Troubleshooting 1989 Yamaha 50DETO 2 Stroke, Idle/Low rpm rough running

[99yam40]

My old Snapon light from the 70s just clips on the plug wire to get a signal and it also has clips to hook up to a 12 v battery to make it work.
the light is bright and you can see how steady it is blinking along with what the timing is doing when aimed at the timing marks

[YAM50DETO]

Thanks, my old timing light isn't working so I've ordered a basic one for the weekend and see what results I get? Did I read a post you've made when you were troubleshooting your cdi issues? By the looks of if idle is straight forward enough but need to find a good test write-up/video too.

At some point probably worth popping the flywheel to visually inspect the stator as apparently even if the peak voltage reads ok it can be intermittent and difficult to diagnose.

[YAM50DETO]

OK, so my timing light arrived and this is what I think I'm seeing if someone with more experience could sense check?
I have captured some stills as the videos don't easily show up what I can see...

Timing Specifications:
Full retarded position: ATDC 7° (Chalk mark)
Full advanced position: BTDC 25°

1. When it first starts and it runs ok the ignition is being retarded to 5° BTDC. After a few seconds the timing is advanced to 7° ATDC and it struggles to ide and stalls
2. If I use the, 703 control, neutral throttle lever to increase the idle rpm and keep it running, the ignition is being retarded to between 1° - 4° before TDC.

Flywheel.PNGBTDC.PNGATDC.PNG

IMG_7490.PNG
Timing Video 1:

Timing Video 2:

So to me it looks like the timing is set correctly and working ok but it struggles to idle at the correct idle timing?

If this sounds correct and the carbs are cleaned and synced then I'm thinking the stator may be supplying an intermittent spark and would be worth pulling the flywheel next to visually inspect and swap out with the other engine?

[YAM50DETO]

checked idle timing and looks ok

Will post a fix when I eventually get there!

[99yam40]

just for your information
BTDC is advanced, Before top dead center
ATDC is retarded, After top dead center

Not sure what you are really seeing in the videos, camera must be taking pics at different time than the light is hitting.
does the light hit steady at all RPM or timing?
Does the timing stay steady on the mark or is it jumping around?

the light should hit each time there is spark current thru the wire you have it hooked to,
so it will show if spark is dropping on a plug if you move the pick up to each of the plug wires .

If the spark to each plug is steady and not jumping all over the place there is no need digging into the coils, you have other problems(fuel to air ratio)

[YAM50DETO]

Thanks for clarifying.

As far as I can tell the light is steady on all three wires with no obvious jumping around.

Took the boat out yesterday and upto 2k rpm the engine is misfiring but runs perfect after that. That would seem to tie in with the idle jet circuit? I have a small ultrasonic cleaner arriving this week and some recommended carb solution so will strip and clean all the jets and carb bodies. Separately I've also ordered a new prime start diaphragm as the one on the original carbs was pretty see through but that will take a while as it is on back order and not sure even if the other one is the same if it would cause these symptoms.

Thanks again for the help offered

[YAM50DETO]

I checked all three cylinder timings and look ok to me or at least all the same. The video is better in the shade but not sure if the frame rate is causing it to show intermittently,when it first starts and is running the advanced timing, as it is virtually constant flashing to the eye?

#3 Cylinder

#2 Cylinder

#1 Cylinder

[99yam40]

Still cannot tell anything from videos, but from what you say time to clean carbs better
good steady spark when motor is misfiring and timing is in spec

[YAM50DETO]

I've stripped and cleaned the carbs in a small ultrasonic cleaner (1.3L) for 25 minutes @ 60 degrees Celsius using Allendale Ultrasonic Carburettor Cleaner Concentrated Solution.

Result is it now idles without stalling and appears to misfire significantly less up to 2k rpm. Will get the boat on the water in a coupe of weeks to confirm but looks like it is fixed or if not completely fixed probably good enough?

Below is the engine started and run for 5 minutes without stalling or needing to use the neutral throttle lever to increase the idle rpm as before. Timing is correct at ATDC 7°.

Would be curious on opinions if it sounds like job done or there might be anything else worth checking.

Idling after ultrasonic carb clean

Thanks for all the help and advice.

[99yam40]

sounds good to me, what RPM is it idling at?
sounds a little high, but once in the water with more back pressure on the exhaust it will change a little.
need to set idle RPM when on the water and warmed up.
and fine tune pilot screws at that time also.

Most people never worry about doing it tho

[YAM50DETO]

Thanks, yes I thought so too, but when the timing moves to idle it's running at 750-800 rpm which I believe is in spec (800rpm +-50rpm). Will try fine tuning on the water, certainly off the water I wasn't noticing much change with half a turn in or out on the pilot screws with a starting point of 1 3/4 turns out.

If all goes well on the water I'll close this thread as fixed!

[99yam40]

Thanks, yes I thought so too, but when the timing moves to idle it's running at 750-800 rpm which I believe is in spec (800rpm +-50rpm). Will try fine tuning on the water, certainly off the water I wasn't noticing much change with half a turn in or out on the pilot screws with a starting point of 1 3/4 turns out.

If all goes well on the water I'll close this thread as fixed!

I believe Rodbolt said in the past that the factory settings should be fine if the carbs are cleaned properly.
So I would not worry too much about readjusting unless you notice a problem

[YAM50DETO]

OK tested on the water yesterday and it is improved as in it doesn't stall at idle and up to 2k rpm is running better but there is still a misfire. You can hear it in the videos below and the tacho drops from 700rpm to 500rpm on each misfire at idle. Adjusting the pilot air screws didn't seem to make any noticeable difference to idle.

For reference I had cleaned in the ultrasonic cleaner the other set of carbs for longer (40 minutes) and tried them today on the water hose and there was no difference so I think it is safe to say two sets of cleaned carbs currently sharing the same prime start as I won't have a new prime start diaphragm for a few weeks/months and I'm not sure if it could be contributing to the issue or could be disabled to test in the meantime? I have only stripped one of them but considering they are both from 1989 and it is rubberised I imagine they are both in a similar condition and needing replacing.


Otherwise still scratching my head on this one...

Thanks

Adjusting idle on the water:

Air box on:

Tacho when warmed up:

[YAM50DETO]

Replacement Prime Start diaphragm fitted and tested. The engine is idling and running better up to 2k rpm but there is still something else causing an intermittent misfire/backfire.

Biggest improvement from ultrasonic clean of carbs and syncing. Fuel pump and prime start diaphragms slight improvements.

Things to check over autumn winter...
1. Remove exhaust cover and check passages not clogged
2. Remove and inspect reed valves
3. Remove flywheel and inspect stator coil

[99yam40]

did you sync all 3 carbs together with the throttle plates completely closed not just at the idle position?

those videos sound like a lean sneeze on one of the cylinders to me