Carb Tuning

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F-BIRD'88
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Re: Carb Tuning

Post by F-BIRD'88 » Sun Oct 07, 2018 9:22 pm

So when you are driving along steady speed, at cruise at a speed high enough to be on the pri main jets, what is the AFR?

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Re: Carb Tuning

Post by BobbyB » Mon Oct 08, 2018 6:41 am

14.5 to 15.5

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Re: Carb Tuning

Post by BobbyB » Mon Oct 08, 2018 7:39 am

Tuner, do you remember how much vacuum you had at idle with your 289?

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Re: Carb Tuning

Post by F-BIRD'88 » Mon Oct 08, 2018 2:02 pm

Tuner can show you a few good tricks and mods to make the 3310 into a even better carb.

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Re: Carb Tuning

Post by BobbyB » Tue Oct 09, 2018 8:01 pm

I put a 4.5 power valve in the 750 carb and tried to test it but could not get it to idle at all. I think the front needle seat is leaking. (Today was the first time the carb ever had fuel in it since I bought it new in 1988ish.)
So, I upped the front main jets in the 650 quick fuel from 66 to 67 & went for a spin. Car drove great with afr at cruise from about 14.3 to 15.3 in the 25 miles I drove today. Did not try wot today.
Not sure when I might be able to get back on the 750.
Thanks for all the input you guys gave me.

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Re: Carb Tuning

Post by Tuner » Sun Oct 21, 2018 4:31 pm

BobbyB wrote:
Mon Oct 08, 2018 7:39 am
Tuner, do you remember how much vacuum you had at idle with your 289?
18-20" Hg. It was a stock '66 220 HP 289. The difference in advance curve for your engine vs. a stock (non smog) engine is sporty cam timing needs more timing at idle and below 1500 RPM. The stock engine timed at 6 initial instead of 18 and the primary spring let it advance from 6 degrees at 600 or 700 to 18 or so at 1500. Sporty and radical cams simply need more initial, but the curve above 2000 will be similar to a mild cam stock engine. Engines almost always want the same advance curve in the power band, usually adding 1-1/2 to 2 degrees per 1000 RPM from the torque peak up to the power peak and beyond. Some engine want more, some less, but they nearly all run better with a full RPM range curve than locked timing. Besides optimizing advance for best torque and power, when the advance mechanism does not hit a mechanical stop the weight and spring mechanism acts as a pendulous absorber and isolate the timing trigger from engine torsional noise.

What did you get worked out with the carbs? If you want to use the 750 vac. sec. it will need the little nipple in the choke-side primary bore that amplifies the secondary opening signal.

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Re: Carb Tuning

Post by BobbyB » Tue Oct 23, 2018 8:00 am

Between hurricanes and cold weather, I have not driven the car in over a week. The last change I made was to give the crane adjustable vacuum advance 2 turns clockwise to increase total vacuum advance. The change seems to have made it even better at cruise. I reduced the idle speed in park from about 1050 rpm to 1000 rpm. Afr gauge shows 12.5 in park.
Hope to take it for a spin in the next day or two, weather permitting.
Is there any reason not to add some stabil to the gas now since I doubt I will buy more before spring?

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Re: Carb Tuning

Post by treyrags » Tue Oct 23, 2018 10:32 am

BobbyB wrote:
Tue Oct 23, 2018 8:00 am
Between hurricanes and cold weather, I have not driven the car in over a week. The last change I made was to give the crane adjustable vacuum advance 2 turns clockwise to increase total vacuum advance. The change seems to have made it even better at cruise. I reduced the idle speed in park from about 1050 rpm to 1000 rpm. Afr gauge shows 12.5 in park.
Hope to take it for a spin in the next day or two, weather permitting.
Is there any reason not to add some stabil to the gas now since I doubt I will buy more before spring?
Did you put a timing light on it after you added the 2 turns to check the amount of advance added? 2 turns is a significant change in timing advance on the canisters I've messed with.

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Re: Carb Tuning

Post by BobbyB » Wed Oct 24, 2018 9:36 am

Treyrags,

No, I did not check the timing with a timing light after adjusting the vac advance 2 turns CW. However, it does not "rattle" on hills as if it has too much vac advance.

Tuner,
650 quick fuel carb on for now. May try the 750 again in the spring.

Fbird,

I saw where I missed your question about the car being a mustang. No, it is a 63 Mercury Comet 2 dr hardtop. I do have a 68 mustang gt fastback that I hope to put a stroked Cleveland and 4 speed into someday, if I don't get too old to do the work.
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Re: Carb Tuning

Post by GRTfast » Mon Oct 29, 2018 10:07 am

Figured this is a decent spot to ask this question. I've been getting my primary accel pump (30cc) dialed in on my 850 double pumper. I have it working great, no hesitation on tip in, smooth gentle acceleration, or stabbing it (street big block chevy).

