weber 38 question

[accord upset]

hey i gots a weber 38 stuck up on our manifold but i forgot to mark the wire that went to the choke. it keeps getting stuck on fast idle im thinkin cause the choke and some times it will diesle a lil after i cut it off i think cause the fast idle and choke. lemme know what u guys think, and some one please till me what color wire goes to the choke on a 86 4 door lx

[A20A1]

Hrm... check your ignition timing and ignition advance for #2, #25 should only work when cold.

As for the wire I think it was blue and white but then I could have broke the original and forgot that I replaced the wire with a different color.

I'll try and find out.

I think the one wire to the solenoid at the back of the carb was red and green. so it wont be that one.

I don't have my car with me so I can't go out and check like I normally would.

[2ndGenGuy]

Yes you're right, that is the choke heater not being connected. Mine fell off a while ago, and thats exactly what my car stated doing. In the 84-85 there is a wire that goes to the carb that is +12v only when the ignition is on. It's a black wire with a yellow stripe. Not sure if it's the same for 3geez or not, but I know they're very similar. It's in a 3 wire harness that went to the original carb.

If you can't find the wire, any wire that is hot when the ignition is on should work. So if all else fails you can wire your own line to it.

[accord upset]

ok any 12v that is "hot in run" will work for the choke then huh?,,, ok a20a1 umm theres supposed to be vacume for the advance at both #2 and #25 when cold only??? i thought there was supposed to be vacume when u accelerate so it would advance it then. if not oops and what timeing should i be running? my emmisions sticker says like 20 something degrees <that may not be the exact number been a lil since i looked at it> , i was shure that if base timeing was advanded to far it would overheat.

just to clearify there is no black box on my car there is no big scary vacume system, it is carbd but its a weber 38/38 not stock kiethlin there is one vacume port on the back but i cant tell if it says its for egr or for vacume advance. my goal is to figure out how to make the egr work right and have the distrubutor advance to work no other crazy vacume lines.

[2ndGenGuy]

I just plugged that vacuum port. I think it's there for convenience. You can use that or the vacuum ports on your intake manifold. I think to make the EGR work, all you need to do is run a vacuum line to it. How come you're keeping the EGR system and not deleting it?

And to make your distributor advance work, all you need to do is run a vacuum line to the vacuum advance port, I believe. I think that will advance it when the car is accelerating. I played with my vacuum advance and couldn't see any difference when it was connected or not.

[2ndGenGuy]

Aah after some research, I'm not so sure I'm right on that last post. The port on the carb might be a venturi vacuum. That means that there will be vacuum when you're giving the car gas, as opposed to the vacuum on the intake manifold which is vacuum only when you're cruising / idling.

It looks like the vacuum advance diaphragm is only advancing the timing when there is no vacuum present. So you should just hook that to the intake manifold as suggested.

Looks like the other port advances timing when the car is cold, using one of them crazy thermovalves, which requires more vacuum lines.

I'm not 100% sure if I'm right on this one... can anybody verify?

I found some info on this thread if you wanna check it out:
https://www.3geez.com/forum/showthread.php?t=55091

[A20A1]

Well vacuum is present durring idle so actually I think the vacuum retards the ignition... but as you open the throttle and vacuum drops the spring inside the diaphragm advances the timing.

Though i could be backwards on that.

[2ndGenGuy]

Well vacuum is present durring idle so actually I think the vacuum retards the ignition... but as you open the throttle and vacuum drops the spring inside the diaphragm advances the timing.
Though i could be backwards on that.

So either way you gotta hook the vacuum advance to the intake manifold.
Now if you wanted to hook the cold idle advance up like it's supposed to be, does it matter which thermovalve you connect vacuum to? Do they each operate in the same manner, only opening when the engine is cold? Or does one open when the engine is warmed up? Hmmm... maybe I should do some searching on the forum before I ask a bunch of noob questions.

Is that vacuum port on the carb actually just manifold vacuum or venturi vacuum then? It would be kinda cool to hook that to the cold start advance diaphragm and get some extra vacuum advance when you're accelerating...

