Sputtering and popping, need diagnosis

[JettaKnight]

Hey, anyone remember me?

So I've dusted off the scooter for another year. But it's not so happy, just the same as when she went into hibernation.

Symptoms:
It misses, pops and occasionally backfires. It starts fine, idles fine, but at I open the throttle/rev up it will start missing more and more. It's quite steady and predicable.

The plug looks mocha brown on one side, white on the other.

What I've done:
1. Hooked up timing light to clearly see when it misses.
2. Replaced CDI
3. Replaced spark plug
4. Ran through two tanks with seafoam.
5. Tried to replace the coil last night. Didn't start with new coil, but then didn't start with old coil. uh oh.

How can I check the stator? Check coil resistant when off?

Or, is it a carb issue?

[JettaKnight]

I forgot specs.

NCY big bore kit and head
Prima pipe
Jets: bigger (105? 110?)
Dr Pulley weights (12.5 g?)
Aftermarket CDI and coil
Stiffer clutch springs (reds?)
Stiffer contraspring (yellow?)

Last winter I overhauled everything, and since then I've forgot the values.

No, wait, it was two years ago! How time files...

[JHScoot]

valve adjustment

good a guess as any and my favorite one!

[easy]

exhaust leak with your mods being 2 yrs old you might hv bad prima exhaust. seems likethey had a bad batch of them couple yrs ago

[JHScoot]

these diagnosis threads really are fun. its like trying to be a scooter repair Medium

[Raiderfn311]

The Scooter Whisperer?

[JettaKnight]

these diagnosis threads really are fun. its like trying to be a scooter repair Medium

Doubtful, but I'll check. My pipe is 5 years old - before the batch of bad ones.

As for the valves, I was thinking this was done before I quit riding, but it never hurts to check I suppose.

Maybe the main jet is clogged. It's been two years since I cleaned the carb. But that shouldn't cause it to missfire with the timing light, right?

[JettaKnight]

Bad ground wire from the coil.

Ran a new wire and it's happy again. Thanks for playing at home.

[ericalm]

Bad ground wire from the coil.

Ran a new wire and it's happy again. Thanks for playing at home.

Good one! Glad you got it fixed. No tear down required.

[jrsjr]

Bad ground wire from the coil.

Ran a new wire and it's happy again. Thanks for playing at home.

Good one! Glad you got it fixed.

Agreed! And, if memory serves, one of the earliest troubleshooting success stories we heard was a similar one. Shades of 2006 and Keys Electrical Troubleshooting Thread!

[JettaKnight]

I think playing wit ht coil was the last straw. It must have been a weak connection and finally broke.

After driving my F150 I am so ready to ride!!!!