4bbl Bogging down
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Mine is a '68 F100 long bed. I'm using the Clifford water heated intake and their 6 into 1 headers, Comp cams 268H, had the bowls in the head polished and Holley 390, Pertronix ignition. I bought my carb new and it did not have the check ball in it. For tuning the carb I found a book in the "Speedpro Series" called "How to Build & Powertune Holley Carburetors" by Des Hammil to be of great help. Especially the section on initial set-up of the carb. The problem I was having was that I was opening the primary throttle blades to far in order to have a stable idle, as a result I was losing the transition phase of the throttle sweep. What was explained in that book was that the secondary and primary throttle blades should be opened about the same amount. I closed both throttles til they were seated in their bores then opened the primary 1/2 turn on the idle screw and then adjusted the secondary idle screw to achieve the desired idle. It's easier to adjust the secondary idle screw if you have one of those right angle ratcheting screwdrivers, that way you don't have to remove the carb to get at it. I'm using 55 on my main jets and the brown spring in the secondary. I haven't had to change anything as far as the secondary metering block goes. 
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Joined: Jul 2003
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From: Nashville
Actually took a sec and called Holley, they say the 4160-8007 comes w/ the ball installed and size 51 main jets. When I get the chance I'll double tripple check to see if that ball is indeed in there. I'm running the stock cam for now, so not too sure about needing to up the primary jet size. What percentage change does each jet size make??
I'm idling fine since the ignition upgrade, but I'll take a stab at re-tuning and see if it helps anything. I've never touched the idle screw settings on the secondaries. Honestly forgot it existed. I'm a pro at tuning Quadrajets, but this is my 1st Holley.
I'm idling fine since the ignition upgrade, but I'll take a stab at re-tuning and see if it helps anything. I've never touched the idle screw settings on the secondaries. Honestly forgot it existed. I'm a pro at tuning Quadrajets, but this is my 1st Holley.
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I'm not sure what the percentage is, but the size 51 jet is 0.050" and the 55 I am using is 0.054". I also have an in dash air fuel ratio meter installed which is hooked up to an oxygen sensor in my collector pipe and a vacuum gauge in the cab. Both of these together along with a tach, helped a lot with the tuning. Good Luck. 
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Joined: Sep 2004
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I have the same manifold on my 300 and I started off with a 390 Holley and had the same secondary bog too. After endless jet changes, float level adjustments and secondary opening rate adjustments I got fed up and bought a mechanical secondary double pumper 650 cfm Holley 4010. This eliminated the problem and all I think I did tuning wise is lean out the primary jets one size. Having an accellerator pump on the secondaries is the key. I also recently installed a 1" carb spacer from Trans-dapt with some little grooves in the primaries to swirl the fuel at idle and low speeds. I would definately recommend one of these too as it really improved the low end response and smoothness and improved fuel milage by about 1mpg. They are available from Summit part #TRD-2431 The only querk I have now is a slight hesitation when making a hard right turn due to the carb sitting sideways and the fuel sloshing away from the primary jets, but I can live with that.
Last edited by noshoesreqd; Sep 13, 2004 at 01:57 AM. Reason: added info
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From: Nashville
Just got back from a 5000 mile round trip to Nevada's Black Rock Desert and the 300-6 did a bang up job of motivating the 5400lb van plus 3000lb worth of trailer and cargo.
Two changes made prior to the trip made a huge difference in overall performance and eliminated the bog under any normal driving conditions: Change #1 was installing a modern multi-spark CD ignition box. The factory duraspark II and it's low voltage coil just wasn't enough to properly ignite the heavy charge when the secondaries were open. The van now runs better at all RPM ranges.
Change #2 was switching from a 3.00 rear end to a 3.50. Not a huge gear change but boy did it make a difference towing. This year we could maintain 65mph in 3rd gear up grades that slowed us to 45-50 mph in 2nd in previous years. In relation to the bog problem, with the 3.00 gear the vacuum vs. rpm curve was such that the secondaries were opening too soon unless the heaviest [black] spring was installed. Problem is [was], with the black spring the secondaries won't ever open fully so you lose top end power. Now running the brown spring and things seem pretty well balanced for both daily driving and towing. FWIW: gas mileage was not harmed by the lower gear.
Two changes made prior to the trip made a huge difference in overall performance and eliminated the bog under any normal driving conditions: Change #1 was installing a modern multi-spark CD ignition box. The factory duraspark II and it's low voltage coil just wasn't enough to properly ignite the heavy charge when the secondaries were open. The van now runs better at all RPM ranges.
Change #2 was switching from a 3.00 rear end to a 3.50. Not a huge gear change but boy did it make a difference towing. This year we could maintain 65mph in 3rd gear up grades that slowed us to 45-50 mph in 2nd in previous years. In relation to the bog problem, with the 3.00 gear the vacuum vs. rpm curve was such that the secondaries were opening too soon unless the heaviest [black] spring was installed. Problem is [was], with the black spring the secondaries won't ever open fully so you lose top end power. Now running the brown spring and things seem pretty well balanced for both daily driving and towing. FWIW: gas mileage was not harmed by the lower gear.
