A few years ago I rebuilt the W1 on my friends '49 3100. Based on the information at carbking's website it is a model 684S which was used in production for only 1949. It has the flat steel bar that was added to provide a fast idle feature when the choke was closed.
The carburetor worked fine until about 2 weeks ago when he could not get the engine to run at idle. The problem was a piece of crud in the idle circuit. Things are are running fine again (at least with the carb on my '37).
During the troubleshooting process ! found 3 interesting items.
One is that the piece of "crud" appears to be a small flake of rust. When I removed the float bowl cover and drained the fuel I could see some rust in the bottom of the fuel bowl. There were even more particles in the small chamber below the accelerator pump lower check valve. Any ideas no how to prevent that rusting? Should he keep Stabil or Seafoam in the fuel year-round? Or is this a situation where ethanol fuel might be better because it absorbs moisture?
Another interesting feature is the position of the spring on the accelerator pump. The 1948-51 Chevy shop manual states that in 1949 the accelerator pump spring was moved to above the piston. In this carburetor the spring is attached to the bottom of the well so it is below the piston. I did not try to pull on it very hard to remove it. It sure seemed to be firmly in place. I found the rebuild kit I used. It included a longer spring which appears that it would fit above the piston. Should I change the spring configuration?
Should there be some type of retaining clip on the short shaft for the accelerator pump lever arm? There is a groove in the end of the pivot shaft but I do not remember ever seeing a circular clip in that position on this carburetor.
Yes, the low speed jet has a very small opening and is easily plugged up. The crossing of #3 amd #r plug wires and causing the back fire makes for an easy clean out. The opening was enlarged in 1941 but still very small...
The rust is coming from the gas tank. Remove the fuel bowl on top of the fuel pump and clean and remove the screen in that location and clean and add a filter in FRONT of the carburetor to catch the rust.
The 1949 carb. has several changes and uses some different parts and the pmmp spring belongs on the top.
There is a small retaining horse shoe clip used on te link. The mechanics called it a Jesus clip.....
We have a filter on the fuel tank outlet and it is a new fuel tank. That filter and the bowl on the fuel pump are clear. The fuel line from the pump to the carburetor is new so I doubt if it is adding any crud to the system. I was really surprised to see the rusted surface in the bottom of the fuel bowl body on the carburetor. I scraped as much of it off as I could.
I figured there was a “Jesus” clip there. Now to find one that fits!
I wonder how this carb got the spring on the bottom. It is really stuck in there.
I actually had a telephone conversation with Jon about this a year or so back. Apparently in the past some cast iron carburetors were treated to prevent rust using a method somewhat like the bluing on old rifles. Essentially you put a coating of "good" iron oxide on the surface to prevent "bad" iron oxide from forming. "Good" iron oxide is dark (magnetite) and when formed doesn't expand and flake off the surface and thus continue to expose new iron to further oxidization as "bad" iron oxide does.
If I remember right, Jon said he used to send carburetor bodies to someone else to have them treated, but no longer does.
Carter used to sell and promote their own special black carburetor paint as well, which was to be used inside and out on the cast iron body. It was supposed to be impervious to gasoline etc. and I imagine it prevented rust from forming in the bowl.
At any rate, if I read you right, the rust you are talking about in the bottom of the fuel bowl is rust that actually formed on the cast iron bowl itself, true? If so, it is a sure sign of pure water having sat in the bottom of the bowl. And yes, an occasional dose of alcohol in the tank will prevent it.
Yes, this appears to be rust that formed in the fuel bowl due to moisture in the fuel. The truck sits a a lot in a garage that is insulated but with no heat/ac or regular ventilation. There are lots of opportunities for temperature and humidity changes that will create condensation.
This is one of those scenarios where adding Heat or Stabil or Seafoam all the time might help. I keep pushing Steve, the owner, to drive the truck more! That would at least minimize the problem during the good months.
Thanks for sharing the information from Jon about the “good” iron oxide coating. I was thinking along the same line as Gene about an epoxy coating or maybe a coat of a gas tank sealer.
On the other hand this is the first time this has happened in 4 years.
Gene made the comment that the 684s used a lot of different parts.
Many of those were in the pump circuit:
(1) the pump cylinder is much shorter than other W-1's (2) the pump is longer (3) the pump spring does go on top (4) the "spring" pump link introduced on the 574s, hated universally by all carburetor rebuilders, was deleted, and a new pump link used.
And yes, there should be a "pin spring" part number 150A-10 was used on the pump link.
