Generally vacuum advance improves the fuel economy of a vehicle. It advances the timing under light engine loads to allow more time for more complete combustion of the fuel-air mixture.
If the load increases on the engine the vacuum drops which makes the timing advance go away. This prevents engine knock under load.
Is it measured by RPM's or ??? How does the engine know it's under a light load versus a heavy load versus just my fat a** riding in the truck? So could disconnecting lead to excessive knock?
The engine "knows" whether it's under a light versus heavy load by how much vacuum is being developed in the intake manifold. The vacuum developed in the intake manifold depends on how open the throttle plate is in relation to the speed the engine is running at. For example: If you are idling along in high gear and suddenly open the throttle wide open... in the time before the engine has a chance to speed up, and the engine is more heavily loaded, the engine is no longer "sucking" against the throttle plate so the vacuum in the manifold drops. Then, as per Rusty above, the vacuum advance goes away to prevent knock.
If you are worried about a non functioning vacuum advance, they can be found. I see them on eBay at times. The 1937 advance is more readily available and is easily modified to fit your truck. The advance characteristics will be a bit different, but likely not noticeable. If you want to know more, PM me and I will try to help.
Thanks for the explanation fellas. The reason I ask is that the line that goes into my carb sits right about the throttle linkage and it seems to restrict the linkage from being able to open up the throttle all the way. I am going with the original linkage that was on the truck when I bought it, but I suppose that doesn't make it correct. Maybe I need to bend the linkage so it does not in fact hit the fitting/line for the vacuum advance.
It might help,if you could post a picture or two. Then the experts could offer better guidance with your situation.
When you buy one of these older classic vehicles you spend a lot of time trying to determine what is original and what has been put in place to keep it running. For example, in your truck which portion is non-original? Is it the linkage, the line, or the carburetor?
Just because a parts catalog from a supplier lists that a part fits your make and model does not mean it looks or fits like the original.
For example, my ‘37 originally came with a split choke Carter W1 carburetor. I have no idea where that carburetor is if it even exists today. When we bought the car in 2006 it came with a Carter YF. When I compare my setup to pictures of original ‘37’s I can see a few little tweaks that were made to the linkage and vacuum line to make it fit.
Thanks for the pictures. Those do show what you are struggling to fix.
It sure looks like the flat portion of the throttle linkage has seen its fair share of twisting and tweaking.
One idea that might help would be install a 90 degree elbow fitting to connect to the vacuum line.
Have you been able to determine if your carburetor is the original model or a later one? I often spend time searching the internet for photos of the same year, make, and model vehicle to help identify what might have been changed. I start by searching for vehicles for sale. Just looking at the pictures really helps.
I have not determined if the carb is the original one, but even if it is, they may have changed the linkage, no? I think that if I went with any fitting regardless of angle, I think the throttle linkage will still hit it, unless I am misunderstanding you.
The only thing that I could do is to plug the hole in the carb where the vacuum advance goes to or bend the linkage possibly to the point that it doesn't hit the vacuum line.
I believe Carbking will be the expert on this, but here are my thoughts.
The carburetor you have is not original to the truck. The original would likely have been a Carter 285s, but they were somewhat problematic and were often changed up to later improved versions of the W1. The vacuum port on the original carburetor was oriented differently and pointed about 45 degrees up and more inline with the lever on the throttle shaft. I am attaching a picture I found to show what I mean.
Probably your best solution will be to remove the vacuum line, and take the brass fitting out of the vacuum port in the carburetor. Then, as per Rusty above, install a 45 degree "street elbow" in it's place and position it so it faces away from the throttle arm. Then screw the original fitting into the "street elbow". Then bend/rework your vacuum line to fit being careful to make gradual bends and not kink the line.
This should fix you up. Hope it works for you! :-)
I believe Carbking will be the expert on this, but here are my thoughts.
The carburetor you have is not original to the truck. The original would likely have been a Carter 285s, but they were somewhat problematic and were often changed up to later improved versions of the W1. The vacuum port on the original carburetor was oriented differently and pointed about 45 degrees up and more inline with the lever on the throttle shaft. I am attaching a picture I found to show what I mean.
Probably your best solution will be to remove the vacuum line, and take the brass fitting out of the vacuum port in the carburetor. Then, as per Rusty above, install a 45 degree "street elbow" in it's place and position it so it faces away from the throttle arm. Then screw the original fitting into the "street elbow". Then bend/rework your vacuum line to fit being careful to make gradual bends and not kink the line.
This should fix you up. Hope it works for you! :-)
I couldn't find a 45 degree fitting, so I decided to try a 90 degree one and that worked perfectly. I had to cut the line some, but now the linkage moves freely. Thanks again.
I believe the throttle arm/lever on your carb originally had an offset bend. This would have moved it away from your vacuum line. 1936 and earlier carbs had a straight lever and a different location for the vacuum port. The straightening of your lever has made it longer than the correct straight lever which will result in reduced travel.
You can easily checks throttle travel with 2 people.
Remove the air cleaner. With the choke plate open look down the carburetor bore. Watch the throttle plate move as the other person pushes the accelerator pedal to the floor. The throttle plate should be vertical at full travel.
