speedtigger

iTrader: (16)

I wanted to share my recent learning experience with my fellow LS carb neanderthals. If you are an OCD car guy like I am, you likely have a wideband on your ride. If you do, you undoubtedly noticed that your A/F ratio varies wildly at part throttle and sometimes at idle and WOT too. This thread details what I recently learned and the result I achieved with that knowledge.

Most anyone with a carb knows how to change the main jets for max ETs or for a target A/F ratio. And, most everyone knows how to adjust their idle A/F ratio using the idle screws for "best" idle characteristics. However, if you have an aftermarket Holley, you will notice that your part throttle will be rich as hell regardless of how you set your idle screws. At this point, some people say: well, I guess that is just the way Holleys are. Then they never think another thought about it. Then, there are those who say: Dammit, there has got to be a way. Well, there is. Here is where I found the info and what I did with it:

The answers are in the air bleeds and the metering plate. In the past, I had always had the rule: play with the jets and the screws, but don't touch the main bleeds or the metering plate. That was beyond my area of knowledge and that "voodoo" was more likely to get me in trouble than to work out. Fortunately, I found some people that had a lot more knowledge and experience than I do. Reading the thread below helped me immensely to understand and to achieve success:

http://www.yellowbullet.com/forum/sh...d.php?t=490296

Using the information in the thread above, I modified my carburetor to idle in the mid 14:1 range and maintain between 14.1:1 to 14.8:1 at part throttle cruise and light acceleration ranges on flat and inclined roads. Anyone with a wideband knows that these aftermarket Holleys will get well into the 11:1 range at some points and sometimes richer. So, you can imagine my delight to achieve such a clean running carburetor.

Some history on emulsion packages
In the above thread, Mark and Yeti provide interesting reading. The premise is that the old OEM Holley carburetors had a much "smaller" emulsion package with less emulsion ports and smaller bleed sizes including a smaller main air bleed. This produced the much leaner part throttle fuel mixtures necessary to maintain strict emissions standards and fuel economy goals required by the OEMs.

They go on to say the the "larger" emulsion packages that we see today are nothing more than a monkey see, monkey do scenario where one "carb guru" copied another supposed guru until these practices became standard procedure. It seems bizarre to me that no one along the line might have said: Hold on a minute, but that is what they say has happened. And, this change in emulsion packages is so industry wide that Holley even does it on their new HP carbs.

Anyway, their recommendation is basically a return to the old Holley OEM style carburetor emulsion packages, thus bringing back the leaner part throttle mixtures that help us keep our spark plugs, oil, exhaust and air cleaner.

One concern I had is that this new "cleaner" emulsion package would not run as hard and fast at WOT as the factory Holley HP or the "Guru" style emulsion packages at the drag strip. Not the case for me. My car had a new-best last visit to the track. However, in all fairness, it was not a back to back test and the weather conditions were great. With that said, knowing my car as I do, I am quite sure I have not lost anything in the performance department. I believe I have gained. The carburetor also responds and revs better than ever.

Here is my new set up:

Carburetor: Holley 950 HP
Pump Squirters: 40/40 (nozzle style)
Pump shot size fr/rr: 50/30
Metering Blocks: Quick Fuel Billet (4 emulsion port model)
Emulsion Ports: #2 & #4 blocked, #1 & #3 have .028" restrictions as delivered from Quick Fuel
Kill bleed: .028"
PVCR: .069"
Jetting pri/sec: 69/83
MAB (Main Air Bleed): .028"
Primary Power valve: 9.5
Secondary Power valve: Plugged
IFR (idle fuel restriction): (relocated to the low position like the old Holleys had) with a .036" restriction
Idle Air bleeds: .075"



Feel free to ask me any questions, but understand, I did not dream up this information. I learned it from the Yellow Bullet thread above. Mark and Yeti are where all of this came from, so they are the experts. I just successfully implemented their knowledge.

speedtigger

iTrader: (16)

Here is a great picture depicting the inner workings and plumbing of a Holley metering plate:

speedtigger

iTrader: (16)

Here are some Holley diagrams defining each port's function:



1. To discharge nozzle from acc.pump. 10. To timed spark port
2. To main air bleed. 11. Fuel bowl vent
3. To main discharge nozzle. 12. To main air bleed.
4. To Idle air bleed. 13. To main discharge nozzle.
5. Used w/auxiliary air bleed. 14. To Idle air bleed.
6. Not use (not drilled). 15. Dowel for metering block.
7. Dowel for metering block. 16. Used w/auxiliary air bleed.
8. To curb idle transfer slot. 17. To curb idle transfer slot.
9. To curb idle discharge. 18. To curb idle discharge.




