Holley Carbs

[Blue MK3]

What's the reason for the infatuation with these cantankerous devices? I have one (a 650 double pumper) on my 347 stroker engine. I've had the car only two months and the carb has been irritating, at best. And poor gas mileage too. Can't seem to get it adjusted properly and when I do, it goes out again. No auto mechanic I've talked to who is reasonably knowledgeable about carbs has anything good to say about Holleys. Hard to keep in tune, not very driveable on the street, made only to run wide open, etc., etc. So what's the infatuation with them?

[speed2much]

What's the reason for the infatuation with these cantankerous devices? I have one (a 650 double pumper) on my 347 stroker engine. I've had the car only two months and the carb has been irritating, at best. And poor gas mileage too. Can't seem to get it adjusted properly and when I do, it goes out again. No auto mechanic I've talked to who is reasonably knowledgeable about carbs has anything good to say about Holleys. Hard to keep in tune, not very driveable on the street, made only to run wide open, etc., etc. So what's the infatuation with them?

I'm no expert but I haven't had to touch mine once I got it dialed in. I purchased this book.... http://www.amazon.com/Holly-Carburetor-Handbook-4150-Hp473/dp/0895860473/ref=pd_sim_b_20
They do take a bit of tuning to provide optimal results.
And that does vary from one vehicle to the next. I'll also add that it will never be as seamless in operation as your fuel injected daily driver.
I have a 302 and get 22+ mpg in highway cruising.
Finding an auto mechanic today that can actually tune a carbed setup is hard to find.

[Blue MK3]

OK, no response from anyone. I guess I left off the question of available alternatives. What other carb or type would give better service for a street driver? Maybe another brand and with vacuum secondaries? Or go the whole nine yards and spring for one of the throttle body EFI systems?

[skullandbones]

I have a somewhat modified EFI so that might give you a hint about how I feel on the subject. I did have a 427 Chevy with an 850 DP Holley. It ran like crazy and was pretty managable for a DD. But I don't think most people would ever call it efficient except in the performance mode. I got horrible gas milage (but it would fly!) and I never had to tinker with it. So maybe the quality of their product has gone down. My other big block hot rod (396 Chevy) had 2 625 AFBs on a tunnel ram which I ran on the street. It actually got 15 mpg on a trip of 1K and drove pretty well considering the Z11 cam and other mods. So I don't know if you have a "lemon" or if it is just out of adjustment. Depending on how much you have worked on the jets sizing, etc, that could be the answer. Many people have great results with the Holleys but some have issues like yours. The only Holley component I have in my engine bay is a EFI intake that makes the 302 scream. You might be better off doing the EFI thing with all the problems you've had. JMO, WEK.

[edwardb]

OK, no response from anyone. I guess I left off the question of available alternatives. What other carb or type would give better service for a street driver? Maybe another brand and with vacuum secondaries? Or go the whole nine yards and spring for one of the throttle body EFI systems?

Holley has been around for a long time, and for many years was standard equipment on millions (literally) of OEM builds. Now with FI standard for OEM's, they've changed to more of an aftermarket/specialty manufacturer. They've gone through a number of owner/management changes, and recently a couple of bankruptcies. So maybe this has affected their quality. I don't know. But they have decent products, and I'm surprised about your mechanic comments. Around here a number of speed shops have Holley specialists, and they are able to get them working fine. Having said that, I changed out a marginally performing Holley with a Quick Fuel SS-650 double pumper on my Mk3. The quality difference was apparent out of the box, and the carb runs great. A big upgrade. Please don't go from a double pumper to a vacuum secondary though... Wrong direction! Carbs do take some tinkering, and rarely will get the same fuel economy as FI. Maybe that's something you should consider.

