Timing and Idle

[79camaro]

Hi All. Working on my timing today. Looks like it should be 1 BTDC. I replaced the distributor and it seems to start up ok, but when I bring it to 1 BTDC it stalls out. SHould I adjust the idle or is my timing the issue? Maybe I didn't put the distributor back in properly?

 

[alldodge]

Hi All. Working on my timing today. Looks like it should be 1 BTDC. I replaced the distributor and it seems to start up ok, but when I bring it to 1 BTDC it stalls out. SHould I adjust the idle or is my timing the issue? Maybe I didn't put the distributor back in properly?

1BTDC I don't think so, what engine do you have, year of the motor and better yet how about a serial number

Edit: looks like 1 BTDC isn't that far off but not correct for your motor

 

[alldodge]

79Camaro - it would help to use the one you started about this issue, but in review of the other post, I see your serial number is OM384628

With that manual 26 states for S/N 0L341000 and above (this would be for you) it should be set at 1 degrees ATDC not before

 

[Bt Doctur]

 

[bruceb58]

Are you using the timing plug to put your distributor into base timing mode? You have the EST distributor right?

 

[79camaro]

Thanks fellas. @bruce, no I used a plastic stick and cranked the motor "feel" for TDC. Yes its EST. It's firing right up now and I can rev the motor just fine in neutral, so I assume I put it back in correctly?

 

[bruceb58]

You have it on correctly but you aren't setting the timing correctly. You need to install the shunt and set it.

http://www.marinemechanic.com/site/page229.html

 

[havoc_squad]

Camaro, I don't think you understand bruce's key question, and that was: "Did you put the distributor in base time mode?"

So far to my knowledge, all Mercruiser carburated engines equipped with EST distributor based ignition systems specify in the service manuals that the engine timing is to be set while in "Base Time Mode".

If you're doing timing adjustments without a timing gun, stop adjusting it and buy one first.

If you adjust the timing without putting the Mercruiser EST distributor in base timing mode, you are in fact making the wrong timing adjustment and will mostly over-retard the timing to where it runs rough.

I believe for your serial number info, Mercruiser Service Manual #26, starting at the bottom of page 4B-9 to 4B-12 highlights the procedure for Base Time Mode. Those are the same pages I had to look at carefully.

FYI, base time mode will always run rough, even if you do have it adjusted to spec on timing. What makes it worse is if you're carb is running too lean or too rich when at Mercruiser service manual specified minimum idle range in gear under load.

Where I messed up involving timing adjustment of a Mercruiser EST distributor was when I had my 3.0L distributor jump time on me this spring (probably the locking arm wasn't torqued good enough).

So I went and made a bypass jumper for the EST distributor to put it in base time mode, but I did not know that the shift interrupter had to be bypassed, directly connecting the ignition with the shift interrupter wire going to the distributor. I thought it just had to be disconnected.

Well, I made a timing adjustment to -1 BTDC per service manual but couldn't figure out why the engine wouldn't get out of base time mode, back to 12/14 BTDC at idle after I unplugged the bypass jumper. The engine kept running rough and would eventually die on me.

The problem was I was never IN Base Time Mode when I made the adjustments.

So I was informed here at the forums I missed the shift interrupter wire bypass connection.

I corrected the timing adjustment back to previous, put the engine in base time mode, made the timing adjustment in base time mode, removed the bypass jumper, and reconnected the shift interrupter wiring.

Timing issue resolved, made very minor carb idle mixture adjustment to smooth out idle. Running near spot on good idling per service manual specs.

 

[MikDee]

Are you using the timing plug to put your distributor into base timing mode? You have the EST distributor right?

There is a certain procedure for setting the timing on your motor with the EST distributor, that must be used or it'll never be right!

 

[bruceb58]

https://www.youtube.com/watch?v=-swDhVcEdh0

It will be running rough when it is being set to your base timing. After setting, the distributor will advance and idle a lot better.

Make sure you put the shunt in once the engine is running, not before.

 

[79camaro]

Ah. Yes I have the two wires from the distributor connected, but I started it with it connected. What about the shift interrupt switch, the manual reference this but not that video.

@havoc, yes I am using a timing light.

Thanks!

 

[Bt Doctur]

the switch needs to be unplugged and the 2 harness wires plugged together. I believe this puts 12v into the ecm for timing purposes along with the dist jumper

 

[havoc_squad]

Ah. Yes I have the two wires from the distributor connected, but I started it with it connected. What about the shift interrupt switch, the manual reference this but not that video.

@havoc, yes I am using a timing light.

Thanks!

https://www.youtube.com/watch?v=-swDhVcEdh0

It will be running rough when it is being set to your base timing. After setting, the distributor will advance and idle a lot better.

Make sure you put the shunt in once the engine is running, not before.

Ack, this video is not a good reference for using the standard way way to set Mercruiser EST distributer base time mode. It is not BAD, but it is not good either.

This was the initial video I watched, and then looked at the service manual. The problem is it did not cover in detail the steps needed to get the ignition in base time mode, as any help video worth their salt would explain the common mistakes in setting the timing and explain how to avoid the mistakes.

I probably would have been better off reading the service manual two more times and ignoring this video, probably would have figured this out much faster without wasting a ton of time caused by assumptions caused by this video.


Timing strategy suggested:

1. Make sure shift interrupt wires are properly connected or disconnected. No bypass.
2. Make sure you have the bypass wire at the distributor disconnected.
3. Get the boat engine warmed up and the timing gun ready
4. Get a timing reading of it very close to 700 rpm's.
5. From your serial number info, it should be 15 degrees(+/-2 degrees) BTDC at normal ignition mode at idle around 700 rpms. (Assuming serial number information listed above is correct.
6. If it says -1 BTDC or close to it in normal ignition mode, then you incorrectly adjusted the timing without being in base time.
7. If timing is not correct per service manual at idle in normal timing mode, revert the timing change back to the previous spot that it was while in low idle (700 rpm's) before messing with the timing. Unless it is riduculously high number (+20 BTDC). Worst cast, set it to 15 BTDC at 700rpms to fix the screwup.

8. Install the bypass jumper at the distributor.
9. Disconnect the purple connectors and the white connectors at the shift interupt switch.
10. Have the distributor locking arm losened, but tight enough not to move until ready for adjustment.
11. Connect the purple bullet connector at the shift interruptor from the 12v ignition source to the white female bullet connector that is going to the distributor.
12. You should be in base time mode, the engine should be running rougher and slower idle speed.
13. Adjust the timing per the service manual specification for base timing mode for your serial number of your engine. (From info given, that is 2 ATDC in base time mode)

14. Torque down the distributor locking arm when set, and make sure with the timing gun that the timing doesn't move while tightening. Doing it too fast will jerk the distributor.
15. Disconnect the purple and white shift interruptor wires that were joined and reconnect them to the shift interrupter.
16. This should cause your engine to exit base time mode.
17. Pull out your bypass jumper at the distributor.
18. Verify timing is correct per mercruiser service manual for normal timing mode at 700 rpm idle.
19. If all checks out, you are done with timing.