DVA stator testing

[Eoughphilly]

Hello iboats friends. On idle, I have a misfire occuring pretty regularly. I ohmed out the ignition system and everything comes up good there. When I do a DVA test on the stator high speed while engine is running, the reading is unstable and bouncing around, but above the 20+vdc . When I do a reading on the low speed, I get a solid reading above 180+vdc.

Could this be an issue with the stator?

 

[Texasmark]

Since you are dealing with electromagnetics and the energy comes from a fixed magnet on the flywheel, V = L di/dt. L is fixed in the windings and core of the pickup coils and the electromagnets embedded in the flywheel. Di/dt is your rate of charging which increases as RPM increase (since time per cycle is reduced) causing the voltage to increase.

So my guess is that you have a voltage breakdown problem in the stator or leads, or more likely your test leads are picking up static from the ignition system which is more prevelant at the higher speeds/outputs. With multi-megohm input impedance in today's digital multimeters this is a very real possibility. Twisting them together with a loop about every couple of inches, or get some aluminum foil and make a tube and lay both leads in it side by side and wrap them up...the idea is to shield against radiation or equalize the input to both leads simultaneously which will cancel on it's own....can't drive current when both sides are at the same potential.

 

[Faztbullet]

If the miss is at idle and DVA reading is fine on low speed its not the stator. High speed does switch over till around 2000RPM in switchbox.

 

[Bt Doctur]

Stators will produce a square wave AC voltage

 

[Eoughphilly]

Here is a video if the motor running.

Ive done a compression check, I have pulled the carbs, cleaned and adjusted. Replaced fuel filters, installed temporary clear fuel line in front of carbs to check for air bubbles, replaced fuel with fresh fuel, replaced spark plugs, tested ignition system. I cant seem to find anything wrong yet it runs like crap. I can't get it to idle low enough to allow me to put it into gear while under load. It just dies. Any thoughts on what to do next?

 

[Sea Rider]

Electric/electronic components have 3 stages : Works spot on, are fully shot or failing with intermittent issue, the latter being the most difficult to troubleshoot precisely, should be tested when at load pushing a boat. Also could be a CDI, switch box, ignition coil issue failing intermittently ?

Happy Boating​

 

[Eoughphilly]

Electric/electronic components have 3 stages : Works spot on, are fully shot or failing with intermittent issue, the latter being the most difficult to troubleshoot precisely, should be tested when at load pushing a boat. Also could be a CDI, switch box, ignition coil issue failing intermittently ?

Happy Boating​

Thank you for the input. I replaced the switch box yesterday as it was the cheapest and easiest to get to. I pulled the coils today and examined them, they look to be in good condition.


I'm ok with spending the money to replace the stator and trigger since I'm in there. I just have a hard time doing it because I cant confirm it's actually going to resolve the problem. I cant get it to idle good enough to put it in gear under load.

 

[Sea Rider]

Thank you for the input. I replaced the switch box yesterday as it was the cheapest and easiest to get to. I pulled the coils today and examined them, they look to be in good condition.
View attachment 339425

I'm ok with spending the money to replace the stator and trigger since I'm in there. I just have a hard time doing it because I cant confirm it's actually going to resolve the problem. I cant get it to idle good enough to put it in gear under load.

Gearing from idle under load it's a different scenario that when the motor is running middle to max wot rpm range under same load, range where the electric components begins to misbehave and boater turning crazy....

Happy Boating​

 

[Eoughphilly]

I uploaded some video showing a 7/16" spark gap test for each cylinder. To me it looks like the bottom might be missing, but you can hear it so I'm thinking it maybe a weaker spark then the others.

Gap test top

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Gap test middle

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Gap test bottom

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[Faztbullet]

Index the flywheel and check timing on each cylinder. The idle staying high and runs like crap makes me lean toward a sheared flywheel key

 

[Eoughphilly]

Index the flywheel and check timing on each cylinder. The idle staying high and runs like crap makes me lean toward a sheared flywheel key

The high idle is because I have to give it some throttle to keep running. I cant put it in gear when I have the throttle at that point. if I pull the throttle back all the way to a normal idle, it will spudder and die from the popping. After a few minutes of it warming up I can let it finally idle, but still sounds like crap and if under load will die. Instead of indexing the flywheel I could remove it and check the flywheel key as i have not ventured into that area yet on this motor.

