Carb Tuning
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Re: Carb Tuning
It can improve vaporization and idle quality If the hole in the butterfly is located so the jet of air issuing from the hole impinges on the fuel discharge from the curb idle and T-slot. Locate the hole midway between the throttle shaft screw closest to the idle discharge port and the bore wall. Put a drill bit in the curb idle discharge port and eyeball it while you think about the most likely best location for the hole so the jet of air can do the most good. Withing reason, the closer the hole in the butterfly is to the idle fuel stream, the better mixing of the air and fuel there will be.
Locating the hole on the opposite side of the throttle shaft, toward the center of the carb on the downstream side of the butterfly, admits the dry air where it has less chance of mixing with the idle fuel, such that the A/F mixture in the manifold will be more stratified, less homogenized.
A carb arranged to include air bleeds in the center around the air cleaner stud (like some modifiers do to Dominators) locates that dry air entry in the center of the carb about as far from the idle fuel entry as it can be.
A similar problem of a less thoroughly mixed A/f charge occurs when the secondary butterfly is open too far with no accompanying fuel to mix with the air at the location of air entry. The OE carbs that were for sporty cam engines, such as the R-2818 on '64 & '65 350-365 HP 327, incorporate a "poor man's curb idle discharge", which is an auxiliary idle discharge orifice in the secondary bore in similar location and orientation as the primary curb idle discharge orifice, and is connected to the primary curb idle by the "snake passage" in the top side of the base, which traverses around the bores to connect the secondary auxiliary discharge port to the primary, so both are adjusted by the primary curb idle screw. If the carb base has the "snake passage" a discharge orifice can be drilled in the secondary so idle fuel enters the manifold with the air from the secondary throttles if the secondary needs to be opened some to allow closing the primary some correct an excessive primary T-slot exposure.
Locating the hole on the opposite side of the throttle shaft, toward the center of the carb on the downstream side of the butterfly, admits the dry air where it has less chance of mixing with the idle fuel, such that the A/F mixture in the manifold will be more stratified, less homogenized.
A carb arranged to include air bleeds in the center around the air cleaner stud (like some modifiers do to Dominators) locates that dry air entry in the center of the carb about as far from the idle fuel entry as it can be.
A similar problem of a less thoroughly mixed A/f charge occurs when the secondary butterfly is open too far with no accompanying fuel to mix with the air at the location of air entry. The OE carbs that were for sporty cam engines, such as the R-2818 on '64 & '65 350-365 HP 327, incorporate a "poor man's curb idle discharge", which is an auxiliary idle discharge orifice in the secondary bore in similar location and orientation as the primary curb idle discharge orifice, and is connected to the primary curb idle by the "snake passage" in the top side of the base, which traverses around the bores to connect the secondary auxiliary discharge port to the primary, so both are adjusted by the primary curb idle screw. If the carb base has the "snake passage" a discharge orifice can be drilled in the secondary so idle fuel enters the manifold with the air from the secondary throttles if the secondary needs to be opened some to allow closing the primary some correct an excessive primary T-slot exposure.
Re: Carb Tuning
It will lean the A/F from the T-slot at small throttle opening and high vacuum such as level road cruise up to about 40 or perhaps 50 MPH and make the idle mixture screw leaner and less sensitive. If the bleed is threaded you should try it out to see how lean the engine will run and then just richen it enough it doesn't act stupid. If the bleed isn't threaded, thread it and get some set screws, make bleeds.
Re: Carb Tuning
This engine likely just needs more initial base timing at idle. Before drilling this that and the others, give it ALL the base spark advanve it wants at idle.
If the cam is 228 or bigger lock out the diz mech advance set at 32-36 ish. Locked. Now set up the carb.
Especially with a stock stall converter.
Pcv valves are not all the same. A cammed up motir will want a different pcv ,han a stock cammed motor.
No need to drill throttle blades.
If the cam is 228 or bigger lock out the diz mech advance set at 32-36 ish. Locked. Now set up the carb.
