Horsepwraddict

iTrader: (12)

Made a few changes over the winter and ive been retuning the carb. My afr's are exactly where I want them at idle, transition and primary mains. My problem is (maybe not a problem?) that to get my cruise I had to jet up the primaries, I currently have 72's in the front, up from 67's before. Now my WOT is pig rich, around 10.5-11:1 and my secondary jets are 71's. I have never seen smaller secondary jets. I hate to go down in the rear to reach my target AFR, it just doesn't seem right.

Quick Fuel HR650
.035 IFR's
65 IAB
28 HSAB (maybe too small?)
Primary jet-72
Secondary jet-71
10.5 PV

VLS1

Try this maybe;

HSB 32
FR JET 72
RR JET 78
PV 6.5"

The IAB sounds a touch small going by typical specs as well.

LQ4BU

I'm getting ready to try to tweak my demon carb just like you are doing. If you had your WOT on the money, but your cruise was lean, did you try smaller air bleeds to richen up the cruise afr? That way you dont have to make any changes to the main jetting, or a very slight change at the very least.

Are you tuning for peak power(racing at the track) or street driving with all around efficiency? If tuning for peak horsepower, I would get my WOT dead on and leave it, and then get my cruise and idle as close as I can without affecting peak power.

Horsepwraddict

iTrader: (12)

im tuning for all around street performance/efficiency. I have made some big changes lately and made some headway yesterday. I will report back soon with results/updates and details. This carb has been very finicky ever since I got it, ive put so much time into it that I cant give up though. I WILL win LOL.

Horsepwraddict

iTrader: (12)

I spent a few hours with a local engine builder over the weekend and came up with some interesting stuff. This motor has never run perfect with the performer RPM, the carb always had metering problems just off the transition slot into the primaries. We tried everything, I was always able to bandaid it and cover up lean/rich spots with unconventional tuning practices, while they worked...I wasn't happy because it wasn't 'right'. One of the biggest issues has always been getting the overlap between the two circuits nailed down, either the idle/transition circuit would lean out too soon causing a dead spot or the primary circuit would be so fat that the cruise AFR's were in the 10's...the carb simply couldn't do it.

The biggest headway I made was throwing my ignition curve and vac advance out the window. I dropped my idle timing down to 16 degrees, this allowed me to expose more transition slot which began to help tremendously...but it wasn't enough.

Friday he gave me a Victor Jr. to try for the weekend. I took the carb off, put it back to out of the box settings. set my timing to 16 at idle and 29 from 1000-infinity. I fired the car up, tuned the idle for 13.5:1 on my wideband and took it for a ride. I barely made it out of the shop before I pulled it back in. It needed WAY more aggressive accelerator pump shots. I put a 35 squirter in it and It ended up being happy with the blue cam in the number 2 position. Took it for a drive again and I could instantly tell it was better. It still wasn't perfect, pink cam in the secondary in the number 2 position and a 31 squirter was good, I need a 33 though. Sometimes from a roll it just isn't enough and it ever so slightly hiccups. I drove the car around for 5 miles or so taking it real easy and making pit stops for jet changes. She is definitely thirsty with the victor jr. I ened up with 74/80 jets. The car drives absolutely seamlessly, I mean fuel injection smooth. If I didn't know any better I would think I was in my 2011 Sierra with a 5.3. It is definitely a little soggy at lower rpms but pulls strong when you stab the throttle, I can absolutely tell the loss or torque down low, even my shifts are softer.

The conclusion? Extra plenum volume and balanced cylinder signals were the key. For some reason my combination just wouldn't work. I already ordered a victor Jr. for myself and he wants to buy my performer rpm. The next step is spend a day on the dyno with the two intakes. He doesn't know it yet but my next step is to take the performer rpm and chop the divider out of it to see if it has the same affect. If it does, I think im going to stick with the dual plane, cut down the plenum divider and throw a 1" spacer on it and see how it does.

I couldn't be happier, the car has NEVER driven this well. While the intake isn't fitting for my cam I don't care, I have never been this happy with how the car drives.

LQ4BU

Wow thats a big difference just between changing intakes. Glad to hear that it is working. I used the Vic Jr on my LQ4 from day one, I'd be curious if anyone else noticed such a drastic difference between the two intakes??

I did go through the same issue as you with the squirters, accelerator pumps, and cams. I had my Demon 750 on a sm blk 406 with a Vic Jr previously, then put it on my LQ4 without touching anything, and I experienced the same exact bog as you. I couldnt believe how much more pump shot it wanted before it was happy.

