Trigger Control Arm Linkage Adjustment

[kbahus]

Finishing up replacing a trigger on my 99 150 EFI and discovered the linkage measurement is slightly wider than .688" as measured from the center of the rod. If I adjust it to spec what will it affect? I was hoping for a simple swap, but it seems like I am about to go down the rabbit hole. I am guessing that if I bring that into spec I am going to have check and adjust the timing. While I have a timing light and the service manual, I am short a TDC indicator/gauge. Never seem to have enough tools!

[rgsauger]

Any time you mess with the trigger, you sure do need to at least check your timing. Just fyi.

[25two.stroke]

You shouldnt need a dial indicator to set the timing on a 99 150 EFI. Set that linkage to spec (11/16") and then check your timing with a timing light. Be sure to disconnect the bias wire between switchboxes before checking. Only time you would need a dial indicator is if you have a flywheel without timing marks or you happened to move the pointer.

[kbahus]

Thanks for the info, I will adjust it properly and then check the timing. Guessing it is off. I am also considering removing the idle stabilizer box too to simplify things. Still running oil injection for now, I mostly run low rpm and lower speeds as the lakes I am on are small. Learning a lot of great tech info on this site, it is a great resource for these Merc 2.5’s.

[25two.stroke]

Ya, I ran oil injection to 90 mph on the boat in my signature below. Its not a good idea, but the systems normally hold together to about 6200 +/- 200 rpms. I fished with them for years, just make sure you see a little smoke all the time. Idle boxes always got ditched. Every motor, no question.

[kbahus]

Ran it on the hose and it seemed ok, also checked running idle timing per manual and it was in the normal range. Today I decided to be safe and check the timing so I don't smoke this powerhead. I used the factory manual and Dave Raymoure's guide to get it dialed in. My max timing was only 10*btdc which surprised me, could replacing the trigger have caused it go so far out (I don't know what it was prior)? I adjusted it to 20* per the VST information label. Here is the procedure I used just to make sure I didn't mess something up:

-Adjusted trigger link rod to spec.

-Used a dial caliper and spark plug adapter to measure tdc, verified the .462 mark on the flywheel was dead on with the pointer. No adjustments necessary at this point.

-Disconnected white/black wire at bullet connector for idle stabilizer.

-Disconnected ECU harness plug

-Leaving cyl #1 plug and plug wire installed, removed all other plugs and used alligator clips to ground all of the plug wires to the block.

-Disconnected throttle linkage.

-Kill switch in run position, used second person to crank engine from helm.

-Checked max timing first, noticed 10*btdc (left of zero), adjusted to 20*btdc.

-Checked idle timing, minor adjustment needed for 8* aftdc (right of zero).

-Rechecked max and idle timing and put it all back together, I still need to run on the hose as it raining this evening.

This is the first time I have adjusted timing on one of these outboards, did I miss anything?

Also, I am hoping to keep the idle stabilizer disconnected. If I want to completely remove it, it appears I just need to disconnect all of the associated wires (red/white and two white/black) and remove the box/wires? I am aware that I need to leave the wire in place that bridges the two switchboxes. Is it kosher to simply leave the white/black wire disconnected at the bullet connector for now without causing trouble?

Thanks!

[25two.stroke]

I can't remember where the bullet connector is but I would ditch that module and all its wires now. The problem there is that the red wire takes power from the stator and if the box or the wire failed it can send your stator power straight to ground. I don't know if disconnecting the white/black wire is enough to ensure the safety of the system. You will find out as soon as you start it. Side note, even though the book says for idle timing to be ATDC most find it happy somewhere real close to TDC depending on the motor. So don't be afraid to play with the idle timing to get the motor to run its best. This idle timing is not critical like the WOT timing. Shoot, some racing motors have it locked out all the time so it doesn't change! 20 vs 10 is a ways apart for a trigger replacement but it does not sound unreasonable.

Funny story: my boss bought a "pacemaker" which is what they used to call the mercury re-manufactured motors. Say, if a motor blew up under warranty you would send it back to merc and they would probably drop a new PH on it and sell it as a pacemaker. He got a 1995 2.5 200 pacemaker and put it on his 22' boston whaler. He ran it for 15 years in the ocean and everywhere with no problems, he would always talk about how fast it was and quick out of the hole even with a load. And it was true, the boat would do like 50 mph but he rarely if ever ran it hard. He went to sell it and on the test drive he burned it up. We all assumed it was a failed oil injection system, but he tore it apart and everything was intact and oil everywhere. New piston and hone and he had it back together that evening to sell. I told him to check the timing and he replied, "Why? its factory set and the glue is still there to prove it!" I checked it and the timing was set at 32 BTDC instead of 23 BTDC...someone at the factory had a bit much to smoke or something and mixed the numbers up. I wouldn't doubt that is why the original motor blew up and when Merc put a new block on they just swapped over all the components and didn't re-check the timing. I bet that incorrectly set timing burned 2 blocks before it got fixed!

