change an EFI to carb?

jimijuggernaut · 02-10-2003, 09:09 PM

i am wanting to convert my speed density EFI to carberation.
i'm not sure exactly which parts i need to convert. if any one has done this please let me know the details. thanks

crazypete · 02-11-2003, 02:55 PM

Ok... here's what you'll need:

mechanical fuel pump + eccentric + timing chain cover : $170?
A carb (duh) I like the holley street performers: $350
An intake: $150
85 mustang distributor with vacuum advance: $50
steel gear for dist + installation onto dist: $50
Good ignition box (MSD AL6): $300? (your computer cannot control spark anymore)
aircleaner assembly: $100?
You can fasion a throttle cable bracket from the efi throttle cable bracket by sawing off the end and leaving a notch, pounding it 90 degrees , drilling a hole and using this notch as the mounting plate.

You'll need to do some wiring to get the dashboard guages working, but it's not a huge deal. Just flip over the guage cluster and the printed plastic is labelled. Trace to the harness , splice the temp sensor wire to the temp guage wire for instance.

It's so much more fun to have a carb and the milage isnt that bad at all. I have never had the car fail to start since and the worst that has happened is a little sputtering when not set right. No more "engine dies mysteriously" scenarios.

Oh yeah, have fun stripping down the enginebay. I reccomend you do this: Airpump outlet tube directly to the crossovertube behind the heads (Doesnt really backfire if the carb is set properly). You dont have a computer to control the tab/tad solenoids anymore. Rip that wiring and tubing out. Hook the oil filler neck stem to the underside of the air cleaner. now you have pcv. I tried doing EGR, but the car refused to run, so I tossed the system. I reccomend scrapping the vacuum tree since you dont really need it anymore and run a hose over to the brake booster (and tee it at the booster and get a vacuum guage hooked up inside. You'll need it to tune the carb). Dont waste your time with fuel pressure guages since with a mechanical fuel pump, this is rarely an issue.

Have fun

jimijuggernaut · 02-11-2003, 07:24 PM

thanks for the info Crazypete!!!

it is very helpful. thanks.

BLACK85GT · 02-11-2003, 09:43 PM

You can use an aftermarket electric fuel pump if you dont want to mess with the eccentric. I think you have to do something with the gas tank too to get rid of the stock intank fuel pump.

crazypete · 02-12-2003, 02:03 PM

Here's how to modify the fuel tank, pump and pickup real easy. Unbolt the fuel tank and lower it gently. Tap the fuel pump retainer ring off, get the pump out and unbolt the actual pump and toss it. Get a piece of rubber fuel line a little bit longer than the pump was deep. This way, when the hose reaches the bottom of the tank, it will turn a bit to the side. Never had any problems. Now you dont have to switch fuel tanks or any of that nonsense. Feel free to cap off the return line on both ends.. you wont need it.

Electric fuel pumps have volume and pressure variations that can be very annoying to a carb and you'll need a $75 fuel pressure regulator. You'll also need your return line. Just save yourself the headache. TRUST ME... I've tried to bugger it every way humanly possible from reducing stock fuel pump voltage to inline regulators at full voltage and the mechanical pump is the way to go. The eccentric is a snap to put in, just get one off an 85 mustang or get one from a dealer, bolts right up to the timing gear on my 91. Cost me $30

red82gt · 02-12-2003, 03:35 PM

With a carter electric fuel pump and a $20 holley regulator (no return line) I get a steady 6 1/4lbs of fuel pressure at all times (total cost $80 USD.). Also, don't put a rubber line in the tank unless you like stuck needle and seats. The fuel erodes the rubber and then causes the needle and seat to stick. Instead, use a piece of 3/8" aluminum tubing and bend it to fit. The 85 mustang distributor should already have the proper drive gear for the rollercam as well. For $5 at a junkyard, you can use a throttle cable from just about any carbed 302 or 351 motor (2 or 4 barrel) rather than messing with the efi throttle bracket, might as well grab the cable as well.
Not trying to bust ony Crazypete, just letting him know a better way to do it.

87BOSS351C · 02-12-2003, 03:50 PM

There are a lot of fuel pressure regulators out there for less than $75 for carb pressures. I have a Summit regulator (SUM-G3135) that cost $40 and is made by Aeromotive. There are atleast six different regs under $46 at Summit. However, I don't think I would just use the stock EFI pump with a reg on it for a carb.

