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What is involved with carb swapping a tbi 2.5?

2063 Views 39 Replies 8 Participants Last post by  tmbrake84, 
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I have a 1987 2.5 s10 5 speed and have had an extremely difficult time with my computer and getting everything running with the computer so I was wondering what all it would take to just carb swap the 2.5 tbi?
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944v8indfw
HEI distributor and a carb to greatly simplify an answer.
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944v8indfw said:
HEI distributor and a carb to greatly simplify an answer.
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Would I not need an entirely new intake?
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944v8indfw
DnS1821 said:
Would I not need an entirely new intake?
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As i recall there is an adapter you can use. Let me see if i can find it.
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944v8indfw
www.ebay.com

2 barrel 4412 HOLLEY 500, 350, TO CHEVY TBI manifold adapter 44mm 1.75 USA | eBay

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944v8indfw
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Adapter Holley 2 barrel 4412 Autolite To Chevy GM TBI intake manifold USA MADE | eBay

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944v8indfw
The first is a composite plastif of some sort, likely 3d printed. The second is aluminum. Just from my own mindset of durability i would do the aluminum.
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944v8indfw
www.speedwaymotors.com

Proform 67093 Iron Duke GM 2.5 Liter HEI Distributor

These units offer calibrated advance curves that are optimized for maximum combustion efficiency and for the elimination of detonation damage and throttle ping. Assembled from precision-made parts for advance curve smoothness. Offers longer term durability and a higher voltage spark that permits...
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944v8indfw
There may be less expensive Distributors let me check ebay as i recall there were some small body distributors that used an ford / dodge box.
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944v8indfw said:
There may be less expensive Distributors let me check ebay as i recall there were some small body distributors that used an ford / dodge box.
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Thank you so much. What all vacuum lines would you need to make this work? Just the vacuum advance?
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944v8indfw
You will need advance vacuum from the carb and manifold vacuum for climate control and of course brake booster as well as pvc which normally is a port on the carb
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944v8indfw said:
You will need advance vacuum from the carb and manifold vacuum for climate control and of course brake booster as well as pvc which normally is a port on the carb
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Thank you! Do you know if a Holley r 7697 a would fit on that adapter? I found one relatively cheap that I can rebuild instead of that $400 I’m seeing everywhere else
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944v8indfw
If it has a 3.460 x 5.160 bolt pattern don't see why not. There are some overseas knockoffs of the autolites that are under $200 new as i recall.
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944v8indfw
www.amazon.com

Amazon.com: 2 Barrel Carburetor Carb 2100 Carburetor 2150 Carburetor Compatible with Ford 289 302 351 Cu Jeep Engine F100 F250 F350 with Electric Choke Mounting Gasket - 302 carburetor by BOOTOP PIN : Automotive

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944v8indfw
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For 1964-1979 Ford F150 F250 F350 289 302 351 2-Barrel Carburetor Carb 2100 A800 | eBay

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944v8indfw said:
www.ebay.com

For 1964-1979 Ford F150 F250 F350 289 302 351 2-Barrel Carburetor Carb 2100 A800 | eBay

Find many great new & used options and get the best deals for For 1964-1979 Ford F150 F250 F350 289 302 351 2-Barrel Carburetor Carb 2100 A800 at the best online prices at eBay! Free shipping for many products!
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Thank you so much! One more thing, what wiring changes will I need to make? I plan on installing my own fuel, rpm, volt, speed, temp and oil pressure gauges so I won’t have to worry about those. How will I power my ignition and things like that?
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944v8indfw
Not many wiring changes needed. Only one i can think of is power to the new distributor while cranking and running. Should be able to pick that up at TBI ignition coil hookups.

Food for thought: The couple other things will be a regulator on your fuel pump or a new pump as the tbi pump pressure is more than double what a carb needs. The fuel pump relay wiring would need to reworked a tiny bit so that it would work with the carb. Basically your safety would be the oil pressure switch. Don't want it running key on without motor running.

I believe all your gauges are analog so no worrier there. I am about 90% sure your speedometer is mechanical with a drive cable to the transmission. I would touch zero dash wiring until you have the carb setup working if you are so inclined. If you add an external tach you can pickup the signal on the HEI distributor.

Other thing to think about is your truck has a catalytic converter that may not play nice with your carb. You will still have a o2 sensor sending info to your computer. However by the sounds of things computer is not functional so may be a moot point.

All in all i would not generally be in favor of swapping carb for fuel injection, however in this case it may be a good choice. The other thing to consider is if you are in an emissions testing state I doubt if a carb conversion will pass.

Rambling a bit, spitballing the challenges to make the convert successful if i were doing it.
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944v8indfw said:
Not many wiring changes needed. Only one i can think of is power to the new distributor while cranking and running. Should be able to pick that up at TBI ignition coil hookups.

Food for thought: The couple other things will be a regulator on your fuel pump or a new pump as the tbi pump pressure is more than double what a carb needs. The fuel pump relay wiring would need to reworked a tiny bit so that it would work with the carb. Basically your safety would be the oil pressure switch. Don't want it running key on without motor running.

I believe all your gauges are analog so no worrier there. I am about 90% sure your speedometer is mechanical with a drive cable to the transmission. I would touch zero dash wiring until you have the carb setup working if you are so inclined. If you add an external tach you can pickup the signal on the HEI distributor.

Other thing to think about is your truck has a catalytic converter that may not play nice with your carb. You will still have a o2 sensor sending info to your computer. However by the sounds of things computer is not functional so may be a moot point.

All in all i would not generally be in favor of swapping carb for fuel injection, however in this case it may be a good choice. The other thing to consider is if you are in an emissions testing state I doubt if a carb conversion will pass.

Rambling a bit, spitballing the challenges to make the convert successful if i were doing it.
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Could you elaborate a little more on the fuel pump relay wiring changes? I’m not the greatest in the world with wiring but I can almost always figure it out in the end but I’m not exactly sure right now why or what would need to be changed there. I already have budgeted for a fuel pressure regulator and all of that so everything else should be good. I’m extremely appreciative of all of your help!
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944v8indfw
Without looking at details of wiring diagram for a 87 the computer primes your pump for 3 seconds with key on then once started the oil pressure switch activates the relay once running. The ignition signal from distributor tells injectors to open / pulse. With the computer not getting signal i dont know if it would shut down the pump relay or not. perhaps the yoda of wiring diagrams @oldeerslayer can enlighten.

My way of thinking and i may be way wrong: Use the oil pressure switch to trigger the electric pump relay, which it already does, for a safe way of operation. No oil pressure no pump. With a carb you should have plenty in the bowl to get it started and build pressure for the switch to activate the relay. There is also a prime terminal under the hood for the pump if the float bowl is dry. I am not sure it works if computer for all intents and purposes is gone.

To me the saftey issue is you do not want the pump running without engine running.
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944v8indfw
And oh yeah i would definately get the carb with electric choke, not the one with a hot pipe connection to manifold.
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