I am stumped. 125cc 4T scooter ills

[SL350]

I've reread the whole thread and I want to go back to when the idle was set so high the scooter ran off. I'm guessing it could maintain running if you had not killed it. That tells me it might have been drawing from the main jet. Could this be a plugged idle jet? Or if the float is too low sometimes the idle jet can't use it but the main jet can like when you are running out of fuel and bump the throttle and it hits until it dies completely.

Getting another carb is always a good idea if you can. Just swapping a good one lets you know right away whether the problem is carb related.

 

[mr72]

OK, real quick.

At some point before I posted here, I had already cracked open the carb and cleaned the pilot jet. I also verified the float needle was working correctly. And I've verified fuel is getting into the float bowl.

The choke is not a traditional choke, but it's an enrichment circuit. The fact that it runs when the choke is "on" indicates it probably is getting fuel fine.

It feels like it's like intentionally shutting off. My current theory (which I can't verify) is that it has a "ignore the sensors" start up mode that expires after a few seconds. I need to actually time how long it will run each time. If it's an actual time that's consistent, then it will bolster my theory. The theory is that it starts in this special startup mode, then after some fixed time, the PCM evaluates the sensors and then finding it's "not running", cuts off the ignition. The crankshaft position sensor is used to fire the ignition so it won't run or start at all without that. But the throttle position sensor could be bad and cause this? Maybe?

OK...

I just went out and tried it again. It started and ran with a very fast idle, probably 2500 rpm, for about 45-50 seconds, then idled down and stalled. It would restart immediately but just barely runs for like 2 seconds and stalls like the idle is set way too low. I cranked the idle up a little bit at a time and tried restarting it and it tried to catch a couple of times then refused to even catch at all and the battery went dead.

So my theory that it's an electronic cutoff is probably wrong. It might be that the electronic choke was never working right to begin with, remember I worked on it not long ago and though I had fixed it, and maybe it's working but just for 45 seconds and the idle is plain old too low, but I can't get it to run long enough to set the idle speed. You would think the idle speed would not have changed with it sitting all winter, and that at least I can adjust that and get it running if that's all that's wrong, since it's a thumb screw that I can easily access.

Anyway. I have a new carb on the way, and that certainly can't hurt.

 

[Brapariah]

If you don't have access to one, and want to give the current carb a bath in an ultrasonic you can come give it a dunk. I recently picked one up and it saved the day for me Tuesday after a lot of trying and failing to get a bike running that had been neglected by its previous owner, now it just sits in the shop waiting for its next mission.

 

[mr72]

hm, that's a very appealing offer. I'm going to wait until I get the new carb in my hand before I crack it open again, but the orig carb might be a great cadidate for this, once I remove all of the rubber and plastic parts.

 

[Brapariah]

No worries, send me a PM if you want to give it a shot.

 

[mr72]

The new carb arrived far earlier than I expected.

I was halfway expecting it to not be the right part. It's tricky ordering parts for an Italian scooter made in India by a company that's been out of business for 5 years. But this was exactly the same part, just brand new.

Swapped it in today at noon, and after turning it over enough to fill the float bowl, it fired up and ran nearly perfect immediately. I rode it up and down the road and around my cul-de-sac a few times, and once it got a little warmed up it started bogging a little bit, so I adjusted the pilot mixture. It was 2.5 turns out, I set it for 1.5 turns out and it ran much better. I'm sure I'll do more pilot mixture tweaking once I can ride it and get it fully warmed up.

So the good news, less than $100 in parts and I fixed the temp sensor issue and fitted a new carburetor. Should be good for the next 800 miles! or more, we should hope.