'89 DT75 dropping a cyl at speed

[mphelle8vld]

The alarm will not sound for an over-rev condition, I would check for a spun prop hub.

[Solarman]

Ok. Reading over your symptoms again. Don't think it's going into protection mode.

Check the back-side of needle valve seat for possible obstruction (might be pieces of "clear disc" check valves from fuel pump lodging and restricting fuel flow in float bowl), this could cause similar symptoms. Likewise, if clear discs have fragmented the fuel pump would likely pump less fuel.

Another possible scienerio would be a pinched /worn wire, not shorting out until at higher rpms, similar to plug wires breaking down (jumping spark at higher spark output). Have you tried securing boat to a dock, then running rpms up till problem occurs (without hood on, at night?). Looking for signs of a shorting wire, arcing?

Sometimes we are too smart, and overlook the simple things, maybe because we put new plugs in, forgetting that, sometimes, even new plugs are bad out of the box.

I know you've replace and tried many things, but something is being overlooked, not necessarily your fault, but something simple. Lol, I've been there before.

Good luck, post back when able to let us know how it's going.

[Flatsboy]

It's not an over-rev issue. Running steady at anything over 3,400 triggers the rpm limiter (if that's what's limiting it). Prop hub is not slipping.

I get the carb idea but I can't wrap my head around why it runs so well aside from the rpm limit after a while. Poorly seating needles or stuck floats usually cause other symptoms at least in my experience. I'll go through the carbs again just in case though.

If it was suggested I wax the flywheel I'd do it at this point ;-)

Thanks for the quick responses!

[Solarman]

FB, this is a 1989, motor. This being said, they did have limiting mode on certain things back then. Usually overheat, and no oil flow. In some of the motors as i mentioned, they had a flow switch, at the heat sensor.

I am not trying to mislead you in any areas here. I am serious about plugs, and wires breaking down at higher rpms, even if new.

If a clear disc check valve fragments, some pieces can restrict fuel causing float to empty, and act like running on one cylinder less (limit mode), as limit mode does the same thing.

Good luck, post back when able to let us know how it's going.

[mphelle8vld]

The Suzuki monitor gauge would tell you if it's in limp mode and cut your troubleshooting in half. If your friend with the cdi has one you can borrow or find a used one on ebay, it would be a useful tool. If your friend has a gauge but it's installed and doesn't want to remove it, I have an extra 18' cable, you could back down the ramp next to him and hook your motor to his gauge.

[Flatsboy]

I've been watching some on ebay and may go that route although I've gone far beyond what it could tell me at this point. I've heated thermostats, OHM'd and AC/DC metered every conceivable sensor, coil, wire, trigger, etc.

Have also put on new plug wires and sever sets of plugs.

Talked to the dlr at length today at his shop, service mgr and lead mechanic. They said that era small DT series was over-engineered and they've had these needle-haystack issues too. They didn't get that I wasn't getting an alarm when protection mode kicked in, the mgr suggested it could be a short in the main wire loom to the control box or the control box. Don't think so, it's too consistent and the alarm does work at start up.

Rebuilt carbs today and ran in the lake, re-checked TPS at .5v, same result. I'd like to think it's something basic I'm overlooking but I've triple check and replaced many components. Starting to think about another Merc or Yamaha, I know those well.

[mphelle8vld]

I mailed my spare monitor gauge to a guy in Tasmania and never heard from him again, the cable is yours if you decide to get a gauge.

http://www.ebay.com/itm/OEM-SUZUKI-K...1Zlfnm&vxp=mtr

Is the 10 sec delay consistent (always 10 sec)? Does your model have the small plastic tach control unit (34250-87D11) next to the cdi?

[Solarman]

Flats, if able, try another (known good) TPS for your motor, i don't believe it is going into safe mode.

When you had carbs off, did you visually inspect the reed valves?

Post back when able to let us know how it's going.

[Flatsboy]

I mailed my spare monitor gauge to a guy in Tasmania and never heard from him again, the cable is yours if you decide to get a gauge.

OEM SUZUKI KIT MONITOR GAUGE + HARNESS + POWER SUPPLY HARNESS NOS NIB | eBay

Is the 10 sec delay consistent (always 10 sec)? Does your model have the small plastic tach control unit (34250-87D11) next to the cdi?

Thanks for the offer, I'll check for the tach control and get back to you.

[Flatsboy]

Flats, if able, try another (known good) TPS for your motor, i don't believe it is going into safe mode.

When you had carbs off, did you visually inspect the reed valves?

Post back when able to let us know how it's going.

I don't have access now to another TPS, I did get the OEM test harness and mine checked out. I wouldn't blink at spending the $175 for a new TPS if I knew that was it but I've already replaced a lot of components. That's fine if I'm going to keep this motor, it gives me piece of mind for a 28 yr old unit but if the TPS isn't it I'm pretty much at a dead end again.

Yes, I did check the reeds carefully and they look fine. I've had reeds that look fine cause issues and that may be the next replacement. Removing/replacing these carbs takes twice as long as a Merc, Yamaha or OMC, not a job I look forward to. Don't mean to come off as negative towards all Suzi's but this one is definitely over-engineered and is a PITA ;-)

[Flatsboy]

Thanks for the offer, I'll check for the tach control and get back to you.

Is your harness the monitor gauge harness 36660-92e20 or the power harness 36630-92e00? Thanks again!

[Solarman]

I wouldn't just continue replacing parts, if the reeds are damaged, or have gaps (not sitting flat), then they may be bad, otherwise probably not.

When you tested TPS, was yours staged (throttle sensor changes voltage at certain positions), or smooth on voltage change between zero throttle and WOT?

Post back when able to let us know.

[mphelle8vld]

It's a gauge harness from a 91, the cables and meter changed through the years, if your cdi has a free six pin connector and a free pink/blue stripe, grey, and black wires in the vicinity it should work. Finding the correct gauge could be a challenge. One like this is a possibility...

Suzuki DT Gauge Oil Level Monitor Water Indicator 34701-92X50 Outboard | eBay

Is the interval exactly 10 sec or around 10, does your model have the 34250-87D11?

[mphelle8vld]

Sorry for butting in Solarman but the repeatable 10 sec caught my attention. I haven't got an answer yet but if it's exactly 10 sec, that's a unit used by the cdi for an over rev. Not that it's actually over revving but perhaps a short in the wiring is causing the limp mode. A clogged carb would give that symptom but it would take longer to drain the bowl at 3500 than at 5500, not the same 10 sec every time.

[Flatsboy]

I haven't timed it exactly but I seem to remember it's random, not exactly 10 secs. I'll get it on the lake and document. I noticed yesterday after warming it up idling about 5 minutes, I took off at full throttle (about 4,700 rpm) and it cut back well before it did when I ran it up from the same spot and took it to 3,800 or so several other times. That made me think it may be overheat related but I've replaced both heat sensors (puck and duckbill) with new.

I haven't used a Suzuki gauge. From what I see it warns of over-rev, temp and low oil, correct? Or does it also warn of oil flow? I can see where this might help direct a search but won't pinpoint failed components.