Holley Carb - Running too rich

[Mike Van Veghten]

Inches of vacuum, not PSI (pounds per square inch).

Mike

[thunderations]

I'm betting that any good power valve would work a whole lot better then a blown one. Those things are available at any parts store and are probably the generic value that is used in rebuild kits. When I was driving early T-Birds I had a couple extras in trunk at all times. One little belch and half the time the power valve was toast.
To get other value valves would probably require going to a performance center of some sort.

[bensherb]

First, the Carter AFB used by the factory on the '63-'64 GT, 289 CI is a spread bore rated at 637 CFM. It has 1 7/16" primary throats with .089 primary jets ,and 1 11/16" secondary throats with .077 secondary jets and a metering needle/rod of .069 in the cruise portion and .058 in the power portion.

The 390 Holley is not intended for a full size V8, it is made for 4 and 6 cylinder engines. It worked great on my 2 liter (122ci) Ford Pinto and in fact my '63 VW has more carb than that, (584cfm, two 2bbl carbs at 292cfm each) on it's 2110cc (129ci) air cooled engine.

A Holley 1850, 600cfm vacuum secondary carb would be a much better choice. It too is a 4160 and all but identical to the 390 you have but will pass more air. (it's cheaper too) If you talk to Holley they will tell you an engine that large will run rich with a 390 on it, it simply won't pass enough air. It's intended for engines around 200ci and smaller.

Remember, unless you drive at full throttle all the time, you only have a 195cfm carb on there. The Holley 600 is extremely common, you should be able to get one at a swap meet for $20-$40. $30 for a rebuild kit and you're good to go; really go; and should get better fuel mileage too. New they're $275-$310.

The power valve in the Holley preforms the same function as the metering rods in the Carter do. The vacuum value number marked on them indicates the manifold vacuum reading at which it will open. Low speed circuit transition can be tailored by changing the value of the power valve. similar to changing the metering rod springs in the Carter.

To test the power valve: While at idle, turn your Idle mixture screws all the way in. If the engine dies, the power valve is not blown.

[altair]

I don't know anything about a Holly but I guess it has two floats and two needle valves, possibly a needle valve is leaking. I have a Carter with two floats and two needles and one needle was leaking causing a rich mixture.

[JoeHall]

First, the Carter AFB used by the factory on the '63-'64 GT, 289 CI is a spread bore rated at 637 CFM. It has 1 7/16" primary throats with .089 primary jets ,and 1 11/16" secondary throats with .077 secondary jets and a metering needle/rod of .069 in the cruise portion and .058 in the power portion.

The 390 Holley is not intended for a full size V8, it is made for 4 and 6 cylinder engines. It worked great on my 2 liter (122ci) Ford Pinto and in fact my '63 VW has more carb than that, (584cfm, two 2bbl carbs at 292cfm each) on it's 2110cc (129ci) air cooled engine.

A Holley 1850, 600cfm vacuum secondary carb would be a much better choice. It too is a 4160 and all but identical to the 390 you have but will pass more air. (it's cheaper too) If you talk to Holley they will tell you an engine that large will run rich with a 390 on it, it simply won't pass enough air. It's intended for engines around 200ci and smaller.

Remember, unless you drive at full throttle all the time, you only have a 195cfm carb on there. The Holley 600 is extremely common, you should be able to get one at a swap meet for $20-$40. $30 for a rebuild kit and you're good to go; really go; and should get better fuel mileage too. New they're $275-$310.

The power valve in the Holley preforms the same function as the metering rods in the Carter do. The vacuum value number marked on them indicates the manifold vacuum reading at which it will open. Low speed circuit transition can be tailored by changing the value of the power valve. similar to changing the metering rod springs in the Carter.

To test the power valve: While at idle, turn your Idle mixture screws all the way in. If the engine dies, the power valve is not blown.

The original WCFB on the 352 CID V8 motor in 1956 Stude Golden Hawk was 385 CFM, and it ran 120-130 MPH from the factory. For years, I have ran 450 CFM, "baby 4 barrel" Holley 4360s on 56Js. Either carb feeds the 352 plenty of air.

