Gas Issue, Vacuum Issue....not sure  By  scripting25 (Read 3,516 times)

He swapped his out for one he knows works, and symptoms are still the same.

I'll get a new spark plug and test soon. the current plug might look bad since the scooter has been acting up for a while, and die'ing and sputtering out hasn't helped it's look too I'm sure.

I'll also check around to see if I can an adjustable needle diaphragm that can drop in.
I'll look at getting an adjustable carb if not.

That's fine and dandy but I don't see how that will help resolve the issue it's having unless by it running to rich cause's the motor to stop running after it's warmed up.
Or unless a weak spark cause's it to not work. That's been 1 of my questions all along, does a spark having anything to do with the motor after it's been started? could the motor be looking for a stronger spark as it warms up and a weak spark can't supply that extra spark so the motor dies out.....kinda thing?

agreed the plug looks like the engine is running too rich,,,have you checked the air filter?

Curious if you ever pulled the spark plug right away when it wouldn't start to see if you have spark or not?

Use one of these if you like to spend money



spark tester

Yes. Sounds like a vacuum leak. I assume you have a vac operated fuel pump or petcock. 

Yes, I do have vacuum petcock.
I ordered a new 1 but the gasket where the nut threads on wasn't 100% correct and it was leaking so I put the original back on.
I'll take the petcock with me and check on a gasket designed for gas flow and I'll switch it out and test.

Ladies and Gents, I think there is two problems. his coil or CDI is bad.... and when running at WOT, the vacuum pet cock is closing (if if pump equipped, the pump quits pumping)

On many of these scooters, when you run wide open, the pump or petcock (depending on where your tank is) will quit and it will act like it's out of fuel. It gets worse if the belt is old or the valves are out of adjustment, they will act up more. It's a balancing act.

If the coil is bad, it will have ok spark when cold, but then as it warms up, the spark can get weaker. The higher the revs, the more juice the plug will require to fire. Remember at 3000 rpm, which is just above idle, the plug fires 50 times a second or 100 times a second at 6000rpm. Once on the compression stoke, advanced timing will fire just before power stroke and once just before the exhaust stroke is completed. This puts tons of stress on the coil and CDI. CDI's typically act up when warm and at random when it feels like it. They are cheap enough, I'd change both.

As for the Vacuum problem, it happens when you are going down the road happily, at full throttle, then all of the sudden, the scoot just dies.... the way to tell, is to immediately close the throttle for about 5 seconds while it's slowing down, and then start to open the throttle, slowly, about half way and see if it starts running again. Not running at full throttle for extended periods of time is the only fix, other then putting in an electric pump or manual petcock. A worn belt seems to aggravate it as you tend to run WOT more often.