soft seize or hydrolock

[boostedmax]

i have a 90cc 1e50qmf, stock zuma exhaust, pwk 21mm carb, 70cc head to raise compression.

its been running good for a couple of weeks then today while riding it suddenly shut off as if it soft seized with 95 main jet but started right back up. so i pulled over and replaced the jet with a 103 and rode around for a while and it died again but this time it would not start right away and the motor felt locked would not start with starter or kick start. so i pulled over and waited 30mins and it finally started again.

pulled the plug and it is black so now im wondering why my motor is shutting off since black should mean running rich.

any ideas on what to do?

[boostedmax]

pulled the plug, put a new br8hs in and 90 main jet to do a plug chop

[bradswims11]

Tell us how the plug looks now you have replaced it.

Also may pay to clean the carb and air filter. Check you exhaust is bolted on nice and tight, also maybe check for leaks on the intake.

Cant really think of anything else apart from no spark, so it could be the coil too

[boostedmax]

The carb and coil are brand new. I have noticed some burnt oil on the exhaust flange

It's deffinetly not a spark issue cause it runs fine up until it shut off and started right back up

The weird thing is it was running fine for a couple of weeks without issue now all of a sudden its giving me problems

Do u think it could be cause I'm using a stock exhaust with a bigger carb?

[90GTVert]

Those sound like soft seizes to me. If your carb were dumping in so much gas to try and hydrolock the engine it would never run right. Make sure you don't have anything clogging up the air shrouds. I would suggest checking for leaks around the intake, crank seals, and case mating surfaces.

49ccscoot.proboards.com/index.cgi?board=yamajog&action=display&thread=425
49ccscoot.proboards.com/index.cgi?board=yamajog&action=display&thread=506

[boostedmax]

With the 90 main I'm getting a dark brown plug still

[felliott]

Have you adjusted the needle at all? You may need to lower the clip one groove.

[boostedmax]

I thought the needle only controlled partial throttle and my plug being black means running to rich right?