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carb replacement 71 mustang


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My father in law has a 71 mustang and the old autolite 4300 has given up.  He doesn't have any intentions of replacing the stock intake.  He wants to keep it as original as possible.  The car only has 52,000 miles on it and for the most part is factory.  We would like to know what would be the best replacement carb that would give him stock performance.  I've read about a few carbs like the summit sum-mo8600vs. It sounds like a great carb but I read I will need a carb spacer to make it fit.  So if it needs a spacer, will the stock breather still fit?  Do I need a kick down adapter? I really don't know much about FORDs so any help will be greatly appreciated.

We really want a bolt on and go option if that is possible.  What about the autolite 4100?

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There is a guy in NY called KP Carbs that rebuilds the 4300's back to stock original like new. If you google KP Carbs you will find him. He was recommended by my local builder here and one of our European members recently sent a carb to him to have rebuilt. Just an idea if you want to keep it original. Plus I think he only charges in the $250 range for a 4300 or less.

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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Just as a suggestion. I can't comment on the Summit carb, never seen one, but as the 4300 is a 4 barrel, I would get either a Holley Street Avenger 670 or 770 or a Quick Fuel 750, not sure of the exact model you'd need, but these are very good carbs and will pretty much run right out of the box, with minor adjustments. If your engine does not have ram-air, you can use a spacer without issue. I run a 1" fiber spacer without any clearance issues on my 351C 4V with the stock air cleaner. You would need to change your fuel line to the carb and that could be rubber Hose or better yet a solid tube connection, but that takes some extra know-how. If you use rubber hose, make sure it is high pressure fuel injector hose as it will be ethanol resistant and PLEASE don't use gear clamps!!. Buy proper fuel line hose clamps. VERY important on both counts IMO! Used carbs are out there pretty cheap, but that's what you get and you'll likely end up spending almost as much just getting it running, a waste of money unless you are able to find one that is known to run correctly.

If originality is important, yes, get the Autolite rebuilt professionally, but in the mean time a Holley or QF will give great performance at reasonable cost.

Geoff.

 I learn something new every day!

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The Summit carburetor comes with a Ford kickdown and will not need an adapter. The 4300D intake manifold, which is a spread bore, would need an adapter.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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The Summit carburetor comes with a Ford kickdown and will not need an adapter. The 4300D, which is a spread bore, would need an adapter.

 

He has a 4300 not a 4300D. Different animal as you know.

Edit: OK I just realized what you were referring to....... IF he got a 4300D he would need an adaptor, kick down and base.

Geoff.

 I learn something new every day!

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I edited it, actually I meant if his intake manifold were for a 4300D he would need an adapter for the Summit carburetor.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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I edited it, actually I meant if his intake manifold were for a 4300D he would need an adapter for the Summit carburetor.

 

Okay, I see what you meant to say now. I think he said it was a 71. If so it would be a square bore. 72-73's are spread bore. Oh well, he'll sort it out.

Geoff.

 I learn something new every day!

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OK, thanks for the info.  I say I have a 4300 but could it be a 4300D?  The motor is the Cleveland.

 

 It is easy to tell. a 4300 has all 4 bores equal in diameter for a 71, a "square bore". a 4300D is a spread bore, secondary's larger then the primaries and was the 71 Boss carb if I'm not mistaken, but could also have been used on the 72-73's. Those are not my years of familiarity. No doubt someone will set me straight!

Geoff.

 I learn something new every day!

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Mike's Carbs online has rebuild kits for pretty much every carb on the planet. If he wants to stay stock, rebuild the original, its not that hard at all!

 

 Good to know where to get those parts. You are right it is not that hard to rebuild a 4300 as long as you follow the instructions........... well at least I'm hoping. I plan on rebuilding my original 4300 at some point just to have it, but not necessarily to use it.

Good info.

Geoff.

 I learn something new every day!

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Mike's Carbs online has rebuild kits for pretty much every carb on the planet. If he wants to stay stock, rebuild the original, its not that hard at all!

 

 Good to know where to get those parts. You are right it is not that hard to rebuild a 4300 as long as you follow the instructions........... well at least I'm hoping. I plan on rebuilding my original 4300 at some point just to have it, but not necessarily to use it.

Good info.

