1903 Won't Respond to Tip-In Procedure

[bry593]

Edelbrock 1903 to be used on HT383, 9.1:1 static, 196/206 .431/.451 109, 10 initial + 22 mech @3k.

Calibration as purchased used, but never ran on this engine.  Note this carb was all black inside.  Was running rich!
Hot Air Choke
Needle Seat .130
Float 7/16
IT .033
UIAB .070 (in body)
DCR .055
LIAB .064
IDP .084
IABP .052
SMAB .052 (in horn)
Jet .073
Primary Rod 50M
APT Spring Silver
Acl Well .040
2ndy Rod DR
2ndy Hanger S
2ndy Bleed Tube .026
2ndy DP .052
Choke Pull Off 2.5
2ndy Spring 7/8

Second calibration per Cliff.  I could not get this to idle down until I plugged the IABP.  However, it still ran on even on 91 octane.  Pull off vac hose and idle goes up.  Zero response to APT tip-in procedure.  No hesitation off-idle or thru 2ndy.  Engine tries to die when let off throttle to complete stop.  Electric choke works fine, but loads up.
Electric Choke
Needle Seat .156
Float 7/16
IT .036
UIAB .070 (in body)
DCR .055
LIAB .064
IDP .089
IABP Plugged
SMAB .052 (in horn)
Jet .074
Primary Rod 50C (Cliff custom full taper)
APT Spring DkBlu
Acl Well .040
2ndy Rod AX
2ndy Hanger S
2ndy Bleed Tube .026
2ndy DP .052
Choke Pull Off 2.5
2ndy Spring 7/8

3rd Calibration.  Leaned it out, trying to kill the run-on and overly rich condition.  Bushed primary shaft.  Idle screws 4.0 turns out and turning in kills engine, bad off-idle stumble in cold weather (have to flutter acl pump), no engine run-on, pulling vac hose increases idle, zero response to APT tip-in procedure, choke works
New Primary Shaft Bushings
New Needle & Seat .135 <-Found tool chatter in the larger seat
New Float <- Old and new both weighed 6.5g, but new had heel farther away from fulcrum
Float 7/16
IT .031
UIAB .041 (moved to horn 6-32 setscrew, plugged old with sinker lead)
DCR .047 (8-32 setscrew)
LIAB .064
IDP .089
IABP plugged
SMAB .052 (in horn)
Jet .074
Primary Rod 50C (Cliff custom full taper)
APT Spring DkBlu
Acl Well .040
2ndy Rod AX
2ndy Hanger S
2ndy Bleed Tube .026
2ndy DP .052
Choke Pull Off 2.5
2ndy Spring 7/8

4th Calibration.  Opened IABP since idle seemed to want air when removing vac hose.  Idle screws 3.5 turns out and turning in kills engine, bad off-idle stumble in cold weather (have to flutter acl pump), pulling vac hose increases idle, zero response to APT tip-in procedure, choke runs rough
Seat .135
Float 7/16
IT .031
UIAB .041 (moved to horn 6-32 setscrew, plugged old with sinker lead)
DCR .047 (8-32 setscrew)
LIAB .064
IDP .089
IABP .052
SMAB .052 (in horn)
Jet .074
Primary Rod 50C (Cliff custom full taper)
APT Spring DkBlu
Acl Well .040
2ndy Rod AX
2ndy Hanger S
2ndy Bleed Tube .026
2ndy DP .052
Choke Pull Off 2.5
2ndy Spring 7/8

5th Calibration
Pulled the 1903 off and replaced with a junk 70 series from a 350 truck.  Runs fine, but no choke (I have vortec heads).  Surprised how much quieter the exhaust is with this carb.  No run-on, no stumble, no dying when quickly decelerating to a stop.  Pretty good for an old junk carb.

Got to say, I've spent way too much time and money on this thing.  Pretty frustrated.  Can anyone see where I've gone wrong?  Never had this much "fun" with a quad before.

I'm scared to go back to a bigger idle tube, since it already seems rich regardless of what I do.  Setting the float to 9/32" doesn't seem like it would help.  Why is this not responding to the APT Tip-in? 

[Kenth]

The main issue is the single main airbleeds size. Less air equals more fuel from the same jetting.
As the tip-in is done at over 2000 rpm´s the idle circuit is out of the equation.
.052" SMAB were used in 1977-78 Truck Q-jets with small (.064") jets and rods (38B-40B) and 1979 and later Truck Q-jets with 350HD or 454 engines.
All other 1979 and later Truck Q-jets uses .087" single main airbleeds.

I would use the 3rd recipe, open the SMAB to .087", the DCR´s to .055" and the IBA to .080"-.087".

