95 Chevrolet K1500 5.7 TBI to Carb Swap

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If you post another thread about that issue we can probably help you get to the bottom of it. There's a lot of smart TBI people here. Which is one of the reasons you're going to get so much flak for considering a carb swap. Lots of members here (myself included) would consider that a huge step backwards.

EDIT - Looks like you beat me to it. :lol: Hope you get it figured out!
Well I’m not sure why carb gets so much hate, i haven’t seen a lot of people go back to TBI or even regret it after carb swapping lol
 

df2x4

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Well I’m not sure why carb gets so much hate, i haven’t seen a lot of people go back to TBI or even regret it after carb swapping lol

Of course not, once you make a mistake that big you can't just admit you were wrong, you have to own it and ride it out. :lol:

Seriously though I don't hate carbs, I believe they have their place. I just don't see the logic in downgrading a vehicle with factory fuel injection. Any perceived gains in simplicity are outweighed by what you give up in function IMO. A carb will get worse gas mileage, be harder to start in cold weather, and introduce other difficulties with the factory computer controlled stuff like running the transmission as you mentioned. I see it as a hack swap for people who are scared of computers. (No offense intended to anyone)
 

Schurkey

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Well I’m not sure why carb gets so much hate,
I don't "hate" carbs. I've got three of 'em on my ElCamino. Q-Jet on a '66 Toronado, and a Q-Jet will replace the 2GC on a '77 Nova. I've rebuilt a hundred carbs, I saved the instruction sheets from them since I was in high school. I've got a nice big bundle.

But taking off fuel injection to go backwards to a carb is nuts when you already own the fuel injection and the vehicle is already set up for it.

Biggest issue is folks won't buy a decent scan tool and a service manual, and without those, they can't figure out what's wrong with the computer system. So they get mad and tear off the FI so they can bolt on Primitive Pete.

i haven’t seen a lot of people go back to TBI or even regret it after carb swapping
After making the big sacrifice to ditch the FI, and then having to kludge all the problems that creates...I suppose it's a point of pride to say they made it all work. Anything less would be admitting they made a mistake.
 

Schurkey

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Of course not, once you make a mistake that big you can't just admit you were wrong, you have to own it and ride it out. :lol:

Seriously though I don't hate carbs, I believe they have their place. I just don't see the logic in downgrading a vehicle with factory fuel injection. Any perceived gains in simplicity are outweighed by what you give up in function IMO.
Beat me by a minute!

A carb will get worse gas mileage, be harder to start in cold weather,
Carbs can be tuned to run leaner than stoich at part-throttle/cruise. They have the potential to get BETTER fuel economy than feedback fuel injection that's tuned to run at "14.7:1" if the carb and engine are tuned to run at 15:1 or leaner. But guys are still trying to correct full-throttle fuel ratio on Holley carbs with the MAIN JETS, so it's not likely that you'll find one set up for lean cruise. Carb tuning in general is still apparently a skill that most folks don't have, even for plenty of folks who think they do.

The biggest problems with hard starting are
1. Folks who can't properly adjust the four things on a choke system that need to be correct;
2. Gasoline that may no longer be blended for proper vaporization in cold weather, and
3. Empty float bowls after the carb sits for a period of time--overnight, or a few days. The engine won't start until the float bowls have gasoline; and that takes considerable cranking unless you've got an electric fuel pump that can "prime" the empty carb.

Get the four choke adjustments (choke coil, choke pulloff, unloader, and choke-blade-to-fast idle cam) set properly, get the carb float bowls filled with fresh, winter-blended gasoline BEFORE you start cranking, and a carbed engine will start at -20F. MAYBE it'll even start at -40. In the early days of fuel injection, a properly-set-up carbed engine was MORE likely to start than a fuel injected one when the temperature went to the wrong side of "zero".

The properly-tuned carbed engine will probably need a faster idle, and is less-likely to meet emissions targets especially during warm-up, when the choke is on. That's where FI shines.


and introduce other difficulties with the factory computer controlled stuff like running the transmission as you mentioned. I see it as a hack swap for people who are scared of computers.
Complete agreement.
 
