Suzuki DT85 -93, rev limiter in hard weather

[Fabbe2]

Hej everyone! I am new to the forum but already got some useful information from older posts.

My boat is a 5,5 meter Swedish day cruiser from the mid 60s in good shape, it is equipped with a 93 Suzuki DT85. Running very well, even while wakeboarding if the sea far up in the north doesn't freeze.

Unfortunately there is one issue with the engine that I couldn't figure out:

The engine runs well under all conditions when I stay above approximately 3000rpm which is about 20kn/h. In calm weathers without bigger bumps to the boat there is no problem going full speed but if there are more waves and it's getting bumpy the engine will slow down to a rev limit under 3000rpm. No waring light will appear, no warning buzzer sounds.
Trying to idle for one sec as mentioned in the manual doesn't solve the problem. I have to shut down the outboard and start again. After this procedure it revs as normal up to higher rpm with no limiter.

Things I have checked:

-Fires good on all 3 cylinders, spark plugs replaced and in perfect condition.
-Spark plug wires, caps and coils normal reading with ohmmeter.
-Oil flow, oil level, block temperature and water flow sensors checked without failure.
-Carbs clean, fuel hoses and filters with no problem.
-Primary compression checked, good and equal pressure on all 3 cylinders.

So here we are. Seems like an electronic problem.
Does anyone experienced problems like these?
What to check next? Wiring? CDI?

Thanks for helping out!

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Was on a trip with the boat during the last 3 days. After all tune ups remains only the rev problem. Otherwise is the motor doing fine.

Was wondering about some wiring problems as mentioned before. Wouldn't a failure in wiring show in different ways every time? I mean the problem is really reproducible. Bumps against the hull, motor going down to limit without any warnings.
I also went through the books again, seems to be a sensor for these conditions which makes the engine slowing down.

What i also thought about is to test the rev limiter. Is there a save way doing it other then really over rev? In case the rev warning should show and I could exclude that the problems connected to this sensor.

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

There is one issue I couldn't figure out yet. I was replacing the old spark plugs of the engine with new ones using:

NGK BR8HS as recommended in the manual. These come with a resistor of 5k ohm.
There is a sticker on the motor saving you should use NGK B8HS the ones without resistors.

I am a bit confused about what to chose. Later models with CDI need to have resistors to protect the electronics. With the original spark plug caps (having a 10k ohm resistor) you come up to 15Kohm together!! What seem to be a lot.

What type of spark plugs / spark plug caps do you use on your engines??

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Tried something else with the engine today. Read in another thread that there was a problem with the solenoid spring on a DT115 which caused similar problems running higher rpm.

So I blocked the choke and took the wire off. To make it short: that wasn't the problem on our Suzuki. Still running the same problem when hitting the waves.

Back to the start... more ideas someone?

 

[sk]

Re: Suzuki DT85 -93, rev limiter in hard weather

Have you check to make sure your alarms are working properly?

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Yeah I checked the alarms, buzzer and gauge lights working. Checked the sensors separately and got alarms on every unit.

The only sensor I wasn't able to check " in use" is the rev limit when over revving.

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Here are today?s check up's:

* Checked the fuel system, installing new fuel hose connectors, checking the fuel hoses and even running with separate fuel tank. Doesn't solve the problem.

* Checked PTT for shorts and function without finding any failure.

* Also checked the wires from stator, rectifier and CDI: no burned wires, no shorts.

* Cooling water sensor again. I disconnected the sensor and connected a cable between the black, coming from ground and violet/white going to CDI.
What was interesting was that I didn't get an alarm while running. No buzzer and no water light on the gauge. On the other hand is this unit not directly connected to the gauge but directly to CDI only.
Hope I get this right: the sensor shouldn't cause any alarms but measure the coolig water temperature for the CDI by resistance???

* What I didn't do yet is to check the throttle valve sensor. Could this unit explain the problems on the engine? I mean the motor's running perfect except for the rev problems. At least it is mechanical and could malfunction under bumpy conditions.

Suggestions anyone??

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

And on it goes:

* Measuring the hole wiring from CDI to separate unit without any shorts or broken cables.

* Also checked the throttle valve sensor with normal readings in idle and WOT.

I'm running out of ideas what to check next.

_________________

Something I didn't mention before is the fact that if the rev limit (if it is a limit and not something else) kicks in I need to switch the engine totally off.
Restarting directly doesn't solve the problem- the limit is still on and I cannot accelerate above approx 3000rpm.

Waiting about 15 sec with ignition completely off resets the problem and I can go full speed again.

The whole problem does never occur running the engine below 3200rpm.


Would really appreciate any help with my issue!!

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Btw: i did a list of the wiring, mainly from CDI including some readings of my coils.

Can help getting a quick overview even for other issues.

 

[99yam40]

Re: Suzuki DT85 -93, rev limiter in hard weather

I am not sure how that Suzuki limits RPM or what would cause it,
but you might check to see if the timing is changing or there is loss of spark on a cylinder when problem occurs just to narrow things down some.
If timing and spark are good then you may need to be looking at a fuel issue

 

[mearguy71]

Re: Suzuki DT85 -93, rev limiter in hard weather

did you try the NGK B8HS plugs?

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

I did actually some more testing today. Checking every kind of unit doesn't lead me anywhere.
So I started right from the beginning as Commander suggested, getting her out on the water and riding some waves until the problem occurred.