HTH

[Cliff Ruggles]

Lets go back to basics here as you missed something along the way.

First post says 383CID, 9 to 1 compression and tiny 196/206/109 camshaft.

The 1903 wouldn't have needed much help to be flawless on that engine. 

Did you block the vacuum supply to choke housing when converting to electric?

How much timing is being added by the vacuum advance?

Manifold or ported vacuum to the VA?

What intake manifold is being used and does it have an exhaust crossover in it?

Lots of SMAB later carburetors will have smaller MAB's and since they are indirect they will not have a huge impact on the jets/metering rods required.

Edelbrock patterned their later SMAB units after 17080213 units so they will have small lower IAB's and smaller MAB's in the airhorn.

They don't need a lot of idle tube for what you are doing and stock .055" DCR's would have been adequate with the stock upper and lower IAB sizes.

I suspect the issues early on were due to leaking at the N/S assembly or some fundamental issue which started you on the path of adding fuel to the idle system and moving the upper IAB's to the airhorn.  That move would NOT have been needed and sent you into a rich condition.

Keep in mind here that the main system is fed thru the transfer slots so it does impact transition from the idle to the main system and will add some fuel at cruise at very light throttle openings.

The Edelbrock 1910 is basically the same carb you are using with a rich idle calibration and the secondary airflap stop ground off some to provide a little more CFM.  They used several different calibrations in the 1910's the most common is nearly identical to the 1903 with only larger idle tubes and a little more bypass air.  They are known for idling very well on engines with pretty "hefty" cams in them and lower vacuum at idle speed.

I've build hundreds of these carburetors and they are very nice units, but I have found numerous fundamental issues with them over the years which we can discuss later after you answer the basic questions above.

In any case it should have been pretty close right off the bench with just a few minor enhancements which would have included good rebuild parts and slightly larger idle tubes and possibly just a tad more bypass air......Cliff

[bry593]

Hey thanks guys.  Appreciate you guys listening to my woes.  This thing is driving me crazy and it's a short trip...

Q. Did you block the vacuum supply to choke housing when converting to electric?
A. Yes, per your recommendation I blocked everything except the timed, aux and PCV ports with 3/16, 1/4 and 3/8 Al bar driven in and red Loc-Tite.  Zero vac leaks from those ports (did a smoke check).

Q. How much timing is being added by the vacuum advance?
A. I had the factory ZZ4 dizzy advance, but the curve started at too low of Hg.  After discussing with you, I bought your higher Hg advance unit.  Don't have my notes at the moment, but IIRC is 14 degrees.  Cured my transition ping from cruise to light throttle. 

Q. Manifold or ported vacuum to the VA?
A.  At first I was running ported to lower the rpms and help prevent the ignition off run-on.  After the seat replacment and throttle shaft bush, I switched over to manifold

Q. What intake manifold is being used and does it have an exhaust crossover in it?
A. GMPP Vortec, no crossover in Vortec

Lots of SMAB later carburetors will have smaller MAB's and since they are indirect they will not have a huge impact on the jets/metering rods required.
Yes, seemed small but worked well with Calibration 1.  Only issues were engine run-on and could not get APT to go lean.

They don't need a lot of idle tube for what you are doing and stock .055" DCR's would have been adequate with the stock upper and lower IAB sizes.
Are you sure stock DCR was .055?  I thought someone had drilled these out? 

I suspect the issues early on were due to leaking at the N/S which started you on the path of adding idle fuel and moving upper IAB's to the airhorn.
I reduced idle circuit from IT .036 to .031, but still unable to get APT to go lean.  At 2000 rpm tip-in engine slowed even with APT screw turned all the way down.  Why?

Keep in mind here that the main system is fed thru the transfer slots so it does impact transition from the idle to the main system and will add some fuel at cruise at very light throttle openings.
Yes, IT .036 to .031 killed my transition fuel.  Bad hesitation especially in cold weather.

I've found numerous issues with them over the years we can discuss later.
I've checked piston arms for level, blown air thru channels, checked well plugs, etc.  So far everything checks out.

It should have been pretty close right off the bench with good rebuild parts and larger idle tubes and a tad more bypass.
It's all good stuff from you except the second needle and seat (Hygrade).  I soldered up your .036 idle tubes to .031, but can easily drill them .033.  Are you sure IDCR .055" is original?  I thought it was supposed to be .047?  What size should I make the UIAB now that I've moved it to the horn?  Should I also reinstall the 50M rods and 73 jets?  I was thinking .086" IABP.

[Cliff Ruggles]

Moving the upper idle bleeds to the airhorn made it go rich at idle and didn't help part throttle either.