Especially with a stock stall converter.
Pcv valves are not all the same. A cammed up motir will want a different pcv ,han a stock cammed motor.
No need to drill throttle blades.
Re: Carb Tuning
This motor will likely end up wanting 26 to 36 base idle timing.. 18 is not enough. Give it all it wants.
Re: Carb Tuning
Cam is:
229 deg at .050, .533" lift both intake & exhaust.
Events are:
11.5 deg IO
37.5 deg IC
47.5 deg EO
1.5 deg EC
13 deg overlap at .050 lift
Current set up uses 17 degrees initial with the lightest springs that Cranes send with the adjustable vac advance kit. This gives about: (I'm at work notes at home). Vac advance is using ported vacuum which is working better that full manifold vac FOR ME, (not saying this is always best). Vac advance is crane unit that is adjusted to never spark knock on small hills, not sure how many total degrees it adds with current setting, but it is all it can stand without spark knock.
650 rpm=17 deg BTDC
1000 rpm=17 deg BTDC
1500 rpm=17 deg BTDC
2000 rpm=20 deg BTDC
2500 rpm=25 deg BTDC
3000 rpm=30 deg BTDC
3100 to 6500 rpm=31 deg BTDC
I am told by cam guy that engine should need 29 to 32 degrees BTDc max.
Fbird & anybody else, please tell me the timing curve you suggest.
timing BTDC at 650 rpm in gear?
BTDC at 1000 rpm?
BTDC at 1500 rpm?
BTDC at 2000 rpm?
BTDC at 2500 rpm?
BTDC at 3000 rpm?
BTDC at 3500 rpm?
Thanks!
229 deg at .050, .533" lift both intake & exhaust.
Events are:
11.5 deg IO
37.5 deg IC
47.5 deg EO
1.5 deg EC
13 deg overlap at .050 lift
Current set up uses 17 degrees initial with the lightest springs that Cranes send with the adjustable vac advance kit. This gives about: (I'm at work notes at home). Vac advance is using ported vacuum which is working better that full manifold vac FOR ME, (not saying this is always best). Vac advance is crane unit that is adjusted to never spark knock on small hills, not sure how many total degrees it adds with current setting, but it is all it can stand without spark knock.
650 rpm=17 deg BTDC
1000 rpm=17 deg BTDC
1500 rpm=17 deg BTDC
2000 rpm=20 deg BTDC
2500 rpm=25 deg BTDC
3000 rpm=30 deg BTDC
3100 to 6500 rpm=31 deg BTDC
I am told by cam guy that engine should need 29 to 32 degrees BTDc max.
Fbird & anybody else, please tell me the timing curve you suggest.
timing BTDC at 650 rpm in gear?
BTDC at 1000 rpm?
BTDC at 1500 rpm?
BTDC at 2000 rpm?
BTDC at 2500 rpm?
BTDC at 3000 rpm?
BTDC at 3500 rpm?
Thanks!
Re: Carb Tuning
With the stated stock torque converter lock out the mech advance curve. Set timing at 32-34 deg. Fixed. At idle.
Set up carb. Remove carb and flip it over and pre set the primsry and secondary throttle idle setting so that about .020" of the edge of the idle transfter slot is just showing at the throttle blade edge at idle on all 4 barrels.
Use a 4.5" rated power valve. Install and set up
Set idle mixture screws for best idle quality and manifold vacuum at idle not by afr.
Minor idle air bleed size tuning may be required.
Start with a .062" primary IAB and tune the finished size by hand with the drillbit as required based on the near off idle transition by afr. Around 14.7:1. It need not be exact but in the zone of 14.7:1 in the off idle transition.
Use ported vacuum advance limited to about 12 deg max limit. The rate in and out based on throttle input while driving the car has to be found and adjusted by drive testing the car.
Do this all first, dial it in and report.
This will get yu 98% there.
