setting the timing on 1989 4.3 OMC

[isle71]

Hello, I am searching for info on ignition timing, having just replaced points and condenser with
Petronics Electronic ignition kit.
I am a bit confused how to set the timing..should the timing be set when motor is under load?

Thank you

 

[Lou C]

Those Prestolite distributors have a centrifugal advance system under the points plate. Simple set up of flyweights and springs. The standard setting for timing is 6* BTDC. This is set at idle speed.
As far as spark advance total timing advance the centrifugal advance adds 12* at 3200 or so RPM for a total of 18* advance. Keep in mind that OMC recommended 89 octane fuel, if using 87 they recommended less base timing like 1*.
Idle speed is 500-600 rpm in gear in the water.
I have the same engine mine still has points.

 

[isle71]

Thanks for the reply Lou C
When I apply the timing light at idle should the 6* be set at the left of zero which says on engine reference mark BEFORE or to the right of zero marked AFTER? (looking at the front end of motor)

 

[Lou C]

What you need to do is clean up the harmonic balancer which will have a slot on it (I put a dab of white paint on it so it shows up) and the timing tab that’s attached to the timing chain cover. This has notches that represent 0*, 2*, 4*, 6*, etc, BTDC (before top dead center) will be to the left of the zero mark (or TDC). You want to set the base timing at idle where there is no advance occurring. Also the advance unit should be lubricated by putting a few drops of motor oil and in a lubricating wick that is inside the distributor shaft. To access it just pull off the distributor rotor. I oil that once each season. When I get a chance I’ll post a pic of the Chevy timing marks.

 

[isle71]

Thank you again Lou C
Appreciate your help.
Attempted to send pics but having issues with iphone camera.

 

[Lou C]

I think it's a website issue.

 

[Lou C]

Uncovering The Secrets Of Ignition Timing

Finding Top Dead Center and Setting up Timing Curves All engines have personalities – some are aggressive, some are demure. Some are rough around the edges and downright skittish below 3,000 rpm. All respond to ignition timing a little bit differently. Timing the arrival of the spark at...

www.streetmusclemag.com

Ok there is a pic if you scroll down that shows you exactly what your timing tab looks like. It's the one with the engine block painted blue.

 

[isle71]

Wow lots of info..clearly explained, boat is going in the water tomorrow and
look forward to seeing how the new Petronix ignition works.
Cheers!

 

[isle71]

Good morning
Have taken my 20 ft Limestone out for the day and the 4.3l runs well and generally sips fuel, what I question is the vibration from around 2200 to 3200 rpm, but levels out at about 3500 with no vibration at all.
Timing was set at 6*BTDC with 89 fuel, new plugs and petronix electronic ignition, prop is not new but in very good condition.
Just hoping to get some feedback.
Thanks
Isle71

 

[Scott Danforth]

pull your drive and inspect the alignment and u-joints (this is part of annual maintenance)

 

[Lou C]

I’d also check the propeller for damage & prop shaft for run out.
That early 4.3 has an even fire crankshaft but that didn’t totally eliminate the vibs inherent in a 90* V6; these will have a vib you can feel at about 1500-1700 rpm that you can feel even in neutral. However this also depends on what shape the engine mounts are in. The later 4.3s with the balance shaft should be just about as smooth as a V8…

 

[isle71]

Thank You.

 

[Lou C]