Cadunkle, rebuttal? LOL As to the CFM if I need to swap carbs in the future I will do so but I want to see what happens with this one. It'll be a learning experience if anything. And I can sell the old one on eBay if need be.

 

Conventional wisdom says that the smaller the carb the better the mileage unless you are heavy on the throttle. But Cadunkle's experience says otherwise. Will be interesting to see your results.

 

The carb won't be in until next week sometime. After I get it on and tuned I'll let you know what I find.

 

Reason for the negligible difference in fuel consumption is likely that the CFM requirements of a big engine will result in a undersized carb running more throttle opening, running on the secondaries, and possibly on further enrichment as well in scenarios that a properly sized carb would not be into the secondaries or any enrichment circuits. I can say for certain that when switching from a 600 VS to a 750 DP that to accelerate brisky or maintain speed I had significantly less throttle opening with the 750.

 

Cadunkle, that does make sense. Like having too small a furnace for your home. You think you're saving money but you're more likely to have a higher heating bill. Better to have too much than not enough. Makes me kind of curious why they put a 600cfm carb on the truck to begin with though. If I notice that I have to shift down during a load I'll probably upgrade to a 750. That won't be until early next year when I start pulling the dirt track car again.

 

Blown power valves are really a non-issue. Every Holley made in the last decade or more has come from the factory with a check valve. Retrofit of an older carb is cheap and easy. The only scenario a power valve will blow on a Holley without the check valve is if the engine has mechanical issues (non-sealing intake valves, timing too far advanced, etc.) or the carb is otherwise damaged or way out of tune (extreme lean condition, failed/clogged accelerator pump, etc.). I've never had issues with blown power valves on new or rebuilt carbs on properly running engines in good condition, regardless of lack of power valve check valve. Regardless, this issue was resolved a long time ago.

I've never had a Holley accelerator pump leak externally. In many years of owning and driving vehicles with Holley carbs (almost every car, truck, boat I've owned has had a Holley 4150 or 4160), I've only ever had one fail. It was on an old 600 CFM VS 4160 and it failed on a 500 mile trip. No leaks, no problem. Just had to go easy on the gas from a start. Amazingly despite a couple backfires it didn't blow the power valve, even without a check valve. This carb had likely never seen a rebuild. I've also never had, seen, or heard of accelerator pump screws backing out. If this has happened I would be inclined to believe the screws were not installed properly or an old or damaged diaphragm was used.

I believe it is extremely rare for an accelerator pump failure to result in an external fuel leak. Accelerator pump can and will fail with age and use. I have had to rebuild Quadrajets with AFB style pump that had failed. I don't believe there is much difference in failure rate though Holley pumps look and feel more durable to me. Beyond that, a Holley accelerator pump is far more tunable than an AFB style pump. You can have options for accelerator pump size, discharge, duration, and curve which can be customized. AFB style carbs give you less tuning options for the accelerator pump circuit which will result in more wasted fuel on the accelerator pump circuit.

I've already addressed the power valve issue. Warped bodies are addressed on rebuild. Part of the process is to line sand/file/mill/whatever the main body and sealing surfaces to ensure a clean and flat surface that does not leak, internally or externally. If your carb was leaking, it was not rebuilt properly. The newer style gaskets are also far more forgiving than the old sticky nasty cork and other style gaskets. Even so, I never had leaking issues on carbs with the old style gaskets even after years of use, unless trying to reuse them. In fact it's exceedingly rare for me to come across a Holley leaking externally for any reason.


The most common reason I see a Holley leaking externally is a stuck float or crud in the needle and seat resulting in fuel flowing freely out the vents. In a marine or off road application with bowls vented down the venturi this result in a severe flooding condition but no external fuel leaks. In a standard automotive application some fuel will leak down the venturi and some will leak out onto the intake, as an external fuel leak. AFB style carbs will behave similarly, though most fuel should be contained down the venturi, similar to J vent tubes on a Holley or connecting the vents with vacuum hose that is slotted for venting.




All the issues you mentioned are either non-issues due to either user error or being resolved long ago. Holley is a far more adjustable and tunable design than teh AFB style carb. This is why they are used in high power and race applications that demand maximum power from a given engine. There is simply more adjustment and tunability on all circuits. Where the AFB has an advantage over Holley is the metering rods. This allows a smoother transition to enrichment and not an all or nothing approach. On a properly tuned Holley, you are rarely into the enrichment circuit though, so I do not see this as a worthwhile benefit of the AFB design when considering the many advantages of a Holley over an AFB.

If a more progressive enrichment is desired, there are two stage power valves which will provide two progressive levels of enrichment. I've never had an application that I found this necessary as I've never had to overly enrich the mains to avoid a lean stumble on transition from main to enrichment. Proper single stage power valve sizing has also got me smooth enrichment while avoiding unwanted enrichment while cruising and light acceleration. Regardless, the option is there is a more progressive enrichment is desired. Furthermore, staggering power valve ratings across primary and secondary sides can result in another level of progression in enrichment, particularly if running two two stage power valves with different ratings on primary and secondary sides. Again, I've never personally encountered a situation where this was necessary or desirable, but it is possible to do a "4 stage" enrichment circuit on a Holley.

