Idle circuit problem?

[Severe Duty]

Well, all the prepwork and inspection seems to have paid off. I had a visit from my brother and we started the PW. It came to life without any trouble, and ran (in my opinion) quite proudly! It had been sitting in the Barstow, Calif. area for many years, and perhaps the dry desert air was helpful in keeping rust at bay, and unlike my 1941-2 PW that suffered California redwood forest moisture for the last 30+ years (nice electrical connections and door rot, 'bro!).

One of the tasks during pre-start preparation was to rebuild the carburetor (only the second time I've ever done that. The first was for a 1972 Ford F350, but that problem was actually solder beads from the fuel tank fabrication process gravitating towards the suction tube, indicating fuel starvation- but only at high RPM/load.) I'm glad I took the time to fully disassemble and get all the varnish and scale out of this carb, it wasn't too bad, but it was a great learning process.

Anyway, it seems like there may be an issue with the idle circuit. I can start and run the engine just fine with first attempt, but the choke must be carefully manipulated, even after the engine warms up enough for the radiator to start spitting at me through its leaks. The accelerator linkage works great, and seems properly adjusted. Once I get the engine to idle by itself with a piece of baling wire standing in for the choke cable, I manipulate the accelerator and I can easily change the RPM. Then, after I re-take manual control of the choke and manipulate it slightly, the engine dies. It also dies without acute control of the choke cam.

During our initial run up, there was a lot of smoke from the exhasut, but today when I played with it, there was very little visible smoke is present, and it smells more like a rich mixture than oil (good news, in my humble opinion).

My brother feels this is probably due to a failure in the idle circuit, with one of the ports most likely fouled. It's possible I missed that clean-out operation during the rebuild. I don't really know much about carburetors, and the way he explained it made good sense to me once I thought about vacuum changes and fuel flow during both acceleration and idle. They are seprate operations in my understanding, which seems to explain why it will work just fine during acceleration, then not at idle without assistance.

Vacuum leaks have been checked and eliminated.

This truck is a 1952 B3PW and the carburetor is a Carter E7S1, ungoverned and on a stock 6 cyl engine. I hope this link helps for a stock picture (not mine):

http://t137.com/ClintDixon/Images/E7S1.jpg

QUESTION/COMMENTS: I need input on my problem from those ahead of me on this path. What can I do to correct the idle problem?

Thanks!

Steven Johnson

[Jason Mills]

I am not clear in my understanding: is the engine running with the choke open, fully closed or somewhere in between? As I read your post, It sounds like the truck runs with the choke somewhere between half and fully closed, is that correct?

[Gordon Maney]

Well, all the prepwork and inspection seems to have paid off. I had a visit from my brother and we started the PW. It came to life without any trouble, and ran (in my opinion) quite proudly! It had been sitting in the Barstow, Calif. area for many years, and perhaps the dry desert air was helpful in keeping rust at bay, and unlike my 1941-2 PW that suffered California redwood forest moisture for the last 30+ years (nice electrical connections and door rot, 'bro!).

One of the tasks during pre-start preparation was to rebuild the carburetor (only the second time I've ever done that. The first was for a 1972 Ford F350, but that problem was actually solder beads from the fuel tank fabrication process gravitating towards the suction tube, indicating fuel starvation- but only at high RPM/load.) I'm glad I took the time to fully disassemble and get all the varnish and scale out of this carb, it wasn't too bad, but it was a great learning process.

Anyway, it seems like there may be an issue with the idle circuit. I can start and run the engine just fine with first attempt, but the choke must be carefully manipulated, even after the engine warms up enough for the radiator to start spitting at me through its leaks. The accelerator linkage works great, and seems properly adjusted. Once I get the engine to idle by itself with a piece of baling wire standing in for the choke cable, I manipulate the accelerator and I can easily change the RPM. Then, after I re-take manual control of the choke and manipulate it slightly, the engine dies. It also dies without acute control of the choke cam.

During our initial run up, there was a lot of smoke from the exhasut, but today when I played with it, there was very little visible smoke is present, and it smells more like a rich mixture than oil (good news, in my humble opinion).

My brother feels this is probably due to a failure in the idle circuit, with one of the ports most likely fouled. It's possible I missed that clean-out operation during the rebuild. I don't really know much about carburetors, and the way he explained it made good sense to me once I thought about vacuum changes and fuel flow during both acceleration and idle. They are seprate operations in my understanding, which seems to explain why it will work just fine during acceleration, then not at idle without assistance.

Vacuum leaks have been checked and eliminated.

This truck is a 1952 B3PW and the carburetor is a Carter E7S1, ungoverned and on a stock 6 cyl engine. I hope this link helps for a stock picture (not mine):

http://t137.com/ClintDixon/Images/E7S1.jpg

QUESTION/COMMENTS: I need input on my problem from those ahead of me on this path. What can I do to correct the idle problem?

Thanks!

Steven Johnson

Please explain more about that phrase. What did you discover?

[Severe Duty]

Thanks for your reply...

