The Stovebolt Site Forums The Shop Area Engine Shop Carter W1 carb...hesitation and backfires after rebuild.

I know that this is a long winded thread but please bare with me.....

When I bought the truck it would run but only when the choke was held somewhat closed. I decided to rebuild the Carter W1. I removed all of the parts of the carb and I went through all the procedures for cleaning, using simple green and an ultrasonic cleaner. I also blew out all the passages with compressed air. Using the ID number on the tab on the carb (684S), I order a rebuild kit and a new float. Upon installing the kit and float I found that the accelerator pump in the kit was a different size than the one in the carb. The stem of it was much longer. I sent a side by side picture of the old pump and the one in the kit to the kit vendor and they said that given the size and style of the old pump that the carb was not a 684S and gave me the correct pump to purchase. At this point I realized that the carb had probably been rebuilt at some point in its life. I still do not know what "model?" my carb is. I received the new pump, installed it and mounted it back in the truck. The truck started but would not accelerate correctly..terrible hesitation and backfires. In contacting the kit vendor I was told to check for vacuum leaks around the carb. I did and there were none. From my days of working on "newer" Rochester and Holley carbs I assumed that this was an accelerator pump issue. I then did the basic accelerator pump test I remembered from long ago...look down the carb throat, hit the throttle and look for a squirt of gas. I did get a squirt but it was quite anemic. Now this is where it get a little weird...I again contacted the kit vendor and the following was what I told them:

"I am still at a loss as to how this accelerator pump works. Here is my problem. I have attached some pictures to show you the issue so that maybe you could shed some light on a solution. First is the diagram of the Carter W1 carb. I have circled the accelerator pump circuit. It shows that the spring sits below the dashpot and that both slide into the cylinder in the body of the carb. This cylinder that the spring and dashpot ride in goes from the base of the carb body to the top of the bowl. The next picture is of the bowl in my carb. You will note that the cylinder is very short and only projects up about 1/4 of the way making it impossible to place the spring under the dashpot and then into the cylinder since there is not enough of the cylinder to hold the spring and dashpot". Their answer was..."With the short accelerator pump housing, you don't use a return spring. It's nearly impossible to find schematics that show the short pump well, I haven't had any luck over the years."

Note: When I dismantled the carb, the spring was ON TOP OF THE DASHPOT and that's' the way I put it back together. If there is no spring in the circuit the arrangement of the pump shaft and the fulcrum will not allow the shaft to move up and down. Therefore the pump will not work. The diagram I have attached shows three hole in the fulcrum that allow you to adjust the amount of "squirt". My carb does not have this type of fulcrum. On my carb the linkage from the top of the shaft to the fulcrum just slides along the fulcrum point (See picture). Effectively the throttle will open and the fulcrum will pivot and the linkage will just slide on the fulcrum and not ever move the shaft. So my solution was to try to secure the linkage to the bottom of the fulcrum to see if I could get the shaft to go up and down (see last picture). It seems to help the issue but it still hesitates and backfires under any load. Any help would be greatly appreciated....Again sorry for the long winded thread.

I'd put the longer shot pump back in and see if this improves things by moving the leverage point to a better position from the fulcrum.

Your carburetor was probably one of those Fitzall carbs, cobbled together from random parts that Western Auto or whomever kept on the shelf.

Post the numbers found on the body, bowl, etc. That will help carbking figure out exactly what you have.

You might end up better off buying a correct, rebuildable YF core and rebuilding it with the correct internal parts for your specific vehicle.

I had to do that because the carb on my truck was made from various Willys Jeep parts from different years.

The short accelerator pump cylinder is found ONLY in the 684s carburetor, and the pump spring goes on top of the accelerator pump. And YES, you DO use a pump spring!

The accelerator pump is also unique to the 684s carburetor, and I unaware of a source (when we sell a kit, I literally make the accelerator pump from scratch).

And I have never seen a diagram.

Jon

Jon,
Great information. I am learning very quickly that getting information on this truck takes a village, as it were. So my carb tag was correct and the way the carb was assembled was correct. If I post a picture of the pump that was originally in the carb can you tell me if it is the correct one for the carb? Also on the 684S does the fulcrum have a slot in it or does it have 3 holes like the diagram that I posted? Additionally the vendor told me, other than the pump, the parts in the kit were that same as the old ones in the carb. Is this correct or is there a difference between the jets, etc in the 684S vs the other types of W1's? I am thinking I should go back to the beginning and get a kit from you and re-rebuild the carb. Thanks

Mike

Mike - the slotted fulcrum is correct for the 684s.

The other kit parts are the same as those for a 574s or 483s.

EDIT - the pump spring is different in the 684s also.

The original pump is longer than the pumps for other W-1s, also made differently at the bottom, as there is no metal cup on the bottom to hold the spring.

I would suggest looking closely at your original pump. If the leather cup is not torn, soak the pump in a light machine oil (3 n 1, gun oil, sewing machine oil, etc.) overnight and reuse it.

Jon

Are you sure you do not have a vacuum leak somewhere other than the carburetor?

Jon,

So I don't know if the spring that was in the carb is the correct spring. Any way to tell? Below are some pictures of the old accelerator pump. Can you tell from these if it is the correct pump? The 2nd pump I got from the vendor is identical to this one.

Good question. I don't think so but I will check all the other vacuum hoses...thanks

The pump for the 684s is on the top; the pump for the 574s is on the bottom.

Jon

Note the 684s pump does not have the metal cup on the bottom. As the spring is now on the top, there is no need for the metal cup. The purpose of the metal cup was to position the spring.

Trying to use the 574s pump will result in the leather cup rolling when the leather cup rises above the brass cylinder; as it has on the pumps in your pictures.

And the 684s pump in the picture is a used original that I saved as a pattern, not one that I would send in a kit.

Jon

So it looks like I have a 574 pump? As I said before the new pump is exactly like the old pump I pulled out.

Did you replace the gasket under the carburetor?
If so, check to make sure that a small passage hole on the bottom of the carb flange lines up with the small hole in the new gasket. If it doesn't, Make a new hole in the gasket that does.

Correct.

Jon

That's a great question about the gasket. I just used the gasket that was in the kit and did not know to check that. I will pull the carb and check...thanks

Jon has you on your way figuring out the accelerator pump, now, how did you set up the metering rod? You can have a lean condition if the rod depth is not correct. Carter had a depth setting tool for each model, bending the linkage set proper depth ( rod into the main jet ). From the throttle shaft, the long linkage rod runs up to the pivot that controls the metering rod and accelerator pump. Make sure all the holes are good and the rod isn't worn, the pump and metering rod should move the moment the throttle is moved, if there's any slack, you can get a lean condition. Without the correct tool to set the metering rod, it's a trial & error sort of adjustment.

Good point Joe. I didn't set up the metering rod. I just cleaned it, checked it for wear (there really was none) and reinstalled it. I will ask Jon if he knows where I can find / borrow the tool for setting the rod.

Jon,

Can you tell me if this is the correct size spring for the 684S? (picture below) This is the one that was in the carb when I took it apart.

Mike - it looks correct.

Jon