[Blue MK3]

Thanks for the feedback. I tweaked the carb this afternoon and it seems to be doing a bit better. I'm taking it in tomorrow morning (weather permitting) to a speed shop for a look-over. The owner there is to check the timing and other items. If it still isn't right, he suggested switching to a vacuum advance carb for better fuel economy. He likes the Quick Fuel brand. I'm not hung up on economy all that much, but 7-8 mpg is a problem for me when I hear others say they get 20+. I couldn't drive my car more than 100 miles without stopping to gas up the way it is. I'm a street driver, no plans for track time. I want decent power with a modem of economy. The local Cobra group is talking about a cruise from here in Raleigh to the Gulf coast and back, total of 12-1,500 miles. No way would I consider it the way things are

[edwardb]

Do a search on the other forum (lots of history) on vacuum vs. mechanical secondaries. Be prepared to read. It's a widely debated topic. I'm admittedly biased, but those that change go from vacuum to mechanical. Not the other direction. The bottom line is that vacuum secondaries are not a good fit for these cars. Manual transmission and high power to weight = mechanical secondaries. I too was talked into vacuum secondaries for my Mk3 build, but never could get it to run right. Switched and haven't looked back. While there may be a very slight advantage to vacuum secondaries for fuel economy (not using much gas when it's sitting there bogged down and hesitating ;)), it's not the difference between 7-8 and 20 mpg. A well tuned DP will give decent mileage, and performance fitting to the car. Hold out for getting your setup right vs. changing carbs.

Also (just re-read your thread) don't buy the logic that vacuum secondaries are for street cars, DP's are for race cars. My Quick Fuel DP is far more streetable than the vacuum secondary carb I started with. Not even close. It's all about the right match for your car and the right setup.

[Garry Bopp]

I've got a Holley 770 Street Avenger on my 422" Windsor (vacuum secondaries). It ran great right out of the box and I've gotten as much as 17.5 mpg at 70 mph ... with 3.73 rear gears. Just lucky, I guess.

Garry

[Greg_M]

A properly tuned Holley vacuum sec 570/670 and a properly tuned Holley 600 DP will each return over 20+ mpg if driven the same on a 302 or 347. I have personally experienced all three. If your car is getting 7-8 mpg then it's running way too rich or you have it floored most of the time :). At a given engine demand any tuned carb will deliver an air/fuel mix at the correct ratio for the engine's requirement, all else being equal.

Holley carbs have several modes of operation and each is tunable:

1. Idle
2. Off idle/transition/acell pump
3. Lean cruise
4. Cruise with power valve enrichment
5. WOT/secondaries

It can be a challenge to get each mode optimized or it might just work perfectly out of the box. A wideband O2 logger is the best tool for the DIY home tuner. It will reveal problems you didn't even know you had. For example, your car is running great by the seat of the pants dyno but the wideband might reveal your lean cruise mode is 10:1 AFR and that's why your mpg is so low.

Greg

[Blue MK3]

Thanks for the comments. Obviously, I'd rather get the carb tuned correctly than replace it. I'm watching the weather and working with the speed shop to schedule it in for some analysis/tuning. Not today (rainy and he's busy), maybe tomorrow. Some details about the car I had left out for the sake of brevity. So here they are. Read if you choose, otherwise ignore.

I'm the fourth owner. According to a notebook full of receipts and information that came with the car, it was built during 2006-07. The builder sold it (don't know when) and then the second owner sold it to a guy here in the Raleigh area in May of this year. I bought it in late September. It had 5,400 miles on it at that time. That works out to less than 1,000 miles per year. So it's possible the car sat around for long periods of time without being driven, which isn't very good, given the nature of today's fuels. I started having carb problems in mid-October.

The carb is a Holley 650 DP HO model. It was tweaked by AED and built in August, 2005. The engine is a 347 stroker with Edelbrock Air Gap intake manifold and aluminum Dart Pro heads. Cam is a Comp Cam with .556" intake and .514" exhaust lifts. T-5 transmission with 0.82 5th gear and 3.73 rear, so the rpm's stay pretty high. The engine won't run very well below 2,000 rpm, so I guess that's why the gear ratios are the way they are. According to the dyno printout, the engine develops 445 hp at 6,100 and about 430 ft.lb from 3,300 to 5,300.

First problem was that the primary idle screws vibrated in and leaned it out. Got that fixed and then fixed it myself the next time it happened. AED sent me some new O-rings to install to prevent the needles from turning on their own. Then they backed out and it was running way to rich and was stumbling under load. Adjusted again and then wired the needles in place.

Then more starving for fuel under load, so I pulled the carb and tore it down and cleaned out the passages and openings. Found a bunch of jelly in the secondary float bowl. Some of the internal ribs in the bowl were actually breaking down and disintegrating from the contamination, but none in the vicinity of gaskets, jets, power valve, etc. Cleaned all that out and ordered and installed a kit. Still couldn't get it right. The plugs were black, sooty, and some were actually wet. Gas mileage dropped from the original 12-13 to about 7-8. More tweaking with a vacuum gauge and got it closer to correct. The plugs burned cleaner and the last gas fill up indicated about 10 mpg. Getting better, but still not where I want it. I've been adding StaBil with every fill up.

