Intake plenum gaskets

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
4,232
Reaction score
5,167
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
I got the carb off the truck and apart today, got the air horn off ok. I poured the gas that was in there out. The power valve with the two needles was stuck and a little bent, and the needle valve was completely off and the wire spring that holds it on the float was off. How did that happen, did I do it pouring the gas out? don't think I bent the power valve part, and I think I got it straightened out ok, but maybe the needle valve fell off when I poured the gas out? I put it back together and hung it on the float, should I get a new one? Having trouble figuring out how to check the float level. I found a really good video that is pretty helpful but this is kinda scary for me. Not sure how I'm going to get the needles on the power valve into the jets, and I don't want to try until I know if I should get a new needle valve.
Yes, needle likely fell off when you turned it over to dump the gas, it just hangs on there by the spring normally. The power valve hanger can easily get bent if the last person to assemble it didn't make sure the needles were lined up inside the jets before assembly. It's kind of a pain to get everything lined up and in the right spots in the air horn gasket while assembling it. If you slip and it slides out of the jet and moves a bit to the side, then it will jam up sideways and then get damaged when someone tries to keep bolting it down.
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
4,233
Reaction score
6,209
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
I got the carb off the truck and apart today, got the air horn off ok. I poured the gas that was in there out. The power valve with the two needles was stuck and a little bent, and the needle valve was completely off and the wire spring that holds it on the float was off. How did that happen, did I do it pouring the gas out? don't think I bent the power valve part, and I think I got it straightened out ok, but maybe the needle valve fell off when I poured the gas out? I put it back together and hung it on the float, should I get a new one? Having trouble figuring out how to check the float level. I found a really good video that is pretty helpful but this is kinda scary for me. Not sure how I'm going to get the needles on the power valve into the jets, and I don't want to try until I know if I should get a new needle valve.
I would replace the needle and seat. Get a non windowed seat. And leave the clip off that holds the needle to the float. After your non windowed seat is in fill the bowl with liquid of your choosing to just below the top of the seat. Walk away,come back later and see if there is a puddle underneath the carb. Yes? You have leaky plug wells,we can walk you through that. No puddle? Put it back together.
 
Last edited:

yellowdog5

Full Access Member
Joined
Nov 3, 2019
Posts
78
Reaction score
35
Location
Oregon
First Name
Faith
Truck Year
1979
Truck Model
k20
Engine Size
400
So it runs good enough to pull a horse trailer down the highway? Seems only problem then is the priming issue?
No it used to run good enough to pull a trailer, priming has been a problem for a long time even though I had it worked on twice, then it started getting worse so I was afraid to try pulling the trailer, it was weak at low speeds and I don't know if it would have pulled a hill. I hauled 4 loads of hay 10 miles on flat ground, pretty puny uner a load and it finally quit. I installed the accelerator pump, cleaned the carb up (wasn't very dirty) and checked the float level to the best of my ability, put it back on the truck and now it starts without priming and runs pretty strong, still seems alittle rough so not sure it's perfect but it does run a lot better. I'll haul another load of hay after I change the oil today and see how it does.
 

yellowdog5

Full Access Member
Joined
Nov 3, 2019
Posts
78
Reaction score
35
Location
Oregon
First Name
Faith
Truck Year
1979
Truck Model
k20
Engine Size
400
How come 2 "mechanics", one in a shop, couldn't figure out it needed an accelerator pump? I know for a fact the first one used the old one because a new one didn't come with the kit. Just venting here, I have a lot more questions about the truck since I am using it quite a bit now, but will save them hopefully until I get all the hay hauled. A big thank you to everyone that helped.
 
Last edited:

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,390
Reaction score
14,943
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
How come 2 "mechanics", one in a shop, couldn't figure out it neede an accelerator pump? I know for a fact the first one used the old one because a new one didn't come with the kit. Just venting here, I have a lot more questions about the truck since I am using it quite a bit now, but will save them hopefully until I get all the hay hauled. A big thank you to everyone that helped.
Sadly that is the way a lot of "mechanics" are nowadays. Integrity is no longer a trait the majority possess.
 

Grit dog

Full Access Member
Joined
May 18, 2020
Posts
6,102
Reaction score
10,258
Location
Washington
First Name
Todd
Truck Year
1986
Truck Model
K20
Engine Size
454
How come 2 "mechanics", one in a shop, couldn't figure out it needed an accelerator pump? I know for a fact the first one used the old one because a new one didn't come with the kit. Just venting here, I have a lot more questions about the truck since I am using it quite a bit now, but will save them hopefully until I get all the hay hauled. A big thank you to everyone that helped.
Because many of us here aren’t even mechanics by trade but are mechanically inclined. Helps that everyone here has some connection to 70s-80s GM vehicles. And at some point I bet all of us got hornsshwaggled by a “mechanic.” And like you either out of necessity or frustration said “fck it. I’ll do it myself!”

Glad to hear it’s running better.
 

yellowdog5

Full Access Member
Joined
Nov 3, 2019
Posts
78
Reaction score
35
Location
Oregon
First Name
Faith
Truck Year
1979
Truck Model
k20
Engine Size
400
I hauled hay this morning, started up with 3-4 pumps. It runs ok but seems rough, sometimes hesitates when taking off. I know this doesn't explain much but I think it still needs help, not sure where to go from here.
 
Last edited:

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,390
Reaction score
14,943
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
How's the timing?
 

yellowdog5

Full Access Member
Joined
Nov 3, 2019
Posts
78
Reaction score
35
Location
Oregon
First Name
Faith
Truck Year
1979
Truck Model
k20
Engine Size
400
How's the timing?
The guy that looked at it recently checked it and was happy with it, I need to learn how to check it myself, something I have never done. I just looked at a video of it, I need to see if my timing light is a good one or a cheap one, hopefully it will work. Edit: My timing light is Innova 3551, it's pretty old but last I knew it worked fine (not used by me, by my late husband and his father).
 
Last edited:

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,390
Reaction score
14,943
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
The guy that looked at it recently checked it and was happy with it, I need to learn how to check it myself, something I have never done. I just looked at a video of it, I need to see if my timing light is a good one or a cheap one, hopefully it will work. Edit: My timing light is Innova 3551, it's pretty old but last I knew it worked fine (not used by me, by my late husband and his father).
I personally am not familiar with that brand of timing light, but I am sure it's more then capable to check it and set it.
 

yellowdog5

Full Access Member
Joined
Nov 3, 2019
Posts
78
Reaction score
35
Location
Oregon
First Name
Faith
Truck Year
1979
Truck Model
k20
Engine Size
400
I personally am not familiar with that brand of timing light, but I am sure it's more then capable to check it and set it.
Okay now I just need to learn how. Hope I can see well enough to see the marks.
 

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,390
Reaction score
14,943
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
Okay now I just need to learn how. Hope I can see well enough to see the marks.
It helps to have a clean mark on the dampener as well as a clean tab on the timing cover.
 

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,390
Reaction score
14,943
Location
Right where I am
First Name
Bagoomba
Truck Year
1981
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s
Engine Size
Carb'ed Vortec 350
If you have the oem air cleaner housing, follow the instructions on the label.

On mine, if I time it like I learned to, it'll be off. On mine, it needs to be up to operating temperature, all carb adjustments done, rpm set, and everything hooked up like you would drive it. Then I can set the timing. It goes against everything I learned and what people say to do. I say this so you can follow the correct procedure, granted it has the sticker on the air cleaner
 

Latest posts

Forum statistics

Threads
42,349
Posts
914,140
Members
33,855
Latest member
3dbello
Top