Trigger sticking, cause of low RPM at WOT and misfire? (video)

[creol]

Please see the video for a demonstration of the problem: https://www.youtube.com/watch?v=v7Ht2x4NM80

As you can see, the timing advance lever is not moving through its full range of motion, because the trigger will not advance enough. I ran into this problem while doing link&sync: found out that the max timing was at 23 degrees BTDC and I was trying to correct that -- (28 BTDC @cranking speed is correct for this engine) but obviously making any adjustments was impossible, since the lever was not going all the way.

I'm posting because I'm wondering, why my WOT RPM is only 2000 (I bought the engine as faulty, the previous owner said it "will not rev properly" and I accepted the challenge for a reasonable price). So in addition to the RPM being limited to around 2000, the engine misfires intermittently during WOT. Idling in forward gear goes smoothly, no hesitation or bogging. So I'm hoping the timing issue is behind this. I will proceed to pull the flywheel and sort the trigger out, if you guys think a difference of 5 degrees makes my engine act as described.

Compression on the engine is 115-120 PSI on all three cyls, carbs have been thoroughly cleaned and adjusted per factory manual, got new plugs, new fuel lines, new fuel filters (water separator + inside cowl), cleaned and filed all grounds nice and shiny, put in a new impeller as well. The fuel pump had been serviced w/ new gaskets by the previous owner. I have checked out all wiring and everything seems OK. So I'm really, really hoping the limited timing advance is the issue with this one.
EDIT: The engine is a 90hp 3cyl 1991 model, carbed, made in Belgium (serial 9570635)

 

[Faztbullet]

Trigger wires pinched behind starter not allowing full movement....and no will not cause your problem. Look for ignition problem such as cylinder dropping out or erratic spark. My bet is switchbox...

 

[creol]

Thanks Faztbullet, the trigger wires were indeed routed so that the movement wasn't complete. I fixed that and did link&sync, ending up with only slightly better performance of the engine, please see the test run videos. They're both showing the hole shot performance of the engine after all things done mentioned in the first post + link & sync per factory manual. No DVA tests done so far to any of the ignition components, since I did not manage to find a DVA adapter yet. Will most likely be soldering one of those myself, because it seems that not a single hardware store in the Finnish capital region is selling such a thing...!

EDIT: forgot to mention that the tachometer has shown erratic numbers throughout my test runs during last weeks. Battery seems to be charging as it should; 13,8 volts at idle.

First run, warm engine:
https://www.youtube.com/watch?v=YcgOYNrMZa8
Second run, right after the first one:
https://www.youtube.com/watch?v=D1N929MmpXY

 

[creol]

Alright went through the DVA test sequence as stated in the Factory manual. Got out results that indicate a faulty stator:

Low speed: Blue stator lead & Red stator lead: specified resistance 3.6-4.2 kΩ, I got 3.44 kΩ
High speed: Red stator lead & ground: specified resistance 90-140 Ω, I got 105 Ω

Prior to this, I got out results from ignition test sequence as follows:
1-A: Coil primary Coil + & Coil - : spec 145-250 V; i got 100 V times three
2-A: Switchbox stop circuit: Black/yellow switchbox terminal & ground: spec 215-340 V; I got 192 V
3-A: Stator (low speed): Blue switchbox terminal & ground: spec 215-340 V; I got 185 V
3-A: Stator (high speed): Red switchbox terminal & ground: spec 10-55 V; I got 43 V

Now my question is, the low speed stator resistance is not that much out of spec. But I assume it's enough to make my engine perform as the videos are showing? Should I check anything else to make sure it's the stator and not something else (like the switchbox)?

 

[creol]

No Title

More testing and a surprising find I hadn't noticed before: one stator magnet has a dent. Could that be affecting the resistance of the stator?

Additionally, I did a test I found from the CDI troubleshooting guide:
For 70-90hp 3cyl Mercs, stator w/ glued-in magnets, 1977-1994
Blue to engine ground, spec 3250-3650 Ω; I got 3640 Ω
Red to engine ground, spec 135-165 Ω; I got 106 Ω
DVA blue to engine ground, spec 180-400 V; I got 267 V
DVA red to engine ground; spec 25-100V; I got 40.2 V

To conclude: factory manual tests say I've got too low of a resistance on low speed windings of the stator. But the CDI guide's test says I've got a too low resistance on HIGH speed windings. I'm thinking I need to get a new stator, if that does not help I'll get a new switchbox too (the recommendation seems to be to change them in pairs, anyway).