I have also ran 500-650 CFM AFB type carbs on 352 motors. I like the more responsive, larger primaries, but at WOT there is little difference from the 385 or 450 CFMs.

Have also ran a 600 CFM Holley, with vacuum operated secondaries on 352 for awhile. OK, but just OK.

I have an old Holley book that tells of model 4360 tests on several GM, 350 CID motors, and one 402. In every test, it got better MPG than the original Q-jet, with only minor drop in HP and torque. That is consistent with my experience, in comparing them with larger carbs.

In your assertion the 390 Holley is not large enough for a 259/289, maybe you are thinking they live at higher RPMs. Most of them live at 2000-3000, with shifts around 3000-3500.

[bensherb]

I very very rarely drive at WOT so the primary response is of far more importance to me. However having run Holley's with both mechanical and vacuum secondaries, I will say the secondary response is far more evident with mechanical secondaries, which I'm sure is part of the reason for the vacuum secondaries in the first place as well as why the MPG is better with vacuum secondaries.

I also replaced a Q jet with a Holley 600 vac, on a 350 Chevy. I found the normal drive ability to be improved, and literally doubled the MPG with only a small loss of secondary response due to the vacuum secondaries. On that same vehicle a 650 Holley mechanical secondary carb performed much like the Q jet but with slightly better primary response and a 30% improvement in MPG.

I currently have a 390 with a Holly 600 vac on it and it runs great and gets decent mileage, I could trade MPG for performance with a different carb but nobody wants less MPG on a street car. I also have a 390 with one 320 cfm 2v (venturi, re:2 barrel) Holley and two 350 cfm 2v Holley's on it. Now, that sounds like it would be a total of 1020 cfm right? Well, yes and no. 2v and 4v carbs are flowed differently. 2v carbs are flow tested at 3" of mercury and 4v carbs are tested at 1.5". To make an accurate comparison of a 2v to a 4v carb, take the total of the 2v and divide by 1.414. So the total of the three 2v carbs on my 390 is equal to a single 721cfm 4v carb. This is a factory set up on this engine.

My intent was not to intimate that a 390 carb is too small for an engine of 259/289ci displacement, but that this particular carb is too small. Again, call Holley they will tell you the same thing, and that it will run rich with this carb. Changing jet sizes may help, but this carb is just not meant for this application. I have seen it run in pairs on full size V8's successfully when the owner wanted the look but didn't need more carb.

I figure if Studebaker felt that a 637cfm 4v carb was the best choice when they installed the AFB on the '63 289ci, when they had hundreds of different ones to choose from, (carter made 505 different AFB's) why reinvent the wheel? They already did most of the work. At least to the size of the carb. FYI, Carter's "auxillery air valve", used on almost all AFB's, is basically the same as Holley's "vacuum" secondaries, basing secondary air flow on engine demand instead of the drivers whim. On motorcycles they call carbs that work like this a "constant velocity" type carb.

Personally I prefer the simplicity of the Holley over the Carter, which explains why my GT is the only car I have with a Carter carb. Except for my VW's which all have Weber's all the rest of them have Holley's.

[Kato]

Thank you gentlemen, you have offered some tremendously good advice here. I obviously need to do a little more research and possibly a different carb is in order here.

[bezhawk]

Don't guess at what you need. We can keep arguing over what to do, and what carb is right for your application. They are ALL wrong....to a certain extent. You need to see what your particular carb is putting into the engine. The BEST way to do this is with a AFR gauge. All other ways is just educated guess work. It doesn't matter what CFM you are running as long as stoichiometric AFR is achieved.

[jpepper]

The 350 CFM Holley flows more air than the Stromberg 2 barrel as used on a 289. A small carburetor will restrict upper RPM limits. Part throttle response should be great. Your rich idle is no doubt a ruptured power valve. Use Holley parts kit not an off brand. I used a 6.5 in stock Studebaker applications. It is a simple carburetor. Carb and choke cleaner will soften metering block gaskets allowing them to be removed with a soft brass brush.
I once used a 500 CFM Holley on a 429 Ford engine. It worked great except the engine laid down at about 5000 RPM because the small carburetor was an airflow restriction.