Would indexing and checking with a timing light also test other potential problems?

 

[Faztbullet]

"Would indexing and checking with a timing light also test other potential problems?"

Yes...like sheared key, misfiring switchbox...have you done a correct sync and link on carbs???

 

[Eoughphilly]

"Would indexing and checking with a timing light also test other potential problems?"

Yes...like sheared key, misfiring switchbox...have you done a correct sync and link on carbs???

I was getting started on indexing the flywheel. When I pulled the brand new plugs out, I noticed the top had minor oil on it, the middle was clean and had the smell of gas, but the bottom was black. I'm wondering if there is an issue with spark because, in my above videos showing the spark gap, the bottom seemed to be a little weaker than the rest and looked like it wasn't firing at all times. Suppose indexing could help in this area too, I'm picking up a timing light after work this afternoon.

Any other reasons a single plug will foul like that? My carbs are rebuilt and adjusted with a link and sync.

 

[Sea Rider]

Does the motor counts with a 3 independent ignition coils ? if so, the lower one isn't doing its homework right and on its way to fail at any time provided that the lower plug works right. If not that costly change all IC for new ones.



Won't find on 2 stroke motors clean plugs, usually one fouls way more than the rest which is quite normal.

Happy Boating​

 

[Eoughphilly]

Does the motor counts with a 3 independent ignition coils ? if so, the lower one isn't doing its homework right and on its way to fail at any time provided that the lower plug works right. If not that costly change all IC for new ones.

View attachment 339532

Won't find on 2 stroke motors clean plugs, usually one fouls way more than the rest which is quite normal.

Happy Boating​

I got the timing light hooked up and at about 1500 rpms it's at almost 20 degrees. The manual says it should be 0-4 at 650 - 700 rpms. Does this mean my timing is way off?


Afterwards I pulled my plugs to see how they looked and the bottom was all fouled only after a few minutes of running at 1500 rpm

 

[Faztbullet]

Either #3 carb is acting up or ignition is firing late will cause it to be black. You can swap coils and see it weak spark follows coil. Check the keyway first. Put #1 at TDC and see where points shows on flywheel.

 

[Eoughphilly]

Either #3 carb is acting up or ignition is firing late will cause it to be black. You can swap coils and see it weak spark follows coil. Check the keyway first. Put #1 at TDC and see where points shows on flywheel.

I swapped #2 and #3 coil, there was no change in the fouling of the plugs. I got the motor warmed up to allow me to let it idle and threw the timing light back on. It is showing 3 degrees at 700 rpm. Not looking like the coil or the timing.

 

[Texasmark]

I got the timing light hooked up and at about 1500 rpms it's at almost 20 degrees. The manual says it should be 0-4 at 650 - 700 rpms. Does this mean my timing is way off?
View attachment 339544View attachment 339545

Afterwards I pulled my plugs to see how they looked and the bottom was all fouled only after a few minutes of running at 1500 rpm

View attachment 339546View attachment 339547View attachment 339549

 

[Texasmark]

#1 looks normal
#2 looks like water is getting into the cylinder. Move each cylinder's piston to or near TDC and looking through the spark plug hole, compare each. If #2 looks new and carbon shows up on the others you have a water intrusion problem.
#3 is obviously fouled

"In my opinion since I have had water ingestion in engines before and know what it looks like."

 

[Eoughphilly]

#1 looks normal
#2 looks like water is getting into the cylinder. Move each cylinder's piston to or near TDC and looking through the spark plug hole, compare each. If #2 looks new and carbon shows up on the others you have a water intrusion problem.
#3 is obviously fouled

"In my opinion since I have had water ingestion in engines before and know what it looks like."

I did look inside and can see carbon on the #2, doesnt look much different then the other pistons. #3 looks fouled like that after idling for a few minutes. I did another ohm test this morning while the engine was cold, I'm getting 3560 from red to blue when specs say it should be 3600-4200. Would that be anything to consider? It's not much out of spec at all