Sa50 shutting off

[Mrhyde20027]

Hey all, I put a big bore kit on my sa50 2 stroke. I also drilled the main jet. The scooter runs great for a while and then it will shut off. It fires right back up and runs great for a while again. I checked all the fuel lines and I don't see anything wrong. I'm thinking its not getting enough air or to much air from carb. I did drill a couple holes in original air box when I did the 80 kit. Any ideas on what could cause this? Or what I can try to narrow it down and trouble shoot. Thank you

[Rip_City_Spree]

id start with getting a temp sensor to be able to see if its getting to hot or not. trail tech makes a good cheap one. soft seizing is not good. not saying that is whats happening but if you dont know how hot its getting then you dont know if you have an air leak that could be an issue.

[vintagegarage]

I had the same problem with one of my SA50s and it turned out to be a bad fuel valve. Carry a small screwdriver with you and when it stops again, coast to the side of the road, and do not hit the starter button, or use the kick starter. Instead, use the screwdriver to open the drain screw on the lower side of the carb. You can do this with the body on. If fuel runs out or the carb dran, then the problem is not your fuel valve. If no fuel runs out, then close the drain valve and restart the engine and change out the fuel valve when you get home. Hard to believe, but for some reason, my fuel valve would start working again after a few pumps on the kick starter, and then the scooter would run fine until it stopped again.

Before you ride again, practice outside your shop opening and closing the fuel drain on the carb so you know where it is, and where the fuel runs out when you open the drain. If it is not the fuel valve, then I agree with Rip_City.. get a temp gauge. They work great and you will learn a lot by watching it while you drive.

[scootfast]

Sounds to hot to me. That has cost me a lot. Get temp sensor

[Wheelman-111]

Greetings:

Soft seizes SLAM to a halt, often locking up the rear tire momentarily. If it is Sputtering to a halt it sounds like fuel starvation. Check mesh ftamk filter, remove inline paper filter, verify vac line to petcock is sound & firmly clamped. If none of those, recheck float valve for stickum.

[Mrhyde20027]

I got the jet size from someone here and also did other research. I believe it was taz. I will check the fuel valve, however I do not kick it to start, it fires right back up with electric start. It sounds like soft seize....it shuts off all if a sudden and it's scary how it throws you forward some. I will also get a heat gauge and see, but I'll have to do some research to see how hot it should/shouldnt be. Thank you all for looking and responding

[Mrhyde20027]

I jet the main to 102 and drilled 4 3/4" holes into airbox. I have the gear upgrades but have not installed them yet. I kinda wanted to get this straight before I do that, but I read the gears will help keep it from getting hot.

[Wheelman-111]

Greetings:

I don't believe gears will do a blessed thing to change your engine temperature. They connect the engine to the rear wheel in some altered ratio, but the mid-range RPM is entirely under the control of the roller-weight/contra spring balance. The only time the gears directly influence engine RPM is once the variator is fully shifted, which would not appear likely since your engine seizes well before that happens.

You didn't mention several key elements of your build. Which "big-bore" did you install? What if anything have you done to ensure adequate oil delivery now that you've increased engine displacement by at least 44%? If you're still running the pump and straight gasoline in the tank, STOP!! You can add one oz. per gallon of oil - and be exact about this - OR you can purchase a pump-delete plug and pre-mix at 32:1.

That said, based on my own experience this won't be fixed by swapping jets or modifying your air box because you likely have an air leak. Assuming the shiny new bore and piston isn't already scored, don't even fire it up again until you pressure test the engine and find it. Whether or not the soapy water produces bubbles, I suggest you perform a compression test too.

[Mrhyde20027]

I have to ride it almost full throttle for about 10 mins before it cuts off. Basically like I'm driving it on main road for 10 mins. I got the 72cc kit. And I bought a new stock carb and drilled the new jet so I will still have the original stuff. I also bought a split cable so it will adjust oil with throttle plus I run 1-2 ounces in tank as well.

[MrJumps]

1 Sounds Like an air leak, remove the plastics and fan shroud and visibly inspect it and look all the gaskets for blown out oil residue, even a bit can be causing this.
2 Do you have an ct intake? If you do it is probably there.
3 What pipe do you have, the stock pipe may be too small and restricting heat into the engine.
4 When you installed the kit did you test compression?
5 What kind of fuel are you running? Highest you can buy at the pump is best.
6 what plug?

You gotta be pacific with these motors.
They make is sound like cake putting a bbk on, but in all reality its an lot of work.