Great carb, except for the cost of the unique accelerator pump!
Jon, I am assuming that the Carter BLACK BODY FINISH product has long gone by the wayside. What’s your recommendation for a comparable replacement product? Randy
I use low gloss Rustoleum low gloss engine paint. Seems to resist today's gasoline and though a little less glossy is close. It is the 500 deg. type, don't use the high temperature paint as it take heat to cure.
Don't know about what would prevent interior rust, but from an aesthetics standpoint, 60 percent gloss black, or satin black is really close.
Generally, the only problem with rust occurs in the horizontal idle cross-passage (close to the top of the casting). With the idle jet removed, attempt to blow compressed air in the idle passage from the location of the idle jet. It should exit at the idle port (behind the idle mixture screw). If it does, great; if it does not, then remove the access plug for the cross passage, and carefully clean it. I use a very small orifice drill.
I had lots of air going through the passage. And I could squirt lots of liquid through as well (tried carburetor cleaner and lacquer thinner).
But my engine still ran poorly, even after trying 2 different carburetor bodies, one of which had been redone by a reputable rebuilder. I knew I still had a problem in the idle system as the engine always seemed to be running lean at idle/off idle/light load acceleration and the idle screw could be turned nearly all the way in or out without making any difference.
I finally got exasperated and pulled 2 plugs from one body. I determined the gauge drill size for the passage itself by trying bit shanks in the hole entrance. I determined the drill size for the economizer jet from Carter specifications I have. I only cleaned the cross passage to and through the economizer jet, and the vertical passage down to the needle and ports. There didn't seem to be much in there, but...
What a difference! The idle screw now makes a difference and I'm finally happy with the way the engine runs.
I think for me plug removal will be standard procedure from now on.
PS I had even found and installed brand new idle jets previously, with no improvement.
Many thanks to all for continuing this thread. It has added value for me. I will offer my update.
I was able to clear the idle passage. It turns out that I had used the method described by Jon in his post yesterday The blockage was in that upper horizontal passage. I was able to clear it with compressed air. I did not have to remove any of the plugs. I did use Jon's trick about opening up the low speed idle jet slightly with an ice pick before I re-installed it. That way I knew that it would seat properly.
I spent a whole $0.35 for an E-clip to attach the accelerator pump arm to the pivot.
Now for the interesting part! I was really confused by the accelerator pump spring location. While I have not rebuilt near as many carburetors as some of you, I have done enough over the years to know how important it is to pay attention to details. I could not figure out why I had installed the pump with the spring below the piston. I dug back through my stash of parts (why we never throw anything away!) and found the kit I used for the rebuild. I do not remember where I ordered it from (I think Chev of the 40's) but it is a Daytona Parts kit. I found the instructions which showed the spring below the piston. At the time I also had looked at the Carter Service Bulletin 3369A. I missed that it was outdated and that there had been a change in 1949. I had not referred to the Chevy truck service manual.
I still had the longer spring which I believe is appropriate to install above the piston. I applied a little more pull and the shorter spring did come out of the well. I measured the brass sleeve on the well as 17/32" high. The pump piston assembly I removed look like the new one I installed. It is obvious that it was not the original one. So maybe the spring was below the piston when I took it apart.
I reassembled the accelerator pump with the longer spring above the piston. One change I noticed is that with the spring in this position it pulls the throttle open when it is not connected the throttle rod in the vehicle.
At this time I did not do anything to address the rusting inside the fuel bowl. I had painted the exterior of the cast body with Rustoleum semi-gloss black. That paint is holding up well. We'll see if we have issues again.
Hopefully we will get the carburetor back on the truck this weekend. If we get motivated enough to do it in our Iowa summer heat * humidity!
Things ran fine…for about a week. Then we were back to the same problem. The engine would not idle. The idle mixture screw had no effect on the idle.
We tried the switch #3 and #4 spark plug wires trick first. That did not correct the problem.
We could not get air to blow through the passage that provides fuel to the idle and low speed circuits. We were using the various access points provided by the screw-out brass plugs.
I removed the pressed-in plug at the top of that vertical channel and shot air down it. We never saw any dirt come out but we did get air flow. We reassembled the carb and put it back on the engine. It runs fine again.
We still need to figure out how to deal with the rust flakes in the float bowl.
The other issue is to figure out what I need to do to make a more permanent replacement for the plug at the top of the channel. I just put some non-hardening sealer on the old one and seated back into the top of that passage.
What is the proper repair/replacement for those pressed-in plugs?
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