[Lynn]

Joe Hall is on the money.

I would CERTAINLY try to fix that carb before replacing with something bigger. You have an engine with 289 CI. Think about how many Ford 289's were built with 2 barrel carbs smaller than your Holley.

Absolutely no reason you can't dial that carb in to work great. In fact, even with a bigger carb, you would NOT UNDER ANY CIRCUMSTANCES ACHIEVE HIGHER HP at anything under 4800 RPM. On top of that, you COULD add new problems with mid range response.

How much time do you spend above 4800 rpm? If the answer is anything under 5% of the time (and I suspect it is less than 1%) you will be much better off with the current carb.

One of the biggest "hot rodding" mistakes is following "MORE'S LAW" which simply put is: "If some is good, more is better." More's Law is a farce. It is matched components that make a great driver.

PV is a good start. Do some research. Those Holleys have lots of adjustability. You won't be doing yourself a favor by going with a bigger carb. That one is matched just fine for your 289. Just needs to be in good working order and possibly dialed in. Then again with a new PV, may be spot on just as it is.

[Kato]

Don't guess at what you need. We can keep arguing over what to do, and what carb is right for your application. They are ALL wrong....to a certain extent. You need to see what your particular carb is putting into the engine. The BEST way to do this is with a AFR gauge. All other ways is just educated guess work. It doesn't matter what CFM you are running as long as stoichiometric AFR is achieved.

The 350 CFM Holley flows more air than the Stromberg 2 barrel as used on a 289. A small carburetor will restrict upper RPM limits. Part throttle response should be great. Your rich idle is no doubt a ruptured power valve. Use Holley parts kit not an off brand. I used a 6.5 in stock Studebaker applications. It is a simple carburetor. Carb and choke cleaner will soften metering block gaskets allowing them to be removed with a soft brass brush.
I once used a 500 CFM Holley on a 429 Ford engine. It worked great except the engine laid down at about 5000 RPM because the small carburetor was an airflow restriction.

Joe Hall is on the money.

I would CERTAINLY try to fix that carb before replacing with something bigger. You have an engine with 289 CI. Think about how many Ford 289's were built with 2 barrel carbs smaller than your Holley.

Absolutely no reason you can't dial that carb in to work great. In fact, even with a bigger carb, you would NOT UNDER ANY CIRCUMSTANCES ACHIEVE HIGHER HP at anything under 4800 RPM. On top of that, you COULD add new problems with mid range response.

How much time do you spend above 4800 rpm? If the answer is anything under 5% of the time (and I suspect it is less than 1%) you will be much better off with the current carb.

One of the biggest "hot rodding" mistakes is following "MORE'S LAW" which simply put is: "If some is good, more is better." More's Law is a farce. It is matched components that make a great driver.

PV is a good start. Do some research. Those Holleys have lots of adjustability. You won't be doing yourself a favor by going with a bigger carb. That one is matched just fine for your 289. Just needs to be in good working order and possibly dialed in. Then again with a new PV, may be spot on just as it is.

I never realized there were so many opinions on carburation! Makes good sense that the AFR is the only way to know for sure the carb is right. Also makes sense that if the 2bbl Stromberg were enough then this Holley should be as well, except at high rpm, which as you say is rarely encountered. Even as is the car runs down the road pretty well. It is the rich idle that is the biggest issue which hopefully is nothing more than the PV. One other concern I have is that this car runs nice and cool. On a very hot day last summer (90F +) with the AC running the car barely got above 180. Can't help but wonder if the rich running carb is part of the reason or hopefully just a good clean engine interior and rad!

Thanks again for all of the great advice, I've learned a lot from this thread. So appreciative that you guys share your wealth of knowledge!

[Dan Timberlake]

This is what Chevy says a 4 bbl carb did for the 265 at full throttle in 1955.

[Kato]

This is what Chevy says a 4 bbl carb did for the 265 at full throttle in 1955.

Big difference!

[junior]

Big difference!

I would be willing to bet that most of that difference is due to the dual exhaust, not the addition of the 4bbl. Just saying. cheers, junior