 

[creol]

Today I changed the switchbox, resulting in zero improvement in performance. Also the DVA tests to coil etc. were just as bad as before.
The stator ohm test, when performed again this morning, showed to be within specs so I thought it might be the switchbox that's faulty. But it seems I need to do more troubleshooting.
Here's a video of tonight's test run with the new switchbox. Strongest misfire around 2000rpm, and low power at WOT (plateau hits at 2800 rpm, from there on rpm will not rise). Idles very nicely and will not bog down or stumble when idling.

https://www.youtube.com/watch?v=ug3iC2rae30

 

[creol]

TL;DR: Swapped trigger after found it to be faulty, also found out two out of three coils have cracked ferrite cores -- but to my amazement, the engine runs like a beast now. Read below some odd values concurring with the fact that it runs so well. Great holeshot, over-reving @ 5600k rpm gave 35 knots on a 17ft glassfiber deep-vee boat, propeller pitch 17". Also the tachometer works great now. Long version:

I tested the trigger yesterday and found it to be a little outside the correct values. I swapped it to a used one I got from a salvage yard; the "new" trigger gave better values.

Old trigger resistance:
Brown-black: 1145 Ohm (spec 800-1400)
White-black: 1040 Ohm (800-1400)
Purple-black: 555 Ohm (800-1400)

Old trigger DVA (connected):
Brown-black: 7,5 V (4+)
White-black: 5,2 V (4+)
Purple-black: 3,5 V (4+)
Brown-ground: 2,69 V (1+)
White-ground: 1,88 V (1+)
Purple-ground: 1,2 V (1+)

Old trigger DVA (disconnected)
Brown-black: 8,8 V (4+)
White-black: 6,7 V (4+)
Purple-black: 3,64 V (4+)

NEW trigger resistance: all values around 1200 Ohm (= good)

NEW trigger DVA (connected):
Brown-black: 7,05 V (4+)
White-black: 6,06 V (4+)
Purple-black: 7,22 V (4+)
Brown-ground: ~2,5 V (1+)
White-ground: ~2,5 V (1+)
Purple-ground: ~2,5 V (1+)

New trigger DVA (disconnected):
Brown-black: 8,8 V (4+)
White-black: 7,52 V (4+)
Purple-black: 9,05 V (4+)

I also checked the stator when disconnected from the switchbox, ground and rectifier. Results:

Blue-ground: 260 V (180-400)
Red-ground: 39 V (25-100)

Then I connected the trigger+stator in to the switchbox (but did not connect the stop switch lead); did a DVA test once more:

Stator leads:
Blue-ground: 172 V (180-400)
Red-ground: 33,6 V (25-100)
Coils (+ and -): around 70-90V each

So as the numbers tell, something messes up my stator output voltage when connected to the switchbox. The switchbox is new, not a known brand and chinese make so might still be faulty. The voltage supplied to coils was around 70-90 V when cranking and 120-140 V @ 2000rpm. It should be in the 150-400 V range even when cranking and over 200 when running.

Question: will I damage the ignition components if I disconnect the leads going from switchbox to coils and ground them instead? This way I could isolate the coils as the source of the problem -- even though I have no idea, if the coils could even have an effect on the stator DVA test as described. I already disconnected stator's yellow leads going to the rectifier, with no difference.

After playing around with the DVA meter and switchbox, I then decided to inspect the coils, even though they had given me proper resistance readings (0,9~1,0 kOhms from all three; specification says 1kOhm +/- 10% is ok) -- I discovered that two out of three coils had cracked ferrite parts in them. I put the coils back in place, sprayed some wd40 and made sure the ferrite parts were at least in contact with each other but did not bother to glue them in. I'll order new ones even if the engine now runs as it should.

I'm now lost with the fact that I've got too low DVA readins going into the coil but still the engine performs so well. I'd also like to know how to address this problem, given the fact I have checked out the trigger and stator when unplugged from all other components and verified that they both give out proper DVA readings and resistance when singled out. Seems to me I only have rectifier, coils and the voltage regulator left as potential sources of the voltage drop at the coils. Not sure though how these even could affect the ignition system in the way described.

I need to do some tests under load and will up the prop pitch by 2"; will post results. In the meantime, this is my best holeshot yet, after this video I turned the idle mixture screws out 1/4 of a turn and now have zero hesitation:
https://www.youtube.com/watch?v=jsyBtuKIs48