P250S Wont Start - sputters only

[frugalangler]

'07 People S250 - won't start, will sputter a short burst after repeatedly twisting the throttle (accelerator pump) but won't stay running. Fuel Pump is delivering fuel and if try to start repeatedly, exhaust is warm meaning it is firing but not staying running.

I'm not quite sure what to check, carb has been replaced (suspected of jets plugged), fresh fuel in tank, battery new & charged.

Any suggestions appreciated, did not find similar problem when doing a search, if there is post a link for my review. Thanks

[BettinANDlosing]

Did you replace with OEM carb or China carb? The China carbs stuck. If the jets were clogged why not just clean and use that carb? Checked obvious stuff, air filter? Plug? Check what jets are in this new carb?

[frugalangler]

It's a factory OEM carb w/ all the Kymco labels, not a imitation. I replaced because I got frustrated after cleaning (I consider myself a decent wrench) it but the jets and passages on these small carbs are very small and not always can you get varnish out.

Update, I don't think it's a fuel issue after all, stuck a timing light on it, and when it will fire the T-light flashes, but when it won't fire, no flashes, so I'm now off to discover if it's a coil failing or the signal to it from the CDI/ignition box.

and....

Yes, I've checked all the 'usual' fuel related stuff which is what I first thought because it had sat unused for about 18 months, but this last BFO (Blinding Flash of the Obvious) is taking me in a different direction - wish I hadn't jumped to conclusions on it being fuel and done more diagnostics before I tore into it

[TLRam1]

Keep us posted.

[BettinANDlosing]

Side stand kill switch?

[frugalangler]

Keep us posted.

Update - I didn't have a lot of time tonight, but I put a dwell meter on the coil primary, and when it would fire dwell was in range for a single lunger, but when it didn't fire (most of the time) there was no dwell, meaning there was no signal or pulse coming from the CDI.

Next test: I will put a meter on the output of the pulser coil and see if it is exciting the ignition, that should narrow it down.

What is puzzling is it ran great when I last rode it 18 months ago, CDI units and trigger coils usually don't just quit when not in use, there has to be a better root cause than just a bad part??

And, for the query on the side stand switch, they usually are good or bad, they usually don't come and go when sitting still - but I wont rule it out until confirmed, as it is in the circuit. Thanks.

[zombie]

Someone else just had the same issue, and B&L had the answer. The kill switch was intermittent. Spray it out w/ some PB Blaster, and cycle it a few times. Could be rust on the pulser or stator ends as well. Check all the connections from the stator cause the bullet connectors fail often.
The engine/chassis grounds too.  Fuel petcock could also be fouled from sitting w/ old/bad fuel... Most likely.

[BettinANDlosing]

Zombie the 250 has a vacuum fuel pump, but it most surly can go bad! It's left me stranded before.

[zombie]

I would bet that pump has a stuck flapper from old fuel. It's a simple deal to rebuild it.

Reading back tho I see he is leaning toward intermittent spark.
18 months is long enough for several generations of mice to do some dirty work on the harnesses. I have those "snake oil" posts on the brain so naturally there has to be mice involved somewhere... Maybe the next no start bike...

[wildwildip]

On my P 250S, part of the spark plug boot got damaged. The metal that contacts the plug was bent. It can be removed and replaced. It made the scooter sputter and run good sometimes, bad other times, or just stall.

Seafoam the fuel system to clean it out.

[frugalangler]

Well, I finally got some time to work with the scoot, I've been busy with lots of other chores.

Finally tracked it down - bad connection in the side stand safety switch connector, I had previously checked the switch and it was fine, so plugged it back in not giving any thought to the connector since it was clean and the pins on the switch portion of the connector were clean, but I pulled it back apart and inspected the pins on the harness connector - they were slightly corroded. Exercising the connector w/ some contact cleaner in it appears to have cleared the issue, so I applied a small bit of CRC Silicone Contact grease to ensure the weather doesn't regenerate the problem.

So, this was an interesting problem, because the switch although it interrupts the supply to the ignition, there is apparently sufficient back feed through the other sensor circuits to energize the ignition enough that it would fire a few pulses and then quit, which was quite misleading in troubleshooting.

Thanks to all for the suggestions, as it ultimately was one of the suggestions that was the culprit.

[TLRam1]

Thanks for posting up what you found, I need to go through mine and add some lube.

[Stig / Major Tom]

Well, I finally got some time to work with the scoot, I've been busy with lots of other chores.

Finally tracked it down - bad connection in the side stand safety switch connector, I had previously checked the switch and it was fine, so plugged it back in not giving any thought to the connector since it was clean and the pins on the switch portion of the connector were clean, but I pulled it back apart and inspected the pins on the harness connector - they were slightly corroded. Exercising the connector w/ some contact cleaner in it appears to have cleared the issue, so I applied a small bit of CRC Silicone Contact grease to ensure the weather doesn't regenerate the problem.

So, this was an interesting problem, because the switch although it interrupts the supply to the ignition, there is apparently sufficient back feed through the other sensor circuits to energize the ignition enough that it would fire a few pulses and then quit, which was quite misleading in troubleshooting.

Thanks to all for the suggestions, as it ultimately was one of the suggestions that was the culprit.

That goofy kill switch will allow the same thing....almost starts. It is a fooler!
Stig