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When Nice Boats Go Bad (part 5)

Chuck Buck

Jet Boat Addict
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Sugar Sand
Year
2004
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Mirage
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18
Chapter 7: Sea Trial #2 –Terrifying Excitement.
After digging around in the engine bay countless hours and finding numerous issues and questionable repairs, I fixed everything I could find. With a hose attached to the engine flushing adapter in the driveway, it ran OK enough to test on the water. Adding 10 gallons of fresh Costco premium mixed with Sea Foam, I loaded on all the requisite safety gear, a butt-load of tools, and off I went to the launch, light drizzle notwithstanding. I felt like I was going into battle. Reading about the lack of steerage at low speed didn’t prepare me for how difficult a jet is to actually drive slowly thru a harbor, and I was relieved to see no other boats moving around. Getting up on plane, however, the boat could turn on a dime, but 27 mph was all it could manage. After idling around a while, the WOT speed then increased somewhat, so I surmised the Sea Foam was doing something. Myriad other issues were discovered, and these were carefully documented for future reference. I came home disappointed that my technical brilliance wasn’t rewarded with an acceptable WOT performance yet. Owners of identical boats, with identical engines, report top speeds in excess of 50 mph or so the Germans would have you believe. More sleepless nights, porcelain library time, and shower ponderings…

Chapter 8: The Awakening.
As we learned in a [now defunct] online Jet Boat forum, unlike propeller-driven boats with interchangeable props, the tachometer (or rather, WOT rpm reading) is diagnostic of engine and jet performance; too low indicates an engine problem, too high indicates a jet problem. So, our distinguished author and intrepid diagnostician came to the conclusion that the tach must be fixed, come heck or localized flooding. I traced the tach wire back to the rectifier (signal source) and found no open/short to GND/short to B+. I then checked the voltage at the tach and at the rectifier, but that didn’t tell me much. I took the tach out and brought it in to Gary “Chicken Marsala” our resident Super Genius® at work to test. His signal generator made no difference, so we’re not sure, but seeing that the needle won’t budge off 1100 rpm, we think the tach is fried. Faria will fix it for $125 + shipping, since an exact replacement would be a unicorn lo these 15 long years hence, but they want FIVE WEEKS LEAD TIME. Time being of the essence, I started exploring other options, such as a temporary aftermarket Chinesium stick-on tach or the like. Nothing looked promising, as they’re all inductive (wrap a wire lead around a plug wire), the leads are only several feet, and its probly 15 feet to the helm. Anyway, reading further into the PDF OEM service manual ($9.95 CD off fleabay) I learned the rectifier should have an internal resistance of 10k to 30kΩ for the tach circuit. Upon returning home, I measured the rectifier and found 11MΩ. So now, I’m guessing both the tach and the rectifier are shot. Further investigation reveals that the rectifier output should be approximately 8 Volts at idle, and I have 7.7V, so I’m thinking that’s close enough, but I digress. Not letting this obstacle block me, I dusted off my trusty Sears Best Craftsman Engine Analyzer ($99.95, and not a penny less in 1978. UGH!). Connecting the inductive tachometer pickup on plug wire #1 (top, starboard bank), I fired up the engine and the meter indicated 2000 rpm at idle. This seemed high, and I later deduced since it’s a two-stroke, I need to cut this reading in half (1000 rpm is the base idle). As I was thinking perhaps I could use this instrument on the water, as it reads up to 7000 rpm, but then thought I’d rather not for reasons. Playing around further, I decided to put the inductive clamp on the #3 wire, then the #5 wire. All reading 2000 rpm. I then went to the port bank and tried #2, same reading. However, #4 and #6 showed nothing – ZERO impulses. AHA! This poor engine has been ruining on no more than 4 cylinders! So, I thought, “is it the coils or the control circuits?” I swapped the positive coil wire and plug lead for the #2 and #4 coils, and retested. Same result: no impulse at #4 and #6 plug wires. OK, so the #4 coil is OK, no point in checking the #6 coil at this time, and off we went!

