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Carb questions
#1
So, the 429 is topped by an Autolite 4300 carb. At sea level it ran great, up here at 7,000+ feet it runs rich and performance sucks (but the engine sounds great). I have a couple questions:

1) I've been told the carb needs to be rejetted for high altitude. I know I have to retune it, but my experience with carbs is minimal. I've got a bunch of books I've been reading, but they are lean on 4300 information. How tough would doing this stuff be?

2) Should I look at investing in a better carb? I've read very mixed reviews on the 4300 (it was rebuilt ~10 or 12 years ago and only has about 50 miles on the rebuild).

3) For the 429, does the 4300 flow enough or should I look at a carb that flows better?

Note: I'm not looking at racing, just cruising. Also, MPG's are good!

Steve



[Image: 25yvyp3.jpg]
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#2
In my opinion re-jetting your 4300 would be a good bet. See if you can find a parts breakdown to figure out how to replace the jets. I'm not sure where to find them, maybe the Ford dealer.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#3
Thanks Jeff, I'm surprised how little information I've been able to dig up on the interwebs but it doesn't look all that tough to re-jet. I just don't know what size to put in (I don't even know what size is currently in there). I posted over on 429-460.com as well, if I get any good info from over there I'll cross-post in case other newbies have questions.

Steve



[Image: 25yvyp3.jpg]
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#4
pull the top off, the jets are brass right under the float. You can simply get a set of small bits and drill them out. I'd go about .002 larger
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#5
don29163;20078 Wrote:pull the top off, the jets are brass right under the float. You can simply get a set of small bits and drill them out. I'd go about .002 larger

Really? I thought I'd have to go smaller to get a leaner mix (granted, I know next to nothing about this stuff!). Higher altitude and all...

Steve



[Image: 25yvyp3.jpg]
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#6
sm3570;20081 Wrote:
don29163;20078 Wrote:pull the top off, the jets are brass right under the float. You can simply get a set of small bits and drill them out. I'd go about .002 larger

Really? I thought I'd have to go smaller to get a leaner mix (granted, I know next to nothing about this stuff!). Higher altitude and all...

Hey sm3570,
I keep a little sticky on my tool box to remind me the 101's about jettings. I use this for my motorcycles and I'm sure it's the same for cars.

Smaller Jet = Higher Altitude (Leaner Condition)
Larger Jet = Lower Altitude (Rich Condition)
Air Temperature High = (less air so you have lean out the mixture)
Air Temperature Low = (more air so you have to richen the mixture)

Altitude High = (lean the mixture)
Altitude Low = (Richen the mixture)

Humidity High = (Lean out the mixture)
Humidity Low = (Richen the mixture)


Also, the autolite 4300 is 605cfm and the 4300D's were 715cfm. I just replaced my 750 for a 600 on my 351C and it runs like a champ straight out of the edelbrock box. I recently picked up a 71 with a 429 and it has a holley 850 on it. Never got around to firing it up yet, but I will soon.
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#7
FasTnNefariouS;20089 Wrote:
sm3570;20081 Wrote:
don29163;20078 Wrote:pull the top off, the jets are brass right under the float. You can simply get a set of small bits and drill them out. I'd go about .002 larger

Really? I thought I'd have to go smaller to get a leaner mix (granted, I know next to nothing about this stuff!). Higher altitude and all...

Hey sm3570,
I keep a little sticky on my tool box to remind me the 101's about jettings. I use this for my motorcycles and I'm sure it's the same for cars.

Smaller Jet = Higher Altitude (Leaner Condition)
Larger Jet = Lower Altitude (Rich Condition)
Air Temperature High = (less air so you have lean out the mixture)
Air Temperature Low = (more air so you have to richen the mixture)

Altitude High = (lean the mixture)
Altitude Low = (Richen the mixture)

Humidity High = (Lean out the mixture)
Humidity Low = (Richen the mixture)


Also, the autolite 4300 is 605cfm and the 4300D's were 715cfm. I just replaced my 750 for a 600 on my 351C and it runs like a champ straight out of the edelbrock box. I recently picked up a 71 with a 429 and it has a holley 850 on it. Never got around to firing it up yet, but I will soon.

That's kinda what I figured, but how much smaller is the question. I'll tune the carb first and see how it goes. I know the 4300 came stock on the earlier 429's and since I'm not racing it then 600cfm might suffice, but I guess I'll just have to see. Thanks for the feedback!

Steve



[Image: 25yvyp3.jpg]
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#8
ooops !
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#9
don29163;20099 Wrote:ooops !

Lol, not many people realize the altitude that I'm at. I feel the elevation every time I strap on my running shoes!

Steve



[Image: 25yvyp3.jpg]
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#10
is the 429 bone stock? if so, then maybe a new 650 carb would do the trick. summit have their own carbs that are very inexpensive. if its not stock then most 460's can do absolutely fine with a 750.

just a fyi, having a too small of a carb can hurt just as much if not MORE, than having a too big of a carb.

for changing jets on holley's, the front four bolts in the front of the carb will drop the entire front bowl and the jets will be exposed.
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