Hi there, interesting question you bring up...Surprised this question didn't seem to have popped up in the past as I see your dilemma.
I'm going to try and spell it out just for future reference so just bear with me on most of the info below.
If you use your serial number in a parts diagram search it seems to list the incorrect manual part number evident by looking at the models covered; 'Plus other examples seems to be different ignition system parts/components in this Merc manual which is Merc part number 90-8613291 which happens to be manual number 26 all of which covers newer models starting with serial number 0L010042 and above 1998+....There's nothing about a 1988+/- engine year range.
Being your engine serial number is 0B775060 (making it an 1988 3.0L Model Number 430S000AS), there doesn't appear to be any 4 cylinder service manual by mercruiser that specifically states you should use manual number such and such. Manual number 10 starts off with 0C856450+ for the 3.0's while the 140 HP's ends with S/N 0B450800 and the Sea Ray models start with 0B787205.
Your 3.0/140 engine is not listed in Manual # 3 nor in manual # 8 but did notice though that MCM inline 180 Alpha One serial number range 0B436391 - 0B775248 puts your serial number in to a range but nowhere correct....So ignore that.
Though the parts guide incorrectly suggests to use
SERVICE MANUAL, Engine Manual (#90-8613291) # 26
in the
MISCELLANEOUS PARTS\ACCESSORIES section, Here is your correct parts guide otherwise,
https://www.perfprotech.com/mercury-marine-parts-catalog/umodel/29064
3.0L GM 181 I/L4 1987-1989 0B450801 THRU 0C856558
Now if you happen to need any Remanufactured Carburetor info, I found your engine serial number range in another chart for you too.
| 3.0L | 181/ L4 | 1987 - 1994 | 0B450801-0F603999 | M2/MerCarb | 860070R02 (NLA) |
http://sterndrives.com/Reman_Carb_Chart.html
So with all the worded confusion above...In the end Mercruiser would be considered covered in all of this as their service manual index cover shows your engine model type listed along with your serial number since the index says "
ALL" under serial numbers.....Number 10 should be the correct manual to use.
https://www.scribd.com/doc/136181601/2008-Mercruiser-Service-Manual-Index
S/M # 10 / 90‑14693‑1R1 / Jan 1994 / Engines: GM 4‑Cylinder
All Serial Numbers / 1985–1989.
What ignition system do you have?
CONVENTIONAL IGNITION COMPONENTS or
DIGITAL IGNITION COMPONENTS ?
If you're tuning the engine up then double check the top of the engine covers/flame arrestor as there should be some engine specifications listed on some stickers such as spark plug gap, timing, etc. to help compare the specifications found in the manual.
It would be interesting to see what MerCruiser Customer Assistance has to offer should you decide to get their opinion,
https://www.mercurymarine.com/en/ca/contact/mercruiser-customer-assistance
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