Jeezus

iTrader: (4)

So I have a car now with a bridgeport 12a and holley carb.

Never owned a bridge before, but have a few questions:

How does the bridge pull? The one in the car feels stockish until about 4500rpm, then starts to get up and go until about 6000rom where it feels like it falls flat.

Also, the motor is "quiet" until it hits the 4500rpm pickup, begins to scream (secondaries start opening kind of sound) then gets back to quiet at the same 6000rpm.

I can't tell what kind of holley carb I have. I can't find any numbers on it. All I know is it is nothing like my stockport with the wraparound Weber 45DCOE.

I have adjusted the secondaries to open with the set screw on the linkage when the throttle is pushed about 1/3 of the way down. I know that when it is floored, all 4 barrels are wide open.

Is this a typical bridgeport experience? I always thought that with the port, the power would stay and build as RPMs rise. This feels like it falls on its face when revved past 6k.

Exhaust is Racingbeat Road race header into Racingbeat muffler, no presilencers just straight tube.

EDIT: Will be ditching the carb and intake for a Weber 48IDA when I can.

peejay

What is the rest of the setup? Air filter? Are you SURE you're getting full throttle? The overhung cable bracket is easy to bend and keep you from getting full throttle with the pedal. Check it!

Bridge ports are very sensitive to exhaust. Air/fuel ratios not so much.

The numbers on a Holley are normally stamped into the choke tower, which was probably milled off if it is a RB modified Holley. (A RB Holley has some seriously wide open air bleeds compared to a standard Holley. They're like pinholes normally)

If you can measure the venturi diameters and throttle bores, you can crossreference that to a given carburetor.

I'm curious about the concept of adjusting the secondaries. Every mechanical secondary Holley I have seen has had fixed operation for the secondaries, the only possible adjustment is the idle stop.

RotaryEvolution

iTrader: (30)

that's about where the crappy J-109's peeter out, the holley needs a strong ignition system to burn all that fuel.

also, is the dizzy locked? modified?

Jeezus

iTrader: (4)

Air filter is a holley brand triangle filter, it is mesh with removable foam insert.

Exhaust is racingbeat road race header into their forst gen rear muffler, so power pulse? It is a very nice muffler, but i do not think it will shoot flames out the back.

I do not recall a choke tower on the carb, it may be the rb 465? I will get some pictures up later today, including the secondary adjustment.

Jeezus

iTrader: (4)

Stock fb electronic dizzy, stock coils and ignitors.

I do have a MSD 6A box and 2nd gen coil i plan on using for a direct fire setup, as soon as i can find a place to mount it...

peejay

I bolted my MSD to the bottom side of the upper radiator plate. Works really nice and a lot more clean looking than making a bracket somewhere underhood.

I suggest either running an MSD on the trailing if you want split, or running another coil in parallel to the FC coil and running the trailing through that if you don't mind having no split. The MSD will happily fire two or three coils. My setup actually is just that, an FC double post coil and a single FC trailing coil. (I mounted the leading coil to the trailing coil bracket)

I have found that with a high overlap engine, trailing ignition becomes more important than leading at light throttle openings. I used to wear out distributor caps and rotors VERY quickly and could tell by the way the car would misfire slightly at 60-65mph. I'd pull off at a rest area, scrape the internal terminals with a screwdriver, and it'd drive fine again

On that note - MSD is harsh on caps and rotors. An old racer told me to drill a couple 1/4" holes in the distributor cap, let the ionized air out and fresh air in. After I did that, cap and rotor life went up dramatically. Actually I haven't had to touch them in over 10,000mi.

Jeezus

iTrader: (4)

Are you talking about having the trailing firing at the same time as leading? If so, could i run a second fc leading coil in parallel, and have one msd firing both fc leading coils?

I had the msd mounted where you said on my fb, but had to cut some hood support away

RotaryEvolution

iTrader: (30)

then your ignition definitely needs the upgrade first and foremost. also check the advance on the timing, the bridge will want lots of low end timing but if the distributor is advanced then it may be getting too much timing up top.

something like this would be ideal

10BTDC idle
35BTDC cruise
20BTDC heavy load
22-25BTDC heavy load high RPM

most of this simply isn't doable with the antique dizzy, but you can try by reworking the springs and advance mechanism.

Jeezus

iTrader: (4)

Stock mechanical advance is 20*. I will set it for 10BTDC at idle and double check to make sure it is around 30ish for 4000rpm.

My pulley has 2 red marks on it, I take it the first one is leading?

peejay

That would be WAAAAAAY too much timing!!!!

This isn't a stockport. Even stockports don't like 30 degrees of mechanical, they get unhappy past about 27 degrees. On the bridge ports, I found no functional difference between 18 and 22 degrees and power started falling off above that.

Taking timing awat at low RPM makes the idle much better. I can idle dead smooth at 700rpm if I wanted. Of course, I have EFI so I don't have to worry about making a carburetor happy It's a little lumpy at 1000rpm but that's just fine. 0 degrees at idle, stock 12A distributor set to stock specs, because that is what works best for me.


I am driving one FC leading and one FC trailing coil with the MSD. Leading is direct fire and trailing goes through the distributor.

Jeezus

iTrader: (4)

Attached is the carburetor. There has been some work done to it, looks like the choke tower is indeed milled away, or atleast ground off.

The 2nd picture is of the secondary throttle shaft. The screw is adjusting when the secondaries open.

