Ignition Timing - Distributor

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Ignition Timing - Distributor

Postby Bill Hudson » Fri Nov 02, 2012 8:23 pm

Got back from a two week vacation yesterday and took some of the parts, I received during the vacation, to the Cubhouse to put on my mowing Cub. The Cub starts fine but has a high idle miss. I took a timing light and at idle the Cub is firing at, probably, 32 degress BTDC. At high idle the timing marks are at the top of the pulley.

I have reviewed the owners manual, service manual, and several threads & How Tos on distributor timing and I'm lost. Any help to an electrically challenged Cubber is appreciated.

I have:
On the bench, installed points and condenser. (May have gotten the gear out of time.)
Installed new plugs and plug wires.
Installed rebuilt carb.
Removed and examined the governor and am confident the timing marks are properly aligned.
Tightened up the connections on the governor.

Where do I start to get this puppy timed properly?

Thanks.

Bill
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Re: Ignition Timing - Distributor

Postby challenger » Fri Nov 02, 2012 8:32 pm

Something is not right in the centrifugal spark advance mechanism inside the distributor.
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Re: Ignition Timing - Distributor

Postby indy61 » Fri Nov 02, 2012 8:51 pm

Can't trust any of the new ignition parts these days. Could be anything.
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Re: Ignition Timing - Distributor

Postby Boss Hog » Fri Nov 02, 2012 9:28 pm

Twist the distributor until it comes back to where it should be. I would static time it first and then see where the mark is with the light.
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Re: Ignition Timing - Distributor

Postby RaymondDurban » Fri Nov 02, 2012 9:29 pm

When you bring the engine up to TDC, where is the rotor pointing to?
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Re: Ignition Timing - Distributor

Postby Boss Hog » Fri Nov 02, 2012 9:30 pm

and with a dist it make no difference where the governor is lined up with the marks on the idler
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Re: Ignition Timing - Distributor

Postby Eugene » Fri Nov 02, 2012 9:34 pm

Bill Hudson wrote:The Cub starts fine but has a high idle miss. I took a timing light and at idle the Cub is firing at, probably, 32 degress BTDC. At high idle the timing marks are at the top of the pulley.
Something wrong with your figures. 32 degrees BTDC at low idle and the engine wouldn't start, kick back.

Since engine runs, you can't be far off. Set engine #1 cylinder TDC, 2nd mark to pass the pointer if you have two timing marks.

Remove the distributor. Mark the #1 spark plug cap location on the distributor base. Reinstall the distributor so that the rotor is pointing directly at your mark when fully seated and the 12 O'clock position of the distributor base is at 12 O'clock. May take a couple of tries to get it right. Then static time the engine.
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Re: Ignition Timing - Distributor

Postby lazyuniondriver » Sat Nov 03, 2012 7:31 pm

Bill Hudson wrote: The Cub starts fine but has a high idle miss.


If I interpret the problem correctly, I think you are timed correctly or pretty darn close.

You indicated the timing light illuminates the timing mark on the pulley at the top or 12 o'clock position at high idle, having moved from about 32 degrees BTDC as engine speed increases.

If the timing light was connected to spark plug wires one or four, with the engine running, the mark should be sighted somewhere in the neighborhood of the timing pointer.

If the timing light was connected to wires two or three, with the engine running, the pulley mark should show up somewhere around 180 degrees opposite the pointer, or about the 8 o'clock position looking from the front.

Since you indicated the tractor starts fine, even though the visible timing mark is way off, the ignition timing has to be in the ballpark or it would never start, idle, and run well enough to hold a strobe on the pulley.

Hooking the timing light to any plug wire will only light up the mark in 2 spots, 180 degrees apart from each other so we know timing light connection wasn't an issue.

By indication of the moving timing mark between low and high idle, the mechanical advance mechanism seems to be functional.

I diagnose the pully as having an additional mark, gouge or nick simulating a mark, or was just completely mis-marked to begin with.

Don't adjust anything just yet and try this.

To be certain you have a pulley mark at TDC, bring the number one cylinder up to exactly TDC. Carefully examine the pulley for a mark at the pointer. If no mark is evident, place a mark on the pulley exactly at the pointer with white chalk, nail polish, or paint.

Rerun your mark inspection with the timing light and I'm sure you'll find your new mark closer to specifications. If you are satisfied with the new mark, you may want to make it permanent.

I don't think your high idle miss is a timing issue, but perhaps something as simple as a defective high tension wire, high tension wire connection, or defective spark plug or faulty gap. Go back and check all high tension connections at both the cap and the plugs.

If this doesn't eliminate the miss, isolate each cylinder by removing one plug wire at a time to determine if just one cylinder is causing your high idle miss.

If the cause of the miss can be traced to a single cylinder, the cause can only be between the distributor cap and the spark plug electrically, or mechanically due to a compression issue.

Best of luck finding that miss.

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Re: Ignition Timing - Distributor

Postby Bill Hudson » Sat Nov 03, 2012 8:10 pm

Came in from the Cubhouse just a few minutes ago. Success!!! Thanks to all your excellent advice. I just had to rotate the distributor a bit (a good bit, in my estimation :) ) and the Cub runs well at both high idle and idle. Timing marks show at the pointer, as they should. Sometimes, well OK, always, I get frustrated with the electrical stuff. :roll: Thanks again, you folks have been very helpful.

Now, if it will stop raining long enough that I can mow my grass. :) :)

Bill
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Re: Ignition Timing - Distributor

Postby midmo » Sun Nov 04, 2012 11:32 am

Eugene wrote:
Bill Hudson wrote:The Cub starts fine but has a high idle miss. I took a timing light and at idle the Cub is firing at, probably, 32 degress BTDC. At high idle the timing marks are at the top of the pulley.
Something wrong with your figures. 32 degrees BTDC at low idle and the engine wouldn't start, kick back.

Since engine runs, you can't be far off. Set engine #1 cylinder TDC, 2nd mark to pass the pointer if you have two timing marks.

Remove the distributor. Mark the #1 spark plug cap location on the distributor base. Reinstall the distributor so that the rotor is pointing directly at your mark when fully seated and the 12 O'clock position of the distributor base is at 12 O'clock. May take a couple of tries to get it right. Then static time the engine.


Question Eugene? (12 O'clock position of the distributor base is at 12 O'clock) I have taken my distributor off at the drive housing leaving the drive housing on the tractor. Will I have to take the drive housing off to get it back in time? Looking at the Blue Ribbon Service manual I will.
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Re: Ignition Timing - Distributor

Postby Eugene » Sun Nov 04, 2012 12:11 pm

midmo wrote:Question Eugene? (12 O'clock position of the distributor base is at 12 O'clock) I have taken my distributor off at the drive housing leaving the drive housing on the tractor. Will I have to take the drive housing off to get it back in time? Looking at the Blue Ribbon Service manual I will.
No need to remove the distributor drive housing because the distributor is also gear driven.

The trick is to replace the distributor in the distributor drive housing, engine already set on #1 cylinder TDC, so that the ignition points are just starting to open (or as close as you can get), rotor centered on the #1 spark plug tower, and the distributor centered within it's rotation range. Then static time the ignition system.

and the distributor centered within it's rotation range
Some distributors have a slot which limits it's adjustment range. The Cub does not have the slot. So the 12 o'clock position on the distributor should wind up at or near it's upright position when installed and static timed.

It's quite common to get the distributor/rotor timed off several teeth. This normally doesn't cause a problem starting the engine and at low engine rpms'. At higher engine speed/rpms the distributor advance moves the rotor location. If the rotor location is off far enough the ignition system faults for several reasons.
I have an excuse. CRS.
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