Intermittent spark | GTAMotorcycle.com

Intermittent spark

Matt Rain

Matt Rain

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Bike's been acting up for a while now. Sometimes it'll start and run fine for a bit, but I always end up losing power, sputtering, etc. When it bogs down, it only runs on cylinders 2 & 3 and pipes for cylinders 1 & 4 are much cooler. Plugs are wet with gas AND show dark brown/black deposits when I check them, which seems to indicate that combustion happens at first, and then not. I've narrowed it down to an intermittent spark issue on all four cylinders - check it out:

[video=youtube;oqdfGz3GNDs]https://www.youtube.com/watch?v=oqdfGz3GNDs[/video]

I've already checked and cleaned every single connector on the bike. I've upgraded the coils, wires and caps. The only thing I have yet to do is open the right-hand side switch box with the kill switch. Hoping it's just a loose or dirty connection in there.

What else could it be? I'm really hoping it's not the CDI box.

This is getting frustrating. I wanna ride, dammit.
 
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Yup; coils, wires and caps. If these are fine then it's your triggering system.
Very probably original 1985!
Hopefully there's just some mung or whatever in there and you can clean it up inexpensively.
Pretty sure 1 & 4 trigger simultaneously, also 2 & 3. So it fits...
Good luck bro, let us know how it all works out.
 
Sometimes the coil low tension wires need to have the connectors gently crimped a bit tighter where they fit on the spade terminals. This can lead to a hard to pin point intermittent misfire.
 
I just stripped both screws that hold the handlebar switch box together. These old screws are like butter.

Ima try bypassing the kill switch.

This is going well.
 
Tripletrouble said:
Sometimes the coil low tension wires need to have the connectors gently crimped a bit tighter where they fit on the spade terminals. This can lead to a hard to pin point intermittent misfire.
Click to expand...

Would that show up merely by testing the resistance, or just under load? I get a solid 3 ohm reading at the connectors. No voltage before starting the engine though, the current goes to the CDI box first.
 
Bypassing the kill switch didn't change anything.

Just for fun, I connected the coils in reverse so that the left-hand side coil would fire cylinders 2 & 3; right coil to 1 & 4. I swapped both the wires and the 12v connectors. Turns out that 2 & 3 are again the only ones that get warm.

Could be an issue in the wiring between the CDI box and the connector that normally goes to the left coil.

Anyway I ran out of shop time today, will have to resume detective duties later this week.

This blows.


Sent from my iPhone using Tapatalk
 
Check your petcock, probably plugged. Trust me. :)
 
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I'm able to ride as much as I want now. I figured out that if I keep the RPMs low and wiggle the bike side to side at red lights, I get enough fuel flow. I'll clean/rebuild the petcock this week.

We keep on truckin'. :hello1:
 
So you had mittent spark all along. Dang!
 
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