So the next step is to get in into a shop and let a specialist go over it. Could be timing, a vacuum leak, bad compression numbers, who knows? It's not burning any oil or losing any coolant. I'll let him figure it out.

In the back of my mind, I have to wonder what might happen to the internals of an engine that MAY have sat around too long without being driven. Don't know if that happened, but 5,400 miles on the carb over seven years makes me wonder. I'll report the results of the tune-up after it's done.

[Kevin Davis]

Greg is right on. It took a while to get mine dialed in, and after putting it on the dyno and tuning it for max curves, it still has a very slight stumble from cruising to WOT, but not enough to be an issue.

I have a 570 Street Avenger on my 302 with an e303 and ported explorer heads on it, with an edelbrock intake.

It seems like a lot of guys end up with "too much carb" for their application, and that makes it okay for WOT applications like drag strips, but daily drivers, you're either spitting out fuel or just can't get it dialed in for cruising around. I don't know enough to say if a 650 DP is too much for that 347, but it might be contributing to it.

As far as finding guys to work on them, your best bet is to find a high performance shop, or an off-road shop where they have a little more "old school" knowledge." Finding a guy over about 55 is a good thing too.

[Blue MK3]

Nice web site, Kevin. I'll explore it at length later. As for the carb being too much for the engine, that idea has been brought up by some folks I've talked to. Then there are others who say no, not too much. Eventually, I'll know.

[Kevin Davis]

Nice web site, Kevin. I'll explore it at length later. As for the carb being too much for the engine, that idea has been brought up by some folks I've talked to. Then there are others who say no, not too much. Eventually, I'll know.

Cool. I actually have a 2nd 570 here that will eventually go on my wife's engine. If you want to pay for shipping back and forth, you're welcomed to borrow it to try it out (might not be worth it vs. just buying a 570 on ebay.) I've seen a few posts saying it's a good match for the 347, but sometimes rejetting it might be needed. Good luck!

[Blue MK3]

Kevin, I really appreciate the offer of the loaner. After I get in the tuner's shop (hopefully sometime this week) and if he can't sort things out, I might take you up on the offer. I'm learning more each day about the car and the setup. With the engine being unhappy below 2,000 rpm, the 3.73 rear, the Koni coil over upgrade the builder installed, very wide tires and 17" wheels, big double piston breaks and rotors, etc., it all leads me to think this car was built for some type of short track driving and not for a casual cruise on Sunday afternoon to Goodberry's for ice cream. I figured I'd replace the plugs today, just in case. They're currently Autolite 3922. Not in stock and the parts manager remarked that they are VERY cold plugs. I had suspected as much and will probably swap them out for something a bit hotter in my quest for better running. We shall see. Now to Kevin's web site.

[Kevin Davis]

Cool, just let me know, happy to help.

My car is a so lopey under about 1250, I turned the idle up a little. I'd rather run it at about 800 or so, but it just sounds like it's trying to die. I ended up putting a spring-float as well in mine so if I do autocross it, I don't get as much fuel slosh. I'm living with the stumble for now, but I can understand the frustration. I work with computers every day, and just couldn't bring myself to put one in the car, even if they can be easier. I'm just an old-school carb guy. I'm running 17's and big rear tires too, and it's pretty good. It doesn't ride like a Lincoln, but it's not supposed to. ;->

One thing I learned as well, is it's not just about one component, but a few of them. I researched my setup on hot rod sites for a while before I got my distributor, carb, intake, fuel pump type (mechanical), etc. Sometimes, even the cam itself can make it difficult to dial things in for your ice cream cruises. I don't know much about the 347's, though, this 302 is pretty much perfect for me. I'd like a little more juice, but the ability to absolutely put my foot in it without feeling like I'm going to lose it makes a difference.

Good luck, let me know if I can help! BTW, I noticed my build site has some dead pics, so I'll try to figure out what happened. I must have moved some picasa stuff around.

