I have a 2013 jonway yy150t-12 150cc bike with just under 1700 miles.
I took it out earlier today for a ride and it was running great for about the first 3 miles then it started to feel "funny". I was going around 45mph when it started losing speed. After about another mile I was at full throttle but only going around 10-15mph & slowing. I pulled over and stopped expecting the bike to die, but surprisingly it kept idling. I drove about another mile or so when it started happening again. At a stop light it began idling very low & I had to keep giving it gas to keep it from dying. I milked it about another mile and pulled into a parking lot where it did die (before I parked it). It started back up after turning it over for 8-10 seconds and giving it gas, but wouldn't idle.
I got it home and took a look, nothing appeared out of place/missing or broken. I replaced the ignition coil, checked the spark plug ( plug seemed ok, maybe running a little too lean), and pulled the carb. I went thru the carb ( I didn't have carb cleaner, so wasnt able to clean it, but the carb is only about a month or so old). I pulled the diaphragm and jets to make sure nothing was wrong and everything looked clean. Put the carb back on and started the bike up. It did start up after a couple of tries but idled low, about 500rpm. Reved the engine up to 7k rpm and let off the throttle and the rpms went down and down til it promptly died.
I'm not afraid of going part by part to figure out whats going on, but with my (minimal) knowledge, it seems like a lot of possibilities to go thru.
Any thoughts or ideas of where I should go for here would be greatly appreciated!
Adjust your valves they are tight and staying open usually the exhaust valve is the one that gets tight and stays open and the motor will loose compression and they will not hold low rpms. Set both valves to .004 inchs. Alleyoop
So I adjusted the valves...exhaust was too tight. Bike starts & in general idles until i rev it a bit and then it nearly dies. While idling the rpms go up and down a bit (2-300 rpm) where it didn't before this started.
I also changed the fuel filter out...old one looked clean but did have a little bit of debris in it, nothing substantial.
Pulled the vacuum line off the petcock and did see a small amount of fuel at the tip but nothing in the line.
If the idle is bouncing on you it is LEAN it needs more fuel, so turn the fuel ratio mixture screw COUNTER CLOCKWISE about 1/2 turn and see if it settles down. You may want to re-Adjust the carb right since the valves have been adjusted. Follow these procedure and take your time 1/4 turn in either direction can make a big difference. Alleyoop
If the plug is black then it is RICH and when overly rich they will come down to idle and want to die. So try LEANING the Fuel ratio screw some. Turn it CLOCKWISE and listen for the RPMS hopefully the rpms will climb as you turn it 1/4 at a time clockwise. Alleyoop
I got lucky and figured it out. It was a bad petcock.
I spent the morning changing out the fuel and vacuum lines, replaced the spark plug, pulled the carb and sprayed carb cleaner thru everything and then adjusted carb without anything helping.
I tried pinching the vacuum line at the petcock and my rpms went way up (from 1500 to 3k ish). Pulled the vacuum line off and noticed a drop of gas again. I happened to have an extra petcock and decided to give it a try and it runs right again (lucky guess lol)
Thanks allyoop and cyborg for your help. I very much appreciate the help!