Holley 4010 tuning

[svocapri]

My Dad and I installed a Holley 4010 on his 83 Capri back in the late 80's and that was the first carburetor I ever worked on. I now have a few of these Holley 4010 carburetors and I want to get the one on my 85 working better. I have always thought that the low speed jets were too rich, and I have to set the idle screws at 1/4 turn out to get it lean enough at idle. Since I have accumulated some spare 4010 parts, i am going to try my hand at significantly altering this carb for the better.

I have started by going through the carb, cleaning all the passages, replacing gaskets, installing new needle and seat valves, and installing a new power valve. I also installed new throttle shafts since the originals didn't have provisions for the throttle shaft seals and I wanted to seal it up a little better. While doing the basic rebuild, I measured and photographed all the jets and air bleeds to establish the baseline which I have recorded below. Once I get the carb back on the car, I'll drive it and datalog the AFR as well as report the driving characteristics.

Hopefully some of the carb gurus on this site will be able to help me out.


Primaries
.038 low speed jet
.044 first low speed air bleed
.055+ low speed emulsified jet
.044 second low speed air bleed

# 66 main jet
.022-5 main well air bleed
.044 anti siphon air bleed
.041 power valve channel restrictor
6.5" power valve

.034 accel pump nozzle
218 accel pump cam

Secondaries
.038 low speed jet
.044 first low speed air bleed
.055+ low speed emulsified jet
.044 second low speed air bleed

#76 secondary jet
.022-5 main well jet
.044 anti siphon jet

.034 accel pump nozzle
234 accel pump cam

[Walking-Tall]

What's the LIST #? ... right off the top of my head, if this is some kind of 600cfm, the ".038 low speed jet" is jumping off of the page... incredibly similar to a Autolite/Motorcraft carburetor... if we're talking about a 1-9/16" throttle bore 600cfm variation of a four barrel, that needs to be 0.028", or preferably 0.026" for good sensitive function of the idle mixture screws, as well as in combination with the correct size idle air bleed for lean/best off idle cruise fuel efficiency... why do you think the orifice in the first picture, seemingly at the base leg of the booster, which is connected to the main well not the idle well, is the "low speed jet"? In Autolite/Motorcraft carburetors I have worked with, the restrictions in your third picture are the equivalent to modular Holley's idle feed restrictions (and similar to dickheads today creating fancy multiple "e bleed" metering blocks with the idle feed restriction up above the fuel level, where it very simple function gets messed with by air from the idle air bleed)... and with an Autolite/Motorcraft carburetor, whichever is the air bleed for the idle well is what experimenting is needing done with, to find lean/best fuel efficiency...

[svocapri]

What's the LIST #? ... right off the top of my head, if this is some kind of 600cfm, the ".038 low speed jet" is jumping off of the page... incredibly similar to a Autolite/Motorcraft carburetor... if we're talking about a 1-9/16" throttle bore 600cfm variation of a four barrel, that needs to be 0.028", or preferably 0.026" for good sensitive function of the idle mixture screws,

The choke horn is stamped R84012 and below that is stamped D240. It was purchased new as a 600 CFM mechanical secondary carb. The throttle bores measure 1.675, while the venturi measures 1.250. The throttle plates are stamped 172 & 173. I have two of these and an additional set of booster clusters so I went through the booster clusters I have and chose one stamped 1 and one stamped 2 beacuse of their smaller accel pump squirters and low speed emulsified jet. The others I had were stamped 21, 32, & 34. #1 & #2 measured as follows.

#1
.??? low speed jet
.046 first low speed air bleed
.045 low speed emulsified jet
.044 second low speed air bleed
.022-5 main well air bleed
.046 anti siphon air bleed
.025 accel pump nozzle
1.100 emulsion tube length from boss

#2
.038 low speed jet
.044 first low speed air bleed
.058 low speed emulsified jet
.044 second low speed air bleed
.022-5 main well air bleed
.046 anti siphon air bleed
.025 accel pump nozzle
1.175 emulsion tube length from boss

why do you think the orifice in the first picture, seemingly at the base leg of the booster, which is connected to the main well not the idle well, is the "low speed jet"?

I had removed the idle tubes and emulsion tubes in that picture, but as you can see here the idle tube feeds to the orifice I had labeled as low speed jet. On the Summit version of this carb, the emulsified low speed jet is replaceable and Summit calls that the Idle jet. It does have an air bleed on the downstream and upstream side of it though. I think I want to plug the bottom of the idle tubes with a lead solder ball and then drill it to a .026 like you were suggesting, and see if effectively moving the idle jet under the fuel level would improve things. What do you think?



Here is a picture with the Emulsion tubes and the idle tubes.

[Walking-Tall]

I misspoke above (it's been a while since crawling around inside the Autolite/Motorcraft style circuits, lol), the outer, upper brass restrictions are known as IDCRs (idle down channel restrictions)... and a peek at the Holley Numerical Listing for R84012 shows what I thought right away for number 172 & 173 throttle plates, that the throttle bores on that carburetor are the same as 750/780cfm vacuum secondary and (up to) 800cfm double pumpers, with 1-11/16" throttle bores & with 1-1/4" venturi diameters... and the rest of the listed factory specs are 67 primary jets, 77 secondary jets, 6.5"Hg power valve, and 0.026" accelerator pump shooter sizes...