I save that move for heavily modified engines with hefty cams in them and very little vacuum at idle speed.

If you do move them to the airhorn in a later SMAB carb a .052" UIAB, .070" lower, and .034 idle tube with .046" DCR's would be enough idle fuel.

Adding timing at idle speed typically raises vacuum some and lowers the throttle angle.  I would doubt if your engine combo would need much beyond 10-12 degrees initial timing to be happy, although I'm not familiar with that particular camshaft on a 109 LSA so don't know exactly how it would behave in a 383 build with some compression in it.

If it helps some the toughest engines to tune I've ran into over the years were larger CID, moderate compression and tight LSA camshafts with early intake closing.  I've had a few pulling my hair out to get them to work well everyplace, and it's a good thing I'm nearly bald because I would have been by the time I got finished with them!

As far as "fundamental" issues with Edelbrock q-jets I've ran into a few that had one or both jet holes machined at different depths in the casting or too deep in the casting making tuning difficult if not near impossible.  It's not uncommon for them to miss drilling passages by either not connecting them/missing the intended target.  Most of the time that problem was with secondary POE which wouldn't really impact anything you are doing.

In any case the cold intake isn't helping things and all tuning needs to be done when it's fully heat soaked, so give it plenty of warm up time before making idle adjustments and changes to the idle system.

The 74 jets and 50C rods are fine and not making it rich.  I've used that combo in quite a few of those carbs and had to get the APT up to 3.5-4.5 turns for most of them before they had adequate fuel at light load/part throttle. 

[bry593]

Thanks Cliff, I'll give that a try.

For sure the direct horn UIAB is much more sensitive to tiny changes in the circuit.  Also a lot easier to get plugged up than the larger and down pointed body bleeds.

I have another question which assumes a return to original 1903 calibration.  Is it possible to tap the main body UIAB #4-40, insert a brass SS and drill the center to .070?  Or will this not work the same as the original .070 drilled hole? I didn't see this technique mentioned in your book, only the Al tig rod and resize.  I have both 3/32 and 1/8 rod on hand, but it seems like it would be easier to drill a setscrew.

[Cliff Ruggles]

About the biggest you can drill a #4-40 will be .059" if you stay on center. 

The stock idle airbleed sizes in the 1903 are fine for what you are doing.

The 1910's showed up with several different calibrations as it seems like Edelbrock was playing around some there but they are the exact same unit.  The most common 1910's have .038" idle tubes but I've seen them with .040's.

They used the same smaller MAB's and 74 jets with 50M rods, pretty sure the 1903's got 73 jets.

Looking at your engine combo it has a very small cam in it for the CID and compression ratio.  Not sure why they ground it on a 109LSA as that would close the intake pretty early with such short seat timing and may make your engine octane sensitive, or at least you may experience some pinging at light throttle if you add too much vacuum advance and heavy/full throttle as well if the mechanical comes on too quick or too much of it.

Have you taken a vacuum reading at idle speed, 700-750 rpms with around 10-12 initial timing and no additional timing from the advance?

Anytime I've tuned larger engines with tiny cams in them they have not wanted, liked, or responded well to a lot of timing at idle speed and adding timing has made them difficult to tune as the throttle plates were pretty well closed at idle speed.

As mentioned previously the only thing I'm not sure of is the small cam on such a tight LSA.  I did work on a 355 last year with a 194/204/108 cam in it.  The owner brought it here for idle issues.  I did the carb for it about 10 years ago for the stock 305 engine and this new combo wasn't happy about it. 

I went in and opened up the idle tubes .002" and DCR's to .055" and that's all it needed.  Even so I was not impressed with the engine anyplace.  It had a "quirky" idle and even though the engine builder dubbed that cam a "torque monster" in a 350 build, I thought is was "weak" compared to 350's I've done with the 194/204/112 cam in them......FWIW......Cliff

[bry593]

Haven't checked the vac since last year, but it seems like it was around 18" Hg.

Yes, you know how GM is with crate motors, they just throw whatever they have lying around at it.  The cam is left over from the Ram-Jet 350.  This HT383 also has cold piston slap due to the short 880 block bore combined with a stock 5.7 rod.  I wouldn't recommend it. 

For drilling setscrews, I made a jig to hold the screws.  It's just a piece of 20 gauge sheet with a 4-40, 6-32 and 8-32 nut epoxied to the sheet.  You simply thread the setscrew into the nut with the cup point up.  The cup point acts as a centering pilot for your pin drills.  Maybe not the best method, but works okay for me.

[Cliff Ruggles]

I usually drill them in place but have a piece of flat aluminum about 3/16" thick tapped part way with 4-40, 6-32, 8-32 and 10-32.  I just seat the brass set screws and drill the desired hole size in them, not really fussy and only take a few seconds.

