1990 2-Stroke DT100 Limp Mode problems

[Kaistarohmu]

Hi guys, i thought maybe here i'd find a bit more advice than from Finland where no-one seems to have this engine.

I bought this couple of days a go and it ran normally.
When i shut the engine down after 1-2 hours of normal driving with WOT runs and started it again it doesn't like to go over 3000rpm while in gear and under load. When i use enough trim and transfer all the weight in the front, it starts planing little by little. When the rpm passes 3500-3700 everything is back to normal.

The instrument panel "water" light went on and i thought that was the problem (limp mode maybe, if engine this old even has one). I checked thermostats, no problems -> checked flow sensors -> other seemed to be faulty and i checked also the water channels -> no corrosion, no visible problems.

I disconnected the flow sensor and thought maybe that was the cause of problems. Still no running above 3000rpms.

It seems to rev perfectly normal in neutral but while in gear, sounds like the ignition doesn't allow the engine to run higher than that, or it gets too much gas and just isn't able to get enough rpm.

This doesn't seem like a fuel related issue because it ran normally without any flaws and just started bogging down on the next run after maybe being 1 hour with no use.

Suggestions?

In short what i've already tried:

Impeller has been changed this summer
Flow sensors disconnected
Thermostats checked --> working
Cleaned fuel lines, new fuel.

Edit: After cleaning fuel lines etc. etc. basic stuff today, i measured the TPS, it showed anywhere from 5 to 8 and seems that it might be faulty. Though i'm not 100% sure that i was able to measure it correctly with a multimeter.

Would this be possible when the tps is faulty? Otherwise i'd just replace everything but it seems that all the parts have to be ordered from USA etc. and takes long time and is actually quite expensive with express delivery, customs etc so i'd rather listen to options before ordering all the possible parts =D

[Solarman]

It is possible that TPS has bad places at lower throttle positions. But you have to measure voltage used with a jumper wire while it is plugged into ECU. You will need the Suzuki service manual for what the proper reading of volts should be.

If your water light is turning on, have you checked the heat sensors?

If it is limited to 3k rpms, how can you "play with it" and get it above 3k rpms, and say it runs fine above 3k?

I am not as familiar with the European model Suzuki motor. Does your motor have a neutral switch on the shift linkage?

Does your motor idle well when in gear?

You mention "flow" sensor? What sensor is it? For the flow of oil? Or flow of water? If your motor has the 3- wire sensor for a heat sensor, it may have a flow switch?

Post back when able to let us know. Good luck.

[Kaistarohmu]

I Believe we have maybe a different version of the engine, mine is V4. ( http://www.brownspoint.com/store/pc/...100(89-00).pdf )

I might have been misleading with the title as previously i thought the engine in limp mode because i couldn't get it revving past 3000rpm.
When i play with it enough i can get it up to normal rpms (5500) although this requires that there is no one else in the boat, under load it won't rev. Previously i was able to get it planing easily with 4-5 people. It almost sounds as it shudders and hesitates when below 3000rpm if the boat is not planing and it takes forever to gain rpm or in cases it doesn't gain rpm at all over 3000rpm. From idle to 2500rpm everything seems normal.

If i drop the rpm below 3000rpm and get back up again while planing, there is no such problem, just a little hesitation. in short, under load it won't rev.

I believe this engine has only one heat sensor, how can it test that? It has only 2 wires.

Flow sensors are near spark plugs in the water chambers detecting water flow. Another of them was faulty, water runs fine and engine is cooling normally.

I do believe there is a neutral switch, it's located in the remote control box but not in the gear linkage.
No problem idling while in gear or neutral. Also no problem gaining rpm while in neutral with the hand throttle.

[Solarman]

You need a Suzuki manual to test these sensors and compare them. It isn't easy to run diagnostics on any intermittent problem.

It does sound like you could have an electrical problem that's intermittent, or a fuel problem, maybe a fuel pump issue?

