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Posted: 12/27/2005 4:21:30 AM EDT
I have a 1990 C2500 w/305 V8. I'm looking to replace the TBI system with a regular old 4-barrel carb. If I'm not mistaken, some came with the 4-barrel. How difficult would it be to do this modification? Would I need a new intake manifold or would the stock manifold work? Anybody have a website or something that shows a tutorial of this procedure? Thanks. MJD
Link Posted: 12/27/2005 8:03:23 AM EDT

Originally Posted By highwayman:
I have a 1990 C2500 w/305 V8. I'm looking to replace the TBI system with a regular old 4-barrel carb. If I'm not mistaken, some came with the 4-barrel. How difficult would it be to do this modification? Would I need a new intake manifold or would the stock manifold work? Anybody have a website or something that shows a tutorial of this procedure? Thanks. MJD


There might be some Chevy forums that you might want to look at...I don't know any offhand.

I think the older ones did.
Link Posted: 12/27/2005 12:09:29 PM EDT
You'll be looking at a decent project to swap to a carb from TBI.

First, the on the intake, the center 2 bolts on both sides are at a different angle on the old carb manifolds than the tbi. This can be bypassed by slotting the holes out, but you do have a chance on vaccuum issues doing that.

Then, you have to switch to an old style HEI or other aftermarket distributor.

Now your computer don't work so well. But you still need it to run the gauges, unless you swap them out for mechanical style gauges.....

YMMV.
Link Posted: 12/27/2005 4:27:39 PM EDT

Originally Posted By moparman71:


Now your computer don't work so well. But you still need it to run the gauges, unless you swap them out for mechanical style gauges.....

YMMV.


The 1990 didnt have a factory tach so thats not a problem. The speedo will still work.
Link Posted: 12/27/2005 7:44:18 PM EDT
I have to ask, why would you be looking to do this?
Link Posted: 12/28/2005 3:49:49 AM EDT

Originally Posted By 455SD:
I have to ask, why would you be looking to do this?




Most people go from carb to TBI or PFI, so this is a little unusual.


I suppose it's possible to do a TBI to carb setup, but I've never done one myself.

Link Posted: 12/28/2005 5:57:11 AM EDT
It would be less money to put a rebuilt TBI on than it would to do a backwards conversion...

Off the top of my head...

Carb $275

Manifold $160

Dist. $180

And then there's the issue with your fuel pump........at a minimum, you would have to rig up a regulator in the system to knock the pressure down to something a carb will handle....
Early morning thoughts.............Boo
Link Posted: 12/28/2005 7:03:24 AM EDT
Reason I ask, the 1990 TBI is a really good reliable system. It is a big step up from the standard carb for everyday use. Did yours take a huge dump or what?
Link Posted: 12/28/2005 7:41:08 AM EDT

Originally Posted By 455SD:
Reason I ask, the 1990 TBI is a really good reliable system. It is a big step up from the standard carb for everyday use. Did yours take a huge dump or what?



Possibly. I'm still in the process of troubleshooting it. Just wanted to see what options I'd have if I did need to replace the whole system. Looks like TBI to carb would be more trouble than it's worth. Hopefully it's just some stupid little electrical problem in the TBI system and nothing major. If the truck was a 4WD I would have swapped out the whole engine a long time ago. I still don't know why GM put a 305 in a 3/4 ton truck. It only makes 170 horsepower and 225 lbs. torque. It's got a 700R4 transmission, 14 bolt rear, so there's really no reason they couldn't put a bigger engine in there. Heck the engine bay could easily accomodate a 454. Anyway, rant mode off. MJD
Link Posted: 12/28/2005 9:26:45 AM EDT

Originally Posted By highwayman:

Originally Posted By 455SD:
Reason I ask, the 1990 TBI is a really good reliable system. It is a big step up from the standard carb for everyday use. Did yours take a huge dump or what?



Possibly. I'm still in the process of troubleshooting it. Just wanted to see what options I'd have if I did need to replace the whole system. Looks like TBI to carb would be more trouble than it's worth. Hopefully it's just some stupid little electrical problem in the TBI system and nothing major. If the truck was a 4WD I would have swapped out the whole engine a long time ago. I still don't know why GM put a 305 in a 3/4 ton truck. It only makes 170 horsepower and 225 lbs. torque. It's got a 700R4 transmission, 14 bolt rear, so there's really no reason they couldn't put a bigger engine in there. Heck the engine bay could easily accomodate a 454. Anyway, rant mode off. MJD


My dad has got a '97 3/4 ton with a 305 2WD and an auto...IIRC it's a 4L80...you could put in a crate motor if you wanted to spend the money. I think the 305 in the '97 has got plenty of power. I want to say it's an SFI system but I'm not sure.
Link Posted: 12/28/2005 10:08:22 AM EDT

Originally Posted By deej86:

Originally Posted By highwayman:

Originally Posted By 455SD:
Reason I ask, the 1990 TBI is a really good reliable system. It is a big step up from the standard carb for everyday use. Did yours take a huge dump or what?



Possibly. I'm still in the process of troubleshooting it. Just wanted to see what options I'd have if I did need to replace the whole system. Looks like TBI to carb would be more trouble than it's worth. Hopefully it's just some stupid little electrical problem in the TBI system and nothing major. If the truck was a 4WD I would have swapped out the whole engine a long time ago. I still don't know why GM put a 305 in a 3/4 ton truck. It only makes 170 horsepower and 225 lbs. torque. It's got a 700R4 transmission, 14 bolt rear, so there's really no reason they couldn't put a bigger engine in there. Heck the engine bay could easily accomodate a 454. Anyway, rant mode off. MJD


My dad has got a '97 3/4 ton with a 305 2WD and an auto...IIRC it's a 4L80...you could put in a crate motor if you wanted to spend the money. I think the 305 in the '97 has got plenty of power. I want to say it's an SFI system but I'm not sure.




You obviously haven't tried to tow much.
Link Posted: 12/28/2005 10:55:17 AM EDT

Originally Posted By highwayman:


Possibly. I'm still in the process of troubleshooting it. {snip} Hopefully it's just some stupid little electrical problem in the TBI system and nothing major. {snip}



So what's your symptoms? I'd bet between myself and the pontiac fan we can help fix your chevy!
Link Posted: 12/29/2005 4:19:01 AM EDT

Originally Posted By moparman71:

Originally Posted By highwayman:


Possibly. I'm still in the process of troubleshooting it. {snip} Hopefully it's just some stupid little electrical problem in the TBI system and nothing major. {snip}



So what's your symptoms? I'd bet between myself and the pontiac fan we can help fix your chevy!



I appreciate the offer, but I already got it taken care of. Turns out the problem wasn't in the injection system at all. The distributor cap and rotor were toast. When I took the cap off, thin pieces of metal fell out. Still don't know where they came from. In any case the rotor button on the underside of the cap was nearly gone and all the contacts were heavily coated in carbon. I changed the plug wires too just for good measure. It runs like a champ now and even seems to be accelerating quicker. MJD
Link Posted: 12/29/2005 9:27:16 AM EDT
Good to hear, glad you're back in business!
Link Posted: 12/30/2005 8:39:35 PM EDT
Well that was an easy fix. Need anything else just let us know.
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