8N Slight Miss at Low and High Idle

Just rebuilt my grandfathers 1951 8N, and have a slight miss at low and high idle. Everything is new (distributor, wiring, plugs, points, condenser, distributor cap, coil, voltage regulator, etc.). I'm using the original rebuilt carburetor, because I couldn't even get it started with a new carburetor. Compression is good using the compression tester I have, but isn't fully operational. Appears to be over a 100 lbs on all cylinders. However, it doesn't hold the pressure and it's hard to see the reading when it's going up and down. I adjusted everything by ear and it idles at 350 RPM's, but ordered a timing light, Dwell/Point/Tach tester, and a compression & vacuum tester to fine tune.

Some observations:

1. The idle screw on the carburetor that controls air doesn't seem to work.

2. When it was 15 degrees out it wouldn't start. When the temperature got up to 45 it fired right up.

3. I thought the new intake valve guides I put in installed way too easily.

I'll fine tune all the adjustments when I get the test equipment.

I'm also thinking about getting a 6V electronic ignition. I've reset the points and checked for points sticking multiple times. With my eyesight and arthritis in my hands I'm thinking it might be me.

When I get the vacuum tester I'll see how much suction there is. I'm thinking it might be the valve guide seals considering how easy they slipped in, and the idle screw not seeming to work on the carburetor. I'll also change gaskets for a third time on the manifold and and carburetor.

If I pull the valves, does anyone know how many pounds of pressure the valve springs should be?

Could there be an issue with the timing gear connected to the cam? The cam and gear looked good.

Any other thoughts of things I can try, or is this how they run?

Or better yet, am I being too much of a perfectionist?

"3. I thought the new intake valve guides I put in installed way too easily."


Did you install the rubber valve guide seals on the intake valve guides?

I've never heard of them installing "easily" with the rubber seals in place.

Yes I did. After reading comments about them I thought I'd be at for a while. They just slipped in. Forget where I got the rebuild kit, but should have tried some other seals I had.

Think that might be it?

(quoted from post at 21:41:59 02/16/20)
Yes I did. After reading comments about them I thought I'd be at for a while. They just slipped in. Forget where I got the rebuild kit, but should have tried some other seals I had.

Think that might be it?

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If the intake valve guide seals are REALLY loose-fitting enough for air to be sucked in past them it sure could case a miss at idle, IMHO.

It can be very difficult to obtain that ideal balance to make an engine purr. On an engine of this age and technology you may not. That said the passages in the carb could be clogged up. When I rebuild an old carb it sits in carb cleaner for a few days in my truck so I can agitate it. I clean out passages with a welders tip cleaner and finish it off with carb spray with the straw on the nozzle. Not starting at 15 degrees could be fuel or spark related. I assume you choke it as soon as you start cranking. If it's not fuel, it may be slow cranking rpm. Keep the battery charged with either a maintainer to make sure you have proper voltage. I plug mine in when it gets that cold (Katz engine heater). I don't believe, based on what you posted you have an issue with the cam gear. Compression seems fine for an older engine. Mine skips a bit, looks good and runs great so I just drive it. Hope this helps.

Usually when the idle needle does not make any difference, it means that it is sucking in air from someplace else. The shaft on the carb throttle butterfly is a place to start looking. These machines never did purr like sewing machine. I did not have any trouble putting the valve guides in but they did not just drop in either. Good luck