Chapter 9: Game Plan.
Now, the coil primary voltage is provided by a “switchbox.” There’s two, one for starboard cylinders 1, 3, and 5 (outer switchbox), and one for port cylinders 2, 4, and 6 (inner switchbox). These take the voltage from the high and low speed charging coils in the stator (under the flywheel), and store it in a capacitor until the trigger signals the SCR in the switchbox to make/break the coil primary circuit, thereby collapsing the magnetic field, inducing high voltage in the secondary winding, and providing electrocity to the spark plug (as we all learned in High Skrool Auto Shop). The aftermarket outer switchbox and trigger have a “CDI Electronics” tag and 2016 date code, but the inner switchbox (origin unknown) has a 2014 date code. It’s highly recommended the switchboxes are replaced in pairs, but this advice (obviously) wasn’t heeded either in 2014 or in 2016. Since the trigger has three coils that control two cylinders each (1 port, 1 starboard), the OEM Mercury Service Manual “helpful tips” says that one coil not firing is probly a bad coil, two coils (1 each bank) not firing is likely a recalcitrant trigger, and one entire bank not firing is likely a kerput switchbox. I, however, do not have these exact symptoms, but I’m leaning heavily towards the inner switchbox. There is one more possible fly in the ointment – while the trigger cannot possibly signal the switchbox for one bank and not the other, the high and low speed charging coils are energized by magnets under the flywheel. The trigger has its own set of magnets glued to the flywheel inner hub, but the charging coil magnets are glued inside of the outer ring. These magnets have a tendency to fall off with age, and they can easily be epoxied back on, provided they are found. Do I think one or more outer magnets are missing? I doubt it, but when I started working on the engine, I determined early on that I needed to go over every stinking thing those butchers touched (and that’s being generous to the “mechanic(s)” who replaced the trigger/outer switchbox) before I can pronounce this craft seaworthy. Seeing the “quality” of their work leads me to believe they would have easily overlooked a missing magnet or two, and just proceeded to throw parts at this engine until they gave up and ran away with their hair on fire. As for me, before I put one cent toward any of these VERY spendy ignition parts, I need to pull the flywheel, inspect the magnets, and confirm the proper installation of the replacement trigger. An aftermarket flywheel puller is already on the way (courtesy of Jeff Bezos) for $31 shipped. If the stator also tests good, I’ll probly bite the metallic cartridge and get two new switchboxes. While I may not have the boat operational by the time the grandkids visit next, when I do, it’s gonna run much better, I got you now! OH, almost forget – before switching the #2 and #4 coil primary wires, I first wrote the wire colors on a piece of tape I stuck to the coil bracket. “#2 = GN/WH, #4 = GN, #6 = GN/RD”. Checking the schematic later while eating din-din, the CORRECT sequence is #2 = GN, #4 = GN/WH, #6 = GN/RD. This applies for both banks. I believe this engine has actually been running ON THREE CYLINDERS. GOOD GRIEF!
 

RedBarron55

Jet Boat Addict
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Jetcraft
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Depending on the stator and flywheel you might be much better off installing a Mercury 200 hp wiring harness and CDM modules than buying all of the old tech CDI switch boxes.
I have done three cylinder force engines with the red stator.
Works good and saves money.
 

Chuck Buck

Jet Boat Addict
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Sugar Sand
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Depending on the stator and flywheel you might be much better off installing a Mercury 200 hp wiring harness and CDM modules than buying all of the old tech CDI switch boxes.
I have done three cylinder force engines with the red stator.
Works good and saves money.
Thanks for the tip, Red! That’s the biggest reason why I’m telling my story – perhaps people can learn from my experiences, and I can learn from theirs. I went to Merc’s site to understand what you were getting at:
“Your outboard's ignition coils or CDMs (Capacitor Discharge Modules) provide a high voltage pulse to your Spark Plugs. Ignition Coils get their voltage from the Switchbox. CDM's are essentially ignition coils with built-in switchboxes.” Basically, ignition module/coils.

