Poor Idle

Art Newland

Art Newland

Well-known member
I'm going nuts trying to get a nice smooth, proper Model A, idle.:confused:
I had my fuel line plug up, so I went through the procedure of flushing the tank and adding the small filter that goes up in the tank on top of the fuel shut off. All good there, I have good fuel flow now. I really cleaned the sediment bowl up while I was at it. But now my idle had become worse, so I pulled the Tillotson off and gave it a good cleaning, new gaskets, etc. Idle not any better, so I put my Zenith on it... exactly the same. It idles very rich smelling, burns your eyes. It actually idles the best if you unscrew the idle mixture screw all the way out! So now I'm grasping at straws, I ruled out vacuum leak because that should make it lean... correct? But anyway I plugged off the wiper tube, I even put a new manifold gasket on it. While I had the manifold off I changed the points and condenser because it's in the way (manifold heater) of the condenser ground screw. Got it back together this morning... no joy. It still lopes and flutters the same as before. On the bright side, the new gasket seemed to seal up some exhaust leaks.:) The plugs are new/gapped. It does have ethanol fuel in it, new and fresh from the fuel tank flush. Road testing it shows plenty of power, pulls strong. Can 10+ percent ethanol make it run this poorly? What am I missing? I've added a video, although it's hard to hear it.
https://www.youtube.com/watch?v=bC0G2G7Atvw
 
I'm thinking at this point I've got bad gas even though it is new. I've located a station that has ethanol free gas, I'm gonna go get some.
 
Hi Art,

1. From the video, as you mention, your engine is not at idle speed.

2. The accelerator rod you move is attached at the carburetor to the carburetor throttle lever.

3. This moving throttle lever has an idle stop set screw at the bottom of the lever to adjust engine idle.

3. Did you try to unscrew this "IDLE STOP SCREW" to reduce idle?

4. It is shown as part #11 in the "carburetor diagram" in Bratton's Model A Parts Catalog.
 
Ok, H.L., that's as slow as it will run. I think you're on to something. By adjusting the GAV fully closed it smooths out some and doesn't run as rough. With the idle :eek:screw turned until it's not touching the carb any more it still runs. So now I'm thinking vacuum leak again... maybe somewhere in the intake manifold that I can't see, maybe where it bolts to the exhaust manifold? If I had any hair left. I'd pull it out! :eek:
 
Sounds like a possibility that your throttle plate, (inside the carburetor ... close to the intake manifold), part #12 on Mr. Bratton's carburetor diagram, is not closing enough to reduce the flow of mixed air and gas.

Some used to drill holes in this round plate; or, make cut outs in it; or alter this plate so it would never greatly reduce the flow of air/fuel; hence, always having a "fast" idle ........ or your throttle shaft lever, part #10, may have been purposely bent to where the throttle plate does not close enough.

Difficult to see from miles away ...... just try something and keep reporting back ..... none of the guys on this Forum are U. S. Congressmen .... they are all willing to help American citizens who work ......... or Citizens who are retired after working most of their lives ...... great people.
 
Art, wishing you luck in finding your problem. Because I have a similar problem with my huckster. I have also put on new manifold gasket, reworked carb, worked on distributor but still runs a lot like yours does. So if you find your problem, thanks a lot!

But I think I will get it in the shop one of these days, and think I will check out a few other things. Like try another distributor, try another carb, check compression, and a few other things (doing one thing at a time). If I get it fixed, will post the results here. Also wish you luck in your efforts.
 
OK H.L., I double checked the throttle plate, no extra holes.:)
There certainly is a pretty good gap around the throttle plate when closed as far as it will go. The Zenith is an EBAY purchase from seller "old_ford_garage_". Name on the box is Tom Lynn. Anyone hear of him? Is he a Ford Barn member. The Tilly had been man-handled a bit by the previous owner, some stripped threads and so-forth. It's why I bought the Zenith, but again it's an unknown quantity at this point. The seller has a 100% customer feedback with 750 sales, seems trustworthy.
 
Fred K-OR said:
Art, wishing you luck in finding your problem. Because I have a similar problem with my huckster. I have also put on new manifold gasket, reworked carb, worked on distributor but still runs a lot like yours does. So if you find your problem, thanks a lot!

But I think I will get it in the shop one of these days, and think I will check out a few other things. Like try another distributor, try another carb, check compression, and a few other things (doing one thing at a time). If I get it fixed, will post the results here. Also wish you luck in your efforts.
Click to expand...

Thanks Fred, I'd take a little good luck about now. I'd love to be able to help you out with your problem too. I can't imagine ignition being the issue here. It always starts right up, and pulls like a mule under hard acceleration. I knew my coupe was a little sickly when I bought it, and everything I've done has made an improvement. The idle just has become progressively worse. Intake air leak is all I can think of to cause my issue.
 
The edge of the throttle plate has a bevel to match the bore angle when it's closed tight, so if someone put it in backwards it should be very obvious.

Also to center the plat on the throttle shaft you leave the screws loose, back off the throttle stop screw, then tap the plate fully closed and tighten the screws.
 
Yes, it should be able to close fully off if the plate is installed correctly and the idle screw backed off.
Do you have any pictures of it?
 
Tom Wesenberg said:
Yes, it should be able to close fully off if the plate is installed correctly and the idle screw backed off.
Do you have any pictures of it?
Click to expand...
Just pulled it off again. There was considerable gap around the idle hole and throttle plate. It was stamped 18 1/2 visible when closed as much as possible. I loosened the screws holding the plate to the rod, couldn't really move it around, so I removed the screws and flipped it over. Moved it to full closed and it centered it's self, screws lined up perfectly. I put the screws back in and re-installed it. I can close the throttle enough now to stop the engine and GAV does not effect the idle any more. So I think I'm making progress.:) The idle is still rough (but very slow). I took more video, I'll post it in a bit.
 
If you disconnect the linkage from the carb, will it idle down? I have had to tweak the arm on the carb and on the arm on the linkage at the firewall.
 
Have you checked your throttle shaft? it goes straight through the cast iron casting and when it wears you get a vacuum leak around shaft. They make oversize ones just to solve this issue.
Google :Model A Ford Zenith Carburetor Throttle Shaft & Lever - Oversize Diameter

Make sure good gasket seal between carb and manifold as well.
 
hale1776 said:
Have you checked your throttle shaft? it goes straight through the cast iron casting and when it wears you get a vacuum leak around shaft. They make oversize ones just to solve this issue.
Google :Model A Ford Zenith Carburetor Throttle Shaft & Lever - Oversize Diameter

Make sure good gasket seal between carb and manifold as well.
Click to expand...

Shaft looks good, new gasket too, new manifold gasket as well.
 
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