Apollo X18 dies after a few minutes - brand new
 

I've been around bikes for years, but this is my first Chinese bike. This is a 125cc pit bike. Brand new, just assembled today. I've done all my homework (I think). Threadlocked everything, drained the oil and put in 10W-40 conventional oil for break in. Its about 80 degrees out and the bike starts fine with no choke - all the way down. If I give it any throttle, I get a loud sucking sound, and the engine will die. The engine also dies after idling for about five minutes and will not restart unless you wait for it to cool.
Is the sucking sound normal with this type of cone filter or is that a clue to the problem? I've listened to some Apollo bikes on YouTube and don't hear this - the sound is loader than the exhaust.

Have you checked to see if the bike has spark after it dies when running for a few minutes? If you have a bad stator sometimes they put out enough to start the bike but as soon as it warms the stator coil stops working.

This happened on a brand new 125 pit bike we bought last year which is how I learned about this. New stator and the bike has run perfectly since that time.

I had to rejet for our altitude but that was expected and normal.

I'll give that a try. I'm pretty close to sea level, so I don't think altitude is a factor. While waiting for the neighbors to wake up, I decided to check the fuel screw. On the 22mm Mikuni clone, I expected it to be on the underside of the carb, but there is no screw... is this "normal"?

The screw is usually under a brass cap. You'll have to try and pry the brass cap out.

You have a 'tamper proof' carb. Mandated by law to keep you from changing anything inside.

Replacement carbs are so cheap it's easy to just buy a new, fully adjustable carb so you can jet the bike properly.

Bye the way, these so-called Mikuni carbs are chinese 'knock-offs' and not real Mikuni carbs.

How about fuel? My manual asked for 91 or higher. Since the choices at my local pump (Shell) are 87, 89, and 93, I went with the 93. Any issue there?

@GrandKidsMX, I tested for spark after it dies, and yes, I still get spark. Doesn't want to start when it's hot though.

Don't forget to check your valves. They could be OVER tight.

I haven't checked the valves yet. I don't have the proper tools for that, but I can have them in a couple days. At the moment I'm looking at the crankcase breather and wondering why no other pit bikes seem to scavenge the fumes into the air filter like mine does. One tube to the crankcase, one to the air filter, and the clear one is plugged - I'm guessing it catches oil overflow.

This might be spot on! If I'm doing this right, my valves have no gap. I can't even slide a K&N sticker (just happened to be nearby) in there. I've ordered feeler gauges to check this properly.

What is the compression ratio on the engine and altitude you are riding?

Unless the engine has a higher Compression Ratio (usually starting around 10 to 1 or higher), the manual is most likely not "translated" from China's RON over to USA AKI Octane ratings/numbers...

In most cases 87 is all you will need to keep the engine happy (85 is fine for "High Altitude riding" 5,000+ above sea level feet)

85 AKI (sold in USA) is close to 90 RON (sold in China)

87 AKI is close to 91 RON

No idea what the compression ratio is. If the valves check out, I can drain the tank and try running regular. I'm pretty close to sea level. The website says it's rated at 6.0KW (7500r/min) - the engine is 125cc.

If you haven't picked up a tunable carb yet, you might want to consider THIS KIT from T-BoltUSA. He is just across the Delaware River in Fairless Hills, PA, you'll probably have it in two days.
BTW, I run the 93 octane WaWa Ultimate gasoline in all my bikes, from a 50cc stocker to a '91 H-D RoadSofa, with no issues at all. It's less than $20 to fill a 5-gallon can.

One other thing no one has mentioned to check, when you open the gas cap, do you hear a hissing sound like the tank is pressurized? You may have a clogged gas cap, and a "vapor lock" of sorts prevents the fuel from going to the carb until you either crack the cap or let the bike sit for a few minutes.

Vapor lock? Worth a try. It has an odd gas cap that has no hose. I'm not quite sure how it breathes. There is a small piece that sort of slides to the side - odd design. Hard to tell in the pic, but there is no opening under the piece that slides... seems more like a key hole cover.

I've checked the valves and they are good. Plug is black, but dry. A new carb may do it, but I'm holding out for the company's tech support. I realize the cost is low, but I don't feel I should have to put more money into the bike to get it running from new.

The company has agreed to send me a new carb. I'll let y'all know if that fixes it.