1981 250 Carb to TBI Conversion

[Moskau]

I have a 71 1/2 GMC with I think a 1981 250. Hasn't ran to good whatsoever for a long time. Put a new carb on but didn't fix anything, still stalls even when engine is warm. I am thinking about doing a tbi conversion...any links or info please?

[78bronzechariot]

First of all before you go EFI and spend the money make sure the carb is actually your problem, not timing, vacuum leaks, or something else. If you are sure about EFI, what route are you interested in going? I don't think there was ever a factory TBI 250. I could be wrong though. You may be able to get away with a setup from a 4.3 v6 (that is about a 265 if I remember right) They ran speed density through '96 (No MAF). I think the only hard part would be the distributor, other than that you should be able to add the sensors that the system would require (MAP, CT, O2, IAT etc.) The distributor from a 4.3 v6 may fit since it has the same housing as a small block V8 does, guys with more 250 experience can verify if the distributor would interchange. The other issue you may run into is bolting the TBI to your manifold. You may have to mickey mouse it with a 4 barrel intake and and adapter to GM TBI bolt pattern.

The other options are going the aftermarket TBI route. Holley makes a simple one called projection. They are available in 2 barrel and four barrel It is simple to tune. Just has some slide switches on the computer to adjust your air/fuel, accelerator enrichment, etc. I think they run about $600-700.

Another option is Professional Products Powerjection. I have on on my 375 horse 350 CI '78 Caprice. It is self tuning for the most part, but is fully tunable with a laptop if you want to go that route. The unfortunate part is that it looks like a Holley four barrel and is just as big. I have the smallest one, which is rated at 750 CFM. I am afraid that it would be two much for a stock 250. They run about $1700-2000 depending on options.

FAST just started offering a self tuning four barrel TBI also, but I have not seen one in use or seen a price yet. I would also be afraid it would be too much fuel for your application.

If you do the EFI route and get the bugs out of it you will really enjoy the increased power, fuel economy and better driveability. Putting the Powerjetion in place of the Holley on my '78 shave a second off 0-60, 1.4 seconds off the 1/4 and gained 1.5 MPG (it gets a dismal 14 mpg highway now!) I did a LSX (4.8 vortec from a Silverado) swap in my '67 C10 and it is just like driving a new truck now.