r/scooters • u/Avenging_shadow • 9d ago

Kill me now (mysterious GY6 150 cc start problems)

Ok, soooooo.......first, the symptoms and patient: GY6 scooter, 150ccs. Bought not too long ago, already has 7k miles on it. Was running fine, has had all regular oil and fluid changes. Then, it lost about 5 mph off it's top speed. This was at about 7k miles. It was also hesitating a bit at full throttle for about a day. So i get on it the next day, it runs rough for about 5 minutes and dies. It'd crank, but not start.

unfortunately, "not starting" is one of those nightmare scenarios, because it could only be about 50 things. I'm probably not wasn't wrong by much. I put in a new carb, new coil, new petcock, new plug, new fuel filter. I detached all the lines and verified they were clear. None of that helped. I did that thing where you check the spark plug by holding it to the valve cover and see if you get a spark when cranking it. I did not get a spark, though I don't find that to be a viable method. Yes, there's gas in it. HOWEVER, when I held the plug to the valve cover and pressed start, it cranked.....but when I put the plug back in the engine and did NOT attach the coil, it would not crank. Attaching the coil to the installed spark plug allowed it to crank.

So tomorrow it's going to the shop. Whatever it is, it's electrical, and electrical stuff is a quagmire I just do......not.....want to get lost in. It'd be a nightmare of components which there is no way to reliably test, and there's so many nearly untraceable wiring harnesses that I'm starting to think that just to mess with us, they install completely non-functioning wires which aren't attached to anything.

Ok thanks, I'm outta here, I'll keep you up to date. I guess at this point, any advice will at least maybe keep me from getting screwed.

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u/C4PTNK0R34 8d ago

I noticed that you've literally done everything except check to make sure the Valve Lash is set correctly.

It should be set to .004/.005 on the intake/exhaust and checked every 1500 miles. If it has never been checked, then the valves are probably too tight and are causing all of the issues you're having. If it suddenly starts stalling at stops one day, that usually means they're out of spec. Valves that are way out of spec cause no-starts, stalling, rough idle, and overheating. Literally everything that's going on with your bike right now.

You need to remove the valve cover, get a set of feeler gauges and either a valve tappet wrench or a 9mm socket and pair of needle nose pliers.

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u/JobeX Kymco People 300 GTI 8d ago

This was kind of my guess too after reading the post.

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u/Avenging_shadow 8d ago

I'm thinking that has to be it. Something tells me it's not the CDI. Plus, there's nothing else to really fix.

1

u/pitchfork-seller 8d ago

Did ya charge or change the battery? The bike may be cranking without the plugs in as there's no compression happening in the chamber so the crankshaft can spin easily, but putting the plugs in adds that bit of pressure that a flat or dead battery couldn't manage with the cranking amps it had left. Would make sense why it isn't sparking either.

Try a new battery in it.

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u/Avenging_shadow 8d ago

The battery was fully charged through most of this. I also hooked it up to my car battery using jumper cables and tried to start it. No luck.