["QUICK-SILVER"]

Originally Posted by Tom Vaught

The best location for the IFR (Idle Feed Restriction) was identified in carburetors and the results reported in NACA REPORT #49 (Part II on page 607) See link below.

http://naca.central.cranfield.ac.uk/...-report-49.pdf

In the conclusions part of the document, conclusion #4 clearly states that:

"Submerged Fuel Metering Passages (IFRs) are free from Instability and Irregularity of discharge when the head is very small."

You can not have a submerged Fuel Metering Passage when the IFR is in the "HIGH" Position, (only the "LOW Position").

There are 10 other conclusions and all of them are correct.

Many Carb Tuners have converted back to the Low Position IFRs even though the Holley Carb came stock with the High Position IFRs.

Hope this helps.

The Report #49 is available on the web and is well worth reading if you really want to understand carburetors.

Tom V.

ANNUAL REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

That line you quoted, line (4), wasn't about Holley IFR's. It was in reference to main jets needing to stay submerged on an airplane engine. It does tell us that Holley carbs wont perform properly when ran inverted.

Holley high mount IFR's stops the amount of fuel weep, out of baseplate, with engine off and float bowls full.

Race type engines, with extremely low vacuum at idle, have a tough time pulling fuel up and over through high mount IFR's. Low mount IFR's helps with idle and transition on those engines. The trade off of added fuel weep is worth it to them.

Street cars with hot cams and extremely low vacuum can have the same problems with idle and transition. That's when you need high powered ignition systems to keep from fouling plugs on start up with low mount IFR's.

Was Report #49 really from 1920? Good read all the same. A bunch of that main circuit running flow tech does apply to automotive carburetors. The kind of stuff that can't be improved on much if any. Like the test carbs you mentioned in the other post.

Clay

[Tom Vaught]

Originally Posted by "QUICK-SILVER"

ANNUAL REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

That line you quoted, line (4), wasn't about Holley IFR's. It was in reference to main jets needing to stay submerged on an airplane engine. It does tell us that Holley carbs wont perform properly when ran inverted.

You really need to stop with generic replies which are wrong many times. Holley built aircraft carbs during WW-II and before.
The Flow bench pictured in Urich carburetor books is a 3000 cfm flow bench. Do not see very many 3000 cfm automobile carbs out there today. Obviously the stand was used for Aircraft Carburetor Testing. Need to bone up on your history there guy.

OK then why does other Carb Guys like Tuner, Markaudio, Braswell, and others offer the low mount IFRs vs only the high mount ones?
Also why did Holley offer the low position IFRs only from the WW-II days until the late 1970s if that was not the correct position? Your statement holds no water.

Holley high mount IFR's stops the amount of fuel weep, out of baseplate, with engine off and float bowls full.

Full bowls should never be "full". That comment says a lot about your carb knowledge.


Race type engines, with extremely low vacuum at idle, have a tough time pulling fuel up and over through high mount IFR's. Low mount IFR's helps with idle and transition on those engines. The trade off of added fuel weep is worth it to them.

This post is in the Street Section. Do not see any RACE ENGINES in this section.
Again your comment does not apply. Some race carbs do not run Power Valves due to the low vacuum you mention, street carbs and engines use power valves FOR A REASON.

Street cars with hot cams and extremely low vacuum can have the same problems with idle and transition. That's when you need high powered ignition systems to keep from fouling plugs on start up with low mount IFR's.

OK.

Again you are mixing apples and oranges. STREET SECTION - STREET SECTION, DOH.

Was Report #49 really from 1920? Good read all the same. A bunch of that main circuit running flow tech does apply to automotive carburetors. The kind of stuff that can't be improved on much if any. Like the test carbs you mentioned in the other post.

Clay

WHY WOULD YOU REALLY EVEN ASK SUCH A QUESTION?
YOU ACT LIKE I MADE UP THE DATE (ACTUALLY published on JAN 01, 1919 SEE BELOW.


Publication Date: Jan 01, 1919
Document ID:
19930091078 (Acquired Sep 01, 1996)
Accession Number: 93R20368
Report/Patent Number: NACA-TR-49
Document Type: Technical Report
Publisher Information: United States
Organization Source: National Advisory Committee for Aeronautics; Washington, DC, United States

Tom V.

You will always have one "Expert" in every classroom, LOL! Most have little knowledge of history and the "Why".

[Tom Vaught]

Even with all of that QUICK SILVER, no question is a bad question.

Tom V.

[Tom Vaught]

So how old were you in 1975-1976 Quick Silver?

Tom V.

[Formula jg]

I think the thread poster mentioned a concern he had as he went applied moderate acceleration the AFR would head in a lean direction and then on a heavier WOT the AFR would drop into mid 12’s.
Isn’t that exactly how a carb should function?
Progressively curve towards the lean side up to approx. 60-70% throttle then swing back richer from 70-100% throttle?
Again this was how I understood it from several carb experts years ago.

[Tom Vaught]

I personally think you are right on the money on your thoughts.

In my mind a moderate acceleration could very well not drop the manifold vacuum to say 6.5" of vacuum where the Power Valve would start to open and provide more fuel to the air/fuel mixture. So you get the leaner mixture on the moderate acceleration on the Air/fuel meter.

If he was at mid 12s on the heavier WOT that is very close to, the assumed ideal 12.7 to 1 air/fuel mixture, for performance.

The Government requires that the Air/Fuel Mixture on modern vehicles stays right at "Stoich". And the engines run fine on the road.

The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air.
For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required.

So he has a lot of "Wiggle Room" on being "lean" with his carburetor without it being an issue.

Tom V.

[92GTA]

Time to post a follow-up after returning from my work travel....

After confirming my initial timing and very little additional tuning, it is running absolutely fantastic. For the first time, even the choke works like it should too! The hesitation is 100% gone with the larger squirters and getting the 4 corners dialed in how the engine wants it after setting the front transfer slot and using the rears to set the idle. Actually, when I took off the carb, the front slots were just about perfect already from my previous tuning, but it was nice to get eyes on them to confirm they are square and that none of the slots front and rear are overexposed.

I want to thanks everyone again for their information and suggestions. It feels great to have this dialed in finally and never needed to change any of the jets.

I do have 2 remaining issues:

1) On a cold start (keep in mind it's low 80s here in CA now) the engine starts, then over the first 30 seconds the RPM slowly increases. I think I'm going to lower the cold start idle just another 100 RPMs so the exhaust doesn't drone in the garage. But what is causing it to fire up at a lower RPM then increase? Is that the choke closed too much? Do I just need to rotate the choke housing a bit looser?

2) After about an hour and a half of driving around town, my AFR gets leaner, especially at lower RPMs. Is that from the fuel lines heat soaking and the fuel being hotter? Or from the base of the carb heat soaking and causing the fuel in the bowls to be hotter? Any suggestions on what can mitigate that?

Thanks!

[64speed]

All of this is precisely why I am going EFI