The combo it likes is a blue cam on the 2 hole with a 0.032 discharge nozzle. The problem is, the blue cam has so much lift that at wide open throttle, the nut on the adjuster screw is lifting off of the pump arm (the lever is traveling further than the throw of the pump). If I adjust so this doesn't happen, there is about 1/8th of an inch of free play in the pump actuation lever, which obviously doesn't. It seems to me that this is unavoidable with the blue pump cam because of the amount of lift it has. I see a few videos and tutorials that say to make sure you have .010 to .015 clearance between the pump arm and the screw at wide open throttle, but I can't achieve this without the aforementioned setting that causes a ton of free play prior to engagement. In short, it seems that a "correct" adjustment isn't possible with the blue cam. What am I missing?

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Re: Carb Tuning

Post by In-Tech » Mon Oct 29, 2018 10:12 am

GRTfast wrote:
Mon Oct 29, 2018 10:07 am
Figured this is a decent spot to ask this question. I've been getting my primary accel pump (30cc) dialed in on my 850 double pumper. I have it working great, no hesitation on tip in, smooth gentle acceleration, or stabbing it (street big block chevy).

The combo it likes is a blue cam on the 2 hole with a 0.032 discharge nozzle. The problem is, the blue cam has so much lift that at wide open throttle, the nut on the adjuster screw is lifting off of the pump arm (the lever is traveling further than the throw of the pump). If I adjust so this doesn't happen, there is about 1/8th of an inch of free play in the pump actuation lever, which obviously doesn't. It seems to me that this is unavoidable with the blue pump cam because of the amount of lift it has. I see a few videos and tutorials that say to make sure you have .010 to .015 clearance between the pump arm and the screw at wide open throttle, but I can't achieve this without the aforementioned setting that causes a ton of free play prior to engagement. In short, it seems that a "correct" adjustment isn't possible with the blue cam. What am I missing?
I use the blue cam alot, really aids in tip in. I've seen that a couple times and seems to be inconsistent geometry in the arms, it never cause me an issue to have it bottom out(maybe Tuner or Mark can chime in if it's a problem). You can always take some lift off the cam with a file or whatnot.
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

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Re: Carb Tuning

Post by GRTfast » Mon Oct 29, 2018 10:33 am

In-Tech wrote:
Mon Oct 29, 2018 10:12 am
GRTfast wrote:
Mon Oct 29, 2018 10:07 am
Figured this is a decent spot to ask this question. I've been getting my primary accel pump (30cc) dialed in on my 850 double pumper. I have it working great, no hesitation on tip in, smooth gentle acceleration, or stabbing it (street big block chevy).

The combo it likes is a blue cam on the 2 hole with a 0.032 discharge nozzle. The problem is, the blue cam has so much lift that at wide open throttle, the nut on the adjuster screw is lifting off of the pump arm (the lever is traveling further than the throw of the pump). If I adjust so this doesn't happen, there is about 1/8th of an inch of free play in the pump actuation lever, which obviously doesn't. It seems to me that this is unavoidable with the blue pump cam because of the amount of lift it has. I see a few videos and tutorials that say to make sure you have .010 to .015 clearance between the pump arm and the screw at wide open throttle, but I can't achieve this without the aforementioned setting that causes a ton of free play prior to engagement. In short, it seems that a "correct" adjustment isn't possible with the blue cam. What am I missing?
I use the blue cam alot, really aids in tip in. I've seen that a couple times and seems to be inconsistent geometry in the arms, it never cause me an issue to have it bottom out(maybe Tuner or Mark can chime in if it's a problem). You can always take some lift off the cam with a file or whatnot.
Yes Mark put annular boosters in the carb for me, and helped me get the jetting and stuff right, he’s great. The before and after was a seat of the pants difference, which is significant.

I’ve just read that having it bottom out can damage the pump diaphragm. Didn’t want to bug him with what I assumed was a fairly elementary question. Thanks for the reply.

The green cam works almost as good (with a slight mod I did to it) and doesn’t have the bottoming issue, but I tried the blue and it is spot on. I can’t go back now!

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Re: Carb Tuning

Post by In-Tech » Mon Oct 29, 2018 10:51 am

You know what, now that I think about it I didn't let those cars go, bottoming out, as it dawned on me that it might fubar the spring. It's been a while, did I change the screw position or file, I'll think about it and post back if I remember and nobody else has replied. Nice car btw. :)
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

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Re: Carb Tuning

Post by GRTfast » Mon Oct 29, 2018 12:16 pm

In-Tech wrote:
Mon Oct 29, 2018 10:51 am
You know what, now that I think about it I didn't let those cars go, bottoming out, as it dawned on me that it might fubar the spring. It's been a while, did I change the screw position or file, I'll think about it and post back if I remember and nobody else has replied. Nice car btw. :)
I can get it to not bottom if I change the screw position, but then it doesn't actuate immediately when I start moving the throttle. I think the solution is going to involve reducing the lift of the cam.

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Re: Carb Tuning

Post by Tuner » Mon Oct 29, 2018 12:40 pm

Adjust the angle of the lever over the cam, bend the tang up to reduce pump travel or down to increase it.

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