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Recently I have developed an idling problem with my 1941 160. It used to run fine at a slow idle after warming up, but now it "stumbles" and runs rough after warm up. When I try to drive it, it will die when I come to a stop or attempt to shift, unless I keep up the rpm's. I have adjusted the idle up, but I know that is not the solution.

My first suspicion is that the timing was out of whack, so I set about attempting to adjust the timing but am not certain which part of the "pointer" above the vibration damper. see picture below. When I attepmt to set to the line shown in the picture, the engine stops.

Must I disconnect the vacuum advance line to the distributor, before attempting to set the timing?

Any other ideas?

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When you find out, I'm interested in knowing too. I have the exact same issue with my '53. Pretty sure it's a timing issue.

The blunt end of that "pointer" which is horizontal across the damper is the timing index marker. If you're setting to 6 deg. BTDC, the 6 deg. line on the damper should be at the edge, just short of disappearing beneath the pointer.

It should not be necessary to block off the vacuum advance to the distributor to get proper timing, but make sure idle speed is normal, once the throttle plates open enough to expose the vacuum port, it will affect your timing.

But from your symptoms are you sure you don't have a vacuum leak somwewhere? I'd suggest putting a vacuum gauge on the intake manifold and checking - it should be between 18 and 20 inches typically for an engine in good running condition at idle, and the needle should have little or no "flutter".

Owen:

Thanks, as always, for your prompt and learned response. I will try hook up a vacuum gauge to the intake manifold and see what kind of readings I get. I will report back.

I just popped the distributer cap to check the point gap and discovered that I couldn't get the feeler gauge through the gap due to a burr on one of the surfaces. I will order a new set of points and new rotor and maybe a cap 1st before checking the vacuum. I also just got the manifold plug out with a little help from PB Blaster.

Assuming the points are reasonably new, you could just run a point file thru them to take off the "burr" and regap them. Small amounts of metal transfer from one point to the other isn't all that uncommon, there is a rule (though I forget the details) about how to tell if the condensor is either slightly over or under capacity depending on which way the metal transfers. Not that a small amount of metal transfer is necessarily anything that calls for corrective action.

A point file in your traveling tool box is highly recommended,.

Point file

http://www.mcmaster.com/#contact-point-files/=gq3pm6

Dave and Randy; I have filed the burr off the points, reset them to .017" and reassembled to do the compression test. I'm happy to say the vacuum gauge holds steady at 19 inches with an ever so slight quiver; so I think I'm OK on the vacuum front.

I read some other posts regarding rough idle and have seen Dave's suggestion regarding looking down the throat of the carb while idling. I see a fairly steady drip stream from the jets, so I've now got the carb off and am preparing to check the float, needle and seat for any abnormalities. I will report back.

Dave, perhaps you can briefly describe the process of adjusting the two idle screws with thw help of the vacuum gauge. Am I looking for an adjustment with each screw that yields the highest vacuum reading?

I plan to do this once I have gotten to the bottom of the float issue, and then I plan to go for the timing adjusment, once I have it idling smoothly.

To set idle mixture screws with a vacuum gauge:

Engine warm and idling at correct (or at least reasonable) idle speed. Turn one idle screw inwards (CW) until the vacuum drops dramatically and the engine stumbles - this should be pretty close to the screw being screwed in to the stop. Then slowly begin backing the screw out (CCW) while watching the vacuum which should gradually increase. At some point the vacuum will cease increasing and reach "steady state". Go back in a bit just be sure you're on the point where it ceases to rise further. You want to be right on that cusp where the vacuum has maximized. Then do the other idle mixture screw, then back to the first again just to be sure.

Dave:

Thanks for the idle adjustment tutorial. I just returned from partial carb disassembly, enough to get at the float, needle and seat. The float appears to be fine, no apparent nicks or dents, and appears to be hollow when shaken; I assume it floats, but didn't test that. I figure if it was leaking there would be some liquid inside, right? I adjusted it to sit at exactly 5/32" below the top as is speced for the Carter WDO 531 SA carb.

The needle and seat appeared to the naked eye to be ok, and seemed to be effective at stopping air that I blew into the inlet, while lifting the needle into the seat ever so gently. The needle appears to have some sort of hard rubber tip that goes into the seat. Is this kosher? All ther other needles I have seen appeared to be solid brass.

I also tested the fuel line pressure to the carb inlet with just the electric fuel pump running and it measured 3.5 psi after going through a pressure regulator. I didnt have a "t" availible to test it while running in tandem with the mechanical fuel pump; should I do this before going any further, to rule out excessive fuel pressure as a cause?

Since everything appeared to be fine, I reassembled only to find that I still have gas dripping into the throat at idle. Does this mean I should order a new needle and seat, and, if so, where might be the best source for a set that would meet the specs for this carb?