Firing Order - 90 deg from manual?

myoldboat2

Petty Officer 1st Class
Joined
Jun 3, 2007
Messages
303
1974 Mercruiser 140 engine s/n 388xxxx
Mercruiser "Late Model I" Stern Drive s/n 390xxxx

I'm curious about this...

The manual for my engine is Mercruiser Service Manual Number 2. Under "models covered in this manual" it includes "Mercruiser Stern Drive Engines", "MCM 140 s/n 3771645 - 4918569", so that's me. On page 8A-1 the firing order for Model 140 refers to Figure 1. Here is that figure (the parts in black):

firingorder.gif


But my plug wires connect as I've numbered in red. Why? I have a Pertronix electronic conversion (no points any more). My timing is set per the spec (I set it a few years ago).

I'm not familiar with indexing a distributor... Does the indexing get set when the distributor is mounted on the engine? Did I probably end up with a replaced distributor (but why would that change the index)? Is the manual wrong?

My engine runs fine at idle, cruise and WOT. There's no way it's firing each cylinder 90 degrees too late.
 

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: Firing Order - 90 deg from manual?

Someone didn't pay attention when replacing the dist. Normally No. 1 on the cap points to no. 1 spark plug. You can pull the dist and re set it, but if it runs I would not mess with it.

Firing order 1-3-4-2
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Firing Order - 90 deg from manual?

Show me what maintenance manual you read this in.
Look at the picture in the original post, it's from the OEM manual. Forget the red numbers though, they were put there by the OP, look at where #1 cylinder wire is hooked. It IS basically aimed at #1 cylinder..


Like cr2k said, the distributor was installed 1/4 turn off. You can either change it, or leave it like it is. It doesn't effect how the engine runs at all.
 

mkast

Lieutenant Commander
Joined
Nov 6, 2002
Messages
1,934
Re: Firing Order - 90 deg from manual?

basically aimed at #1 cylinder..

I'm sorry, now that I look at it, the number one on the cap IS BASICALLY pointing at number one on the block, and number two, number three and number four.
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: Firing Order - 90 deg from manual?

Your engine doesn't care which terminal you call number 1 as long as it is timed to that particular terminal and then follows the correct order from there. So you are good to go! ;)
 
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