30hp 3 cylinder spark problem

[Grumpy]

I have a two stroke 3 cylinder 30hp Suzuki motor (DT30C) that is driving me towards suicide...

The symptoms are as follows; The top cylinder (closest to flywheel) refuses to fire. The engine start on first pull perfectly but immediately settle down on two cylinders only and when opening the throttle, the engine will momentarily fire on all cylinders and go like greased lightning, but then cut down to two cylinders. Closing the throttle somewhat it will sporadically fire the top cylinder for a second or so - much like turning an ignition on off.

I suspected a fuel starvation problem but even when running on the lower two cylinders, I squirted some petrol into the carb and nothing happens, actually get worse. I fitted a new coil and it has plenty of spark but strangely, when its idling on two cylinders and I pull the top sparkplug lead off (sparks all over) and bring it towards the sparkplug and about an inch from the plug the spark would jump and the piston firing up momentarily again but stop although the spark is still jumping the distance or even when pushed onto plug. I changed sparkplugs to no avail as well as swopping the coils around with no difference. What can be at fault

I already did the following;

1. Checked compression and it fine - same across all cylinders
2. Completely stripped and cleaned the top carburettor a few times already
3. Checked the coils primary and secondary - all primary ohm readings as per manual but only one coil have a secondary ohm reading as per manual - even replacement coil does not read on secondary, but that said, all have plenty of spark and changing the coil combinations makes no difference.
4. Checked the charge coil under flywheel and both resistance and voltage output within spec.
5. Gear counter pickup resistance and output voltage within spec.
6. Pickup coils (trigger coils) all three resistance within spec (195 - 197 ohms) similar to gear counter pickup, but the output voltage only 10% of their spec on my tester - 0.45V (spec 2.5V >) on all three pickups, compared to the gear counter coil's 4.6V (spec 2.7V>). Even with low readings, the bottom two pistons runs perfect.
7. All air gaps set to spec (0.75mm) on the pickup/trigger coils
8. Changes sparkplug - hotter and colder to no avail.
9. All spark coils and pickup coils well grounded and can not find any loose connection.
10. Checked reed valves and it seems OK.

Worth mentioning; with only the bottom sparkplug lead fitted, the motor starts first pull and idles. Same with only the middle cylinder.
But when only the top cylinder plug lead fitted, it starts immediately, run for a second or two and dies and will not start again. But put the lead back on any other piston and start then stop engine, the top cylinder will fire first time again when connected only to die after a second or two and will not start again - even with quick start spray. Repeat procedure, and it fires again

Also the engine was reconditioned after two stroke oil pump failure and the oil injection disconnected and oil reservoir/tank removed.

Can anyone help me please.

[redlowrey]

has this problem only happened since you rebuilt the engine or did it run alright. Is the plug wet when you pull it out for a look or dry, to me it sounds like exhaust gas is not getting away out out of the cylinder or exhaust gas is being sucked back in.

[Grumpy]

Thanks for your reply Redlowrey

I bought the motor secondhand and it had this problem, but less pronounced. Had a bit of piston slap/knock and I took it apart and fitted new rings which solved the slap. Just got worse after that.

to me it sounds like exhaust gas is not getting away out out of the cylinder or exhaust gas is being sucked back in...

The other day when ordering a replacement coil from a Suzuki dealer (270km away from my rural town) I spoke to the mechanic on the phone about this and he actually also mentioned this and asked if the top piston was not accidently fitted the wrong way aroud as this would cause such systems due to wrong porting.
To make sure, I took out the motor and split the crankcase and all the arrows on the pistons facing the same way - no problem there.

What else can cause this problems with the exhaust gas and where do I look?
Btw, the sparkplug comes out wet.

[mphelle8vld]

I don't have any first hand knowledge of the dt30, but do you know how the wiring to the oil tank sensor and/or flow switch was addressed when the tank was removed? Maybe the CDI thinks the tank is empty? Also, most CDI's can be damaged by removing the plug wires while running, Suzuki warns of this in their service manuals. Anyway, post the year of your motor and I'll look around.