1988 DT55 not revving up under load, timing issue?

[mcarnogursky]

My 1988 DT55 (starboard) is not revving up under load, goes gutless at about half the throttle. Checked the entire fuel and carb system, put in a new fuel pump, switched fuel tanks & hoses with the port engine, no effect. Checked the compression - all good (~120 psi on all 3 cylinders, cold). Checked the starboard timing and I see it behaving very differently from the port engine. While the port engine ramps up from 0 to 26 BTDC at around 3000-4000 rpm, then stays there, all in line with the service manual, the starboard timing jumps straight to ~35 BTDC as soon as I open the throttle a little bit. I checked the pulser coils, the capacitor charge coil, the main supply voltage, the idle/acceleration sensing switch, the idle adjust switch - all checked out fine. Do I need a new CDI unit?

[Solarman]

Could be the throttle position sensor located on the side of one carb. Or, if you have a flow switch/ heat sensor, the flow switch may be acting up throwing the motor in safe mode?

Do you have the Suzuki manual for your '88, dt55's?

Good luck, post back on what you have.

[mcarnogursky]

Thank you for your prompt follow-up. On my DT55's it's not a throttle position sensor but only a throttle position/acceleration switch. Tested both functions and they checked out. Also, on my version there is no heat sensor, only the flow switch, which is working fine. Btw this condition is present whether the engine is warm or cold. But thanks for the tip about the safe mode, will check the service manual whether the safe mode could apply. That being said, I had read through the ignition troubleshooting earlier today and either water flow or low oil level would be flagged by an audible alarm. My buzzer shuts off ~15 seconds after start as the water starts circulating, as it should.

Having a twin outboard has the advantage that I can compare their behaviors. So, the starboard, which won't rev up under load, has a distinctly out-of-spec ignition timing. Ramps up way fast and caps at over 30 deg BTDC as opposed to the specified 26 deg

[Solarman]

There are two capacitor charge coils (low and high) on the stator/magneto. The low speed charge coil charges the capacitor from start up to about 3000 rpms, the high speed charge coil charges the capacitor above the approximately 3000 rpms.

The gear counting coil, flywheel position, cylinder pulse coils, throttle position switch, and CDI control the timing. The only adjustments for timing (I'm aware of) are the distance between -flywheel and gear counting coil, distance - flywheel and pulse coils, and the throttle position switch. The rest of timing is controlled by the CDI.

There have been instances where the flywheel key had sheared, causing crankshaft to flywheel position change. Guess you can see how that could cause problems.

Good luck, post back on what you find out.

[mcarnogursky]

Where is the gear counting coil located?

Had the flywheel off yesterday, checked that all 5 coils (3 pulser coils, the capacitor charging coil, and the main charging coil) are securely bolted down, woodroof key securely in place, and all. Am yet to measure the resistance of the main charging coil but saw the system supply voltage increase from the battery voltage of about 12.5V to about 12.8V ar higher RPM so I guessed the main charging coil is good. But will check the same voltage on the port engine and compare, hopefully get a clue. Say, on a car, the charging voltage goes to ~13.5 - 14V so maybe the starboard coil is weak indeed, or the voltage regulator.

Ultimately will swap out the CDI units between the engines to see whether the issue follows the starboard CDI unit but prefer to get a better feel beforehand as to whether this is really necessary. Thanks

[Solarman]

Gear counting coil is generally located outside the flywheel and counts the flywheel teeth (or pulses with each tooth). This is why the mounting of this coil is important.

As mentioned, there are two condenser charging coils in the magneto, check the wiring diagram for wire colors, test the ohms by the manual for each.

The TPS (throttle position switch/sensor) has several steps, manual should tell you the position of throttle and how much it changes for testing, but i think it has to be tested with voltage? Manual should tell how to test it. This switch changes the timing with respect to throttle position and speed of flywheel by the CDI unit.

Good luck, post back on what you find out.

[mcarnogursky]

Turns out the gear counting coil is only on the more recent models. Mine is a J model, no gear counting coil or even a voltage regulator, for that matter. Checked with the manual and verified all the impedances/resistances of all the coils - all are in spec. Checked the behavior of the throttle position switch - seems to behave exactly as specified. Getting a new rectifier, just in case. Remembered that I had a short circuit in the instrumentation wiring which blew the 25A fuse between the battery and the ignition switch & controls. Don't quite see how this could have affected the CDI unit or even the rectifier - or could it have zapped any of the electronic modules?

