Vacuum Spark Control

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Kilian

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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.
 

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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.
 
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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)
 
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Not exactly one size fits all, but they should be similar enough for any 350's in that year (except California).
 
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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
 
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Unless you are trying to restore to stock or pass emission, you can just run the vacuum from carb and it will work.
 
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4 Port Check Valve looks like this:
 

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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.
 
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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.
 
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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.
 

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