79 carb desmog help (1 Viewer)

[Mickey Plunkett]

Anyone have info on the bare minimum of vacuum lines/smog stuff that has to be left on a 79 carb? I want to simplify as much as possible and eleminate anything that doesn't help the truck run better. My rebuild has progressed to the point that I have to tackle the carb next.

 

[FJ40Jim]

Bare minimum?
There needs to be power and ground to the ICS.
Fuel goes to the inlet.
choke cable.
throttle linkage.

If you want to keep the systems that make it run good, and eliminate the extraneous stuff, see the desmog info in tech. It's directed at 81-87, but the 79-80 are almost identical.

BTW, Nice looking truck.
The engine lift hook goes on the back 2 head bolts. And there are allen plugs to go in the head where those air injection pipe stubs are sticking out.

 

[F-junker]

wow very nice...

Mr. Clean
I'm in the same boat myself. I'll check back with you on this post. Let me know how you've made out. I've not found the tech section to be too useful for emssion removal.

I have a question about your down pipe, where did you find it? I want to retain my stock exhast system but was worried that connection to the ex manifld would be problematic and thus a header has been contemplated.

good luck with your project, the gentlman JIM who posted is an authority here on carbs and what have you. I may be shipping my carb out to him If I encounter any problems.

 

[Mickey Plunkett]

F-junker
Downpipe is stock as far as I know. I removed, sandblasted, painted w/ POR15 manifold paint, and reinstalled w/ new gasket. I also thought about headers but I installed a PTO on this truck and most headers woun't clear the PTO driveshaft. I saw your comment on another post related to getting to bare minimum vacuum lines/emissions. I'll let you know if I have any luck sorting out the Tech entries for desmog.

Jim-C
Thanks for the correction on the lift hook. My 70 didn't have one and I just put this one back where I found it. The PO bought the truck with the motor in parts and had his shop foreman rebuild it but he got a few things mixed up. I'll get it moved. I guess he's the one that capped all the pipe stubs too. I started to pull pull them out and replace with plugs but had plenty of other tasks that were more important. I'll check the tech entries for Desmog to see if I can figure it out.

 

[Pin_Head]

I don't think that there is a down side to keeping the stock electro-mechanical control of the carb as long as it works. The throttle positioner and power valve control are useful. It is really first generation electronic carburation rather than smog control.

 

[Mickey Plunkett]

Jim C (or anyone else who knows)
I pulled the jimc-approved diagram from the desmog tech page and have a couple of questions/assumptions. Can someone verify my current understanding on these issues?

The charcoal canister has been removed which shouldn't impact performance but does require that I provide a vent to the gas tank. If I use the line that ran from the canister to the tank and put a filter on the end to keep bugs out are there any other issues to consider? Any special consideration needed for the fuel bowl vent that was connected to the canister? If not, that allows me to eleminate not only the canister but an electric valve, vacuum valve, and a water temperature valve that are all part of the canister operation.

My second question relates to the altitude compensation. I can see on your diagram that the HAI diaphram and the HIC valave are connected to each other but it doesn't appear that they are connected to anything else. I don't have any altitude issues in Mississippi but I thought I'd leave the compensation in place for trips to higher locales if I can figure out how it works.

My last question relates to vacuum lines to the distributor. From reading through all the tech entries and several entries on the forum it appears that the large tube goes to the firewall fitting which has a filter on the other side of the firewall. The vacuum line on top of the cap goes to the air cleaner to draw clean air through the dist. via the firewall filter. Why is there a vacuum switch on the dist cap vacuum line? Couldn't that line just go straight to the air cleaner and provide ventilation vacuum all the time? The vacuum advance nearest the dist body goes to the advancer port and the vacuum advance farther from the dist. body goes to the air cleaner(or HIC valve?). Do I have that right?

Like I said, I want the system to be reduced to the necessary items that will make the truck run well.

 

[FJ40Jim]

I don't think that there is a down side to keeping the stock electro-mechanical control of the carb as long as it works. The throttle positioner and power valve control are useful. It is really first generation electronic carburation rather than smog control.

There is no PV or TP controls on 1979-newer USA carbs.