Checked the engine on water running with a timing light while the problem was present ( shaky... ) and I found:

* got and normal timing (idle) on cylinder #1; #2 and #3 firing normally. Motor sounded good in idle just as usual. The problem could not be fixed with the reset switch.

*Next I wanted to test all the warning systems under running conditions. So I bypassed oil flow, oil level and heat warning to see what happens.
I got the buzzer and rev limit on all systems, the reset switch for oil level working perfect.

BUT The rev limit doesn't feel like the problem at all!!!

It is definitely not the rev limiter causing the problem!!! It unfortunately occurs over 3000rpm and seams to block the engines rpm to under 3000.

Narrowing the problem: I thought of:

Fuel pump - perforated diaphragm- not supporting the engine under WOT and bumpy conditions?
Carbs - clogged nozzle- but shouldn't be necessary to shut down engine to recover?
TVS - working good- tested in habor but may get stuck in shaky conditions?
Capacitor Charge Coil - broken cable- should affect idle? But would fit to "reset" when engine is shut down because of time for discharging.
CDI - might still be the cause. But more unlikely

@ mearguy71: I checked with brownspoint and the BR8HS are the right ones. These engines really need that kind of resistance because of the CDI.

Thanks for your replies, really appreciate!!!

So: do my considerations make sense for further testing or should I look somewhere else?

 

[99yam40]

Re: Suzuki DT85 -93, rev limiter in hard weather

Monitoring fuel pressure/vacuum should show any problems with fuel delivery
did the timing advance when you tested on the water? or did it stay at idle timing?

If the timing light was showing spark on all cylinders after you advanced the throttle and the timing advanced properly but RPMs still did not rise then you are left with a fuel problem in my opinion

Some motors have different high speed and low charge coils, but I have no info on your Suzuki.
But you should be able to take voltage measurements with the proper test equipment at the problem RPM to see if everything is functioning properly

I guess trash in carbs could get sucked up into jet and any fuel flow will keep it there, once you shut off motor and stop flow it will fall away and to bottom of bowl again

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Monitoring fuel pressure/vacuum should show any problems with fuel delivery
did the timing advance when you tested on the water? or did it stay at idle timing?

If the timing light was showing spark on all cylinders after you advanced the throttle and the timing advanced properly but RPMs still did not rise then you are left with a fuel problem in my opinion

Some motors have different high speed and low charge coils, but I have no info on your Suzuki.
But you should be able to take voltage measurements with the proper test equipment at the problem RPM to see if everything is functioning properly

I guess trash in carbs could get sucked up into jet and any fuel flow will keep it there, once you shut off motor and stop flow it will fall away and to bottom of bowl again

You are right. Checked with the timing light and the throttle does advance but rpm got stuck. Seams really like a fuel problem.
The engine is equipped with 3 timing coils and a condenser charger coil plus the battery coil. Did not check voltage but resistance with normal readnings shaking the cables.

Not sure how to do a volt measurement as the manual doesn't provide information about it.

Carbs are still on the list but before getting into these I want to exclude other fuel problems.

Due to delivery far up in northern Sweden I don't want to reassemble the fuel pump before having spare parts so pressure testing will be next on the list.

 

[99yam40]

Re: Suzuki DT85 -93, rev limiter in hard weather

You still have not said if the timing advanced properly when having problems with RPM

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

You still have not said if the timing advanced properly when having problems with RPM

I think it does advance but I am not sure if it does properly. I will check one more time.

 

[CHIEF TERRY]

Re: Suzuki DT85 -93, rev limiter in hard weather

If you have a remote control and not a tiller ,check the connection on the neutral safty switch ,you may have two of these one on the engine and one in the helm control box ,it may be loose or has corroion . With a bounceing boat the wire will move and the pcm may think it is in neutal , in neutral the rev limiter kicks in at about 3800, in that range !!
Chief terry

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Thanks for your replies! Thought of something like this too.
Will check the ignition wire (Gr) as it is connected to the CDI but to check the neutral switch is a good point, too.
Will do a TVS test in live conditions, too.

I got a used fuel pump which I am going to overhaul as well as a new CDI, unfortunately from a 88 engine having a separate tach control unit. We'll see if I can wire it up but this comes just before removing the carbs.

Hope to get some updates on the engine tomorrow!

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

Calm sea today so the boat was running as it should. Nevertheless I did some testing.

Checked every connection involving the grey ignition wire and the hole ground wiring without any failure findings. Replaced the installed 25A fuse, to be sure.

Tested the TVS under running conditions, working within specs. But to calm out there today to check if TVS when having the problem.

Will rebuild the new fuel pump and change to see if it works before getting into carbs.
Fuel lines are in good condition, soft rubber, no cracks, all fittings in place.

 

[Fabbe2]

Re: Suzuki DT85 -93, rev limiter in hard weather

I did check the neutral switch without finding a problem. It is installed in the remote. I thing the engine is not equipped with a second one on the engine.

I don't think the CDI gets information about neutral position on this engine. It is just a simple switch providing the starting motor relay with ignition + when turning the start switch to the start position. In case of a problem the engine would not start, connection under running would not cause anything unless there is a faulty ignition switch, too which would cause the starting motor to run.
But worth testing anyway.

Fabbe