81 C10 305 vacuum issues.

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CopperLB81

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Biscoe NC
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Bud
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1981
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C-10
Engine Size
305
Couple weeks back I bought an 81 C10 custom deluxe two wheel drive with a 305 in it two barrel carb. I'm currently driving it everyday. It seems to run well and does great fuel mileage on the highway but around town it's only getting like maybe 8 miles to the gallon the truck is bone stock engine wise. The previous owner deleted the air vacuum pump off of the engine. I was told that he did a vacuum delete on the truck. From what I can tell the thermal switch is still in the intake manifold and the efe valve is still on the exhaust manifold. My issue is the truck is running extremely rich at idle or sitting in traffic the cab fills with exhaust fumes. The charcoal canister is also still in the truck but the ports are open no lines hooked to it whatsoever. Could someone please explain to me the proper way to do this delete or tell me if there is a kit out there to buy to put all the vacuum air pump and emission stuff back on the engine. I don't care about horsepower like I said it's my daily but I would like the fuel economy to get a little better around town and would love for the truck to not run so rich.
Also I've noticed the trans shifts wonderful but as you're cruising along if you go to an incline or slight grade and you go to give the truck a little more gas it almost feels like it shifts into overdrive instead of downshifting or holding steady RPM. Does that issue have something to do with the vacuum trans control switch that is no longer hooked up or has vacuum lines running to it on the driver side front of the intake manifold? Thank you any help would be greatly appreciated.
 

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MarineOne

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Brake cleaner. Only way you'll find the leak

That said if it's running rich at idle it's more likely a car tuning issue as a vacuum leak would cause a lean condition
 

Ricko1966

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It looks like all your components are there. Look at your vacuum diagram and hook all that stuff back up. GM knew what they were doing when they put that stuff on. Yes,that will help milage. Make sure your vacuum advance is functional. As @MarineOne said spray around the carbureator base and around the intake manifold perimeter with carb cleaner if the fuel(carb cleaner) gets sucked into a vacuum leak idle will change.Make sure the choke is fully open when the engine is at operating temperature. Describe your transmission situation better,I'm not understanding what you are trying to say. Spraying for vacuum leaks I use carb cleaner,not brake clean supposedly burning brake clean creates some very toxic gas phosgene or something,I don't know know if its true,but no reason to chance it.
 

AuroraGirl

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Brake cleaner. Only way you'll find the leak

That said if it's running rich at idle it's more likely a car tuning issue as a vacuum leak would cause a lean condition
or a propane torch, unlit, which will not degrade the plastics which are old and brittle already AND wont cause a fire in the same way. rememeber, propane is heavier than air so you dispense it above the area looking to check
 

AuroraGirl

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can you remove your air cleanerr and show us the carb? also, you have an electric choke ,thats good. YOu also have a miussing pipe from the air cleaner to the valve cover where that stick-in-breather goes. your air cleaner has that opening in it, it looks like the filter media is missing from the opening too.
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heres some parts you may need down the road.. also, I Would like to see under your distributor cap. take it off , set to the side, and show us the mechanical advance with the rotor off as well, then show us the contacts on the cap where the rotor transfers spark
 

MarineOne

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or a propane torch, unlit, which will not degrade the plastics which are old and brittle already AND wont cause a fire in the same way. rememeber, propane is heavier than air so you dispense it above the area looking to check
Fantastic idea I've never heard of
 

Ricko1966

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Fantastic idea I've never heard of
What I don't like about the propane,is it is a good idea and a piece of heater hose over the end about 18 inches long helps,but the fan tends to blow it away before I can find the leak,it's also good for hard starts stick the hose in the snorkel givebut a little juice,then start it.
 

AuroraGirl

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What I don't like about the propane,is it is a good idea and a piece of heater hose over the end about 18 inches long helps,but the fan tends to blow it away before I can find the leak,it's also good for hard starts stick the hose in the snorkel givebut a little juice,then start it.
You could pull the fan belt if its not too hard to loosen for you, but most fan belts are the 2nd or 3rd back belt, i think, the ps and the alternator are usually further ahead?
 

SquareRoot

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Ether. And it smells good too. :insane:
 

Craig Nedrow

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turn my back fur a couple minutes, and Mike's huffin ether!!
 

Trucksareforwork

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1. The two vacuum switches in your picture showing the thermostat housing (one is orange, one is red) are basically an open vacuum leak. They don’t look capped. You will want to cap them if nothing else. Your truck will run better. May have to adjust idle up afterward.

2. As somebody else said, look at the vacuum diagram for your truck or go find one and re-install the vacuum hoses. For some reason some bubbas think that ripping out vacuum lines is an “emissions delete.”

3. For your transmission: you should have a vacuum modulator line to the transmission. Just be sure it’s connected to the intake manifold. I don’t think your truck would have an overdrive transmission being an 81. Should have a th350. The th350 has a kick down cable that should be attached to your throttle linkage. Can’t see that in the pics. If that isn’t attached you won’t get a kick down quickly when you press the gas pedal down. If for some reason your truck has a 700r4 (with overdrive) , then yes you should have a kick down vacuum switch on the firewall. If it isn’t connected you won’t get proper kick downs.

4. Probably need to be sure your egr and vacuum advance are attached properly too. It looks like your vac advance is connected but the EGR is not. That can affect performance as well particularly on a 305 where IIRC the richer mix (less oxygen with egr active) can help prevent pinging.

If you post pictures with the air cleaner off some of this can be seen.

Edit: don’t worry about the air pump. That isn’t for vacuum and won’t appreciably change the way the truck drives. The air pump was to add air to the exhaust post combustion to aid the old catalytic converters. Totally different from the vacuum actuated systems that you need to have operating.
 
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Ricko1966

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The two vacuum switches are not presently attached to a vacuum source,so capping them is not necessary. They are suppose to have supplied to them and they open or close based on water temperature to control components. See what you can figure out from your vacuum schematic, if you have trouble,let's us know we can pitch in and tell you what goes where.
 

Trucksareforwork

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The two vacuum switches are not presently attached to a vacuum source,so capping them is not necessary. They are suppose to have supplied to them and they open or close based on water temperature to control components. See what you can figure out from your vacuum schematic, if you have trouble,let's us know we can pitch in and tell you what goes where.
Oops. that's right. they aren't in manifold they are in the coolant. My mistake. I can't believe I misremembered that.
 

Trucksareforwork

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visually similar to a vacuum tree so you are forgiven
True and exactly where my mind went, but I deserve 40 lashes because I changed out the TVS’s on my 85 305 only a year and a half ago. I shouldn’t have remembered that wrong let alone written “advice” about it.
 

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