[edwardb]

The carb is a Holley 650 DP HO model. It was tweaked by AED and built in August, 2005. The engine is a 347 stroker with Edelbrock Air Gap intake manifold and aluminum Dart Pro heads. Cam is a Comp Cam with .556" intake and .514" exhaust lifts. T-5 transmission with 0.82 5th gear and 3.73 rear, so the rpm's stay pretty high. The engine won't run very well below 2,000 rpm, so I guess that's why the gear ratios are the way they are. According to the dyno printout, the engine develops 445 hp at 6,100 and about 430 ft.lb from 3,300 to 5,300.

A properly tuned 650 DP is not too much carb for this motor. In fact, probably a 750 would work. Don't put an SA 570 on it. Not nearly enough carb. That's what I originally had on my 306 with AFR heads and a decent cam. Wasn't enough for that motor, and I'm probably 50 HP behind you. The Quick Fuel SS-650 DP was a perfect match for my setup.

[Blue MK3]

A properly tuned 650 DP is not too much carb for this motor. In fact, probably a 750 would work. Don't put an SA 570 on it. Not nearly enough carb. That's what I originally had on my 306 with AFR heads and a decent cam. Wasn't enough for that motor, and I'm probably 50 HP behind you. The Quick Fuel SS-650 DP was a perfect match for my setup.

Edward, after reading all the comments here, I've come to the conclusion that whatever issues I have can be resolved by having the carb tuned and that all the other engine systems (timing, compression, etc.) are OK. The worst case is to replace the carb with a duplicate or a similar 650 DP. Hopefully I'll get it in the shop tomorrow and resolve this.

[PaulW]

I had the same issue with a Holley with vacuum secondaries. The real problem is finding a mechanic these days that has even seen a carburator let alone knows how to tune one. I switched over to powerjection and haven't looked back. Infinitely tuneable and if I don't like a change I have made then I just reset to default and start over. The best part is with a laptop hooked to it and a friend in the passenger seat I can drive and we can adjust everything woith the engine under all kinds of load variables.

[Blue MK3]

I had the same issue with a Holley with vacuum secondaries. The real problem is finding a mechanic these days that has even seen a carburator let alone knows how to tune one. I switched over to powerjection and haven't looked back. Infinitely tuneable and if I don't like a change I have made then I just reset to default and start over. The best part is with a laptop hooked to it and a friend in the passenger seat I can drive and we can adjust everything woith the engine under all kinds of load variables.

I researched EFI systems and came up with four brands. Powerjection was one of them. I like the return-less fuel line aspect of the system. Switching to EFI is not out of the question if all else (fixing my Holley) fails. I have EFI on the back burner.

[Blue MK3]

Well, I'm back from the shop where I had the car checked out. The timing was off and the idle mix screws were set way too rich (which I had suspected) to compensate. The timing was reset correctly and then the screws and fuel levels adjusted. Car seems to run much more smoothly now and a lot cleaner. During the 15 mile trip from my house to the shop, the gas gauge dropped about a third of the way down. Mileage has recently been terrible, 7-8 mpg. On the way back home, it didn't appear to drop at all. Let's hope that improves. Some have said a properly tuned Holley can get 20+ mpg. We shall see after a couple of tanks are used. More later.

[Kevin Davis]

Yep, that makes sense to me, it's a bit of a ballet with these systems, air, fuel, spark, rinse, repeat. But, once you find it, I much prefer it.

[carbon fiber]

go with fast efi, looks like a carb, programs itself.

[Avalanche325]

I think you are under carbed. Most 347s with decent heads that I have seen or read about are running 750 - 800 cfm. Several started with a 650 and moved up, gaining hp in the process.

I had a holley on a 66 Mustang daily driver for 9 years without touching it after initial setup.

[tirod]

Holley has been around for a long time, and for many years was standard equipment on millions (literally) of OEM builds.

Not so much. The Holley four barrel was developed in the early '60s at Smokey Yunick's garage for NASCAR racing. It's a racing carburetor first and foremost. The design is all about access to the internal jets, which meant vertically split fuel bowls, meter plates, etc. Those create potential leak points, and the carb was intended for frequent tear down, and is high maintenance.

OEM carburetors don't do that - they have main bodies and top plates for access. Look at the Autolites, Rochesters, Carters, on and on, which outnumbered Holleys on the street ten to one in the day. Significant differences in design to prevent fuel leaks, access to jet changes not considered. That's because they are build it once and run them for 100,000 mile carburetors. Completely different design philosophy.

