Holley/Demon Carb stumble
I really and truly think it has to do with the timing of the rear transfer slot and the ventures. but have now way of proving...let alone fix it.
The length of the restriction is a factor(at least it is with jets).
It is, but not enough to make a huge difference.
Just something to be aware of when changing types of restrictoions.
If its .033 and short, and then you drill your own through longer section, then maybe .035 will create about the same restriction.
After i turn in the idle mixture screws in about half of a turn(around 3/4 to 1 turn out) it idle just fine and there is no super strong exhaust smell at idle, like there was last night.
so i think i'm ok with with that....for now.
On a four corner idle, you've double the flow.
If there is decent manifold vacuum in gear, will need less fuel through each idle mix screw than when using a two corner, everything else the same.
Can't mix and match, unless maybe you're someone Braswell and setting up for a very specific narrow range.
Go with what works. Its damn hard to get consistant fuel when there's too much air in the fuel.
Two holes around .026 - .028 or Three hole around .021 and even that is going to require more experimentation.
You need to start with a stable starting point.
I'm really beginning to think the stumble is a RICH stumble, not Lean stumble. when i whack it to the floor, in gear, if i don't hold some throttle after the full throttle stomp it will die. Then i have to hold the throttle part of the way open to restart.
Reasonable conclusion. It takes time to recover.
I wasn't able to drive it today but the stumble is still there. whack the throttle in neutral, primaries only no problem. To the floor and stumble. when completely heat soaked stumble goes away. In gear, in 3d gear stomp and stumble.
A little confused here.
It sounds like what you saying is when the engine is warmed up, you tested to the floor with the primaries disconnected???? Throttle braking?? or launching it??
I say warmed up 'cause heat soaked is what when the engine block is pretty much as hot as it will get after a couple hours of driving. It take a lot of load. Generally you don't get turned quick enough at the strip to run a fully heat soaked engine. Its one reason a little quicker advance curve can be effectively used in the 1/4 mile. Cylinders are little bit cooler than circle track or hill climber engine will be run at.
Maybe i should point the Gopro at the secondary venturi and see what the fuel pattern look like.....
can't do this while i'm driving, but in neutral.
Sorry just grasping at straw.
I think you were on the right path testing but jumped ahead.
a. Set fuel levels where they should be. dribble on standard site plugs, and mid window on the big window bowls.
They can be adjusted for a some fine trimming but for now leave them alone.
b. Get the primary transfer working with no accelerator pump. Open the primaries as slow as possible to reduce the role of pump contribution and there should be no hesitation or flat spot. If it it passes in neutral, then do it driving. As slow as possible from stops.
c. Check the primary transfer under load. Should be able to accelerate or drive up moderate sloped hills at 25 - 40 mps without it dying.
^^^These are the checks and tests for the initial throttle position, idle feed restrictions, and idle air bleeds.
Then go check and adjust the primary main circuit. As above, test for steady conditions first.
Assuming the MAB and e-holes are now ball park...
a. Drive it steady at 50, 60, 70 mph whatever it is to be sure fueling is mostly from the venturis.
b. If you have safe place to test, go leaner on the primary main jets until the engine revs and wants to die - it may even die.
Slow down, restart and take it back to rejet up.
^^^^^^Now the primaries are ball park - at least for mid rpms.
With these idle - transfer and boosters established at steady conditions. Then use the accel pump to cover whats needed with rapid throttle openings.
(Remember the jetting found was for cruising only. Not test the power valve channel restrictions, so may want to jet richer yet on track to start on the safe side.)
Once you feel good about the primaries being in the ballpark, then reconnect the secondaries.
The secondary IFR and IAB, and throttle position are all things to adjust that will effect the secondary fueling when opening.
The secondary MAB and e-holes will effect the secondary booster start up.
Remember the MABs effect the slope of the AFR curve. They also can encourage or discourage the booster startup. Sometimes larger MAB will encourage startup. This is one of the things that some people find frustating. It's not a simple cause and effect.
You've tried these high emulsion 'modern' setups. My suggestion is exorsize that demon by starting with an old school based line like 'Tuner' and 'jmarkaudio' have posted in those links, as well in Speedtalk, the Innovate foum, and a few other places. They're both real people with lots and lots of real carburetor testing and experience. Tuner has worked on more mopars and street motors. Mark has carb shoot championship to his name. One thing you'll notice is they not trying to sell a bunch of parts or magic answers. Dom's another guy you can work with.
I started this post by saying can't mix and match,
By that I meant if someone suggests a MAB, e-hole, jet positions and sizing - then that's a package. They all relate.
We can take a small IFR and a small IAB and get the same fueling at idle as a larger IFR and larger IAB. The difference will be how they continue to carry fuel through the top of the transition. So if someone says they have had success using an IFR, IAB
and a transition slot restriction, we can't take the IFR/IAB and expect it to work without the transfers restrictor.
Hope this makes sense and is of some help.