Misfiring confusion.

[DunbarLtd]

88 Force 85hp.

During an outing yesterday I noticed a few things regarding misfiring and wasnt sure what to make of it.

Apparently these engines dont like idling for too long because they will carbon up the spark plugs and cause running issues.

With mine, it will sputter and miss like crazy until I get up to speed and it eventually "clears out". After that, at speed, it will run fine with no miss.

So I got curious and when it started missing again after idling around for a bit i hooked up a timing light.

First of all , I marked each TDC cylinder on the top of the flywheel with white paint so i could easily see when the cylinder was firing. Interestingly, on the flywheel there are notches that coincide with the three marks. I numbered them 1,2,and 3.

When hooking up the light as its missing I noticed with the lead clipped to #1 plug wire.... #2 and #3 would light up intermittently. As I hooked the lead to #2 and #3 coil wires the same thing would happen.

Very similar to what you see in this video here: https://www.youtube.com/watch?v=D-hBeGdE6oE

I am not sure what is going on. If a spark plug were to get carboned up and misfire, when I hook up a timing light; wouldnt I just see the #1 mark show up on the flywheel intermittently?? Why would a fouled plug cause #2 and #3 to spark at those times like in the video? In the video that are saying its an indication of a faulty trigger.

To further my test I again hooked up the light after i made a run making sure the engine had cleared and wasnt missing. Shifted into neutral and kept it running.

Every single cylinder was firing exactly as it should without any misfiring according to the numbers on the flywheel showing up.

Why would #2 and #3 be firing when I have the lead hooked up to the #1 wire during a misfiring episode if its clear that the trigger or stator is not bad?? If they were it would misfire all of the time wouldnt it???


Anyone have any explanation to whats going on?

 

[The Force power]

The three notches you are referring to are most likely the 28 / 30 / 32 degree marks.
You set the timing at full throttle mode while cranking at 28 degrees (try to stay a tiny tiny bit before 28)

For checking the stator/trigger/CDI-boxes go to;
http://www.cdielectronics.com/wp-content/uploads/2013/02/CDI Troubleshooting Guide - 2012.pdf

 

[DunbarLtd]

No they are like J shaped hooks on the very top edge of the flywheel. Looks like perhaps a hook to attach a rope in case of emergency pull start but i could be wrong. The marks you are describing are on the face of the flywheel. Or i guess the profile side. These other hooks are on the top outside edge and just so happen to be tdc for each cylinder and where i made my own marks. Those marks dont line up with the block pointer with the motor running but you can shine the light and see when each cylinder fires. Its pretty close to 28 degrees btdc. So the mark i made will be to the LEFT of the block pointer when running. At cranking speed the number one cylinder will line up with the block pointer(28 degree mark) as it should.

https://www.ebay.com/itm/1990-FORCE-...QAAOSwIJNeGTwI


I did all the tests with a dva adapter, disconnecting each wire at a time according to the service manual (not seloc) and all were within specs while cranking the engine over.

The fact it clears out after running full speed and testing with the timing light right after and seeing no misfire is whats confusing.

Even if the spark plugs are carboned up, shouldnt the cylinders still fire at the correct moment which is 28 degrees btdc?

When its missing and i hook the clip onto plug #1 and turn on the light i can see #2 and#3 showing up randomly. So essentially in that situation when #1 fires and the light flashes, for some reason #2 and sometimes #3 are at tdc. Hopefully that make sense. Its doing exactly the same thing in that video i posted above so you can get a visual.

This doesnt make sense if it were just the plugs being fouled.

Wouldnt the trigger still fire on time even if the plugs were fouled??? Im just not understanding how it works i guess.

 

[jerryjerry05]

If the plug fires on the wrong cyl. that shows the harness on the trigger might be wearing through??
Or the trigger's bad?
Also if the plug wires and harness are old they can bleed through.

"

Apparently these engines dont like idling for too long because they will carbon up the spark plugs and cause running issues. ​

With mine, it will sputter and miss like crazy until I get up to speed and it eventually "clears out". After that, at speed, it will run fine with no miss. "
This sounds like there's an air leak in the system?? Do the starting fluid test and see if there might be a bad gasket?
Carbon can also form when the air screws are set wrong? The fuel system leaking into the motor?(pinhole in the diaphragm)​

 

[DunbarLtd]

It only happens after its been idling along for 10-20 minutes. Thats when it sputters if i try to take off all of a sudden. And its when I noticed the misfiring different cylinders with the timing light.

After I run it and "clear it out" and do another hole shot right away, it will accelerate okay. And during this period when i used the timing light it was not misfiring at all. I checked all coil wires and they all fired as they should. 111111 22222 3333 and so on.

And I should clarify. It doesnt necessarily miss fire as in the spark plug doesnt get voltage. The flash from the timing light is consistent just as it is when i check it while its running fine.

What happens is I will notice the #1 coil will fire when #2 and #3 are @ tdc. Instead of just seeing a 1 pop up every time the flash goes off. 2 and 3 will randomly pop up. So itlls go 11113112111311221113 On all 3 cylinders it will do this. And it clearly runs rough and smokes more.

Once I run it at speed and it seems like its "cleared out" and I stop and retest - it does not misfire once. Ive checked this 3x and it did the same thing each time.

Im sure its because i idle too long and foul the plugs. But why would it shows #2 and #3 are @ tdc when It should only be showing a "1" when i have it hooked up to the #1 coil wire. Even if the plug is fouled the trigger should still send a consisntent signal to the coils. If the trigger was bad then id actually see the flash on the timing light cut out and truly have a miss fire. Meaning no spark happens. This is not whats going on. It sparks every single time. It just seems to spark at the WRONG time when its fouled up and I dont get it.