[NeedOne]

Appreciate this post & the process steps..
I can check on that white/blk wire in a couple days. I think the bullet is just left as-is. Once stabiliser is deleted, do you have to undo the switchbox bridge wire for a timing check?

[Qshot1989]

You shouldnt need a dial indicator to set the timing on a 99 150 EFI. Set that linkage to spec (11/16") and then check your timing with a timing light. Be sure to disconnect the bias wire between switchboxes before checking. Only time you would need a dial indicator is if you have a flywheel without timing marks or you happened to move the pointer.

Never heard of disconnecting the white bias wire when checking timing? What is the point of that?

[25two.stroke]

Someone more intelligent has to comment on that. My coworker tried to explain it to me, but I couldn't comprehend. I timed a 2.4 the other day and just tested it with both connected and disconnected and it made no difference on that engine.

[kbahus]

I did not disconnect mine, I know the manual does not mention it either.

[25two.stroke]

Yeah and at cranking speed the bias circuit doesn't do anything I don't think, so you are probably fine.

[25two.stroke]

Here is an educated guess that concludes that if everything is functioning as it should then it would make no difference:

The bias circuit in the box applies (-) power to the trigger circuit to reference the trigger voltage pulses (+) to ground since the trigger is not grounded. This allows the switch box to fire to the coils at the correct time regardless of voltage fluctuations that occur by varying rpm. This is why the voltage (-) in the bias circuit increases as the rpm increases. The black/wht wire bridges the two boxes so that what one box's bias circuit is doing matches the other, correct? The bias circuits in both boxes should match and if they are too far out then even the bias wire will not balance them out. SINCE when we are checking timing we are only looking at #1 (most of us, I know some really trick people check the timing on every cylinder) then disconnecting the bias wire is essentially isolating that switchbox and cylinders 1, 3 and 5 to be firing at the true mechanical timing rather than being influenced by the other box. Now, if both of the boxs bias circuits are exactly the same it should make no difference (hence my test results the other day). If one bias circuit is a little different than they other then you may see an alternative timing. This can cause more problems than just the slightly off timing. I think based on your initial finding of the timing being so far off is worth checking the bias circuit for proper function. Look up CDI's troubleshooting guide, it goes deep into this issue.


referencing Bill Rodgers:

https://www.screamandfly.com/archive...p/t-87040.html



{{{{{Let me throw a little light on the trigger/bias issue. An SCR fires when the gate reaches +0.6v with respect to the cathode. The cathode is at ground potential when the circuit is inactive (through the coil primary). However, the trigger signal is not referenced to ground. The trigger is cross-connected between switchboxes and is referenced to the white/black connection. The bias voltage on the white/black is negative with respect to ground. The trigger voltage has to overcome the negative bias on the white/black plus go 0.6v positive before the SCR fires. The more negative the bias, the longer it takes the trigger voltage to reach the 0.6v threshold and fire the SCR. So the bias circuit doesn’t really vary the amplitude of the trigger – it varies the trigger reference.

Like Jeff_G said, the trigger amplitude is between 5 and 10 volts peak. It rises to 30 to 35 volts at 5000+ rpm. Likewise, the bias will be in the –30 to –35 volt range at the same rpm. The bias circuit is designed to keep the point at which the SCR gate voltage reaches +0.6v constant over the full rpm range. The trigger voltage increases with rpm and would advance the timing more and more if it weren’t for the bias voltage increasing (in the negative direction) at the same time.}}}}}

[FORBESAUTO]

Do not disconnect bias wire. Wot timing will not be accurate.

[25two.stroke]

Do not disconnect bias wire. Wot timing will not be accurate.

Can you explain why? Ive done it both ways and testing cranking speed timing and real WOT timing under a load and when you disconnect the bias to set cranking and WOT timing, then hook it back up and run it and it reads exactly as it should. Can you explain why it would make it read different if you are just timing off of the #1 cylinder?