I’m no expert on these engines, and while I’m not against modifications per se, the cost of 6 CDM’s and the harness isn’t for the faint of heart either, assuming it would fit my application. At ~$250 a pop, switchboxes aren’t cheap either, and if they keep failing, it’s definitely worth investigating. But my story’s not finished yet! :cool:
 

Chuck Buck

Jet Boat Addict
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Location
Lake St Clair
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Sugar Sand
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2004
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Mirage
Boat Length
18
Love these posts! I dont have a two stroke and some of it is above me but I enjoy reading them!
Thanks 10! Appreciate the encouragement.
BTW, love your boat's color scheme - exact same as my Crownline and that's why it was love at first sight for me.
 

RedBarron55

Jet Boat Addict
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Try looking at this set of CDMs and wiring harness.
Sea Doo Mercury jet drive M2 CDM module ignition coil coils pack 240 EFI 200 745061358768 | eBay

I cannot guarantee that this will work with your stator as I have not researched it like I did for the 90 HP three cylinder Force.
This will give you a set of CDMs and the associated wiring for about $100.00
The key is the applicability of the trigger coil output and the stator voltages.
I don't know exactly what engine you have, if it is a six cylinder force or ? Straight or Vee?
I am pretty sure this could be made to work, but I have no idea if you can work out the wiring.
Look up the manuals for the Mercury and the engine you have.
The CDMs are fed the 180 volts from the stator and basically have that and the ground .
You will have a Ground (Black), Stator (White/ green, Green/White), Trigger (don't know about 6 cyl), and kill switch (Black/Yellow).
I have attached a PDF of the CDM section for the Force Sport jet system
 

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Weeb

Jetboaters Captain
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Nice write up. You have me intrigued but I’m like a kid I need pictures.
 

RedBarron55

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I have no idea about the six cylinder engines, but the Force Sport Jets 90 and 120 HP if they have the late model (red) stators will work with the CDM modules as long as the Trigger coil matches with the flywheel.
There are two types of trigger coils and they are not compatible with the different flywheels, but will trigger the CDMs either way.
(at least mine did).
One could wire up a harness, but the Mercury harnesses can be had at a fair price and modified to work with the Force.
I used a 50 hp three cylinder harness, but had to connect it differently due to a different firing order (I think).
If you look at the PDF file you will see that it is less complicated than the older CDI with the switch boxes.
Basically if your motor has been upgraded with the Red stator that needs the hershey bar adapter for the CDI you have a stator that will work with the CDMs.
I keep a spare CDM in the tool box in case one fails out fishing.
On mine I needed to change the spark plug wires to make then long enough to reach the spark plug.
 

Chuck Buck

Jet Boat Addict
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Location
Lake St Clair
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Sugar Sand
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2004
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Mirage
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I have no idea about the six cylinder engines, but the Force Sport Jets 90 and 120 HP if they have the late model (red) stators will work with the CDM modules as long as the Trigger coil matches with the flywheel.
There are two types of trigger coils and they are not compatible with the different flywheels, but will trigger the CDMs either way.
(at least mine did).
One could wire up a harness, but the Mercury harnesses can be had at a fair price and modified to work with the Force.
I used a 50 hp three cylinder harness, but had to connect it differently due to a different firing order (I think).
If you look at the PDF file you will see that it is less complicated than the older CDI with the switch boxes.
Basically if your motor has been upgraded with the Red stator that needs the hershey bar adapter for the CDI you have a stator that will work with the CDMs.
I keep a spare CDM in the tool box in case one fails out fishing.
On mine I needed to change the spark plug wires to make then long enough to reach the spark plug.
Great information Red! I have the Merc 175 V-6 with three carbs, and I don’t see any red on my stator, but I certainly will keep your suggestions in mind for future reference. Your expertise is much appreciated!
 

RedBarron55

Jet Boat Addict
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Find a copy of the workshop manual as often there is a progression of electronics covered and it will show how the later Mercury electronics were added to the Force block.
This what I did with my 90 ho force.
 
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