 

[The Force power]

This is very interesting although I don't have a clue what's going on, I have to ask
What plugs are you using? and what if you leaned-out the mixture a bit?

Have you tried what jerryjerry05 has suggested???

 

[DunbarLtd]

Champion UL18-V.

Havent tried to lean it out. Set to 1 turn out as Jerry suggested. Did spray some starting fluid. Didnt notice anything. All the intake gaskets are new. Bought all new carb/bowl gaskets as well. I checked the fuel pump diaphragm 3x now and it appears to be ok.

Usually if one of those things are the problem you will have a consistent running problem. The fact it only acts up after i idle for too long leads me to believe its the spark plugs loading up. But the weird misfire condition doesnt make sense. The spark seems to be consistent, even after it seems to get loaded up... it just doesnt spark at the right time. But thats only the case after idling for a while.

When it clears out after i go for a run and i pull the timing light out it will spark on time perfectly. If I was getting a no spark condition then thats one thing but it just seems to be sparking at the wrong time when its running rough. Maybe this is normal when an engine is running rough but i dont understand why.

Hoping someone else might have a clue. If the trigger was bad it would be missing all the time. And it doesnt actually have a no spark condition so im not sure whats going on.

 

[foodfisher]

This is silly, but is the flywheel loose? Worn keyway with loose nut.

 

[DunbarLtd]

No, the timing is fine at cranking. First thing I checked after I noticed the weird firing order when it was running rough.

 

[The Force power]

What if.....you changed the plugs to NGK BUHX
Do not lean out more then one full turn out

Good point of foodfisher about the key

 

[foodfisher]

Dried and cracked plug wires? Check at night and look for jumping spark.

 

[DunbarLtd]

Sure I could try a different plug. And good tip on checking spark at night. I will definitely do that next time out. I always start early before sun up anyways.

I mean, I understand some of these old motors foul plugs from idling too much. But it doesnt explain the erratic firing order when they get fouled up. That just doesnt make sense or else I just aint smart enough to understand it.

Like I said, with the timing light attached (while idling in neutral) the flash is very consistent while its running rough. Its just that other cylinder numbers pop up when i should only be seeing "1". Hope that makes sense. If you watch the video i posted its doing the exact same thing.

However after I run it at full speed and immediately check it, it will fire perfectly. Not miss a beat. Idle for too long and sure enough back to weird firing pattern. Really has me scratching my head.

 

[foodfisher]

Just following your lead, maybe when the plugs are fouled, the spark can't go it's intended route so it looks for the weakest outlet. Thus the errant spark guess. Good luck.

 

[The Force power]

I'm leaning towards jerryjerry05 posts #5 and foodfisher in post #11

If the plug fires on the wrong cyl. that shows the harness on the trigger might be wearing through??
Or the trigger's bad?
Also if the plug wires and harness are old they can bleed through.

I bet you there's the cause & change the plugs to my suggestion (there's lots of reading material in the archives on "the right" plugs)

 

[DunbarLtd]

K thanks guys. Ill see what I come up with. Have a good weekend! Stay safe out there!

 

[GA_Boater]

Some confusion on my part.

You connect a timing light to #1 and when the stumble begins you see flashes at #2 and #3? You have cross spark at low speed for some reason. Have you changed the plug wires? Didn't see that in your posts.

 

[DunbarLtd]

Some confusion on my part.

You connect a timing light to #1 and when the stumble begins you see flashes at #2 and #3? You have cross spark at low speed for some reason. Have you changed the plug wires? Didn't see that in your posts.

Not necessarily flashes AT #2 and #3. But the other way around. #2 and #3 will intermittently flash where only #1 should while I have the timing light lead clipped to #1 wire. In that situation I should only being seeing a #1 show up on the flywheel. So instead of the constant 111111, every now and then a 2 or 3 will jump in there.

But the same thing will happen on every coil wire when its running rough. Then I run it at speed, clear it out and check it again and its perfectly fine and spark is correct. Ive held the timing light on it for about 2 minute or so and it didnt miss a beat.

When its running rough it will immediately cross spark like you say and continue until i put it in gear and get up to speed for a bit.

I suppose the coil wires could be bad and not creating a strong enough spark at idle and fouling the plug. It does smoke a lot when its not running right after idling too long. Does sound like a coil perhaps.

I will look into replacing them and see if it fixes it. Thank you.

Ive done cranking tests with DVA on Stator trigger and cdi wires disconnected from the block like it says in the manual and all checked out okay. The only thing i havent really been able to test is the coils. I do have a spark tester and it seems to have decent spark but Im not sure if its strong or not. I never had an outboard before so I have nothing to compare it to.

 

[The Force power]

I suppose the coil wires could be bad and not creating a strong enough spark at idle and fouling the plug. It does smoke a lot when its not running right after idling too long. Does sound like a coil perhaps.

The only thing i havent really been able to test is the coils. I do have a spark tester and it seems to have decent spark but Im not sure if its strong or not.

Post #11 suggested by foodfisher ( I love his signature, this applies to me as well)

Now...I presume you have the prestolite ignition-system with the Blue or black coils correct?
IF you don't have (tested good) spares kicking around

Since we can not change the cable on the coil and we want to eliminate the cables from "leaking"
You can coat the cable with die-electric grease, it blocks all current & protects for corrosion ( comes in squeeze-tubes)

Just rub in on the cables & boot, Its a cheap remedy but can be effective
Also check the spring for rust (inside the boot) and clean as necessary

 

[DunbarLtd]

Thanks for the replies. I will look into it soon.

 

[jerryjerry05]

If I think the coil wires leaking?? I remove the end and cover with shrink wrap and then coat with liquid
electric tape. Ugly but works good.