I'm not trying to be a jerk, just pointing out that there are some pretty inexpensive regulators out there. Here's a quick list with Summit part numbers and prices:

Edelbrock, EDL-8190, $45.95

Holley, HLY-12-803, $22.95

Mr. Gasket, MRG-9710, $29.95

Spectre, SPE-2517, $19.95

Summit, SUM-G3135, $39.95

crazypete · 02-12-2003, 04:15 PM

I'm using the same rubber hose that came with the holley carb to join the fuel inlets together (comes with 2 long pieces), the braided style "stiff" rubber hose. I cant see holley shipping something in the same box as their carbs thats going to wreck the needles. I order an 85' mustang distributor from some guy in texas and he sent me a 79' distributor instead...shred shred shred, weeeee watch me scrape metal chunks from my oil pan weee. I got an "85" distributor from napa for $50 and I made sure to ask them twenty times if it had a steel gear. They said yes, I installed it.....shred shred shred. Nope. weeee, scraping filings from my oilpan again. I finally bought the fms steel gear myself and pounded it down with a deep socket. Just warning you... when they say it's a steel gear, you'd better check to make sure!

With the electric FP, I found this phenomenon: When you flick the car to "on" and the fuelpump starts running, the pressure will creep up and overflow the bowls if you cant start the car soon enough (It's really cool, though. The motor "coughs up" gas and spits it all over the garage). I had 2 regulators over the time: the holley $20 one (useless) and the mallory $75 multiport adjustable unit with return line. Neither could keep the fp under control. With the engine running, fuel pressure seemed ok, a bit high (8 psi with the adjustable all the way up) though.

Honestly, if you're going carb, you want to do away with electrical relays and and wiring and reduce the complexity of your car. Why else would someone go through all this trouble? I think having electrical fuel systems defeats this purpose.

I feel a fuel pump "holy war" brewing here =P

BLACK85GT · 02-12-2003, 04:36 PM

LOL. Sorry, did not mean to start a fuel pump war, there are ups and downs to both, just like anything. I still use my mechanical pump but know people with electric and they seem to run ok too. But yeah, mechanical is definitely simpler if that is your goal. I believe it does take some horse power away to run the mechanical though, doesnt it? Thats what i have always heard anyways.

crazypete · 02-12-2003, 05:36 PM

I'm sure it draws a hp or two: I found the pump arm kinda difficult to compress by hand. Then again, the electric fuel pump has got to be at least 10-15 amps (wild guess, the wires are pretty thick) and that puts some load on the alternator. Do whatever you think would be the easiest and most straightforward solution for your application. But either way, you gotta drop the tank to get the old pump out.

red82gt · 02-13-2003, 02:00 AM

If I let just the fuel pump run the pressure gets up to 6 1/4 and stays, unless you leave it for like 10 seconds or something (why would you), then it'll overpower the diaphragm. I see the mechanical pump as another source for a leak in the timing cover. Also, my pump uses about 4 amps of current, I think the holleys and barry grants use as much as 6. You're the only person I've heard say that the electric is a problem.
About the rubber line, if fuel is sitting inside it it's one thing, if it's submerged in fuel it's another. Almost every carb builder and racer I know all say the same thing "Rubber is not fuel line" do not use any of it. If you tell them you've had a problem with needle and seats sticking the first question they'll ask is if you have any rubber lines in the fuel system. Also that cheap POS that comes with the avenger carbs tends to draw fire from tech inspectors and they usually get the tape measure out, it's not a quality piece and is damn near 12" of rubber on it's own.

86GT · 02-13-2003, 09:07 PM

If you want to run at an IHRA or NHRA, you can't have more than 6-12" of rubber line in your fuel system. At least that's what I'm told. Other than that, if you want some help on how to do the conversion neatly and nicely, go to http://jason.fletcher.net and scroll down and find the conversion page. Its the best web page for it, and that's how I did my 86 conversion. If you need any help, let me know.

02-10-2003, 09:09 PM	#1
jimijuggernaut Registered Member Join Date: May 2002 Location: FT. MYERS, FLA Posts: 5	change an EFI to carb? i am wanting to convert my speed density EFI to carberation. i'm not sure exactly which parts i need to convert. if any one has done this please let me know the details. thanks