Holley carbs simply beat out AFB style carb on getting the most power from a given engine, and will not sacrifice any fuel economy to do so. I don't see any advantage to running an AFB style carb. If you want smoother transition between circuits, maximum tunability, and greater efficiency you need to look at Quadrajets (which will leave power on the table compared to Holley) or better yet Webers. AFB is not the answer. Please keep in mind, I'm not bashing AFB style carbs. They work alright, they meter fuel and do a good job of it. Holley just does it better... and of course others do it better than Holley, but are far more complex for your average Joe to work with, and in the case of Weber carbs, far more expensive as well.

 

Very similar concept, good analogy. They likely put a 600 on there primarily for emissions reasons. The factory carb was a smog carb and had a smog tune. Most emissions equipment wastes fuel. I've always wondered about that. Your exhaust puts out fewer part per million of "bad" stuff, yet you burn more fuel in order to put out fewer parts per million resulting in more millions per mile. So what is the overall parts per mile of the "bad" stuff on a highly efficient non-smog engine vs a smogged engine with "lower emissions"? I don't know, but I'm really curious. I've never seen such numbers published.

Another part of the reason for going with a smaller carb could be to increase intake charge velocity in an attempt to achieve better atomization. This is likely as the carbs on tehse trucks, if I recall correctly, had annular boosters. The annular boosters support this theory as they will atomize fuel better than straight or dog leg boosters. The velocity is a non-issue as with 460 cubes you have plenty of intake charge velocity with a 750 CFM carb. It's not until larger carbs are required that intake charge velocity will noticeably suffer at lower RPM, but at that point you have enough cam that low RPM will not be significantly affected or even something you care about, as you want max power at the higher RPM as you approach peak.

Aside from that, a smaller carb is cheaper, as is using a 4160 type setup instead of a proper 4150. Or it could have been a misguided attempt to regain some MPG that was lost on the emissions equipment. Another factor I'm not 100% on is the incoming CFM of exhaust gas on these EGR systems. That is contributing to intake charge flow though it is inert and not producing power, in fact hurting power. This may contribute to a lower carb CFM requirement at cruise when EGR is flowing, but would not reduce CFM requirement of clean fresh air/fuel mixture at high load low throttle conditions or high load high RPM conditions.

Basically my supposition for the use of an undersized carb is emissions and cost related. Prior to the smog era junk Ford was running 700 or 735 CFM carbs on 428s and 429s.

 

Cadunkle - Always tough to go first as you give it your best shot and the other guy has the time to sit back and come up with good answers, which you've done. However, you didn't address spilling fuel all over the intake when you pull the bowls.

I will admit that my "love" of Holleys started in '69 when I bought a new Super Bee that had one on it. That carb was a piece of junk from the factory as it had warped everything, and that wasn't unusual for them in that era. And in that day they came with "old nasty cork gaskets" which would not seal on the out-of-the-box warped bodies. But, I guess if you are working with inferior products it is understandable that you naturally have to machine them flat just to put a kit in them. Silly me, I'd grown up with Carters and Rochesters and wasn't used to having to finish the manufacturer's work.

And, as Bill Vose pointed out, the Mopars of that era were prone to backfire through the carb due to their emissions package and not user error, and you could count on losing the power valve when they did. But, I wasn't aware Holley finally addressed the flaw in their design with a check valve since I gave up on their product long ago. However, I doubt the many guys on this forum who've posted about their blown power valves would agree that it is a "non-issue" as you said. The poorly-engineered products are still out there in service and still have the same problem I had with them in the 60's, while the other brand carbs don't have those issues and never did.

I do, however, agree with you that the Holley is capable of getting the last little bit of power out of an engine when tuned by someone who knows what he's doing. So, I think they are a good carb to use on the track.

I also agree with you that the Q-Jet is a better carb than the AFB. In fact, I like it better than the AVS, but would bet on a properly-tuned AVS getting better WOT power than a Q-Jet. However, for street use I prefer the Q-Jet and have considered building one up for my truck. The one I put on my 390 in '72 worked very well.

 

Wow. That was very well thought out. I've dealt with my factory Holley and can't stand it for all the reasons you've stated. It was never meant to be tuned or adjusted so when I started messing with it everything started to go bad. I've since had to rebuild it twice and finally got it to the point where it will start and idle well after it is warm. It still is extremely rich and I haven't been able to get the mixture just right. Maybe it's my inexpertise that is the issue there. I just know a new carb is in the future and for now its an Edelbrock 1406. I may regret this and I'll definitely let you know the outcome. My next carb may very well be a Holley. Who knows. It's all a matter of preference and application. Like my uncle once told me. Opinions are like ---holes. Everyone has one and they all stink. Lol.