1. Acc.pump discharge. 13. Fuel bowl vent
2. Main air bleed from main body. 14. Main air bleed from main body.
3. Main passage to discharge nozzle. 15. Main passage to discharge nozzle
4. Idle air bleed from main body. 16. Idle air bleed from main body.
5. Air bleed to main well. 17. Air bleed to main well.
6. Main body dowel. 18. Timed spark passage.
7. Main air well. 19. Main body dowel.
8. Idle feed restriction from main well. 20. Idle feed restriction from main well.
9. Idle fuel from main well. 21. Idle fuel from main well.
10. Idle transfer to main body to curb idle adjusting screw. 22. Idle transfer to main body to curb idle adjusting screw.
11. Curb idle discharge. 23. Curb idle discharge.
12. Powervalve channel restriction. 24. Powervalve channel restriction.

3pedals

iTrader: (3)

Good post SpeedTigger, maybe it can be sticky'd

Pop N Wood

iTrader: (1)

Interesting info. Will have to spend a week or two with that other thread.

I did find the idle air bleed stabilized my cruise AFR and allowed me to get rid of the 50 cc primary accel pump. But haven't gone so far as drilling out the emulsion ports.

It doesn't help that all the Holley information says adjusting air bleeds without a flow bench will turn the carb into "expensive junk".

Also interesting that they say to go back to the old low point IFR.

man, you sure have some big *** accel pump nozzles.

ZONES89RS

iTrader: (25)

I do say, for our newbs and those still learning(all of us are always learning), I am going to make this and some other posts into a sticky for those always asking how to fix or make better the carbed setups. Thank you for taking the time to post Tigger. Greatly appreciated.

speedtigger

iTrader: (16)

I elaborated and added more info to the original post to explain more of the theory and history behind the emulsion mods.

speedtigger

iTrader: (16)

The accelerator pumps are an interesting topic. If you look through the carb database, you will see a huge range of setups. It made me think about the factors that contribute to accelerator pump needs for a given engine.

Here are my thoughts:

Displacement to intake volume ratio:
A relatively large engine with a small intake tract volume will not suffer as much drop in velocity through the carburetors venturis as a small engine with a large intake tract. Therefor the larger engine will not need as large or as long of a duration of accelerator pump enrichment because the drop in velocity through the carburetors venturi will be less. This means the boosters will be able to supply a more consistent fuel supply negating the need for alternative enrichment. A smaller engine with a larger intake tract such as high volume ported heads and an intake manifold with large ports will suffer a greater velocity drop through the carbs venturis creating the need for more alternative enrichment.

Carburetor size:
Larger carb venturis suffer greater velocity drops at low RPM WOT in a given engine. Therefor the signal suffers and more alternative enrichment is needed. This is why General Motors adopted the spread bore Rochester Quadrajet carburetor. This carburetor incorporated very small primary venturis and very large secondary venturis. This allowed for excellent low speed metering.

Camshaft timing/duration:
Longer period (read larger) duration camshafts are less efficient at low RPM which decreases their signal to the carburetor at low RPM. This reduces velocity through the booster resulting in the need for alternative enrichment.

Stall converter and/or gearing:
Vehicles with low stall converters and/or stick shifts with low numerical final drive ratios will have a longer dwell time in the lower RPMs when launched at low speeds with full throttle. Conversely, a vehicle with high stall converter and a high numerical final drive ratio will not dwell for much time at all at low RPMs when going to full throttle at low speeds. It is in these low RPM situations where velocity through the carburetor is low and alternative enrichment is needed.

Weight of vehicle:
Heavy vehicles take longer to get rolling, thereby longer to get into the higher RPMs where the signal to the carburetor is stronger. This means that, in general, heavier vehicles will require alternate enrichment for a longer duration of time.

If you take the above into consideration, it become quite obvious why my big heavy Buick with ported heads, ported intake, 950 Holley and a relatively low stall for my camshaft car would want more accelerator pump size and duration than your light weight, near stock engine Datsun.

I also want to point out something about the 50cc pump for people considering the upgrade. I have seen a lot of guys install this pump and never change their pump actuator cam on the throttle shaft. 50cc pumps use much bigger cams with taller ramps. If you do not change this pump cam, adding a larger volume pump will do nothing.

S10xGN

iTrader: (11)

I've got a RapidJet metering block in my HP750, it has tunable emulsion ports:

speedtigger

iTrader: (16)

Very interesting. I see it used .028" emulsion ports also.

Cobra4B

iTrader: (9)

I have some reading to do!

speedtigger

iTrader: (16)

At the last race, I pulled my TR6 street plugs to install my BR7 nitrous plugs. I wanted to share a picture of my TR6 plugs. These plugs have about 150 miles of mixed street driving on them:



It give you an idea of how clean the nasty old Holley carb can be if you are willing to put in the effort.

Also, I wanted to share that since the opening post, I have richened up my idle to mid to high 13s. It seems to be a better center point for my combo to account for weather.

Also after some track testing, I changed my secondary jetting to 82s from 83s.

silverls1z28ofdeath

Subscribing and gonna be doing some reading here. My holleys cruising afr of 11.5 drives me nuts and KILLS my gas!

Doug G

Gotta get one of those AFR meters....See how this Demon does.

Putting it on the X-mas list....what ones you all using/like.

silverls1z28ofdeath

I use a innovate lc1...don't know if its good bad or the other, but it is what I use

onefast84

Nice read will have to try this out!