I just took the filter off and found all this grime. Cleaned it up and drove w/o the filter and the car drives the same, except for a higher idle (assuming it was from the filter being dirty)

peejay

That is bizarre. The air bleeds look modified like an RB carb, but it looks like that is a vacuum secondary baseplate. You can also see on the other side of the carb where the stud is for the (missing) vacuum diaphragm would open the secondary throttle. Very strange.

You definitely need a better air filter. Any dust or dirt at all in the engine will destroy the side housings and side seals/oil control rings in a frighteningly short period of time. Try to get a "real" air cleaner that feeds only from the sides, and not one of those top-feeding ones, those are proven to make the airflow into the carburetor turbulent and screw heavily with fuel metering. I recognize that space is at a premium due to the location of the water pump, but top feed air filters are horrible with Holleys.

I reiterate that you NEED to verify WOT with someone pushing on the pedal and you looking at the carburetor.

Jeezus

iTrader: (4)

Full throttle

j9fd3s

iTrader: (3)

agreed. the other P port, my buddies car, is running a stock 12A distributor and with a heavy flywheel, you'd almost not know it was a P port. i think the engine does want more timing in the 2500-4000rpm range (and a bunch less fuel!), its a little flat there.

after last years debacle; it ate an air cleaner bolt, (notice please the wing nut that holds the stock air cleaner on the Nikki will not fit down the Nikki) on lap 2! which was blue ball inducing.

the driver and i are going to abduct it, and take it to the dyno, and actually tune the thing. TBD what the advance curve will look like, but probably about 10BTDC at idle, and ~20BTDC by sometime, and just stay there.

peejay

I think at one point I had a distributor with one advance spring removed so the advance would come in a lot faster, but it actually idled in the advance curve at that point and this made the idle speed unreliable, and I was too lazy to put a stop in or put the spring back in so I just swapped in another stock distrubutor.

On stockports I just yank both springs.

RotaryEvolution

iTrader: (30)

guess it all depends, i haven't had the same experience with the bridged engines. but my bridges generally have a lot of overlap and will in no way ever in a million years idle at 700 rpm. i could idle them at 10*, but they were still happier at 20* and tip in is crisper with more rather than less.

j9fd3s

iTrader: (3)

are you running stock intakes?

RotaryEvolution

iTrader: (30)

nah, it was an RX4 with a RB intake and holley.

perhaps the 12As don't like as much timing with their narrow chamber, flame front moves a bit quicker.

peejay

I wouldn't be able to idle at 700 with a carb either. down that low I think I have about an inch of vacuum. With EFI you can do dumb things like that since you don't have to make metering circuits happy.

Throttle response off-idle is much better if I have the idle speed up around 1500-1800 but I don't like having the idle that high, so I compromise with a lowish idle around 1000-1100 and a respect that I have to walk the throttle in from an idle.

I think my idle vacuum is around 3-4" at 1100 and maybe 6-7" at 1600. This is with a stock 12A distributor (0 at 1000rpm, 20 all-in), zero split, and Mazda Group A bridge ports in a 4 port 13B.

Jeezus

iTrader: (4)

Does anyone have jetting recommendations for a weber 48IDA on a bridgey 12a?

RacingBeat says:
42mm Venturies
240 Fuel jet
170 Air jet
F-11 E tube
300 Needle valve

But this is for open headers... Which I do not believe I will run!

j9fd3s

iTrader: (3)

that seems like a lot of fuel, with the muffled P ports were ending up around 65 idle jet/180-190 mains/F7 e tube (F11's are for VW's) and airs are 110-140 depending. i'm running near the lean limit up until the mains come on (depends on throttle position, 1800-3000rpm) and it richens up to about 11:1

i think the 65 idle jet is pretty safe, but the rest is ymmv!

fidelity101

iTrader: (11)

+1 that foam air filter doesnt filter squat and one good intake backfire and that thing is ablaze, nothing good about it.

peejay

I missed something the first go-round. If you had to cut hood supports to fit the MSD then you didn't mount it to the bottom of the radiator panel

You can't see it on my car unless you are roadkill.

Jeezus

iTrader: (4)

It was under the panel. I cut a hole so it could be seen, but my mounts made it so it was parallel to the ground, not the same downward angle like the panel has. This was on the autox car, so cutting the hood didn't bother me much.

I did the same to this panel, but different mounts so it is flush with the panel. Hood now closes nicely. This angle makes the MSD look like it is sitting too much to the left, but it is centered.

Jeezus

iTrader: (4)

Well, have a timing light, and verified that it is stock timing.

Set the idle according to this website:
https://forums.holley.com/entry.php?...n-Holley-Carbs

The car refuses to idle lower than 2kRPM, and the idle mix screws are 3 3/4 turns out. It will brap (fast) but then not brap, then brap, then not... etc etc. I think this was a carb meant for a stockport or streetport? Went for a drive and it begins to pull around 4500 but after 5000 it feels like the secondaries just close. The pull is gone, the exhaust goes quiet, but I still gain RPM.

Giving up on this carb, never really liked Holleys anyway. Just picked up an IDA manifold and ordered a megasquirt. Looking at ITB's, is there any REAL difference between a 45 and 50mm IDA style ITB? I know the 50 would flow more, but would I lose a lot of low end? I would like to have a setup where I can swap 12a's to 13b's and various portings with just a manifold swap and tune.