slightly.
Are these specs off for a stick low compression 500 or what?
I feel I am starting myself blind here.
I have successfully built and calibrated lots of Qjet over the years, but this one is giving me the fits.

[429bbf]

just a thought , did you take the distributer out of the equation . i had one act similar and i had a set of sticking weights drive me crazy . after i took the carb apart 3 times i finally figured it out. hah

[Marx3]

Yes the distributor is serviced and in good working condition.
Timing is bumped up a bit and using ported vacum.
What problem did you think stuck weights would give, in this case?
Erratic idle?

[429bbf]

it did for me .the way i figured it out was by driving it .if i just puts around say less than 2000rpm everything was fine . once i reved it up 35to4000 the problem started again i blamed the carb of course . finally they stuck and when i rechecked timing i was a mile off. fixed it and been running great. fwiw

[Marx3]

I hear ya. Better re-check. Better than sorry.
Do you have any opinion on these idle specs for a stock huge engine?

[429bbf]

in my opinion (which might not mean anything )they look like it should idle  just fine . the problem i run into most is the cam and how it is degreed.( i hear ya its stock)I've had 2 identical 454s stock 1985 1 tons , both carbs built exact ,they should have run the same . there was no comparison , the one idled and ran like a champ, the other one i messed with for a long time before i got it the way i wanted it. i still haven't figured it out today and that was 20 years ago.i ran into one more thing that caused me some headaches. battery voltage . the thing would crank , if you put it in gear you could drive to town.1980, dodge ,1 ton you could pull start it it would run , when you cranked on the starter it dropped the voltage down to far to start but yet you could crank it for 5 minutes. (i know electronic ) it seems like we always blame the carb. when over half the time it is something else. i guess thats why we are mechanics and like to play around. fwiw cliffs parts have made my hobby very easy , you don't have to do the work 4 times because of junk parts that last as little as 20 minutes.one last note . most the stuff i work on are for young kids (no pun intended )they install monster cams , shootty pistons and build a low comp engine with a 1000 cfm. carb and they got the info from some salesmen thats never had an engine apart. and they wonder why they run like crap. sorry for the long post.

[Marx3]

Thanks for your opinion. I feel pretty confident they arent that far off...
I'll cross my fingers this problem has something to do with something else than the carb.

I know what you mean about unexplainable things... I had a rebuilt carb that would nozzle drip. Stock 350 SBC, idle circuit calibrated a little rich for en upcoming camswap that meant a slightly bigger than stock cam. Nothing wild.
Even if the throttle plates were completely closed shut, it would drip form the nozzles. Nothing seemed wrong anyplace. That carb was just sick, I guess. Cliff couldn't explain either.

I hear ya on those ambitious low compression high performance builds :-) seen too many! it's a damn shame. Those salesmen promise 400 hp and too many people take the bait.
A smooth running 275 hps engine will always feel stronger than the same engine, with mismatched parts, were some of the parts "should" make 400 hp, thats my theory.

[429bbf]

heres another good one . a young mans mom calls me last weekend . her son is having carb problems ,( i built him a q jet a couple years ago)so i stop over after work and take it for a test drive, i tell him its not a fuel problem , you could tell by the way it acted . (it missed constantly)popped the hood and guess what. plug wire had burned next to the header and was shorting out. morale of the story as you get older you do more troubleshooting and less work. fwiw

[Cliff Ruggles]

Had a similar experience here.  We built a 355 SBC small block engine for a customers 85 Monte Carlo SS. We also rebuild the carburetor.  He had the install done elsewhere.  Came pulling up to the shop after the install and said it ran pretty well but not nearly as strong as he thought it should be.

As he pulled up to the big overhead door we noticed something hanging under the car, it was two of his plug wires.

We attached the wires and the engine smoothed out nicely.  Took it for a test ride, stopped on a flat stretch of road and nailed it..........it spun a few feet then hooked up, twisted the driveshaft all up and threw it out on the ground beside the car......OOOPS!!!

[Marx3]

Hah! Great stories. :-)

[Hillbillyenginering]

Guess I'm thgthgrowing my two cents in.
I know you said its rebuilt correctly. But I have seen two posts on here recently where they found,after multiple comments, that one of the throttle plates were slightly off causing similar issues.
Are you verifying with a feeler gauge that the primaries are in dead closing all the way. Anything slightly bent or worn will cause this. I had a throttle cable sticking once. Throttle shaft bushings?
Egr or pcv valve ?