2002 sx250 ox66 frustrating

[scarabsport29]

I am having a frustrating problem with my 250 ox66.
I am running twin 2002 sx250 ox66 on a Scarab Sport29. Both motors will run great all day. I can ***** for hours and at wide open I get 5400 rpms. The problem is if the counter rotating motor sits a few days it wont start, no spark. Full battery, and is getting fuel fine. To start the engine I need to remove the #3 spark plug, crank the engine a few times minus the plug. Put the plug back in, fires up and runs great. It will start fine all day long. Local mechanic says the ECU is bad. Doesn't make sense to me. Has anyone else experienced this and how to remedy it?

[boscoe99]

Don't know a remedy just yet but you can confirm or rebut what the mechanic is saying by swapping CDI boxes. If the problem moves to the standard rotation motor and the counter rotation motor now starts, idles and runs just fine I would agree with the mekanik.

If the problem does not move I would disagree with the mekanik.

[scarabsport29]

I switched the boxes and the problem stayed the same. Took the plug out, started right up. I hope someone might have dealt with this before

[boscoe99]

At least you now know that an expensive CDI is not needed.

I am having a difficult time understanding how one of six plugs can affect the other five. Your motor should run on five cylinders whether or not the number three plug is installed or not. Try it yourself. Once the motor is running turn it off and remove any spark plug lead. The motor should start and run.

Now is it only the number three plug being removed that has an affect on the motor starting first thing in the morning? Removal of any of the other plugs has no affect on the startability?

And to be clear, if the motor sits for several days you are saying that none of the coils/plugs are sparking?

Just for the hell of it, I would remove, clean and reattach all ground leads on the motor. I would disconnect and reconnect all electrical connectors several times just to see what happens. Check all of the wires to verify there is no chaffing between two wires or a wire and some thing. You might have a connectivity issue that is intermittent.

[99yam40]

why do you need to remove the #3 plug to turn it over?
is there too much fuel in the #3 cylinder that the motor does not turn over properly( hydrolock)?

how did you find out #3 HAD TO BE PULLED?

[boscoe99]

why do you need to remove the #3 plug to turn it over?
is there too much fuel in the #3 cylinder that the motor does not turn over properly( hydrolock)?

how did you find out #3 HAD TO BE PULLED?

Damn good question. How was it determined that the #3 plug, and the #3 plug only, has to be removed to get the motor started?

I am assuming that the motor cranks normally but will not start first thing in the morning. Plug is removed and the motor then miraculously starts and runs. Plug is replaced and it runs fine the rest of the day.

Next morning it all starts over again.

[rodbolt17]

dunno
as I am to lazy to swap parts I simply test systems.
test pulser coil output.
test charge coil outputs.
test CDI outputs.

[scarabsport29]

I found out the #3 plug removal worked when I was checking for spark. When I removed #3 and went to crank it over, it fired right up. When I pulled other plugs, it did not fire. Its also not the next day, only when it sits for a few days it wont start. I was just hoping someone had a similar experience.

[99yam40]

Did you try just pulling the plug wire off instead of pulling the plug to see if that caused all the plugs to spark again?

this pulling #3 plug to get spark back to all plugs makes no sense to me at all.

maybe you are moving some wire around getting it to make good contact again

[scarabsport29]

Thank you for the idea. That did work so at least I have a place to start. I disconnected the other wires before the 3 and nothing. Took the 3 wire off and fired right up. I have no idea why. Swapping the coil and plug cap with the other motor to see what may happen.