02-11-2003, 02:55 PM	#2
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Ok... here's what you'll need: mechanical fuel pump + eccentric + timing chain cover : $170? A carb (duh) I like the holley street performers: $350 An intake: $150 85 mustang distributor with vacuum advance: $50 steel gear for dist + installation onto dist: $50 Good ignition box (MSD AL6): $300? (your computer cannot control spark anymore) aircleaner assembly: $100? You can fasion a throttle cable bracket from the efi throttle cable bracket by sawing off the end and leaving a notch, pounding it 90 degrees , drilling a hole and using this notch as the mounting plate. You'll need to do some wiring to get the dashboard guages working, but it's not a huge deal. Just flip over the guage cluster and the printed plastic is labelled. Trace to the harness , splice the temp sensor wire to the temp guage wire for instance. It's so much more fun to have a carb and the milage isnt that bad at all. I have never had the car fail to start since and the worst that has happened is a little sputtering when not set right. No more "engine dies mysteriously" scenarios. Oh yeah, have fun stripping down the enginebay. I reccomend you do this: Airpump outlet tube directly to the crossovertube behind the heads (Doesnt really backfire if the carb is set properly). You dont have a computer to control the tab/tad solenoids anymore. Rip that wiring and tubing out. Hook the oil filler neck stem to the underside of the air cleaner. now you have pcv. I tried doing EGR, but the car refused to run, so I tossed the system. I reccomend scrapping the vacuum tree since you dont really need it anymore and run a hose over to the brake booster (and tee it at the booster and get a vacuum guage hooked up inside. You'll need it to tune the carb). Dont waste your time with fuel pressure guages since with a mechanical fuel pump, this is rarely an issue. Have fun __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

02-11-2003, 09:43 PM	#4
BLACK85GT Registered Member Join Date: May 2002 Location: Tampa,FLORIDA Posts: 340	You can use an aftermarket electric fuel pump if you dont want to mess with the eccentric. I think you have to do something with the gas tank too to get rid of the stock intank fuel pump. __________________ 5.0, Holley heads, 1.7 Scorp Rockers, Stealth intake, Holley 600 carb, Holley Mech. Fuel pump, MSD 6Digital, MSD distributor, Hotchkis upper/lower rear control arms, FMS B Springs, 3:73 (8.8) rear. Production # 9,377

02-12-2003, 02:03 PM	#5
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Here's how to modify the fuel tank, pump and pickup real easy. Unbolt the fuel tank and lower it gently. Tap the fuel pump retainer ring off, get the pump out and unbolt the actual pump and toss it. Get a piece of rubber fuel line a little bit longer than the pump was deep. This way, when the hose reaches the bottom of the tank, it will turn a bit to the side. Never had any problems. Now you dont have to switch fuel tanks or any of that nonsense. Feel free to cap off the return line on both ends.. you wont need it. Electric fuel pumps have volume and pressure variations that can be very annoying to a carb and you'll need a $75 fuel pressure regulator. You'll also need your return line. Just save yourself the headache. TRUST ME... I've tried to bugger it every way humanly possible from reducing stock fuel pump voltage to inline regulators at full voltage and the mechanical pump is the way to go. The eccentric is a snap to put in, just get one off an 85 mustang or get one from a dealer, bolts right up to the timing gear on my 91. Cost me $30 __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

02-12-2003, 03:35 PM	#6
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,514	With a carter electric fuel pump and a $20 holley regulator (no return line) I get a steady 6 1/4lbs of fuel pressure at all times (total cost $80 USD.). Also, don't put a rubber line in the tank unless you like stuck needle and seats. The fuel erodes the rubber and then causes the needle and seat to stick. Instead, use a piece of 3/8" aluminum tubing and bend it to fit. The 85 mustang distributor should already have the proper drive gear for the rollercam as well. For $5 at a junkyard, you can use a throttle cable from just about any carbed 302 or 351 motor (2 or 4 barrel) rather than messing with the efi throttle bracket, might as well grab the cable as well. Not trying to bust ony Crazypete, just letting him know a better way to do it. __________________ 393W: AFR 205's, hydraulic roller, TKO600.

02-11-2003, 07:24 PM	#3
jimijuggernaut Registered Member Join Date: May 2002 Location: FT. MYERS, FLA Posts: 5	thanks for the info Crazypete!!! it is very helpful. thanks.

