Question for Tuner

[Geoff2]

Tuner.

Referring to the Carter AVS carbs that were used on Chrys engines from 1968 to 1971. Specifically, the primary venturiis which are secured with two screws. What I call the 'bridge': the section or arm that connects the main body to the booster ring. I have seen some where there is a hole drilled in the underside of the bridge into the brass discharge passage. Not all carbs have it, & many have the projected boss on the bridge, bit it is not drilled through. There may be other Carter models that have this.

Any idea what hole is for? Thanks.

[Tuner]

What would you say is the purpose of the bleed in the top side of the cast integral in the body straight booster leg in some late '60s and early '70s Mopar Holleys?

[Geoff2]

I am not sure, have not seen those on Holley carbs. Add more air? The holes I am talking about are on the underside of the booster.

[Tuner]

In the Holleys it is a hole in the top of the booster leg midway between the booster and the carb body, similar location as the hole in the bottom of the leg in the Carters you refer to, so it serves the same purpose, but without the effect of impact flow. I don't recall seeing this bleed on any other Holley than the Mopar production emission control carbs which are unique in several ways from other Holleys.

I was hoping you would reply with the obvious that a bleed in that location will kill or delay nozzle signal and with impact air result in leaning WOT A/F, so I could reply the hole underneath the leg serves the same purpose to delay the nozzle start but without the impact air not have so much air bleed effect at high flow.

I recall the boosters with the bleed on the underside of the leg have a very simple main well tube, some with only a single bleed. If you have an example, describe the main well tube. I don't think it is the same as later AFB and AVS Mopar carbs, with lots of small air bleed, or the Federal Mogul Carters and Edelbrock versions with several large bleeds.

Many of the old '50s and early '60s AFBs have just a simple well tube, almost the type of well and nozzle in the first T-Quads Carter called "solid fuel" carburetors in which A/F correction was accomplished by L/D ratios of passages instead of air correction with bleeds.

I think the Mopar Holleys with the bleed in the top of the booster leg were the 3-circuit emissions carbs with the T-slot feeding from the bowl, in which case it continues to discharge at WOT, whereas at WOT the idle circuit with the idle jet downstream of the main jet pinches off idle circuit flow as nozzle depression exceeds that at the slot, and idle circuit flow begins to reverse, then the idle jet becomes an air bleed into the main well reducing WOT fuel flow, the IJ then acting as a high speed air corrector.

When fuel is above bleeds which are below the level of the booster leg, fuel is encouraged by that bleed air to lift and flow toward the nozzle. The bleed in the angle channel is above float level so it initially delays flow until after flow is established and fuel is above it, then the air from the angle channel bleed pushes fuel with it toward the discharge nozzle and so encourages flow.

[Geoff2]

A member has kindly sent me the Fed Mogul manual, which describes this hole. It is an air bleed, purpose of which is to smooth the transition from the low to the high speed cct & improve part throttle economy.

[Tuner]

A member has kindly sent me the Fed Mogul manual, which describes this hole. It is an air bleed, purpose of which is to smooth the transition from the low to the high speed cct & improve part throttle economy.

So then, what does it actually do to accomplish this?

As I recall that F/M manual is very similar to the Edelbrock version and is written for the average enthusiast end user whose familiarity with carbs is from reading magazine articles and possibly doing basic tuning, changing jets and rods, etc. In other words, it is intended to be read by people who have little or no specific carburetor engineering education or physics education.

It describes the result of the bleed, but does not describe exactly how it achieves that result, what it does to the metering signal.

It would be interesting to play with this on a flow bench, or even with a vacuum cleaner and a crude water manometer, and see the effect on metering head at the main jet, with and without this bleed.

What do you know about the purpose of the hole in the tip of the nozzle in Qjets and other double booster venturi carbs, TQuad, YF, etc.

[Kevin Johnson]

These theses at MIT are available to read for free. There are other universities that will allow you to read engineering theses at no charge. If you check out the citations you can drill down and explore topics. However, one large limitation is your budget. Many references have a paywall, like SAE.

If you visit Research Gate many authors provide free copies of papers there.

Google Scholar will often bring up old engineering and physics texts that you can download at no charge.

You can also read old patents wherein the reasons for various features are explained.

Good luck in your investigations:

https://dspace.mit.edu/discover?field=d ... cf3541bb09

[67 Nova]

Tuner, sent you a PM

[Tuner]

These theses at MIT are available to read for free. There are other universities that will allow you to read engineering theses at no charge. If you check out the citations you can drill down and explore topics. However, one large limitation is your budget. Many references have a paywall, like SAE.

If you visit Research Gate many authors provide free copies of papers there.

Google Scholar will often bring up old engineering and physics texts that you can download at no charge.

You can also read old patents wherein the reasons for various features are explained.

Good luck in your investigations:

https://dspace.mit.edu/discover?field=d ... cf3541bb09

Kevin, what a great bunch of rabbit holes to go down. I remember the combustion powered Pogo stick in Popular Mechanics or Popular Science in the mid '50s when the guy made the thing and published his thesis. I get the distinct feeling C.F. Taylor had a sense of humor to encourage a student to do something some people would consider silly and turn it into such a thoroughly engineered masterpiece encompassing so many fields of engineering.

[Kevin Johnson]

These theses at MIT are available to read for free. There are other universities that will allow you to read engineering theses at no charge. If you check out the citations you can drill down and explore topics. However, one large limitation is your budget. Many references have a paywall, like SAE.

If you visit Research Gate many authors provide free copies of papers there.

Google Scholar will often bring up old engineering and physics texts that you can download at no charge.

You can also read old patents wherein the reasons for various features are explained.

Good luck in your investigations:

https://dspace.mit.edu/discover?field=d ... cf3541bb09

Kevin, what a great bunch of rabbit holes to go down. I remember the combustion powered Pogo stick in Popular Mechanics or Popular Science in the mid '50s when the guy made the thing and published his thesis. I get the distinct feeling C.F. Taylor had a sense of humor to encourage a student to do something some people would consider silly and turn it into such a thoroughly engineered masterpiece encompassing so many fields of engineering.

One MIT thesis (of several that were interconnected) was generally about the research that Ford sponsored to remedy a Porsche designed V6. They provided Sloan Engine Lab with the engine. Porsche, Jaguar, Mazda (IIRC) and Ford all had different solutions for the oil pan, oil level and windage tray. There were SAE papers generated as well.

The scripture "seek and ye shall find" appears in Matthew 7:7-8, which says, "Ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. For everyone who asks receives, and he who seeks finds, and to him who knocks it will be opened"