Chuck Buck
Jet Boat Addict
- Messages
- 89
- Reaction score
- 98
- Points
- 97
- Location
- Lake St Clair
- Boat Make
- Sugar Sand
- Year
- 2004
- Boat Model
- Mirage
- Boat Length
- 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!
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!
