DT200 Tachometer doesn't match rpm?

I trailered my boat about 300 miles this past week. When I arrived and put the boat in something was clearly wrong. It started fine and the port water alarm was sounding (both the red light on the gauge and the audible alarm every 20 seconds or so).

Eventually that cleared up but when I throttled up to get on plane the rev limiter kicked in even though there was no other alarm. Took me a secon but I eventually noticed the tach reading much much higher that what the motor sounded like it was turning. Checked for a spun hub and it is fine. Then I noticed the behavior even in idle or while in neutral. The tach seems to be reading about 2x the actual rpm. I don't have an external tach, I am just guessing based on what I know the motor usually sounds like.

I even took a couple videos.

http://youtu.be/pzExr3SmvwI And
http://youtu.be/ybgDQ-JdErI

Can anyone help me understand what might be going on here? Thanks, Chris

Ok .. gonna update my thread in case anyone has some bright ideas (or in case I solve this and it helps someone else in the future),

There are multiple symptoms that feel to me like they may be caused by the same problem. The most obvious symptom is the tachometer giving a reading that seems to be ~ 2x the actual motor RPM. The engine cranks right up and idles very nicely. My handheld tach reads about 650 RPM at idle, but tach gauge reads about 1,00 - 1200. As throttle increases, tach seems to maintain the x2 pattern and quickly the guage is getting close to 4k - 5k rpm. I am VERY certain the motor is not actually turning this fast. I've really only done this once or twice, as I know it's quite bad to rev the motor while not under load. This RPM issue is present whether the prop is engaged or disengaged.

The second symptom is that when engaged and running, it really stumbles and maybe misfires or something and it just can't get much past 1500 RPM (tach reads closer to 3k rpm). I know it's not turning at 3k RPM, because when the motor was running correctly, 3k RPM was quite a bit faster.

So here's what I've tested or done so far:

1. Check for spun HUB - marked prop, ran boat, checked marks .. all still lined up. Of course since RPM issue is present when not engaged, this was probably not productive.

2. Clean the oil flow sensor and filter screen. It did have stuff in it, but didn't seem like enough to put it into limp mode.

3. Bleed the oil pump multiple times, ensure proper oil in the oil tank, use syringe to fill oil pump and oil lines.

4. Check all in-line oil check valves.

5. Finally I removed the oil pump all together and dissassembled it and cleaned all the obvious passages. Re-install, bleed the pump, no change in behavior.

6. Check spark on all cylinders (did with an in-line light type tester). Did not check strength of spark or ability to jump particular gap. Definitely have some spark at all cylinders.

7. Compression check .. very consistent 90psi on all 6 cylinders. Seems like a low number to me, but it's very consistent.

8. Disconnected oil level indicator and disconnected oil flow sensor .. ran motor with no change.

9. About 8 months ago I had the carbs professionally cleaned and I installed rebuild kits on them. At the same time I removed the oil pump, I removed the carbs and gave them a good cleaning, even though they all still looked very clean.

I'm really at a loss now. Someone has suggested to me to check the coil counter at the flywheel. I am wondering if I should also check my throttle position sensor. I don't know the correct procedure for that, but did measure a consistent resistance on it. The shop manual has a set of calculations to conduct on it, but it required the TPS to be on the motor with power supplied. There were some voltage / ohm calcs it wanted me to perform, but since I didn't have the TPS installed at the time, couldn't take the readings. I did however measure resistance with the TPS off. I don't know itf it's meaningful or not, but I got a reading of 9.7 kohm fully closed and 4.1 fully opened, with a smooth transitions between the two.

Here are a couple new videos of the motor running:

Video 1 - With the cowling on
Video 2 - With the cowling off

You can definitely see and hear the discrepancy between actual RPM and tachometer reading. .. and you can see and hear the rev limiter kick in at about 1:30 in the first video.

I've removed the tachometer and inspected it for problems .. It all looks fine.

Any ideas?

i know nothing about suzuki but what is the voltmeter reading when the tach is reading wrong?

papyson said:

i know nothing about suzuki but what is the voltmeter reading when the tach is reading wrong?

Click to expand...

Thanks for jumping in and at least asking a question or two to see if I can learn anything new .. I appreciate it.

When you ask what the voltmeter is reading when the tach is wrong .. do you mean the volts at the tach?

Thanks,
Chris

its time for a suzuki guy to jump in here...but i assume a suzuki tach is driven by the ripple pulses off the rectifier/regulator that also charges the battery just like any other outboard....when the tach goes squirrely thats the first thing i look at...

Thanks papyson,

Hopefully a Suzuki person will jump in. On another forum, it's also been suggested that I look at the gear counting coil as well as the rectifier / regulator assembly. I don't know the proper test procedure (I assume a resistance reading of some value or range, but I can't find the proper readings anywhere).

I'm absolutely not a mechanic and I don't have any experience with troubleshooting any electrical / timing / coil / charging system or any other similar system on a boat or a car, but I definitely feel like there is something wrong with some component in the system. I feel like whatever component has gone squirrely has some responsibility in reporting the correct RPM to the tach and it also has some responsibility in the process of timing at higher RPM. Of course it's possible that I have more than one component that is misbehaving.

It's almost like there must be 2 components that work together to do this job and one of them is bad .. that's why the tach reads 2x the actual RPM. Again, I have absolutely 0 experience diagnosing or troubleshooting these things .. heck, I don't even understand how they work ..

Anyway, hopefully a Suzuki person with some ideas will chime in. So far it's been suggested to check the gear counting coil, check the tachometer control unit, check the voltage regulator/rectifier and even it's been suggested to check something called the "ignition amplifier" .. but I don't know what that is, where it is, or how to test it

Thanks again!
Chris

Ok .. so yesterday my new to me gear counting coil arrived. Seems the resistance reading on the new to me coil is about 190 - 200 Ohms, which is very similar to the reading I got on the old (currently on the motor) coil. So for anyone keeping up with this (and for the benefit of the search engines, in case anyone in the future is looking for this information):

It seems like the correct resistance for a gear counting coil (part number 32150-87D00) on a 1986 Suzuki DT200 is roughly 190 - 200 Ohms.

Whether or not this is what's causing my problem .. don't know yet .. I'll post an update after I install the new coil and lake test the motor, just in case anyone is following along.

Chris