Will it make that much vacuum without a lot of timing and down around 700-750rpms?

I've been building SBC's for over 40 years and have never done or wanted to do a "383" build.

I have several excellent "recipes" for 355's and stick with them.  They make great power with improved rod length to stroke and bore to stroke parameters. 

I actually prefer a 327 or using the shorter 3.25" stroke cranks, but they didn't make a lot of large journal 307's and 327's so they are difficult to obtain.

Compression is also your friend with SBC engines and they are fine on pump gas WAY beyond the proverbial "brick wall" of 9.5 to 1 we see regurgitated on every Forum you log onto by folks who probably haven't built an engine that made chit for power or even have an SBC powered car or truck that moves!.......LOL....

[bry593]

Thanks for all the advice Cliff! The off-idle hesitation problem is fixed.

The power piston spring had tilted and slightly slipped into the vacuum channel and those coils to bind.  This had the effect of a shorter spring and would not lift the primary needles out of the jets at light throttle (too much vacuum with this tiny cam).   Note that I'm using the stiffest (DrkBlu) piston spring. 

To reduce the vacuum channel diameter, I dropped a #8 brass washer into the piston bore.  The OD was too big too fit, so I "turned" it down using the following method.  The washer was sandwiched between the head and nut on a screw, chucked in my drill and sanded with a die grinder while the drill was activated.  Deburred by flat sanding on a piece of 400 grit.

Retained the lean idle calibration (.031 IT, .041 UIAB, .064 LIAB), and added .052 IABP.  Also installed a 195F thermostat to improve efficiency per your recommendation.  With the spring fixed, throttle is instant and seamless through the primaries with only a slight delay in the 2ndy. 

Will run this calibration a few weeks to get a feel for it.  I'm hoping the smaller idle tubes will help achieve a target of 18mpg @ 75mph (1971 3/4 Chevy, 383, 4L80E, 4.10 HO52).

[Cliff Ruggles]

Good news.

APT and vacuum advance tuning will get you there.

Make sure the power piston hanger arms are exactly even, and make very small changes.  It may take several tanks of fuel to find the ideal APT setting.  You can also use the vacuum advance to fine tune for fuel economy. 

Most engines with higher compression, tight quench and smaller cams will not need much, but you still need to look there for best efficiency in the "normal" driving range....

[bry593]

Apparently, I can't leave well enough alone....

Although the lean idle ran well, it was insufficient to support the choke.  During choke operation, there was not enough fuel being pulled to cope with freezing ambient temps.  It sort of worked, but I like my choke to be:  pump gas once, turn key, engine fires immediately and idles at around 1000 rpm.  With this lean setup, I had to feather the throttle a little before the high idle would stabilize.  Just not enough idle fuel.

I considered adding idle fuel by drilling the DCR from .047 to .052 (would this have worked?).  Instead, the idle tubes were increased from .031 to .033 so they will not plug up as easily.  I also drilled the horn UIAB to .052, but left the DCR .047 and LIAB .064.  This morning was 32F and it fired immediately and with a stable high idle.  Seems to have lost a little pep on part throttle, but I suspect I can lower the APT a half turn and regain the lost cruise power.

Out of curiosity, what is the easiest was to verify the APT arms are even?

This HT383 has a poor quench.  The pistons are .040" in the hole, then add the gasket.  Not a great combination to prevent detonation.  Not sure why GM did it this way considering the pistons were custom made by Speed-Pro for GM (383 with a 3.800, not 3.750 stroke).

[tayto]

probably rebuilder pistons that are shorter

[Kenth]

I would proceed adjusting the choke pull-off to open the choke blade a little less, about .160", measured between upper end of blade and rear wall of choke housing and increase fast idle speed some to keep it running.
For off-idle respond at least .052" idle DCR´s will help.

[Cliff Ruggles]

We do NOT add fuel to the idle system to improve cold weather starts or choke operation.

The pull-off unload angle if FULLY adjustable on those carburetors via a screw.  Move quickly on a cold start and simply adjust the flap so the engine doesn't stall out from being too lean and doesn't "blubber" from being too rich.  It's a simple and easy procedure but you have to move quickly and I'd also lower the fast idle speed (cam on the highest step) down some to about 1400-1600rpm's at the same time.

99 percent of the power piston hanger arms on carbs I get in here at bent up, down, and not even.  Spend some time there to get the arms LEVEL and EVEN.  Just pull the tips together underneath the center of the power piston and gently "adjust" the arms till the tips are even.

It's not difficult or fussy but REQUIRED if you want a good end result with these things.......