Timing question

[technec]

I have a 3.0 140hp mercruiser and it has a developed a miss. I have tried to check the timing. I have the shunt installed and jumped, but when I put a timing light on it, the mark on the fly is all over the place, not staying on a mark. Am I missing somethng here? Manual states 1 degree btdc, so I marked it on the plate, but it never lines. Like trying to catch a grasshopper.
TIA

 

[Don S]

Re: Timing question

When you hooked the wires together at the shift interrupt switch, did you hook the wiring harness wires together? Not the shift interrupt switch wires.
Did you also have the engine running when you hooked the two with wires together with a jumper?

 

[technec]

Re: Timing question

I jumped the two wires of Dist., as this has a built in shunt. I connected timing light, and fired motor.

 

[Wotknot]

Re: Timing question

I jumped the two wires of Dist., as this has a built in shunt. I connected timing light, and fired motor.

But as Don asked......... did you jumper the 2 distributor wires together while the engine was running?

 

[technec]

Re: Timing question

No I did not, connection made before starting, and stayed connected while it was running. Am I suppose to jump, start, remove, then time?

 

[Wotknot]

Re: Timing question

No I did not, connection made before starting, and stayed connected while it was running. Am I suppose to jump, start, remove, then time?

I'm not sure these numbers apply to yours as mine is a 2000 model....but the proper procedure is what you need at the moment.

Timing Procedure
IMPORTANT: Failure to follow the timing procedure
instructions will result in improper timing
causing performance problems and possible severe
engine damage.
1. Start engine and allow to reach operating temperature.
2. With engine running, install a jumper wire across
the two WHITE leads on the distributor using
(91-818812A1), or fabricate one using a 6 in. (150
mm) section of 16 gauge wire with two male bullet
terminal ends connected.
a
3. Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch. Temporarily join the
engine harness wires together.
IMPORTANT: Do not fail to reconnect these two
wires to the shift interrupt switch when timing
procedures are complete.
4. With timing light connected, check timing. Timing
should be 1? BTDC.
5. If required, loosen distributor hold down clamp
and rotate distributor to obtain specified timing.
6. Secure distributor hold down clamp, and recheck
timing as above.
7. Reconnect the two wires to the shift interrupt
switch. Remove jumper wire at distributor white
leads.
IMPORTANT: Be sure to remove jumper wire before
returning engine to service, otherwise timing
will not advance.
8. With timing light still connected, and engine at
IDLE, verify that timing did advance to 12? BTDC,
(plus or minus 2?). At 2400-2800 RPM maximum
(total) advance is obtained and should be 27?​

BTDC (plus or minus 2

?).

​