Vacuum Spark Control

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.

K

Kilian

Full Access Member
Joined
Mar 25, 2018
Posts
221
Reaction score
39
Location
Wisconsin
First Name
K
Truck Year
1983
Truck Model
C2500 on its way to a K2500
Engine Size
350
Hello folks, wondering if anyone can provide some photos or info on how the components circled in the attached photo. This is a 1983 GMC 2500, 350 "M" code engine (HD V8). It's a mess of vacuum hoses that don't go anywhere, so I'm trying to get some of the functionality working again, such as spark control for the distributor.

Not sure where the Thermal Vacuum Switch should be located (assume that it's controlled by coolant temp?), and which port on the Q-jet provides vacuum, best place to put the check valve and delay valve, etc.
 

Attachments

  • Screenshot 2024-10-01 095607.jpg
    Screenshot 2024-10-01 095607.jpg
    115.7 KB · Views: 31
Last edited:
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350
All TVS are coolant controlled. I think there are 2 on the 1983 M engine, one 2 port and one 4 port. You are asking about the two port circled only controls the distributor vacuum advance - dashed line goes to the lower port on the TVS and part of check valve nearest carb which is notionally color coded. If you have the check valve and the delay valve, set up is pretty easy. If not, you'll need to find them in a bone yard.
 
K

Kilian

Full Access Member
Joined
Mar 25, 2018
Posts
221
Reaction score
39
Location
Wisconsin
First Name
K
Truck Year
1983
Truck Model
C2500 on its way to a K2500
Engine Size
350
saltdog said:
If you have the check valve and the delay valve, set up is pretty easy. If not, you'll need to find them in a bone yard.
Click to expand...

Thanks for the info. Those parts are no longer on the engine but I want to add them back. Is it one size fits all? So any check valve and delay valve from that time frame would work? (passenger car, truck, whatever)
 
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350
Not exactly one size fits all, but they should be similar enough for any 350's in that year (except California).
 
K

Kilian

Full Access Member
Joined
Mar 25, 2018
Posts
221
Reaction score
39
Location
Wisconsin
First Name
K
Truck Year
1983
Truck Model
C2500 on its way to a K2500
Engine Size
350
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350
Hard to say w/o looking up the part numbers in the GM parts book. The check valve is 4 port, I've not been able to locate one on the interwebs. Delay valve might be available
 
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350
Unless you are trying to restore to stock or pass emission, you can just run the vacuum from carb and it will work.
 
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350
4 Port Check Valve looks like this:
 

Attachments

  • 4port.jpg
    4port.jpg
    111.2 KB · Views: 25
K

Kilian

Full Access Member
Joined
Mar 25, 2018
Posts
221
Reaction score
39
Location
Wisconsin
First Name
K
Truck Year
1983
Truck Model
C2500 on its way to a K2500
Engine Size
350
saltdog said:
4 Port Check Valve looks like this:
Click to expand...
Found a 4 port check valve like in your photo but it's for a 292 6. Would that work on a 350? Thanks for the help.
 
R

Robert Bare

Full Access Member
Joined
Sep 13, 2020
Posts
107
Reaction score
176
Location
MT
First Name
Robert
Truck Year
1978
Truck Model
k20
Engine Size
5.7
I see no reason to "put it back to stock", and with today's fuel you may be upset with the performance.
Heck, back in the day we were bypassing them on fairly new trucks.
 
S

saltdog

Supporting Member
Supporting Member
Joined
Aug 9, 2020
Posts
81
Reaction score
89
Location
US
First Name
Mike
Truck Year
1983
Truck Model
K20 Suburban
Engine Size
350

Attachments

  • 4 port.jpg
    4 port.jpg
    24.2 KB · Views: 20
Last edited:
K

Kilian

Full Access Member
Joined
Mar 25, 2018
Posts
221
Reaction score
39
Location
Wisconsin
First Name
K
Truck Year
1983
Truck Model
C2500 on its way to a K2500
Engine Size
350
saltdog said:
Post a link to the pic or listing.
Click to expand...
This is the one that I found...I went ahead and bought it just to have something to use, even if it might not be exactly right for a V8. I'm going to keep looking at local boneyards but so far haven't found anything used.
 

Attachments

  • Screenshot 2024-10-06 073522.jpg
    Screenshot 2024-10-06 073522.jpg
    80 KB · Views: 19
You must log in or register to reply here.

Similar threads

CopperLB81
81 C10 305 vacuum issues.
2
Replies
17
Views
4K
AuroraGirl
AuroraGirl
77Matt
Qjet to Edelbrock 1400 vacuum line puzzle- I need help
Replies
13
Views
2K
77Matt
77Matt
S
EFE, traditional Heat riser & thermac informational
Replies
10
Views
3K
SirRobyn0
S
NickTransmissions
  • Sticky
TH400 Information Thread
5 6 7
Replies
94
Views
13K
NickTransmissions
NickTransmissions
NickTransmissions
4L80E Information Thread
Replies
14
Views
5K
MrMarty51
MrMarty51

Latest posts

Forum statistics

Threads
44,416
Posts
957,140
Members
36,755
Latest member
square-up
Top