Holleys are popular because the people who buy them think they are a racing car part that gives them superiority on the street. As with ANY race car part used on a daily driver, the disadvantages are glossed over in the rush to brag about ownership. It's testosterone induced social ordering, I've got one, I'm better than you. The guy with the most cool parts ranks higher than him who don't, group dynamics then treats the losers as what they are.

It's NOT about which carb is actually better, Holleys are high maintenance, leaky, gasket eating, and difficult to tune. But, they rank higher with car enthusiasts in that genre, so there it goes. Run a Holley, or don't get off the porch, little boy. Group mindset.

Those who race and win with Webers and Quadrajets know different. But, those didn't resonate with American boys in the '60s, simply because of marketing. Holley won out, but you pay the price if you own one.

[mike forte]

Hi,
I think a Holley carb or any of the copies made today are good in most instances if properly selected first for what will best suit you're driving. If peak HP is desired you choose one way. If drive-ability and good manners is what you want you choose another. If mileage is important, yet another path.
Yes the Q-jet, Autolite, Carters etc are all good carbs in specific applications. Start swapping one for another and you find problems. I personally think many here would do real well with a big 2 barrel to learn the effects of changes made with jetting, power valve, accelerator nozzle changes make. When you master the 2 barrel you can proceed to a 4 barrel (I learned this way and it was fun).

Mike Forte

[edwardb]

Not so much. The Holley four barrel was developed in the early '60s at Smokey Yunick's garage for NASCAR racing. It's a racing carburetor first and foremost. The design is all about access to the internal jets, which meant vertically split fuel bowls, meter plates, etc. Those create potential leak points, and the carb was intended for frequent tear down, and is high maintenance.

My statement said "Holley has been around for a long time" not "Holley four barrels have been around for a long time." Holley has been around since the 1800's and for years did supply heavily to the OEM industry, including as far back as Ford Model T's and as recently as the '60's.

Not sure how your post including your negative opinions and usual bashing of those of us in the performance car hobby contributes anything to the OP's questions.

[carbon fiber]

i have used holley carbs for years. if properly sized to the engine, and set up properly, it will be plenty reliable. i don't know what tirod is talking about. if you go to local dragstrips here, there are everything from daily drivers to full on race cars with 4bbl holley carbs. imho, the carters and quads are the junk. i mentioned the fast efi (there are several good systems like this now) because it retains the looks of a carb, but self tunes and gets better mileage. not cheap, but the best of both worlds.

[tirod]

Edward, you are correct, Holley as a maker has been around nearly as long as cars have been driven.

The OP said: What's the reason for the infatuation with these cantankerous devices? I have one (a 650 double pumper) on my 347 stroker engine. I've had the car only two months and the carb has been irritating, at best. And poor gas mileage too. Can't seem to get it adjusted properly and when I do, it goes out again. No auto mechanic I've talked to who is reasonably knowledgeable about carbs has anything good to say about Holleys. Hard to keep in tune, not very driveable on the street, made only to run wide open, etc., etc. So what's the infatuation with them?

A lot of Holley owners aren't all that sold on them.

Having been in the hot rodding community since I bought a used '66 Mustang in the mid 70's, and having run it with continuous improvements over an 18 year period, I have experienced just how slanted the market has become recently. It's not just an observation based on owning one, but from dealing with juvenile customers across the counter over the last five years.

Juvenile isn't limited by calendar age.

[Wayne Presley]

I'd put a QuickFuel SS650-AN on it and go from there. With a vacuum advance distributor, you should be able to tune it to get 20 mpg and run great everywhere. They come pretty close on jetting out of the box.

[Blue MK3]

I appreciate the various comments and thoughts about Holley carbs. Obviously, there are a lot of different opinions out there. I haven't driven the car since it was tuned last week, except to drive it back from the shop. It's been too cold or rainy. So I'll have to wait and see how it goes from here. If it still isn't right, I'll start looking at other options.

[Greg_M]

Any idea what your AFR's were/are now while making the dyno runs? Knowing them would be a big help toward understanding the poor MPG. So the only changes were timing and idle mixture screws. I can see timing making the biggest improvement in your MPG. The idle screws not so much unless you spend a lot of time at idle.

Greg