EDIT: Some simple searching answered my noob questions. Most of them in the Weber HowTo here:
https://www.3geez.com/forum/showthread.php?t=38161
And some in another thread I found relating to Weber swaps:
https://www.3geez.com/forum/showthread.php?t=50529

BUT one thing confuses me is this diagram:


By hooking that to both advance diaphragms, doesn't that give you full advance while the engine is cold, then full advance while accelerating after the engine is warmed up (because the thermovalve would be open)? In both cases the vacuum is gone.

So if you wanted only some advance while accelerating, and some while the engine is cold, you could hook intake vacuum to #2, then intake vacuum to the thermovalve, then from that #25.

[A20A1]

you're supposed to hook #25 to the thermovalve.

the port at the back of the intake manifold is manifold vacuum but it's connected to the plenum so it'll be a little more stable since it's getting vacuum from all 4 cylinders and not just two.

If I still had my car around I would probably use Air suction valve vacuum and a series of solenoids & rpm switches to control the advance electronicly.

the vacuum port on the carb is throttle port or manifold vacuum, It may not be high enough to get venturi vacuum.

However you can tap a port for venturi vacuum... use the keihin carb as a guide for placement.


use the correct thermovalve... I think each thermovavle has a slightly different operating temp.

[accord upset]

ok guys im looking at diagrams and secmatices from mitchell and chilton with some help from u guys and me + some mechanic friends i understand that there is a white line on the flywheel and a red one i though the white was for base and the red was for timing with vaccume advance hooked up. but im not shure of whitch way the lil vacume pot on the distrubutor works is it supposed to advance with vacume or when it loses vacume it advances that kould make a big difference in where i get the vaccume from because regular manifold vacume is pressent except when you accelerating and above the throttle plates is exact oppisite there is little or no vacume there except when accelerating. oh yea is air supposed to bleed through from one port to the other on the lil vacume diafram on the dizzy.

[A20A1]

No there is no bleed that I could see.

https://www.3geez.com/forum/showthread.php?t=53918

[accord upset]

that helped alot thanks,, the link with the pics is what i needed to see how it worked.

[2ndGenGuy]

Yeah you guys got me thinking a lot today. I went out into the garage and spent a couple hours playing with the timing and the vacuum advance stuff.

My dad came over and was telling me about how to set the timing properly. He says that back in the day he always set the timing with the vacuum advance disconnected from the distributor. So we pulled the vacuum line off of the intake manifold, plugged it, set the timing, then put the line back on. When we put the vacuum line back on, the timing retarded itself quite a bit. And that was at idle. Once you gave it gas, the vacuum would advance itself to normal, and when the RPMs went up, the centrifugal advance would kick it up even more.

The car actually ran considerably smoother after this, idle was much smoother and acceleration is spot on; with the only hesitation due to my small accelerator pump jet.

Thanks for all the info that you guys both contributed. It sure made everything better.

Actually, another thing that I did do, was hook vacuum to port 25. I didn't use the thermovalve, just applied vacuum directly. It didn't seem to make any difference whatsoever in the timing or the way the car ran. I also coudln't find that port in my FSM. It still runs great regardless, but I just thought it was odd.

[accord upset]

2ndGenGuy the one thats supposed to be connected to the thermo valve i think its #25 on the dizzy but any way that should only advance the timing 6 degreeze when cold to help keep it peppy and running for lack of a better explanation and a20 you was right theres not supposed to be any bleed throught the 2 port on the vacume diafram on the dizzy i had to replace mine 60 buck at oriellys but that took kare off all the probs i was having the deisling and the lope at idle it feels like the car has less topend power but more low torqe its workable thanks man.

[2ndGenGuy]

Ah I see how that works, I wonder what temp I thermovalve I should hook it to. There's two of them back there. Guess I'll hook it to the lower temp one just to be safe. The vacuum diagrams in the manual are kinda confusing cos it doesn't show the second port on the distributor. Looks like we've got that sorted out now though, thanks