Vacuum lines on 1985 GMC Sierra

[Gmcfan1974]

Hello I have recently purchased a 85 GMC Sierra as a project truck. I have been out of the mechanic side of things for about 20 years now while I was in the army.

 

What I would like to know is can I do away with all the vacuum lines coming from the carb if I am changing the intake manifold and the carb? I know I still need the vacuum lines for the trans, brake booster and Pcv valve but can I remove the rest of the lines?

 

I am not looking for fuel economy as this is a project truck that will one day be a show truck.

 

Thanks.

[Gmcfan1974]

Jsdirt thanks for the reply. I picked up a Edelbrock performer intake today and I found a guy that had a summit 4bbl 600cfm carb today for a buck and half. So now I can ditch the stock carb as well.

 

Thanks again for the input. Much appreciated.

[gmtech4]

U need to find a schematic but in the end they are there for a reason to operate something .,,,

 

Removing some will not get anymore mileage for you

[Gmcfan1974]

I am not looking for mileage. I want a clean look under the hood and get rid of all the spiderweb of vacuum lines.

 

My last project was a 1974 Chevy Nova and I only had 3 vacuum lines. I would like to return to that setup.

[Jsdirt]

No problem - good luck with the mods. Just to correct my spelling, that brand is ECHLIN ... not what I posted before, lol.

[grampadirt]

Keep in mind this truck has an ECM,if you go disconnecting things you could be seeing a CEL.

[Doug_Scott]

Hello I have recently purchased a 85 GMC Sierra as a project truck. I have been out of the mechanic side of things for about 20 years now while I was in the army.

 

What I would like to know is can I do away with all the vacuum lines coming from the carb if I am changing the intake manifold and the carb? I know I still need the vacuum lines for the trans, brake booster and Pcv valve but can I remove the rest of the lines?

 

I am not looking for fuel economy as this is a project truck that will one day be a show truck.

 

Thanks.

 

Which engine is in your truck? Aren't all 85 truck engines fuel injected? Swapping out the TBI for a carb is far more involved than just a few vacuum lines. At the least you are looking at rewiring ignition system, creating a low pressure fuel system, and depending on location, you may have heat riser valve issues, along with fuel tank venting issues. Depending upon geographical location, you may also have EPA issues with the removal of emission control systems.

Other than that, there are two types of vacuum connections, manifold vacuum and venture vacuum. One has vacuum at closed throttle that decreases with throttle opening, and the other has no vacuum at closed throttle, with vacuum increasing as throttle opens. One would be useful for brake booster and pcv, the other for vacuum advance on distributor.

[Gmcfan1974]

Doug thanks for the reply. I have a 350 in it the truck came with a 305 carb. This truck did not have TBI from the factory it came with a 4bbl carb. As for EPA issues we do not have any in checks in my location for emission controls. I do have a canister for the fuel tank.

 

I am just trying to remove as many of the lines as I can without causing issues. Like I said in the post this will be a show truck or as close as I can get to one with it.

[Gmcfan1974]

Grampadirt thanks for the reply. I have looked for the ECM and I am not able to locate one on this truck and I have spoke to all the parts stores in this area and none are showing one for it.

[Doug_Scott]

Doug thanks for the reply. I have a 350 in it the truck came with a 305 carb. This truck did not have TBI from the factory it came with a 4bbl carb. As for EPA issues we do not have any in checks in my location for emission controls. I do have a canister for the fuel tank.

 

I am just trying to remove as many of the lines as I can without causing issues. Like I said in the post this will be a show truck or as close as I can get to one with it.

 

Found vacuum diagram online, should make it easier to see what you can do.

 

[Gmcfan1974]

Thanks. The engine already has the GM HEI in it.

[Jsdirt]

Your one step ahead of where I was. Good deal.

[Jsdirt]

Yeah 90% of those vac lines are all for emissions b/s - throw it all in the trash. Useless. All engineering bandaids. Been there, done that. I even removed the pcv system on mine - they just vent to the atmosphere thru a PCV valve in each valve cover. I don't recommend that, though.

 

If you have any ignition issues, just find a cheap HEI setup and drop it in. I found a complete setup on eBay for $60!! That's the ENTIRE distributor assembly! Word of warning though - you get what you pay for with the internals. I'd replace all of it with quality components (Eichin from NAPA for example - 3 year 50k warranty) before running it. I had 3 eBay distributors leave me dead in the water. Most I ever got was 7k miles out of the electronics. Replace the HEI module, pickup, condenser assembly, and coil, and it will be as reliable as a stone ax.

 

Just make sure the 3 vac lines you mentioned in your first post are intact when your done. Oh, and block off the empty ports in the carb. I'd ditch the stocker for an Edelbrock IMHO.