Suzuki DT85 -93, rev limiter in hard weather

[Fabbe2]

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

We have been out there today chasing waves and did some complementary testing.

At first: the engine does advance when the problem occurs, when in neutral it is willing to rev up as usual. But in gear- no way, gets stuck under about 3000rpm.

I did check the TVS again when the problem was present, normal readings: 0,47V in idle and 2,39V WOT.

Replaced the fuel pump without any change in symptoms.

To summarize:

Checked:

Electrical:
Spark plugs, spark plug caps, ignition coils, ignition timing coils, capacitor charge coils, battery charge coil, wiring and harness, oil flow sensor, oil level sensor, temp sensor, cooling water sensor, throttle valve sensor, PTT, neutral switch, remote wiring.

Fuel:
New quick connectors, ran the engine with separate fuel tank, visually checked the connections and hoses, replaced fuel pump.

Compression:
Normal and equal compression on all 3 cylinders, about 127 psi or 8.8 bar each.
Spark plugs looking light brown as they should.


I am running out of explanations for this problem. What remains is to check the carbs but I don't think it will solve the problem...

 

[99yam40]

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

Still no conformation of timing while problem exists?

 

[Fabbe2]

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

Still no conformation of timing while problem exists?

No, timing has been checked- works properly while having the problem.
Bout 4? ATDC when in idle up to 17? BTDC at WOT.

 

[99yam40]

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

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

If there is good compression, and good strong spark and correct timing when problems is happening then you are only left with fuel/air mix into the motor

 

[Fabbe2]

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

Sounds totally plausible. Checked with a real expert who is constructing engines and he came up with the same conclusion: Fuel problem most likely the carbs.

I'm getting the spare parts together for giving the carbs an overhaul. May take some time but I'll report.

Meanwhile I'll do the good old trick by spraying fuel directly into air intake to see if engine recovers.

 

[99yam40]

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

running a motor with a problem could just as easy pop pistons if it is running lean

 

[CobraCommander]

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

Is it possible that in rough conditions your lower unit is trimmed to high and air pockets are being picked up? I've heard of people with suzuki's having this problem.

 

[James R]

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

Without going through the drawings, as time does not allow, I recall that there is a water flow switch as well as the temp switch. If your water pump is not putting out as it should then it is conceivable that in rough water the lower is not always fully immersed and the pump may not be able to compensate. The signal goes to the electronics but may not trigger an alarm instantly. I hope I am correct in this.

 

[Fabbe2]

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

@CobraCommander:

Hmm, these air pockets would cause over rev right? The warning system has been checked and works as it should. I also have a tach connected and did never experience over rev in real conditions.

 

[Fabbe2]

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

Without going through the drawings, as time does not allow, I recall that there is a water flow switch as well as the temp switch. If your water pump is not putting out as it should then it is conceivable that in rough water the lower is not always fully immersed and the pump may not be able to compensate. The signal goes to the electronics but may not trigger an alarm instantly. I hope I am correct in this.

I thought bout a water flow switch too but there is none installed on the engine. Also shouldn't the engine overheat in this case?

 

[Fabbe2]

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

Due to lack of time I wasn?t able to get any further with the engine other than to do an impeller change. The old one has been changed for about a year ago and was in really good shape.

But: I'll soon have some time getting into the details again. Got the spare parts for a fuel pump and carb overhaul. Planing to clean the carbs with ultrasound too.
Unfortunately soon to cold to get out with the boat up here in the north.

Keep you informed about further developments.

 

[Tarimes]

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

Hi Fabbe,
do you have more information..?
i read your thread with many interest..
I don't speak english very well but i read it more easily.. i've got a new(old 1988)dt55... and i've also problems of limited rpm..
Thank you for this complete daignosis..

 

[mobilemike]

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

Suzuki had some issues with oil level sensors turning on the rev limit in rough weather.Can't remember the exact fix (some type of delay),but try this: use a wire tie under the oil sensor float to hold it at the top and retest the boat. I'll check some of my old manuals for what it took to fix it if the float trick "solves" the problem.

 

[Fabbe2]

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

Suzuki had some issues with oil level sensors turning on the rev limit in rough weather.Can't remember the exact fix (some type of delay),but try this: use a wire tie under the oil sensor float to hold it at the top and retest the boat. I'll check some of my old manuals for what it took to fix it if the float trick "solves" the problem.

Might help in some cases but I don't think that explains the problems I am experiencing. The conclusion earlier in this thread was that my problem is different from the build in rev limiter. I got the boat out off water but didn't have time to have a closer look inside the engine.
My next step will be the carbs. And I will keep you guys informed!

 

[Fabbe2]

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

Hello everyone. As the snow melted away I got out working on the engine again.
Did the normal spring recovery and checked the ignition with timing light. Also did a compression check. Everything within normal readings.
Sounds healthy, no starting problems after the winter.

Nonetheless I took down the carbs.
- Looked surprisingly good inside. Minor debris on the jets.
- Checked the float bowls, some minor corrections but they were within specs at about 17mm. Needle valves worn, will be replaced.

Ultrasound next...

 

[Fabbe2]

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

Carbs back from cleaning, great job. New needle and seat into the bowls and again adjusted.
Did an fuel pump overhaul, too. New diaphragm and O-rings-> Read about some fuel problems with the one down to the engine. Soaking/ blowing air causing the pump not to work properly.

Too late to fire it up today, but will report!

 

[Fabbe2]

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

Good news everyone!

Problem solved. Where testing the engine today without any problems. Had some nice waves today, wind about 10m/s. Running through it, no slowing down.

What did the job:
I think it was a mixture of several problems, all fuel related. The main problem where the floats in the carbs which where out och specs.
By shaking the engine the needle closed the fuel supply to early so the carbs where running out of gas.
But I also overhauled the fuel pump and checked/ fixed the hoses and connections and did the ultrasound cleaning of the carbs and nozzles.

End of season the engine was running quite hot so I also did an overhaul of the waterpump, the watersupply tube with the brushings, cylinder head gasket, with a new pressure valve (the old one was gone!) and tuned up the oil supply.

So, thanks for your precious help solving this problem and have a nice time out there on the water!!