another 4053 question

[aaronz28]

so - I rebuilt the 4053 on my all stock Z, did some stagger jetting, took the car for a spin -she runs absolutely GREAT. BUT i'm concerned about the idle mixtures, and raw fuel odor at idle.

jetting is staggered, 73/71 on the primary with a 6.5 pv,  79/77 on the secondary with an 8.5

with the carb flipped, you can barely see the transfer slot on the secondary side - i err'ed on the side of too little transfer slot showing.

with the engine idling at 950,  (started with the idle mixtures 1/2 turn out where it seemed to run best prior to the rebuild/rejet)

timing is about 20 initial with 38max wot, using full manifold vaccuum,   I have a pink pump cam in the #1 and a 31 squirter -   the car is super responsive, and pulls very strong all the way up.

when I was adjusting the idle mixutres with a vac gauge, i could seat both and the idle went up - backed the curb idle down again, with both mixture screws seated and still get my highest vaccuum reading of over 12-13in - almost got to 15" hg, but that was with the idle around 1050.

what should I be looking for?  I'm to believe that seating the idle mixures means that its pulling fuel from somewhere? or is it pulling air from somewhere?

the bowls have been off several times, so i could see a bad gasket seal - but no obvious fuel leaking, and again, it runs better than ever.

any help woudl be great.

Thanks

[z28z11]

Any air leakage around the throttle shafts ? Did you rebuild or bush the throttle plate ?

Just a thought -

Regards,
Steve

[TODD]

How much of the transfer slot is exposed on the primary throttle slots. You'll have to pull the carb to tell, if too much is exposed the idle speed screws are rendered useless right?

Todd

[TODD]

Do you have a wideband afr gauge? I'm getting ready to mount mine. I opened my secondary slot up a bit via the secondary stop screw. Idle screws now seem effective at 900rpm and are 1/2L 3/4R and smells less rich. However my tailpipe gauge is not sensitive enough to get a good reading. So I'm installing DLG-1 innovative gauge and starting tune per this. Anyone tuned to this level?  https://www.innovatemotorsports.com/resources/carb_EFI_mileage.php

[TODD]

Oh forgot to mention DLG-1 $343.71 with shipping. Rebate $50 thru 10/31/18 = $293! I'll report back after install tune info.

[Kelley W King]

If I were going to disassemble it I would look close at the PV also. Small leak maybe, when you close the screws it has to come from some where if it will still run. Also if your kit came with new screws you might try the old ones.

[Stingr69]

Verify all the float levels first.
Idle transfer slot opening needs to look like a square. Start there and then reinstall to adjust the mix screws.  Only a guess but if slot opening is too small, you could be pulling more fuel at tip-in.
I actually have used the initial timing to move idle speed around in some cases while the butterflies are left alone in the square slot position.  I just recurve the centrifugal to match 36 degrees at the top once I nail down the idle initial advance.  Just crazy me.

These carbs are pretty rich and it takes a wideband to fine tune them but it can be done.

[X33RS]

How much of the transfer slot is exposed on the primary throttle slots. You'll have to pull the carb to tell, if too much is exposed the idle speed screws are rendered useless right?

Todd

How much of the transfer slot is exposed on the primary throttle slots. You'll have to pull the carb to tell, if too much is exposed the idle speed screws are rendered useless right?

Todd

Do you have a wideband afr gauge? I'm getting ready to mount mine. I opened my secondary slot up a bit via the secondary stop screw. Idle screws now seem effective at 900rpm and are 1/2L 3/4R and smells less rich. However my tailpipe gauge is not sensitive enough to get a good reading. So I'm installing DLG-1 innovative gauge and starting tune per this. Anyone tuned to this level?  https://www.innovatemotorsports.com/resources/carb_EFI_mileage.php

Todd,  that's the only way I do it here on everything.  The tail pipe sniffer is a bit inaccurate as you found.  I weld a bung in every car here.  One side is enough, you can run dual 02's if you wish however.

To answer your other question, yes, the mixture screws become lazy or inactive with too much transfer slot exposed.  Once too much slot is exposed, the carb transitions into the main circuit and will start pulling fuel from the boosters.  With that fuel also mixing in it's impossible to set the idle AFR correctly.   Most of the time this can be seen by looking down the venturi while running.  If you see fuel dripping from the booster at idle you either have too much transfer slot exposed, leaky power valve, a leaking needle and seat, or possibly a warped metering block that isn't completely sealing.

[aaronz28]

I def do not have too much transfer slot exposed,  if anything. Not enough
There is play in my secondary throttle shaft but that would mean - vaccuum leak, not pulling fuel from there.