If you have a timing light, you could connect to each plug wire to see if any plugs are not firing when this problem occurs. If the light flashes equally for each plug, then your problem may be fuel related. If some plugs do not flash equally, then it must be electrically related.

If you have a monitor gauge that does, or does not send a code this could be helpful.

If you have a bad TPS it can act like normal at some speeds (idle, and higher throttle positions), but might be blank (nothing changes in certain spots where throttle is - this would happen repeatedly in that same spot), in some areas, and it won't send an error code (if you have the monitor).

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

[Kaistarohmu]

It's not intermittent as such, as it works the same each time .

The hesitation is always there when throttle is over 3/4 and would be time to start planing at around 3000rpm. When planing, the load of the engine gets lower and it starts getting more rpm and acts normally IF i don't drop the rpm again under 3000rpm.

I've read that the tps gives out reading to the cdi which again adjusts timing and ignition. The fuel system been pretty recently overhauled and i just can't believe that it would be the cause as the engine gets enough fuel on higher revs and lower revs, could it be fuelpump issue when it occurs only at spesific rpm. I just found tps relatively cheap and with fast delivery so i ordered one and will test with new one, if there are any changes.

Does the new tps have to be calibrated somehow?

[Solarman]

I don't think your tps should be adjustable. So no calibration needed. The only thing is to check by voltage with jumper wire to see if voltages are per manual.

You mention rpms going up at 3/4 throttle, but boat slows down, unless you lower rpms? Is there a chance the prop is slipping? Can make a mark on prop hub at cotter pin then run motor a few times to see if mark on hub changes on each run.

"When planing, the load of the engine gets lower and it starts getting more rpm and acts normally IF i don't drop the rpm again under 3000rpm."

I really didn't understand your statement, kind of confusing?
What do you mean acts normal IF you don't lower rpms again? Where before you wrote...

"It almost sounds as it shudders and hesitates when below 3000rpm if the boat is not planing and it takes forever to gain rpm or in cases it doesn't gain rpm at all over 3000rpm. From idle to 2500rpm everything seems normal."

Have you cleaned the carbs? Have you checked to see if any trash has gotten into the carbs? It sounds like the main jets have trash blocking them, or it could be your fuel pumps have bad check valves (clear discs in bottom section) that are broken and not providing full fuel flow?

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

[Kaistarohmu]

Hi!

Maybe i'm a bit confusing as English isn't my best language.

Prop doesn't slip, thats tested. Otherwise the rpm would also rise while boat wouldn't accelerate.

I mean that when the boat is planing, the outboard doesn't have to work under so much load compared to the situation where you accelerate from 0.

Carbs have been cleaned 1-2months before this, but i guess it's a chance that there is some dirt.

[Solarman]

If carbs are cleaned recently, then check fuel pump diaphragm and check valves (clear discs in lower section) for any damages cracks pieces missing. If check valves are broken/ pieces missing, then carbs may have those pieces blocking flow into float chamber.

Good luck. Post back how its going when able to let us know.

[Kaistarohmu]

Ok, thanks. This was the most useful piece of info i've got this far.

Thanks a million, i will check these, change the TPS and report back on what's happening!

[Kaistarohmu]

Hi, i just took carbs apart and one of the reed valves was completely busted. It had been cracked all the way from bottom and was lying in the intake chamber (or what ever it's called in english). I was lucky to notice it, otherwise it could've been sucked in to the cylinder.

Do you think this could have been the root of the problem? I've got a slight idea that 2stroke engines are pretty easy to go wrong if reed valves won't shut or open properly. ordered all 8 sets of new ones and gonna change them as well.

Good that suzuki motorbikes use same parts, othewise i'd have to order from japan or usa but for bikes they seem to have everything in stock in netherlands

[Solarman]

That's a shocking find.

Good to hear you're able to get parts you need.

Post back when able on how it's running.

[Kaistarohmu]

Yep, this corrected the problem.
I changed the reed valve and replaced one faulty water flow sensor ---> no problems, works like a charm.

[Solarman]

Glad you got it working. Happy boating.