 

 

I have used Holley carbs since the 1960s and have never had a problem with blown
power valves or leaking accelerator pumps. They are very tunable and reliable. I have
2 classic muscle cars that both have Holley 4bbls and my 1981 F100 with a 351W also
has a Morocraft-Holley 4180 which runs very well. The afore mentioned cork gaskets
were a pain but the later type gaskets seal well. Most problems with Holley carbs
with warped surfaces are caused by over torquing fuel bowl screws or base plate
screws. I never knew the 1969 Super Bees had Holleys except for the 440 option
with 3 2bbls which were Holleys. I thought the 383s had Carter AVS carbs. But 40
some years is a long time and I could have forgotten and remembered wrong.

 

You and Galen Govier, aka Mr Mopar. As it turns out, there were super Bees and there were Super Bees. I bought the Bee I have now several years ago and the more I was around it the more I thought "this isn't like the one I bought new in '69". For instance, this one says 383 Magnum on the fender, but I could have sworn the one I had said "383 Four Bbl". And, this one has an AVS while the other one had a Holley. And, this engine is Hemi Orange but the other was turquoise. And this one has bright exhaust tips and my original one didn't.

Then, one year at the All-Chrysler meet at Carlisle I saw a "survivor" that said 383 Four Bbl, and the engine was turquoise, and no bright exhaust tips. But, it had an AVS! So, I talked with the guy and found he bought the thing new so was 100% sure it was original - except for the carb. Turns out he hated that Holley so put it on the shelf and installed the AVS.

About that time Galen Govier, who is the guru of all things Mopar, wrote a piece in Mopar Muscle that said all '69 Bees had an AVS, bright exhaust tips, etc. So, that got me to wondering about mine and I did some research. Turns out that all auto & A/C Bees got the 330 HP 383, which was the run-of-the-mill 4 bbl engine, while all other Bees got the 335 HP engine with the better cam, the AVS, a windage tray, etc. In fact, I have a copy of the sales literature for that year that actually explains all that if you know what to look for.

Oddly enough, in '68 the 330 HP 383 had the AVS and the 335 HP 383 had a Holley.

 

Very interesting Gary. Thanks for sharing the history. It is really amazing how the
car companies did things back then.

 

Yes, things were "interesting". Why would Chrysler change the Magnum engine from a Holley carb in '68 to a Carter in '69 while doing exactly the opposite on the non-Magnum engine? And, from what I can tell the carbs were basically the same for the two years, meaning that the '68 and '69 Holleys were the same carb as were the Carters. I'm sure there's a reason, but just can't reason it out.

But, the substitution of the 330 HP engine for the 335 when running auto and air does make sense. I'm guessing the cam was too much to maintain the proper idle when loaded with the 727 and that big ole Airtemp compressor. However, they didn't want us to shy away from those money-making accessories so buried the fact that they were swapping the engines in some obtuse wording which only makes sense when you know the answer. And, they were successful as even Govier hadn't figured it out.

 

Very true, but I think this has been an interesting discussion without any poo flinging. There's not much I can say about fuel spilling when tuning. I hate it. It sucks. Unfortunately it's part of the process of getting a Holley dialed in and once it's done it doesn't need to be changed for the life of the engine so long as no other modifications are made.

What I do to avoid this being a problem, mess, or fire hazard is take a cap from a rattle can and place it under one of the lower bowl screws. Pull the screw and almost all the fuel drains into the cap, then pour back in the tank or once you're done you can pour it down the carb vents so you have fuel right away. I also place a couple rags under the bowl for the last dribble of gas that comes out when you pull the bowl and metering block off. I don't have problems with fuel touching my intake or a messy gas spill. It still sucks though. I particularly dislike tuning carbs in boats for this reason.

I won't deny Holley has had some QC issues over the years. Personally I disassembly every carb I get, brand new or otherwise, and clean up any casting flash, check sealing surfaces, and fix any of the minor issues that some will have. On these lower level mass produced carbs you will find issues now and again. Since you'll be pulling things apart either way to tune, you may as well do a quick inspection and cleanup on the bench before installing. This should be done with ANY carb. It's the same concept as building an engine, you don't just slap parts together. Everything is inspected, checked, measured, documented, and cleaned/modified as appropriate for the intended use. I've seen QC issues is just about EVERY brand or type of part I've used that was mass produced. Attention to detail is what makes an engine run well and last long while getting the most power and efficiency you can from the build.

Same for other manufacturers with emissions equipment. I don't see this as a carb problem, but rather a poor running engine damaging the carb. Doesn't matter if it's new, a smog engine has all sorts of problems that result in poor running characteristics and lower efficiency. This is an engine problem, not a carb problem.

Aside from that, thanks for all the info on Mopars. I enjoy learning the ins and outs of what was going on back then.