Question- should the primary side transfer slots be exposed equal to the secondaries?   I just pulled and flipped the carb, and Id have to make a full turn to turn and a half on the curb idle screw to get the transfer slot on the primary side exposed, which would then raise the idle up to 1700 or more- and it would still run with idle mixtures all the way in.

Advice now?  Carb has two new power valves - suppose one could
Be bad so ill check and replace again.

Thanks

[TODD]

So gauge installed results were kind of surprising:
1) Idle 900 RPM AFR ~13-14 so looks like I'm pretty close on the secondary opening was rich before adjustment
2) Idle to 2500 RPM 13.5-15 with lean spots on accel (probably needs a more aggressive cam on the accel pump)
3) cruise 2800-3500 RPM 11.2-12.3 jets are 72-76 so probably need to go to 70’s?

Eric @ Vintage Musclecar rebuilt the carb and it looks and performs fantastic, just need to tune for my motor. Power valve is a 4.5 and probably needs changed too. Seems lean at throttle roll on at 15-16AFR.
I’ll post a separate thread after I give it a tune-up check: dist curve, timing, dwell. Then I’ll dive into carb tune.
I love the AFR such a good tool.

[X33RS]

I wouldn't change the accelerator pump cam just yet.  I'd swap in a 6.5 power valve first.  That will likely cover the lean spots you're seeing on accel.  My DZ with it's 4053 carb did not like the 4.5 power valve.  Caused a lean spot with mild hesitation on tip in that wouldn't go away with any amount of pump shot tuning.  It just likes the 6.5 even up here where I'm dealing with 7,000 ft DA numbers on a daily basis.

Steady cruise is a little rich.  What elevation and DA conditions are you working in?  You could drop front jet if you wish until you get to a spot you're happy with.  Just something to keep in mind,   Need flat ground and no throttle movement at all to hone in on the cruise AFR.  Any tip in of the throttle at all introduces even a small pump shot or the slight opening of the power valve will skew numbers.  Have to wait for all that to burn off to get a good steady AFR reading.

I found with mine that it cruises in the mid 12's for AFR but I set it up on purpose that way because I'm dealing with extreme DA's and we do drive the car down to sea level frequently where it runs leaner.  Plugs show a little on the rich side up here but stay clean, wife daily drives it and it still knocks down 14 mpg with around town driving at these elevation levels.  It's slightly rich this way on purpose because when I drive it down near sea level it leans out to the mid to upper 13's on AFR and I'm happy with that.  Find a happy spot where the car performs well in both cases so I don't have to keep tinkering with it.  Leave the hood shut and enjoy.

[TODD]

What elevation and DA conditions are you working in? 2497 Quartz Hill Ca it was 4408 on the density calculator this morn. I’ll make sure its tuned before I touch anything carb related, then I’ll start with a power valve change. I need to flip the carb over and start with transition slot, I just guessed and opened the secondary stop a bit and its close. Oh and the idle trim screws now adjust at about 3/4 to 1 turn out.

[X33RS]

We're in Prescott Valley, AZ.  Elevation here at the house is right at 5,000 ft but driving 5 miles in any direction can change 1,000 ft give or take.  I checked DA at 2pm this after noon at the house when it was 91 degrees outside and it was 7,975 ft. 
  Plus we drive down to the valley frequently where elevation is only 1,000 ft, and DA's in the 3,000 range, so the AFR gauge will go lean up to at least one full point to as much as 1.5 points.  That's why I generally set them up a little on the fat side up here and just live with it.  Doesn't hurt anything other than a little fuel mileage.   

So sounds like you're pretty good on adjustments so far, and looks like you're dealing with at least a little bit of elevation and DA conditions.

On mine I switched to headers and a complete 2 1/2" mandrel exhaust system (still transverse muffler) to free up the exhaust side of this thing a bit.  I'm getting those AFR numbers I posted with a stagger jet setup on mine, 70 in the right front, 72 in the left front.  When I ran the original manifolds on the car, and it still had it's born with exhaust system, I had stock 68 jets in the front and it still showed fairly rich up here in these DA conditions.  Just to give you a general idea you are pretty close.

[firstgenaddict]

Aaron...
YOU EITHER HAVE AN INTERNAL PASSAGE FUEL LEAK.. OR you are feeding the engine on the secondaries.
I lean toward the latter...
And specifically the secondaries VS primaries relationships to the idle transfer slots...
You are feeding the engine at idle from the secondaries pulling on the idle transfers... your secondary blades are allowing enough air to travel by the slots at a high enough rate to cause low pressure area at the idle transfers and this pulls fuel in...
Close the secondaries throttle stop a little, this should give you the ability to adjust your primaries and also allow you to actually use the idle mixture screws... 


With really radical cams I have drilled .0625 holes in the secondary throttle blades in order to keep the slots covered.