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84 Mercruiser timing/tune up question

G

GregF

New member
My engine has a slight miss, predominatly at low speeds (1500 - 2000 rpm). It seems to go away at higher speeds. In the past, I have corrected this with a tune up (new points/plugs). The points still look good but it has been a couple years since I replaced them.

I would like to do a complete tune up before winter storage. Timing has always been a mystery on this engine. The shop manual says to plug the vacuum advance before timing. I don't see any vacuum advance. Is there suppose to be one? Should I time it to the spec and ignore manual's instructions regarding vacuum advance? If not what should I do? Also, will any timing light work OK? The manual says something about using a certain light (I don't have the manual in front of me right now). Any other tips on timing or tuneup? One last thing, can I convert this distributor to an electronic igntion? It has very low hours and I'd like to keep it for a while.
Thanks
Greg
 
OK because you said points on a 1984 I will assume this is a 4 cyclinder motor??? INFO INFO INFO!!!!!!!!!!

If it is then

1. you can convert to a electronic system. Pertronics is the typical if not the only. ~ $100.00. SET IT ONCE AND NEVER MESS WITH IT AGAIN, INCLUDING THE TIMING WHICH MUST BE RESET WHEN ONE OF THESE KITS IS INSTALLED.

2. if the book or manual you have for that motor says to plug the vacuum then it is the wrong manual.......NO VACUUM ADVANCE ON MARINE ENGINES with carberators.

3. Timing for a 4 cylinder is typically 6-8 degrees BTDC.

4. the issue you are reporting may not be the ignition, it may be the carb needs to be rebiult......accelerator pump may be worn......
 
Yes it is a 4cyl Mercruiser 140 (Sorry). I don't have the manual with me but it makes sense the wrong manual. I'll go with the 6-8 degrees BTDC. Is there a way to confirm that the accelerator pump is bad? Any thoughts on the type of timing light to use? I'll check out the Pertronics. Thanks for the reply.
Greg
 
Any normal timing light will work. Typically the easiest is the cheaper ones with no adjustable anything....

MAKE SURE your points are st propely first. 28-32 degrees dwell, I forget the decimal gap.....Been a long time since I set em up with a feeler guage. I use a digital dwell meter that reads when cranking over vs only when running....
 
If you can run 89 octane then you may be able to bump the timing up a degree or two it may run better. But if you are stuck with crappy 87 then 4-6 degrees.

Also, IDLE spped is 650 in gear in the water!!!!~ 700-750 out of the water. NO HIGHER or it will shift hard!
 
I do run 89 octane but it has usual 10% ethanol - marina says they have no control on what they get any more. I use a gas treatment product for alcohol (can't recall the name). Thanks for the comments.
 
The dwell for a 4 cylinder engine is a result of 4 cylinders being divided into 360 degrees distributor rotation.
This gives each cylinder 90 degrees for coil saturation time and open time per OEM specs.
The dwell angle will be closer to 40+ sump'n degrees.
See your OEM specs for correct dwell.

Gap is an estimately ONLY of correct dwell..... so set dwell, not gap!


Be sure to not only set/check BASE advance, but look at your OEM specs for TA (total advance).
Make sure that the distributor is offering this, or she won't perform as well.

.
 
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