RabidStreetRacer

iTrader: (1)

I have been fighting a lean tip in on my carb and an issue with it dieseling when shut off through a 5.3 and a LS1 engine. I recently had my carb built and the issues are still there. The builder recommends I alter my IFR and air bleeds. I added a 1" carb spacer and it helped a bit but also gave it a lot more WOT power. I am looking to go to a 2" spacer soon. I also have a Performer RPM. I have read on a few old sites that an open spacer makes great power on a dual plane intake. Did you get a chance to dyno it yet or even mill out the plenum?

Horsepwraddict

iTrader: (12)

Read this thread that I made. It may help you.

https://ls1tech.com/forums/carburete...veability.html

speedtigger

iTrader: (16)

The first question is this. Is your lean tip in constant or only during the transition? If you just barely open the throttle and hold it there, does it hesitate then then clean up, or does it keep missing indefinitely?

If is is just a temporary transitional stutter, you will likely need either an accelerator pump adjustment, or a larger accelerator pump discharge nozzle. In my experience, LS engines like a lot of accelerator pump shot.

If the off idle lean condition is constant, you will likely need to increase the size of your IFR (idle fuel restrictor) in the metering plate. This is also common on LS engines. Just remember, when you increase the IFR, you need to increase the LSB (low speed bleed) proportionately or it will affect your cruise air fuel ratios.

Horsepwraddict

iTrader: (12)

what tigger said. My motor really likes the blue pump cams for an aggressive pump shot right off the bat and levels out as booster signal increases with rpm.

RabidStreetRacer

iTrader: (1)

My Carb:
Holley 3310-4 750 vac secondary converted from a 4160 to a 4150 with a secondary metering block. Has had the air horn milled off and choke removed, ports ported and matched

Primary Idle Bleeds 76
Primary Int. Bleeds NA
Primary Main Bleeds 27
Primary Jets 69
Primary Power Valve 6.5

Secondary Idle Bleeds 27
Secondary Int. Bleeds NA
Secondary Main Bleeds 24
Secondary Jets 76
Secondary Power Valve NA

Primary Shooter 31 with Hollow screw
50cc accelerator pump
Secondary Shooter NA

Primary Venturi Size 1.385
Secondary Venturi Size 1.445

Baseplate Blade size 1.680
Booster Style and Orifice Downleg .160
Removable Air Bleeds No
Needle and Seat Orifice .110
2 corner Idle
Idle Feed Restriction Size .033

Quick fuel adjustable vacuum secondary diaphram

Issues: It idles at 1,000rpm at 12.8 to 13.3 AFR, the pump shot is too much as it will lean out to 10 to 1 AFR if I give it a small blip of the throttle but then jumps to around 17-18 to 1 AFR then climbs down to between 13.8 to 15 to 1 AFR at part throttle cruise. At part throttle cruise if I just very slightly tap the throttle it will go lean to 18 to 1 AFR then go back down to the cruise AFR of 13.8-15.0 AFR depending on the cruise RPM. WOT it runs like a bat out of hell at around 13.0 to 1 AFR.

The cruise AFR slightly went up due to me adding the 1" carb spacer so I know I need to slightly increase the jet size on the primaries. The transition slot on the Secondary's is just barely covered like they are supposed to and the Primaries are just slightly exposing the transition slot. The Idle air screws are about 1 and 3/4 turns out.

So I know I need to order a smaller accelerator pump shooter so it will give the shot at a longer time. I have used 3 different pump cams, yellow, brown and white. The brown seems to do the best out of the 3 but I need to get a smaller shooter to see.

My carb builder recommended I tap the air bleeds to use screw in adjustable ones and try changing the 76 to a 70. He is located up north so I don't have the time to mail it back to him. I am not sure what the best step is to take. If I get some ideas from you all, I will order what I need tonight from Summit racing

speedtigger

iTrader: (16)

If the lean condition is at lower RPMs like 1500 and lower, increase the IFR size. If it is fine down low but slightly lean at higher RPM cruise like 1700 and above, then you might want to decrease the size of the LSB.

The off idle stuff is seldom helped my reducing the LSB. Increasing the IFR works better for off idle lean conditions.

RabidStreetRacer

iTrader: (1)

So help me make sure I understand correctly, I was under the impression that the off idle transition will usually always be lean that is why there is an accelerator pump. So how can I test if it is an off idle lean condition when the accelerator pump might be masking it? At any cruise RPM 3,000 and less if I give it even 5 or 10 percent acceleration it does this lean condition, I can tell if I am at lets say 1,800 rpm and the throttle is barely cracked, the accelerator pump with attempt to compensate a bit as it goes rich for a second then goes lean then goes to the normal cruise AFR. Tomorrow I will record a video of the AFR gauge so you can see exactly how it is performing.

Horsepwraddict

iTrader: (12)

the other thing it could be doing is going so rich on the pump shot that it misfires, a Wideband will read unburnt fuel as lean when it actually is not. You might be choking out the motor with to much pump shot if it pegs the gauge all the way down to 10:1. Just a thought.