My Desmog Thread

[Gabbo]

Hey guys, I'm almost done with my desmog. I'm in Idaho so no emitions testing! The only part of desmogging I need to do now is the part that all hooked to the exhaust. But I wanted to see what you all thought of my progress so far so you can correct me if I've done anything wrong. And hopefully help others who may be wanting to do the same thing.
Thanks!

The Great Gabbo

 

[GLTHFJ60]

Looks great! What are the two red wires coming from the alt connected to? Did you keep the HAC or did you remove it?

 

[Gabbo]

Those two red wires are for my duel battery setup. And I did keep the HAC, I figured I'd need it up here. I do have another question though, the engine runs great when I run a vacume line from the air cleaner to the distributor, but does not run well when I have the VCV setup on the distributor like I think it's suposed to go in the diagrams. Any sugestions or ideas?

Thanks.

 

[GLTHFJ60]

Check the timing settings without any vacuum lines connected to it. Those diaphragms are for the vacuum advance of the dist. With a desmog, you should be able to run at least 15* advance.

 

[Gabbo]

Awesome thanks, I'll try that first thing tomorow morning!

 

[FJ40Jim]

With a desmog, you should be able to run at least 15* advance.

Why?
Wouldn't 15* base, plus 24* cent, plus 18* vac give 57* w/ all in?

Is 57* about 15-20 past optimum?

 

[Gabbo]

Okay, Now I'm confused.

 

[fowldarr]

Hey Gabbo, where you at in ID? (Not a hijack, just working on similar projects and both in idaho, might be good for hands on help)

 

[Matt60]

Why?
Wouldn't 15* base, plus 24* cent, plus 18* vac give 57* w/ all in?

Is 57* about 15-20 past optimum?

so can i run 20* past w/ my dual dellorto set up???

i believe i run 9* w/ sans smog but my truck still lives at 900ft ASL ?

find a wheel chalk and a friend back off a hair or enjoy the holiday good luck

 

[GLTHFJ60]

Alrighty, I'm confused. The vacuum advance is only activated by the HAC, which advances the timing at a certain altitude. From the thread I where I installed my headers, I thought we came to the consensus that 15-17* BTDC was a good setting for the timing.

I run my timing in the neighborhood of 17* advanced - but I tuned it by feel- there is no concrete number. I also live at around 4100' so that may have some to do with it. I run an H42 (soon to be H41 eventually) stock 3.70's, and 33x10.5 AT's. My in-town mileage is about 14 and I regularly get 17 on the highway.

 

[FJ40Jim]

Alrighty, I'm confused. The vacuum advance is only activated by the HAC, which advances the timing at a certain altitude. From the thread I where I installed my headers, I thought we came to the consensus that 15-17* BTDC was a good setting for the timing.

There are 2 vac advancers on the dissy.
The vac fitting nearest dissy is main vac advance, gives ~18*.
The vac fitting on the outer end of can is the HAC advance, gives 6-7*

The main vac advance is activated by ported vac off the carb, which is load sensitive.

The HAC advance is (as you mentioned) activated by the HAC valve above ~4500'.

HTH.

 

[Gabbo]

I'm in Rigby. And two heads are for sure better than one. But now I'm becoming more and more confused about this timing thing. I didn't ever go out yesterday and try anything because it was too cold and family came over since it was Thanksgiving and all. Now all the family is gone for some black friday shopping and I finally have a chance to park in the warm garage and work on it some more. So, if I can't get the timing right, should I drop the HAC?

 

[GLTHFJ60]

There are 2 vac advancers on the dissy.
The vac fitting nearest dissy is main vac advance, gives ~18*.
The vac fitting on the outer end of can is the HAC advance, gives 6-7*

The main vac advance is activated by ported vac off the carb, which is load sensitive.

The HAC advance is (as you mentioned) activated by the HAC valve above ~4500'.

HTH.

Ok, so that means that assuming the vacuum lines are hooked up correctly, and you're above the activation altitude for the HAC to kick in, then the truck will idle at 18* advance via the main advance, correct? Why have the main advance if you can adjust the advance by rotating the dizzy?

 

[FJ40Jim]

Ok, so that means that assuming the vacuum lines are hooked up correctly, and you're above the activation altitude for the HAC to kick in, then the truck will idle at 18* advance via the main advance, correct? Why have the main advance if you can adjust the advance by rotating the dizzy?

If the vac lines are hooked up stock, the HAC advance will give 6*, plus the stock 7*, for a total of 13* idle timing.

Distributors have advance mechanisms to automatically adjust the timing under changing speed & load conditions.

 

[Trapper50cal]

Okay...

So that begs the question...What if I live at 6000ft (which I do) is the HAC advance on the dizzy always activated? And if so, will it wear out? or is it not that sensitive or prone to failure.

Forgive me if that is a stupid question as I don't know how it works...is it a pressure sensitive diaphram?

 

[Gabbo]

Yikes, I hope not... oh, and I still haven't done my timing yet. I know, I suck.

 

[FJ40Jim]

What if I live at 6000ft (which I do) is the HAC advance on the dizzy always activated?

And if so, will it wear out? or is it not that sensitive or prone to failure.

is it a pressure sensitive diaphram?

Yes.

No, not likely.

It is a vacuum diaphragm, so it is sensitive to atmosphere on one side and vacuum on the other.

 

[Trapper50cal]

Yes.

No, not likely.

It is a vacuum diaphragm, so it is sensitive to atmosphere on one side and vacuum on the other.

Ah Thank you

 

[jfnall]

I feel like I am studying for a Doctoral exam. Getting close on my rebuild and i have been scouring these desmog threads. One problem I see is that this thread in particular has several people desmogging in different situations. Some with a Weber, some with OEM carb, some have HAC and some don't.

My first question to clear some confusion, how does the HAC fit into the mix on a desmog? seems most people take it out. AND it is NOT on the JimC desmog diagram. i want to keep it so i don't get out the wrenches when i go on trips.

also, on the carb insulator plate, there is a pipe turned up a 90 degree angle on the driver's side. where does this connect to and what is it called and is it on the diagram?

And, on the intake manifold, behind carb towards the fire wall, there is a tall cooling finned deal with a large and small pipe off it. the large pipe goes to the brake system. what about the smaller? can't fine in FSM and what is it called on the diagram?

thanks for the input. i know there will be more to come.

 

[Gabbo]

Somebody posted this pic and said "Study this, it will make sence eventually." And I felt very much like you. Maybe I had some time to sleep on it when it finally made sence. There are a couple places it has the HAC crossed out, if you want to keep it, prettend it's not crossed out. And the pic in the upper right hand corner is the side of your carb facing the engine. That's probably what took me the longest to realize. That annoying mess of little pipes I took off completely, but used it as a referance to know where everything goes.