The Choke: When 'cold', it required near full closure during cranking until running, then smartly opened only slightly, with perhaps less than a 1/4 inch passage at its widest elipse. The spring-loaded relief on the butterfly disk operates clean, and without sticking. Slight variations of the choke are then made and graduating toward more open than shut until engine is warmer. At this point, I was then able to manipulate the throttle linkage and easily regulate the RPM. I am under the impression that this basically reflects a normal manually-choked engine start/warm up procedure...?

The problem seems to be that: 1) The engine often dies anyway, but is easily restarted. 2) Can be difficult to re-start, having to find a new "G-Spot" with the choke butterfly. 3) Will not idle with the choke fully open, even after warm. 4) I can keep the engine running by keeping the RPM above idle by manipulating the throttle linkage, but returning to idle causes engine to stop.

The vacuum leaks: We found a few obvious or likely sources of vacuum leaks, the base of the throttle body has a vacuum port that connected to the vacuum booster, this was capped. There was a 1/4 inch vacuum line off the firewall side of the intake manifold the likely linked to the windshield wipers. That was also isolated. A spray of brake parts cleaner was used around the top end of the engine and intake while we had it running, and no change in RPM was noted (previously, I had removed the intake manifold and reinstalled using new gaskets). All new gaskets were used reinstalling the carburetor.

Update: Something has changed since two days ago. I can't get the engine to stay running at all now, except when gasoline is dripped into the carburetor. RPM can still be manipulated using the accelerator linkage when running. The fuel filter cup shows full, and five gallons of gas was added to the newly-cleaned tank after I replaced all of the fuel line. Supply should not be an issue.

[Gordon Maney]

My remarks are based on the fact that I truly do not know anything about the physical condition of your carburetor, and upon your described symptoms.

What I hear is that you are too lean. Causes could be low float level, restricted main metering circuit/orifices, vacuum leak(s).

[Severe Duty]

Hmmm...

Preparing to remove the carb, I disconnected the fuel supply line at the carb. I then cranked the engine to ensure that I was really getting fuel. Nope! Although it's not possible yet to use the fuel gage, I shook the rear end/tank listening for fuel slosh, and didn't hear anything. I added three gallons to eliminate that mystery. Where did the five gallons go that I put in last month?

Returned to cranking, still no fuel. The fuel pump was elected not to be rebuilt during the fuel line renewal, as it quickly built up pressure when tested and it also worked great three days ago. So, I'll get into that problem, then back to the carb.

Thanks for your input!

[Severe Duty]

Update- good times!

Fuel problems last time were attributed to insuffcient supply. I must not have added as much fuel initially as I recalled. Anyway, I added four gallons (really!), then I removed the fuel line from the discharge side of the fuel pump, and it splashed happily during cranking.

Carb removed for teardown to see what I missed. There were two ports I overlooked on the top portion of the carb, and I carefully ran a wire down them but they cleaned out without any debris. They were accessed by removing copper plugs. Everything else looked good in there, and I rechecked the float level, then its needle valve. But what suprised me was that the body gasket I used from the kit actually covered part of a passage that the old, original gasket (which I luckily saved) did not. I carefully recut a new gasket making a closer inspection this time that it matches, dammit!

When I got to the throttle portion, I discovered that I grossly underestimated the sealing characteristics of the shaft seals. The governor side was far worse in radial slop (for lack of the proper term) than I envisioned, and the throttle linkage side had a gasket that I overlooked. This may have caused a significant vacuum leak, possibly upsetting the balance between idle and throttle??? The little ports my brother mentioned were given a close look, and a little bit of rust was cleaned away. Also, the edge of disk had built up carbon.

I carefully took this section down to 'parade rest', and cleaned, cut a new gasket, and reassembled everything carefully. The end that had a lot of slop was cured by tamping a wad of lead around it, and retightening the flanged nut. It was a nice, tight fit, then working the disk open and shut several times caused the lead to seat nicely. All the slop was gone, and it was a nice seal around the disk when shut.

Hoping for the best, I reinstalled the carb (all new, hand cut gaskets!) and I was stoked when the engine cranked over, fired up and settled down to idle all by itself as I slowly reduced the choke.

Sweet!

Root cause for my problems seems to be minimal experience compounded less than stellar craftsmanship during rebuild. The gasket kit that was available is not really all that great, but it was helpful. It came with a new plunger, but the length was wrong so I had to shorten it, and I've already mentioned the gasket issue.

Anyway, I loaded my nine year old son up, and I drove it around the block in a victory dance. More chunks of glass fell out from the passenger side shattered window and onto the running board- much to the delight of my son. It doesn't have any functioning hydraulic brakes yet, so the hand brake was used to stop short of my wife's car out in front of our house. I left it out front in proud, dilapidated display while I figured out what to move around in the garage to get the '41 inside.

The Kingsburg police gave my neighbor a note four days ago about the Kingsburg City Vehicle Abatement Program, thinking the trucks were his. He should be so lucky!

[Blisters]

nice