Oh, I see now (like I said, it's been a while), and yes, putting the only or 1st of idle fuel restrictions below the fuel level is always best for rock steady (metering/controlling fuel only, not fuel and air, and therefore not getting affected erratically by air getting behind the restriction from the idle air bleed when mounted above the fuel level, especially an issue with bumpier camshafts) of idle and off idle (fuel mileage) air:fuel ratios. In a traditional modular Holley, an efficient and ideal primary idle feed restriction starting point though for 1-11/16" throttle bores is 0.031", in combination with a 0.070"-ish idle air bleed. What is the restriction size at the bottom of the small brass tubes now?

[Walking-Tall]

Some more thoughts... with multiple idle circuit air bleeds like that, their combined areas for each barrel need to be considered. Two 0.044" air bleeds have the equivalent area to a single 0.062" bleed, at 0.003 square inches... with only that amount of air bleed area, if I had to guess, the openings in the bottoms of those tubes are likely less than 0.031"...? ... because approximately the same amounts of idle transition air:fuel can be had with smaller/smaller and bigger/bigger feeds and bleeds, with a smaller combo hanging on later into the transition of throttle opening, and bigger combos signing off transition air:fuel sooner, ideally either situation happening prior to or with a bit of overlap to the main boosters going into action... and I see that in addition to 1-1/4" venturi diameters, it's got annular boosters, which depending also on main air bleed sizing, but probably fire up pretty responsively and quickly... Experimenting some with idle feed/bleed sizes is where you can dial in perfect amounts of lean/best transition fueling for maximum fuel efficiency, and a usually slightly necessary richer idle air:fuel mixture is adjusted with the idle mixture screws.

[svocapri]

Mike, this is some great info. Thanks! I got the car running yesterday and took it for a longer drive. I haven't yet tried the modified booster clusters with the plugged and drilled idle tubes as I wanted to get a baseline down first. My observations so far is that it runs decent, but a little rich at idle and no/low load. It idles at 13.5 AFR and when crusing slow with the trottle almost closed it is between 12.5 and 13. One problem I am seeing is that low RPM and high load goes very lean (over 17-1 AFR) and it has backfired a couple of times if I open the throttle too fast. I think I might need to go with a 10.5 or 11 power valve as it starts to lean stumble on acceleration once it gets down around 10 InHG. It may also need more accelerator pump shot but I want to dial back the idle jet and air bleeds first. I am surprised though, if I open the throttle slowly in 5th, it will pull up a hill at almost 17-1 AFR with barely a hint of lean surge.

I am modifying the #21 booster cluster with screw in Accel pump nozzles, and the plugged & drilled idle tubes. I think I'll start with .025 Accel Pump squirters, and .028 idle jets. We'll see if that gets me close to stupid lean. One thing I want to accomplish is to fatten the mixture as it transitions to the main circuits as I think it is going lean there, but I'll know more when I change to my modified booster clusters.

[Walking-Tall]

I am surprised though, if I open the throttle slowly in 5th, it will pull up a hill at almost 17-1 AFR with barely a hint of lean surge.

One thing I want to accomplish is to fatten the mixture as it transitions to the main circuits as I think it is going lean there, but I'll know more when I change to my modified booster clusters.

That is the ideal situation to look for. The load is the most it's gonna get when you're in 5th gear, but the actual loading really is only moderate with easy part throttle acceleration, where fueling is still coming from only from the idle transition circuit, not yet the main circuit. ... and yes, pay attention to the vacuum levels and rpm, so you know whether still operating from the idle circuit's transition or the main circuit. Finding out at what rpm in the driveway when the boosters begin to provide the fueling is good to know for all this as well.

Don't fatten things (idle circuit feeds/bleeds) up too much at a time, or more than one small step at a time, and reset the idle mixture screws after each change and then take 'er for a spin. As long as there's no complaints with light part throttle acceleration and moderate loading, however lean it will smoothly run, upwards of or more than 17:1, it will happily and safely do so. Whatever makes it run best is right, and most rewarding, very fuel efficient. The high load and richer main circuit (approx. 12.5:1) AFR is much more important for the WOT business. Doesn't hurt to make a bit of a big jump up (say +0.005" at a time) with idle air bleed and find the stupid lean area, so you know where it is, and then shrink idle air bleed down (say -0.002" at a time) until you find the sweet spot.

[cb84capri]

Did you figure out the backfiring issue you had earlier this year? Are you getting away from the holley/megasquirt setup that was on this car?

Cale

[svocapri]

Did you figure out the backfiring issue you had earlier this year? Are you getting away from the holley/megasquirt setup that was on this car?

Cale

The backfiring issue seems to have been a bad mismatch between the Holley TBI and the old DART heads which had no exhaust gas heat crossover. The Holley TBI injectors spray fuel in a conical shape against the walls of the TBI and then the fuel gets picked up by the high velocity air passing by the throttle blades. Once the throttle blades come open, the velocity is too slow to pick up the fuel, and it just dribble's down the walls of the throttle barrel and onto the floor of the manifold. Once the engine speed comes up and the air velocity increases, then the fuel gets sucked off the walls of the throttle body. I verified this by purchasing a Nascar take off restrictor plate on eaby and putting that under the throttle body. The conical shaped four hole 1 inch spacer increased the air velocity and changed the backfire to a stumble. It also restricted the engine (Like it was intended to do) and made the engine feel weak at the top end.

After figuring out all this, I put the Holley 4010 carb on it and found out that the secondary accelerator pump passage was plugged. That is why it was also backfiring with the carburetor. I got all that fixed and rigged up a TPS on the 4010 so that the Megasquirt can data log everything, and it still controls timing.