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df2x4

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Carbs can be tuned to run leaner than stoich at part-throttle/cruise. They have the potential to get BETTER fuel economy than feedback fuel injection that's tuned to run at "14.7:1" if the carb and engine are tuned to run at 15:1 or leaner. But guys are still trying to correct full-throttle fuel ratio on Holley carbs with the MAIN JETS, so it's not likely that you'll find one set up for lean cruise.

Is running leaner than stoich at part throttle cruise a generally safe thing to do with a carb?

Reason I ask is that I have a wideband AFR gauge on my '70 Monte with an Edelbrock 1406. It's set up to run about 13.5-14.0 at part throttle, that's the leanest it ever gets and I figured that was plenty safe. If I can squeeze some more mileage out of it (currently getting around 12MPG) I wouldn't be opposed.
 

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Sure. Mind you, this is LOW LOAD operation. You'd not run that lean under heavier load, or you'd detonate, burn holes in pistons and/or overheat valves.

15--15.5 and NO MISFIRE under LIGHT LOAD--steady ,moderate speed--and you should be fine.

If you've got misfire, add some fuel back in. And as your cruise AFR goes leaner, you'd have to add fuel to the power-enrichment system, to make a smooth transition from cruise circuit to power circuit. The AFB uses jets and metering rods/power piston; a Holley uses jets and a power valve/power valve channel restrictions.

And, of course, you'd have to verify that the ignition timing is also tuned; including the vacuum advance. Light load (high vacuum) will require more advance than heavier load.

Consider swapping that Edelbrock "Carter AFB Clone" for a Q-Jet. I just love those tiny primary throttles. The Thermoquad is also a good choice, but I don't have much experience with them.
 

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Consider swapping that Edelbrock "Carter AFB Clone" for a Q-Jet. I just love those tiny primary throttles. The Thermoquad is also a good choice, but I don't have much experience with them.

Funny you mention that, I've been thinking about ditching the Edelbrock. I've played with it quite a bit and for whatever reason I can't seem to get the idle to lean out as much as I'd like.

Thanks for the info!

A friend of mine sent me a link to a place years ago that did custom Q-Jet builds for specific applications, they claimed mileage equivalent to fuel injection. Guess they weren't BSing. I'll have to see if I can dig that link up. I've been considering a Holley to replace the Edelbrock but I may have to give the Q-Jets another look.
 

PlayingWithTBI

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They have the potential to get BETTER fuel economy than feedback fuel injection that's tuned to run at "14.7:1" if the carb and engine are tuned to run at 15:1 or leaner.
How about 16.5AFR and 34* advanced with a TBI? Try doing that with a carb, LOL. As soon as I hit the throttle it'll go back into 14.7 or lower depending on TPS/MAP feedback. This is known as HyWay Lean Cruise (you can see the little green light above the speedo). Zero Knocks when cruising either.

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I'm sorry, I still like EFI better. I can sit in my truck and change parameters without turning a wrench or getting smelly from spilled gas.
 

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Yeah, your EFI is no longer programmed to run at Stoich. And the knock-sensor is a great benefit to the lean mixture at cruise.

'Course, your NOx is going to be out-of-sight, so emissions compliance has gone away--but that'd be true of a lean-tuned carb at part-throttle, too. And I suppose you could re-tune faster than the carb owner can swap jets or metering rods.

So, again--given a vehicle that has EFI already, it's nuts to rip that off and go back to a carb.
 

PlayingWithTBI

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Yeah, your EFI is no longer programmed to run at Stoich
It's kind of a hybrid set up, I have to be going faster than 45 and cruising for 30 seconds at Closed Loop (14.7 Stoich), then it'll go into HLC for 4 minutes then back into CL for 20 seconds to check for changes in conditions, then back to HLC, repeat.

And I suppose you could re-tune faster than the carb owner can swap jets or metering rods.
Yep, takes ~4 seconds since I have the capability of 8 different programs (Flash Banks) on board so, I can switch to an emissions compliant (or Valet, etc) .bin on the fly.

So, again--given a vehicle that has EFI already, it's nuts to rip that off and go back to a carb.
I'm totally with ya!
 
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