3.0 L Ignition Timing Question

[Andy J]

I have a OMC 3.0L model 302AMFTC engine and need clarification on where to properly set the timing. My SELOC manual says 6 BTDC but I have seen other charts at 0 degrees. I am running 87 octane non-ethanol fuel and some charts have the timing set different depending on octane.

There is so much different info out there and not sure what to use. If I could get some direction from someone who has experience with this engine setup I would appreciate the the help.

Engine idles a little rough at 500 rpm but smooths out at 800, wondering if timing could be the cause.

Andy J

 

[kenny nunez]

What type of ignition do you have? Breaker point or electronic ? Also with the distributor cap off is there a lot of slop on the rotor shaft?

 

[Andy J]

What type of ignition do you have? Breaker point or electronic ? Also with the distributor cap off is there a lot of slop on the rotor shaft?

It's a original points system.

Rotor is loose on the shaft, was a concern when I first bought the boat. Got a new one from Sierra but the same.I measured both rotors and the ID is 0.060" larger than the rotor shaft. Shaft looks fine and doesn't appear to be worn.

Is this normal?

Andy

 

[Lou C]

I’d try getting an OE one from BRP. I don’t have any play on my original Prestolite distributor. Is it play in the shaft itself or between the shaft and rotor?

 

[Andy J]

I’d try getting an OE one from BRP. I don’t have any play on my original Prestolite distributor. Is it play in the shaft itself or between the shaft and rotor?

Play is between rotor cap and shaft, I can turn the shaft but thats the Mech timing advance. Been 30 years since I have worked on points systems, seems like I remember spring steel on the shaft or inside the rotor to remove the clearance.

I'm new to boating... Who is BRP?

Thanks

 

[Andy J]

Lou,

Any experience with the value? 6 degrees seems like a bunch between specs?

 

[Maclin]

That does seem like a big variance. What other charts are you looking at, they may include some later model units with electronic igntions with electronic advance. On some of the newer ( than yours!) models they need to be put into base mode to set the timing, and most of those settings are 0 or even 1 after tdc.

If I had to guess I would say the 6 degrees BTDC for a points system sounds right.

 

[Andy J]

When searching my model # I get different info.... There's so much info out there and not sure what to believe, just trying to get the engine right step by step.

Thanks for the suggestion, it's set at 0 currently. Headed out to the lake this evening, think I may throw a couple degrees advanced and see how it runs.

Andy J

 

[Lou C]

Play is between rotor cap and shaft, I can turn the shaft but thats the Mech timing advance. Been 30 years since I have worked on points systems, seems like I remember spring steel on the shaft or inside the rotor to remove the clearance.

I'm new to boating... Who is BRP?

Thanks

that does not sound right to me. BRP is Bombardier Recreational Products, they bought the assets of OMC when they went bankrupt in 2000 and they still supply most of the OE parts for the OMC Cobra engines/drives, and are producing the Evinrude Etec outboards. If the aftermarket Sierra does not seem to fit right then I'd try the OE. BTW, if you have any Evinrude outboard dealers near you they can order OMC sterndrive parts. I've used Sierra caps and rotors and they have always fit right.

I'm looking at my OMC shop manual for my '88 Cobra and here are the specs given for the 3.0...
points gap: 0.019"
dwell: 31* to 34*
timing:
with 89 octane gas: 4*BTDC
with 86 octane gas: 1* ATDC
total timing advance @ 2100 rpm = 32* (4* base timing +28* mechanical advance = 32*)
plug gap 0.035"
idle speed 500-600 rpm in fwd gear in the water
full throttle rpm: 4200-4600 rpm

 

[Lou C]

If you're set at zero and using regular gas then you're probably OK. I have read that the 3.0 does not tolerate excessive advance well (tends to blow head gaskets) so its safer to be a bit more conservative on the base timing number.

 

[Maclin]

Was stuck on thinking settings for a V motor I guess, best follow what these guys said!

 

[xltier]

5 degrees btdc is good. will run much better than 0. the 0 or 1 atdc is for the newer 3.0 with the electronic ignition because the TOTAL advance was high enought to blow head gaskets occasionaly.was also attributed to sustained high rpm.

 

[Lou C]

Regardless of the the boat manufacturers and engine companies say I have always used 93 octane marina gas yes it’s more expensive but I don’t have to worry about detonation under sustained high load that all marine engines run at. To me the 2 worst things you can do besides letting it overheatvor run low on oil is to over prop it so it never hits max specified rpm and use low octane gas. The 2 are a deadly cure mbination.

 

[Andy J]

that does not sound right to me. BRP is Bombardier Recreational Products, they bought the assets of OMC when they went bankrupt in 2000 and they still supply most of the OE parts for the OMC Cobra engines/drives, and are producing the Evinrude Etec outboards. If the aftermarket Sierra does not seem to fit right then I'd try the OE. BTW, if you have any Evinrude outboard dealers near you they can order OMC sterndrive parts. I've used Sierra caps and rotors and they have always fit right.

I'm looking at my OMC shop manual for my '88 Cobra and here are the specs given for the 3.0...
points gap: 0.019"
dwell: 31* to 34*
timing:
with 89 octane gas: 4*BTDC
with 86 octane gas: 1* ATDC
total timing advance @ 2100 rpm = 32* (4* base timing +28* mechanical advance = 32*)
plug gap 0.035"
idle speed 500-600 rpm in fwd gear in the water
full throttle rpm: 4200-4600 rpm

Lou,

Sorry for the delayed response, appreciate all the info. I am running none ethanol fuel and it's 87 so maybe need to back timing back down to 0.

Removed the rotor and points plate today and there is some play in the shaft also maybe from the gears in the bottom. Not sure how much backlash is normal. With the timing light at 500 rpm's I do see the timing jumping around 2 degrees or so. Could this be the source of my rough idle?
Thanks,
Andy

 

[kenny nunez]

There is no bushing at the bottom of the distributor body which causes the timing and dwell to not hold steady which causes rough idle. If you were to remove the distributor and remove the shaft it is easy to have a bushing installed in the lower end.
Using a dwell meter is more accurate than a feeler gauge to set the points. Remove the spark plugs and then remove the coil wire from the distributor cap and ground it, spin the engine and adjust the points while reading the dwell meter.