 

I was told that some bushings were out on some rod and it would need to be sent off to be fixed and that its expensive. I have a guy that can rebuild it for $100 but he doesn't have what's needed to fix thosenparts.

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So has anyone used the Summit carb? Other than the gas line what would I need to fit the Summit on the 71'? What about the choke? On the factory carb there is a hard line going to it. What do I need to do for the choke.

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A link to 4300A and 4300D carbs. Notice the square bore 4300A isn't actually "square" bore. The 70-71 intake can be easily modified to accept larger (750 and up) square bore Holleys.

https://en.wikipedia.org/wiki/Autolite_4300_carburetor

 

Chuck

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You'll need to connect the choke to a 12 volts, when key is on, power source.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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  • 2 weeks later...

Ok, so If I choose a holley what all do I need to put it on the car? Thanks

 

 Which Holley Carb? a Street Avenger is a good start, at least a 670 #80670.

 Not much. At least a 1/4" insulator for sure to stop heat transfer and maybe top and bottom gaskets if required. There is a Fel-Pro base gasket with a metal insert you will need on a 71 as it has a heat transfer passage and you will need block this off or it will burn the base of your brand new carb. Re-route the fuel line to the right side. You can use good rubber for now till you get it set up. Use Fuel injector line as it is ethanol resistant and buy proper fuel line clamps, "T" clamps, not freakin gear clamps that everybody uses!! NO glass fuel filter either. Just make sure everything is tight and rechecked before putting gas to it. Electric choke needs keyed power source, been talked about before.

If I forgot anything others will add I sure.

Good luck as keep us up on progress.

Geoff.

 I learn something new every day!

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Ok, so If I choose a holley what all do I need to put it on the car? Thanks

 

 Which Holley Carb? a Street Avenger is a good start, at least a 670 #80670.

 Not much. At least a 1/4" insulator for sure to stop heat transfer and maybe top and bottom gaskets if required. There is a Fel-Pro base gasket with a metal insert you will need on a 71 as it has a heat transfer passage and you will need block this off or it will burn the base of your brand new carb. Re-route the fuel line to the right side. You can use good rubber for now till you get it set up. Use Fuel injector line as it is ethanol ruesistant and buy proper fuel line clamps, "T" clamps, not freakin gear clamps that everybody uses!! NO glass fuel filter either. Just make sure everything is tight and rechecked before putting gas to it. Electric choke needs keyed power source, been talked about before.

If I forgot anything others will add I sure.

Good luck as keep us up on progress.

 

Thanks for the info. I was looking at the 4160 600cfm. What about a kick down adapter? Linkage issues? 

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Ok, so If I choose a holley what all do I need to put it on the car? Thanks

 

 Which Holley Carb? a Street Avenger is a good start, at least a 670 #80670.

 Not much. At least a 1/4" insulator for sure to stop heat transfer and maybe top and bottom gaskets if required. There is a Fel-Pro base gasket with a metal insert you will need on a 71 as it has a heat transfer passage and you will need block this off or it will burn the base of your brand new carb. Re-route the fuel line to the right side. You can use good rubber for now till you get it set up. Use Fuel injector line as it is ethanol ruesistant and buy proper fuel line clamps, "T" clamps, not freakin gear clamps that everybody uses!! NO glass fuel filter either. Just make sure everything is tight and rechecked before putting gas to it. Electric choke needs keyed power source, been talked about before.

If I forgot anything others will add I sure.

Good luck as keep us up on progress.

 

Thanks for the info. I was looking at the 4160 600cfm. What about a kick down adapter? Linkage issues? 

 

 

   Kick down. you will need to buy p/n 20-91, spring and perch kit according to the installation instructions for Ford application. I'm pretty sure your dealer will have this on the shelf along with a host of other repair and tuning parts for these carbs. There are too many pages to copy here, but you can get this on Holley's website.

Without going back over all this, if you have a 351C, especially a 4 barrel, a 600 will not give you the performance you need. I went with a 670, but a 770 or a Quick Fuel 750 would have been a better choice. I'm told by guys here that 351C 4V's like lots of air and I think they're right. I also had some rich running issues at idle, but that may have been more the mild upgraded cam I have. A Street Avenger should run right out of the box, with minor set up, curb idle for example.

