1987 Burb TBI to carb swap

Oaasport

Member
Joined
Mar 9, 2019
Posts
48
Reaction score
34
Location
Arizona
First Name
Justin
Truck Year
1987
Truck Model
Suburban V10
Engine Size
5.7
I am going to start gathering parts for my 1987 Suburban TBI to carb swap. So far heres what i am looking at. 1985 carbureted tank, fuel sending unit and fuel lines. Also have HEI dizzy and of course intake manifold and carb. Having a harness made to run new carbed engine without all the extra tbi stuff. Now for questions. Will my fuel gauge work with 1985 Sending unit in place of TBI sending unit? Can i use just the 1985 Sending unit in the 1987 tank to save some money? If so, im assuming i just use return fuel system and put on a regulator? I never have done a tbi to carb conversion and ive searched but havent found any direct answers
 

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
2,127
Reaction score
2,172
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
I can't fathom why anyone would ever want to do this... it has zero benefit and is going to be an absolute nightmare.

That being said, you are making this way harder than it needs to be. You don't need to swap anything in the fuel tank. An 87 350 should have a mechanical fuel pump boss, so you just need to buy a mechanical fuel pump and pushrod and install it on the engine. Disconnect the electric fuel pump power(either fuse or relay) and then plumb hardline from the mechanical pump into the original fuel line. The mechanical pump will have no issue pulling straight through the electric fuel pump. Make sure you get a three port mechanical pump so that you have a return line to prevent vapor lock. Don't just disconnect the fuel pump connector near the tank or you will lose the fuel level sender signal.
 

Oaasport

Member
Joined
Mar 9, 2019
Posts
48
Reaction score
34
Location
Arizona
First Name
Justin
Truck Year
1987
Truck Model
Suburban V10
Engine Size
5.7
I am doing it because the TBI engine is worn out and i have a fresh built 350 with Vortec heads and all new accessories. The TBI to Vortec manifold is $500, and then a tune, bigger injectors and higher flow pump will near put me at the cost of a used 6.0 engine. Thanks for the help, i greatly appreciate it!
 

C10MixMaster

Full Access Member
Joined
Dec 6, 2016
Posts
681
Reaction score
1,120
Location
Kingman AZ
First Name
Ben
Truck Year
1977
Truck Model
C10 BIG10
Engine Size
ZZ4 350
I can't fathom why anyone would ever want to do this... it has zero benefit and is going to be an absolute nightmare.

That being said, you are making this way harder than it needs to be. You don't need to swap anything in the fuel tank. An 87 350 should have a mechanical fuel pump boss, so you just need to buy a mechanical fuel pump and pushrod and install it on the engine. Disconnect the electric fuel pump power(either fuse or relay) and then plumb hardline from the mechanical pump into the original fuel line. The mechanical pump will have no issue pulling straight through the electric fuel pump. Make sure you get a three port mechanical pump so that you have a return line to prevent vapor lock. Don't just disconnect the fuel pump connector near the tank or you will lose the fuel level sender signal.


pulling through the in tank pump can lead to vapor lock issues. however the pump could be replaced with piece of hard line and a filter sock.
 

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
2,127
Reaction score
2,172
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
pulling through the in tank pump can lead to vapor lock issues. however the pump could be replaced with piece of hard line and a filter sock.
Have you ever actually seen that? I'm pulling through an EP381 and haven't had any vapor lock issues. The design of the pump shouldn't cause there to be much restriction to pulling through it.

Alternatively, you can just keep the in-tank pump and electric pump and run an adjustable regulator. A stock TBI pump only runs 12-14psi anyways, so its easy to regulate it down to the 5psi you want for your carburetor without putting any extra load on the pump. Since you have a fresh 350 with vortec heads, you might have a later block with no mechanical pump provision or a roller cam with no fuel pump eccentric anyways, so just using the factory TBI pump might be the best option regardless.
 

Oaasport

Member
Joined
Mar 9, 2019
Posts
48
Reaction score
34
Location
Arizona
First Name
Justin
Truck Year
1987
Truck Model
Suburban V10
Engine Size
5.7
The block is a 1979 block, mechanical pump. Thats why i was looking into find a carb tank lines and sending unit
 

C10MixMaster

Full Access Member
Joined
Dec 6, 2016
Posts
681
Reaction score
1,120
Location
Kingman AZ
First Name
Ben
Truck Year
1977
Truck Model
C10 BIG10
Engine Size
ZZ4 350
Have you ever actually seen that? I'm pulling through an EP381 and haven't had any vapor lock issues. The design of the pump shouldn't cause there to be much restriction to pulling through it.

Alternatively, you can just keep the in-tank pump and electric pump and run an adjustable regulator. A stock TBI pump only runs 12-14psi anyways, so its easy to regulate it down to the 5psi you want for your carburetor without putting any extra load on the pump. Since you have a fresh 350 with vortec heads, you might have a later block with no mechanical pump provision or a roller cam with no fuel pump eccentric anyways, so just using the factory TBI pump might be the best option regardless.

I have actually been chasing vapor lock on my truck , when the outside temp hits 95+ degrees you can watch the fuel pressure drop to nothing on a hard acceleration or sometimes just pulling away from a light. Adding any resistance in the suction side of the fuel pump is not good. Might get away with it might not just good to know it can cause a problem. I do agree that using the existing in tank set up with a regulator is probably the way to go.
 

Latest posts

Forum statistics

Threads
33,850
Posts
701,571
Members
21,598
Latest member
Rayban
Top