Timing

[Kevinstone]

Another question for the group. When using a timing light, what RPMs should I have the engine running at to verify correct timing? I have electronic ignition

[hanleyclifford]

As low as possible so the centrifugal advance is not operating. Do you already have TDC marked for the light?

[Dave Neptune]

There are no timing marks on an A-4 so a timing light is not of much use. In order to use one you must mark the accy pulley or the flywheel your self unless someone else did.

Timing with the EI is the same as with points, makes no difference, however the choice of advance springs and making sure they are adjusted properly did.

I went through the process of marking the accy pulley and set the timing at full advance at 2000 RPM's and let the idle fall where it did. I set the full advance at 34 degrees and my idle was around 0. I did have the luxury of the use of a distributor machine. I installed new springs in the C-adv that came with the Indigo unit and had to do very little adjusting. The springs were pretty much spot on at a 600 RPM idle to 1750 RPM's the adv hit the stops at 17 degrees which is 34 on the crank which is about perfect. I did check it again after a few years and it was still spot on and ran it until I sold the boat some 15 years later.

Taking the time to find TDC to set the marks was well worth the effort.

Dave Neptune

[sastanley]

kevinstone,
There are a couple ways to do this. If you have access to the flywheel, the roll pin is vertical at TDC. Another way is to stick something in the #1 spark plug hole and note when the pencil/dowell is at its highest point. (making sure you are on the compression stroke, etc.).

On my old C-30, I had great access to the accessory drive, etc., but could not use the roll pin (although I drilled an access hole so I actually could), but I got the motor to TDC, and placed a mark on the accessory pulley as it spins 1:1 with the flywheel. Then I made a pointer out of some hose clamp material, and clamped that to the accessory drive housing, and made a mark on the assy pulley (thanks to my wife for having some crazy sky blue nail polish). From there, using a timing light was easy. Credit for this trick goes to Neil Dutton and thatch. I am not smart enough to think of these things myself.

Later edit - I went back and re-read your post. To answer your initial question, I checked timing at idle which is a bit jumpy since the RPM is so low. I also checked it at my boat's normal cruise RPM, about 1900-1950RPM. I checked at WOT too..the best I ever got with my direct drive/clean bottom/Indigo prop/engine tune/25' LWL was 2,350RPM.

In my opinion, you really want the timing dialed in at the cruising speed/RPM you use on your boat the majority of the time. I think Dave noted above anything over 1,750RPM the weights should be fully advanced, which I can concur with using my crude measurements. On my boat, we cruised at 1900 RPM or so..

[joe_db]

My timing light works, I can set the idle to TDC. I have a light with adjustable advance, so if I want to I can dial in any advance and it alters when the light fires to make that advance show the pin at TDC. If you want to go beyond setting the timing at idle and see your actual degrees, you will want one of these.
For even more fun, you can put a scope on the ignition:

You can see the points open, then close, then open again on this one.