Hope this helps and good luck.

Geoff.

 I learn something new every day!

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A 600 CFM carb is too low for a 4V engine and a 750 vacuum secondary either Holley or my personal favourite, a Quick Fuel 750 slayer series would be a way better choice. Not only will this improve the engines all round performance, but help with it fuel economy. As has been stated the standard 4V intake isn't a true square bore and a 1/2"-1" spacer would help get you around the need to modify the intakes throttle bores and help with any possible clearance issues with the throttle lever on the carb sticking to anything.

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A 600 CFM carb is too low for a 4V engine and a 750 vacuum secondary either Holley or my personal favourite, a Quick Fuel 750 slayer series would be a way better choice. Not only will this improve the engines all round performance, but help with it fuel economy. As has been stated the standard 4V intake isn't a true square bore and a 1/2"-1" spacer would help get you around the need to modify the intakes throttle bores and help with any possible clearance issues with the throttle lever on the carb sticking to anything.

 

 True on the 1/2 to 1" insulating spacer for the reasons you mention. Although on my car when I bought it, it had just a 1/4" insulator and it worked fine. I did machine a fiber spacer 1" thick, with taper bores, for clearance and a bit more insulation from the heat in the cross over...... until I made and inserted block-off plates in the intake. I still use the 1" spacer as it's supposed to make a bit more torque. Hmmm!

+1 on the Quick Fuel 750. If I had to buy another carb, that would be my choice too.

Geoff.

 I learn something new every day!

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So your saying the 4300 was undersized from the factory. So how does going with a larger cfm help fuel economy? I was always told larger CFM means more fuel and that's bad on the wallet. I can get my hands on a 750 holley but I'm not sure what model. Ive been told it will need to be rebuilt. How hard is it to do that?

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So your saying the 4300 was undersized from the factory. So how does going with a larger cfm help fuel economy?  I was always told larger CFM means more fuel and that's bad on the wallet. I can get my hands on a 750 holley but I'm not sure what model. Ive been told it will need to be rebuilt. How hard is it to do that?

 

Absolutely the 4300 at 605 CFM was well and truly undersized for a 4V Cleveland. One thought on the reason for such a small carb was so people couldn't over rev the engine as I haven't seen or speaking with those that had these engines from new could not get them to rev past 5800 RPM and 6000 RPM would be absolute maximum and a smaller carb on the engine is cheaper and easier than fitting rev limiters to every car fitted with a 4V engine. The small carb looked after the engine for warranty purposes by allowing it to rev too high, hence why Ford sold so many 780 Holleys for these engines back in the day to those wanting to unleash the potential from a 4V. If the carb wasn't too small on the closed chambered 4V engines, then why did the Ford engineers go for a 4300D rated at 715 CFM on all open chambered 4V engines. 

The old it's bigger so it's got to use more fuel is just a myth. If the carb meters the fuel better and makes a better mixture, which in turn makes better power across the board with less fuel delivery needed. The 4300 was designed back in the 60's when fuel was cheap and economy wasn't an important factor when purchasing a performance car, whereas modern carbs take not just power, but some sort of economy as well. I have a good friend of mine with a really nice car collection of all makes and engine sizes, the only modified engine is in his Impala which makes just under 600 HP. He swears it's the most economical car out of the lot, a 406 SBC with a modded 850 is more economical than 60's/70's vehicles that are all standard, everything from station wagons to muscle cars to luxury barges that are kept well serviced and looked after better than himself. Since I replaced the valve springs and tuned it, not only does it go heaps better and harder, but the fuel usage is better again. The reason why I only use a dyno as a baseline when the engine is fresh and not as a tuning tool, as a dyno is only as suitable as the conditions at the premises and not where the car actually is being used.

Holley carbs are a very basic carb to build and a very straight forward. As long as the throttle shafts aren't worn, then a kit and a can of carby cleaner and compressed air is basically all that's needed to rebuild one. If the shafts are worn either have them bushed or buy a new throttle plate. Unless the carb is cheap or even better free, then buy a new one with warranty, as other problems like a casting fault in the metering block can ruin your day after doing the rebuild. Trust me chased those problems too many times over the years, thank god for billet metering blocks and throttle plates.

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