Set up carb. Remove carb and flip it over and pre set the primsry and secondary throttle idle setting so that about .020" of the edge of the idle transfter slot is just showing at the throttle blade edge at idle on all 4 barrels.
Use a 4.5" rated power valve. Install and set up
Set idle mixture screws for best idle quality and manifold vacuum at idle not by afr.
Minor idle air bleed size tuning may be required.
Start with a .062" primary IAB and tune the finished size by hand with the drillbit as required based on the near off idle transition by afr. Around 14.7:1. It need not be exact but in the zone of 14.7:1 in the off idle transition.
Use ported vacuum advance limited to about 12 deg max limit. The rate in and out based on throttle input while driving the car has to be found and adjusted by drive testing the car.
Do this all first, dial it in and report.
This will get yu 98% there.
Re: Carb Tuning
.062" is common. 1/16".
Solder up a pair of spair idle air bleeds and redrill to 1/16". .062". Start with this and then hand hone the hole to open it up as required to get acceptable off idle throttle transition afr. Need not be exact. But around 14.7 ish. You just want to set up the idle air bleeds so that the afr does not shift too far rich or lean as you open the throttle from base idle. As long as the afr stays in a aceptable range and the car drives nicely at various part throttle speeds it is good. Do all road testing with the air cleaner installed. Ya it matters.
Solder up a pair of spair idle air bleeds and redrill to 1/16". .062". Start with this and then hand hone the hole to open it up as required to get acceptable off idle throttle transition afr. Need not be exact. But around 14.7 ish. You just want to set up the idle air bleeds so that the afr does not shift too far rich or lean as you open the throttle from base idle. As long as the afr stays in a aceptable range and the car drives nicely at various part throttle speeds it is good. Do all road testing with the air cleaner installed. Ya it matters.
Last edited by F-BIRD'88 on Tue Oct 02, 2018 4:31 pm, edited 2 times in total.
Re: Carb Tuning
This cam 229@.050" 108 lsa. 103/113 will want a 3500 4500 stall converter when in a 302w cid ford sb.
But this setup is about as good as it will get with a "stock" low stall converter.
But this setup is about as good as it will get with a "stock" low stall converter.
Re: Carb Tuning
You must physically limit the travel stop of the vacuum advance to about 12 degress (crank) 15 max limit.
Then dial in the rate of vac adv
Then dial in the rate of vac adv
Re: Carb Tuning
Ford electronic ignition boxes have a built in easy start ignition retard function to allow easy hot restart with this agressive idle base timing. I believe it is the white wire on the oem box. Use it. It retards the base spark adv while cranking. Goes on the ford starter solenoid.
Re: Carb Tuning
Thanks for your input Fbird. I just happen to have a 750 vac secondary carb on hand that is gathering dust.
How do I know where to stop with the max total timing so that I don't hurt the motor?
You are correct on the ford start retard, mine retards 5 degrees. I have used it as a retard for nitrous in the past.
How do I know where to stop with the max total timing so that I don't hurt the motor?
You are correct on the ford start retard, mine retards 5 degrees. I have used it as a retard for nitrous in the past.
Re: Carb Tuning
What is the list number of your 750 holley vac sec carb?
Its stamped on the choke horn.
The recent edelbrock 650 AVS2 carb would be another good choice carb for this motor.
This car needs a high stall converter.
That cam is intended for a 5 sp man trans and lots of gear. Or a auto with a 3500+ stall converter and gears.
Its stamped on the choke horn.
The recent edelbrock 650 AVS2 carb would be another good choice carb for this motor.
This car needs a high stall converter.
That cam is intended for a 5 sp man trans and lots of gear. Or a auto with a 3500+ stall converter and gears.
Re: Carb Tuning
I cannot see your vac adv mechanism to tell u how to max limit the travel stop to 12 deg. Verify it with a timing light while applying vacuum to the diz vac advance while running. To get it right.
This car with 10.4:1 cr will need 92+ octane gas.
This car with 10.4:1 cr will need 92+ octane gas.