Yamaha 30 1986 no spark when engine is warm

[HansYamaha]

I have what I believe is ignition problems with my Yamaha 30DE (6J8) 1986, 3cylinder two stroke ,EU. It has been on land for some years, always worked ok and never had any major issues.


Symptoms:

• Starts without any problems. Always.
• Can hear that engine misfires as it warms up. Ignition tester at spark plug shows decent spark.
• Pulser coils measures ok in resistance (each of the three wires to black gnd), warm or cold engine. About 360-370 ohms.
• Charge coil is a bit low in resistance when engine is cold, 230 ohms, measured between blue and brown cable. Warm engine it gives 280 ohms, within spec. (280-330 ohms).
• Checked with ignition light, it should be 2 degrees ATDC pick-up according to service manual but I had about 5degrees BTDC. If I adjust to ATDC, the engine more or less stops and will not rev up at all when warm (cold engine it revs up).
• With spark tester (light bulb) it is more or less nothing when engine is warm. Same for all cylinders.
• If I adjust to 10-20 degrees BTDC at idle, rev speed increases significantly and it runs much smoother at idle. But will not rev up.

I get resistance specs from CDI troubleshooting document, cannot find any info in service manual.

What else I’ve done:

• Cleaned carburettors and replaced gaskets, floater etc. Cleaned fuel tank. Replaced fuel hose between tank and engine.
• Replaced membrane and outer gasket in membrane pump.
• Changed all three ignition coils and spark plug caps. They were, all but one set, way outside resistance specs. New spark plugs (old ones black and wet).
• Checked compression, ok and very similar for all cylinders, warm and cold engine. I get about 9-10bars.
• Adjusted timing linkage according to manual with engine off. Have not verified TDC indicator position, but it hasn’t moved in the red paint.
• New battery.
• Checked ground connections, firmly attached and clean.

Waiting for DVA adapter to measure peak voltages.

Any suggestions what is could be causing this? If temperature related it doesn’t feel like CDI issues as it shouldn’t change much in temperature.

[99yam40]

what advances the timing on this motor?
mechanical linkage?
is that moving as it should when moving the throttle?

as far a spark,
measuring peak voltages into CDI and out of should give an indication of what is failing when there is no spark.

the kill switch grounds the spark voltage to stop the motor, so find that wire at the CDI and disconnect to see if that brings back spark

[HansYamaha]

It has mechanical linkage for advancing timing. It is adjusted ok according to service manual (marks line up ok). The motor doesn't stop completely when heats up, it just won't rev at all (only on idle).

Measured peak voltages and go the following:
- Charge coil gives about 230V cranking open circuit and similar at idle (200-250V depending on rpm). Should be 175-210V according to specs. I suppose high should not be a problem, gap to rotor might influence this voltage, correct? Removed flywheel and looks as if steel for this coil had been touching the magnets.
- Pulser coil gives about 9V cranking open circuit. Should be 4V according to specs. Cannot measure at idle since cannot get access to cables when connected. So this is too high? Resistance for each of the three coils are the same 360-370Ohms.
- CDI unit output, get 8V cranking (should be 4.5V) and about 230V on idle (should be 190V).
- Verified DVA adapter in wall socket and got 316V so DVA it should be ok.
- Lighting coil gives 12.4V at idle so DVA should be ok also for low voltages.

So I assume either CDI or pulser coil is faulty, any suggestions?

[99yam40]

It has mechanical linkage for advancing timing. It is adjusted ok according to service manual (marks line up ok). The motor doesn't stop completely when heats up, it just won't rev at all (only on idle).

Measured peak voltages and go the following:
- Charge coil gives about 230V cranking open circuit and similar at idle (200-250V depending on rpm). Should be 175-210V according to specs. I suppose high should not be a problem, gap to rotor might influence this voltage, correct? Removed flywheel and looks as if steel for this coil had been touching the magnets.
- Pulser coil gives about 9V cranking open circuit. Should be 4V according to specs. Cannot measure at idle since cannot get access to cables when connected. So this is too high? Resistance for each of the three coils are the same 360-370Ohms.
- CDI unit output, get 8V cranking (should be 4.5V) and about 230V on idle (should be 190V).
- Verified DVA adapter in wall socket and got 316V so DVA it should be ok.
- Lighting coil gives 12.4V at idle so DVA should be ok also for low voltages.

So I assume either CDI or pulser coil is faulty, any suggestions?

seems to me if there was only 8 volts out of CDI to the ignitions coils at cranking the spark plugs would not spark
what about the CPS that sends input to the CDI
if there is good spark at the correct timing to all plugs while problem shows up the you are left with fuel to air ratio is not right when you come off of idle.
possible main jet plugged up

did you use using a timing light to check the actual idle and WOT timing to make sure it is in spec?
and spark while problem shows up?

do you have a working alarm for over heat and low oil level.
have you tested it to see if the buzzer works?
if one of those calls for the RPM reduction mode the RPM will be limited probably similar to what you are seeing

[HansYamaha]

99yam40, thank you for your suggestions! Not sure what you mean by CPS, do you mean Crankshaft position sensor - don't think I have one on my old 2-stroke? Only pulse and charge coil under the flywheel.
Yes, adjusted linkage according to service manual (idle and WOT to marks on flywheel) and after this checked with timing light.
Only over heat alarm on this motor, it works ok (triggers at ~ 95°C) and buzzer is tested ok.

After some more measurements and looking at the specs from CDI electronics that says trigger should be minimum 4V and charge coil minimum 175V(connected)/210V(disconnected), I think CDI is the faulty part. Got a CDI electronics 117-6J8-H1 replacement CDI and now it runs great again after some fine tuning with timing light and pilot screw adjustments.

The CDI unit 117-6J8-H1 has two gray cables that are not mentioned in installation guide. One has about 10V and the other 0.5V. If anyone knows their pupose please let me know!

[99yam40]

sorry, I did not think about it being a 2 cylinder with a waste spark system.
I was thinking about what could fire more than a one spark plug for multiple cylinder motors

I would think their web site should have specs for there equipment