[Solarman]

Looked up the '88, dt55 in parts list at browns point, and in the magneto parts diagram, the gear counting coil is listed as item #24 from 1988 - 1993 models. You also have a primary ignition coil, a condenser charging coil, plus the battery charging coil, and 3 cylinder ignition timing coils.

It's good you have another motor to experiment with, but remember all of these coils rely on good flywheel magnets properly spaced/distanced from these coils. The gear counting coil is the coil that most often goes bad, because it is not as protected by the flywheel (not under flywheel). Loose, missing, out-of-place magnets on flywheel are not acceptable for good timing.

Good luck, post back on what you find out.

[mcarnogursky]

Today I switched the CDI units between the engines but the issue did not follow the starboard CDI. That's pretty good because it rules out the most expensive item (the CDI, $500+). Tested the timing, still the same as before: port side moves exactly as it should, while starboard jumps up to 35 BTDC at a pretty low RPM. Just received a new rectifier so I put it in, in case the short from ~1 month ago could have damaged it. Still no change.

You may be right about the 88 model year having a gear counting coil but I just so don't physically see it there, no connection for it either. According to the wiring diagram, my J version does not have it, even though the parts list does say otherwise. The parts list seems to go by model years, not model designations. Since today I had both CDI units out and then back in I would have noticed an extra lead.

So, as a second-to-last resort, will swap out the low oil warning unit in case that one is screwing it up. Meanwhile I'll get an oscilloscope and will measure the wave forms, along with their offsets, of all the inputs into the CDI: the 3 ignition timing coils, the condenser charging coil, and the battery charging coil. There's got to be some difference somewhere. It's great to have the second engine serving as a reference, has helped me several times in the past. Let's hope it helps this time, too

[Solarman]

It should be a small half circle coil measuring about 1/16" distance from the teeth of the flywheel, usually mounted to the block right behind the flywheel.

Have you tried swapping just the throttle positon switch to see if problem follows the switch.

Have you opened up the fuel pump on the bad motor and inspected the diaphragm and the check valves (usually clear discs near the bottom section)?

Good luck, post back and tell us what you find out.

[mcarnogursky]

No gear counting coil on mine. The J-model differs from later models in that it has a separate low-oil-warning unit separate from the CDI unit, no overtemp sensor, and no gear counting coil.
So today I connected an oscilloscope to the outputs of all the coils and measured clean signal on all three pulser coils of the (good) port engine and on pulser coils 2 & 3 of the (bad) starboard engine. However the pulser coil #1 of the stbd engine has a noisy output, with distinct spurious spikes halfway between the normal signal pulses. That is the one and only anomaly I measured on the bad engine but it could be enough to throw off the timing. So I'll change the coil No. 1 and will report back

[mcarnogursky]

At long last, by swapping ignition related parts between the port and starboard engines, found out that the timing issue follows the flywheel. By swapping the flywheels (a couple of times, to make sure) I got the starboard engine running good while the issue has moved to the port engine, along with the flywheel. Getting another flywheel later this week and will confirm the findings after installing it and testing the boat this weekend.
No idea how a flywheel can go bad - didn't drop/whack/overheat it, nothing. Just all of a sudden, between two outings, it went bad

[Solarman]

Is it possible the magnets have changed somehow? Either by moving, or maybe lost some of their magnetism, or possibly the crankshaft key-way changed somehow? I have seen key stock half shear and throw timing off, but it is noticeable?

The only other thought is that the magnet moved (i believe they are glued in place), or lost magnetism somehow, kind of like when a voltage arc magnetize's a screw driver when a wire is wrapped around it?

Good luck, post back on what you find out.

[mcarnogursky]

Replaced the flywheel last night, tested the timing advance on a hose at my house this morning (max advance was finally in spec), and took the boat on the Potomac. Both motors ran good, nice power, hole shot, and all. So that should conclude that .

Separately, although the same engine, later ran into what looked like a fuel delivery issue - would loose power after 1/2-1 minute of driving nicely, several times in a row between fishing stops. Seems that in the end hand pumping the priming bulb got the boat back on plane; will troubleshoot it further. But the timing issue should be all good now even though I still have no idea what caused it and how likely it is to reappear on either engine. Time will show, the engines served us well for several years so I have faith.

[Solarman]

If pumping the bulb does good, then possibly an air leak between fuel pump on motor, or possibly the fuel pump itself is not pulling fuel from tank to supply the carb.


Good luck, post back on what you find out. Glad the timing issue is ok. A bit strange for the flywheel to be the cause? But a solved problem is good.