02-12-2003, 03:50 PM	#7
87BOSS351C Registered Member Join Date: Sep 2002 Location: Midland, Michigan Posts: 92	There are a lot of fuel pressure regulators out there for less than $75 for carb pressures. I have a Summit regulator (SUM-G3135) that cost $40 and is made by Aeromotive. There are atleast six different regs under $46 at Summit. However, I don't think I would just use the stock EFI pump with a reg on it for a carb. I'm not trying to be a jerk, just pointing out that there are some pretty inexpensive regulators out there. Here's a quick list with Summit part numbers and prices: Edelbrock, EDL-8190, $45.95 Holley, HLY-12-803, $22.95 Mr. Gasket, MRG-9710, $29.95 Spectre, SPE-2517, $19.95 Summit, SUM-G3135, $39.95 __________________ Black '87 LX 5.0 5 spd T-top with 450hp '71 351 Cleveland 4V, C6 tranny, "and some other stuff" Rice Haters Club Member #124

02-12-2003, 04:15 PM	#8
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	I'm using the same rubber hose that came with the holley carb to join the fuel inlets together (comes with 2 long pieces), the braided style "stiff" rubber hose. I cant see holley shipping something in the same box as their carbs thats going to wreck the needles. I order an 85' mustang distributor from some guy in texas and he sent me a 79' distributor instead...shred shred shred, weeeee watch me scrape metal chunks from my oil pan weee. I got an "85" distributor from napa for $50 and I made sure to ask them twenty times if it had a steel gear. They said yes, I installed it.....shred shred shred. Nope. weeee, scraping filings from my oilpan again. I finally bought the fms steel gear myself and pounded it down with a deep socket. Just warning you... when they say it's a steel gear, you'd better check to make sure! With the electric FP, I found this phenomenon: When you flick the car to "on" and the fuelpump starts running, the pressure will creep up and overflow the bowls if you cant start the car soon enough (It's really cool, though. The motor "coughs up" gas and spits it all over the garage). I had 2 regulators over the time: the holley $20 one (useless) and the mallory $75 multiport adjustable unit with return line. Neither could keep the fp under control. With the engine running, fuel pressure seemed ok, a bit high (8 psi with the adjustable all the way up) though. Honestly, if you're going carb, you want to do away with electrical relays and and wiring and reduce the complexity of your car. Why else would someone go through all this trouble? I think having electrical fuel systems defeats this purpose. I feel a fuel pump "holy war" brewing here =P __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

02-12-2003, 04:36 PM	#9
BLACK85GT Registered Member Join Date: May 2002 Location: Tampa,FLORIDA Posts: 340	LOL. Sorry, did not mean to start a fuel pump war, there are ups and downs to both, just like anything. I still use my mechanical pump but know people with electric and they seem to run ok too. But yeah, mechanical is definitely simpler if that is your goal. I believe it does take some horse power away to run the mechanical though, doesnt it? Thats what i have always heard anyways. __________________ 5.0, Holley heads, 1.7 Scorp Rockers, Stealth intake, Holley 600 carb, Holley Mech. Fuel pump, MSD 6Digital, MSD distributor, Hotchkis upper/lower rear control arms, FMS B Springs, 3:73 (8.8) rear. Production # 9,377

02-12-2003, 05:36 PM	#10
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	I'm sure it draws a hp or two: I found the pump arm kinda difficult to compress by hand. Then again, the electric fuel pump has got to be at least 10-15 amps (wild guess, the wires are pretty thick) and that puts some load on the alternator. Do whatever you think would be the easiest and most straightforward solution for your application. But either way, you gotta drop the tank to get the old pump out. __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

02-13-2003, 02:00 AM	#11
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,514	If I let just the fuel pump run the pressure gets up to 6 1/4 and stays, unless you leave it for like 10 seconds or something (why would you), then it'll overpower the diaphragm. I see the mechanical pump as another source for a leak in the timing cover. Also, my pump uses about 4 amps of current, I think the holleys and barry grants use as much as 6. You're the only person I've heard say that the electric is a problem. About the rubber line, if fuel is sitting inside it it's one thing, if it's submerged in fuel it's another. Almost every carb builder and racer I know all say the same thing "Rubber is not fuel line" do not use any of it. If you tell them you've had a problem with needle and seats sticking the first question they'll ask is if you have any rubber lines in the fuel system. Also that cheap POS that comes with the avenger carbs tends to draw fire from tech inspectors and they usually get the tape measure out, it's not a quality piece and is damn near 12" of rubber on it's own. __________________ 393W: AFR 205's, hydraulic roller, TKO600.

02-13-2003, 09:07 PM	#12
86GT Sniffed too much n20 Join Date: Oct 1998 Location: Ont, Canada Posts: 1,018	If you want to run at an IHRA or NHRA, you can't have more than 6-12" of rubber line in your fuel system. At least that's what I'm told. Other than that, if you want some help on how to do the conversion neatly and nicely, go to http://jason.fletcher.net and scroll down and find the conversion page. Its the best web page for it, and that's how I did my 86 conversion. If you need any help, let me know. __________________ 2002 Windsor Weekend Q16 Qualifier

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