I've always connected my vacuum advance to a ported vacuum source. But as l finished up the carb install and started thinking about the next step (distributor install) l noticed for the first time that this carb has 0 vacuum ports above the throttle blades... none... not one.

This obviously presents a problem (at least in my opinion). Use manifold vacuum? I've read that some people do that, but it's counterintuitive. I could go to the air cleaner, but that's not gonna be very consistent.

Those are really my only choices, as l see it. Here are (pretty bad) pics of left side and right side... let me know of you can see something I'm missing...


The bosses are all blind holes..
Is that port up by the carbs mouth useful for anything? It opens up inside above the choke butterfly so even at higher RPM a consistent vacuum signal is doubtful.

 

The port above the choke butterfly is for the choke heat stove. That is where the choke sucks fresh air into the back round piece. You should have a port there for the line that goes to the heat stove. This port on the choke housing will suck air unless you plug it. You should hook it up so it gets heated air. And the air will come from that nipple above the choke housing.

Plug all the ports that you see that you think you will not use. Get the PCV valve hooked up and the brake booster and the plastic manifold on the firewall if your truck has it. Leave the distributor vacuum line disconnected.

Get it started and warmed up, and set the idle mixture screw and the idle speed so it's running nice with a smooth idle at about 6-700 rpm. Once you get it running good, unplug each one of those ports one at a time. If it's sucking vacuum, plug it and go to the next. If you have it idling slow enough, one of them will have no suction at idle. If you find that one, then take and move the throttle to raise the rpm. Then check the nipple again, it should have suction on it at higher rpm. That is the one you want for the distributor.

The position of the port doesn't necessarily give away it's purpose. There are passages drilled in the carb that can have a port that is physically low outside the carb, that are higher up inside the carb.

 

Second picture the port under the float bowl is that not ported?
Dave ----

 

That one is manifold vacuum as far as l know... it opens below the throttle butterfly (double checked on the old carb). I'll know for sure when I've got it running a little later on today (hopefully).

PCV, and brake booster are hooked into the vacuum tree coming from the intake manifold.

As for the choke, are you talking about the hard line from the exhaust manifold? That one is connected on the top side, then there's the piece that comes out the bottom that presumably needs to be connected to.... something.

 

Is that a Chinese replacement clone? Do you still have the original carb?

On the original, look for the ported opening inside the throttle bore. It’s usually a vertical slot close to the higher side of the throttle plate. Spray some carb cleaner in the slot. The liquid should come out of an external hose fitting, for the line to the distributor.

I suspect your clone was based on an earlier carb version that did not have provisions for ported vacuum. Does it even have a boss (undriiled?) where the hose fitting should be? You may be SOL.

 

l have the original feedback carb and another YF junkyard carb that l rebuilt but haven't tested yet.. l got the wrong rebuild kit last year (too late to return it now) and ended up using the kit's accelerator pump, needle/seat, etc but reusing the old gaskets. It's my standby in case this one doesn't work out.
The junkyard carb is from an 83 and has 3 vacuum ports to the new Chinesium-carb's one. I bought it (the new one) in a fit of apathy... ordered it online to be delivered vs driving into town for a new carb kit. Figured that for $100, l would make it work.

l don't know how far back you'd have to go to predate vacuum operated spark advance... l did drive a Model T once that had to be advanced manually via a crank on the steering wheel. That car was... engaging.

l think the single port low on the left side (second pic) is the one l need to use... everything else (brakes, PVC, etc) can pull from the vacuum tree in the intake manifold. I've got some very exciting wiring to do before l crank it up a little later and know for sure whether l'm SOL... worst case scenario is l use the junkyard carb and l shelled-out $100 for an unattractive shelf ornament.

 

FWIW, my 1948 ****** CJ-2A has no vacuum advance. Centrifugal advance only.

Circa 1953, they redesigned the engine and switched to a Carter YF carb. I'm not sure if vacuum advance was added then or later in production.

I looked for some YF history but didn't find much. Carter produced the YF at least as far back as 1937, according to this article:

https://www.stovebolt.com/ubbthreads...27247&page=all


Doesn't necessarily help you, but be aware the YF had a very long production run. Who knows which version they chose to clone at the Fling Dung factory?

If your engine originally used ported vacuum for the distributor, expect headaches switching to manifold vacuum. You'd have full vacuum advance at idle, when originally there was none. You'd have to severely retard the base timing to compensate, and then it would be way off at all other speeds.

 

Yes, that hard line is connected to the choke on the top side part like you have it. The bottom side comes around and goes up to that port that is right underneath the aircleaner in the picture above. That hard line to the choke will be sucking air. It needs to be clean air, so it goes right in under the air cleaner. The air comes around, through the exhaust manifold to get heated, and then the hot air goes up that hard line and into the choke housing to make the choke bi-metal open up and open the choke properly.

Don't panic too much on the ported vacuum thing. For now, ,the engine will run fine without it even hooked up. It's just for fuel mileage and adds timing over and above the centrifugal timing already built into the dist.

If you have a automatic transmission, having the distributor vacuum on manifold vacuum can cause headaches. You will just have to try it, each engine is a little different. When I tried it, on certain engines it would make the idle speed very high. So I would turn the idle down and re-tune everything, and then when I go to put it in drive, the engine will stall. So I find a tree, put the truck in drive and let it sit against the tree in drive while I tune it. Got it running good and smooth, but then when I put it in park, the engine revs way up again. If you drive it like that, the transmission will make a terrible bang when you put it in drive.

I think you will find a ported vacuum source on that carb. It would be rare if it did not have one. You do have to make sure it's running right and the idle is slow enough. If you are having problems and have the idle throttle stop screw too far open, then the ported vacuum port will have vacuum on it. If you end up not having a ported vacuum port, then there are other solutions, like changing the vacuum advance to an adjustable one if it's not already adjustable.

 

Good points you brought up..
l know better than to try to remanufacture two systems at once.. ln this case, fuel AND spark (new carb and HEI distributor). I just ain't that good at diagnostics.
Correction: l flat-*** suck at it.
l got the truck running, but it's eye-wateringly rich and idling high, even w the idle screws backed out all the way out and the mix screw closed... just kept running.
I connected the choke as you said and once the garage is inhabitable again I'll check it's function because l had it wrong and it wouldn't idle at all unless l forced the butterfly to stay open.
At this point it's warmed-up and the choke should've been pulling off, but it wasn't. Probably because l had it hosed incorrectly. Duh.
The truck is a 4sp so l don't have to worry about the throttle valve kick down and whatnot. Once l get it idling properly l can start dealing w the advance. I'm thinking that the vacuum port down low is the one l want... we'll see.

On the plus side, the HEI is throwing spark and working GREAT!

 

If the idle will not lower with the screw backed all the way out, you know on my carb there is a fast idle (choke) adjustment.
Could this be keeping the idle from going lower? Maybe the choke step part is not moving and and even with the choke open it will not lower.

The last would be a vacuum leak but I dont think it would make your eyes tear like it was running rich and you have the idle mixture screw turned in all the way too.

On the running rich if you want to pop the top off the carb and check float level it could be off from shipping.
Once you get that under control we can look into the idle issue.
Or try that rebuilt JY carb as I dont think it could be any worst.
Dave ----

 

For a stop gap measure, you can wire the choke plate fully open. Usually you can secure the external linkage somehow, with a piece of wire or similar. Just make sure it doesn’t interfere with normal throttle operation.

With the choke secured open, you can concentrate on setting the timing, idle speed, and mixture. Then you can come back and fiddle with the choke.

 

I was hoping to avoid cracking the carb open, but that's probably what happens next after l double check all of the external variables.
l may have a small vacuum leak somewhere, but it's not behaving like a vac leak and l did check while it was running yesterday.

Last resort is pulling it off and trying the junkyard carb. Like Dave said, it can't be much worse.

 

I see you took the truck out for a spin around town and made it back home so that is good.

So what became of this carb?
Is it still not right or ?
Don't leave us hanging here man give us the scoop
Dave ----

 

You are correct, sir.
After struggling with it yesterday, l conceded the battle space out of frustration and, not inconsequential, chemical warfare (my eyes were still burning this morning just thinking about it).
Turns out...
Yes, very rich.
Yes, too much timing.
And finally, the choke was snapping shut and creating the overly rich condition.
l double checked the idle and mix screws, reset them to a 0 baseline, and started over w new eyes (still watery, but not pizzed-off anymore).
The old girl started right up and idled like a champ. I've still got the choke issue to contend with and there's some popping in the exhaust. My timing is all over the place (according to my timing light) but it runs and drives.. l have NO idea where my advance comes on, l didnt even get that far today before l needed to drive it back and drop it at the alignment shop.

1) I never went above 35mph (the speed limit in town) so l may still have some timing issues.
2) lm gonna have to deal w the choke... forcing it open is not a long term solution.
3) l need to figure out if the exhaust popping is due to multiple exhaust leaks or an overly rich condition.
4) All of that will have to get sorted next weekend, because it's at the alignment shop until l drag my sorry, flat trucker-butt back home on Saturday.