I got a used 50cc atv not running.I cleaned gas tank put back on.I can get it to run,but will only run with starter button pressed.as soon as you let off starter button it dies.with stater button pressed you can use throttle to rev it up.not sure what brand it is.this is the first atv I have ever worked on.any help would be appreciated.

 

This is a strange problem. Is this a four stroke engine?

Do either of these look your CDI?





The only reason I can think of for the engine stopping when releasing the starter button is if the spark generation stops. The next step will be to measure power voltages to the CDI, trigger signal, Ground and Kill switch connections... But we need to know what CDI first...

Do you see any evidence of the previous owner having hacked the wiring at all?

 

It is a four stroke.will look and see which CDI I have,and yes wiring has been hacked pretty bad.I have repaired what I can.I actually have 2 of the four wheelers.not exact same models but close.have been looking at both to repair wiring.the second one will not fire at all.

 

I do have the 5 pin CDI on mine.thanks for the info.will check all the wiring to it.

 

Good. The first thing to do is to make sure that "no spark" is the reason your quad dies when you release the starter button.

Do the following tests:

1) Remove the spark plug, hook it back up and hold the plug threads against the engine block.
2) Turn on the ignition switch and set all kill switches to the "run" position.
3) Set the parking brake, and make sure you're in neutral. This is important - you're about to bypass all the safety interlocks. If the engine starts up in gear and unrestrained the quad will get away from you...
4) Follow the big fat red wire from the battery positive terminal to the starter solenoid input terminal post. Follow the other starter solenoid terminal post (another big fat wire) to the starter motor. Take a screwdriver and short those two terminals together with the screwdriver shank. Some sparking is normal...

The starter should turn since you're connecting the starter motor directly to the battery via your screwdriver shank.

Do you see spark across the spark plug gap?

Repeat the test above exactly as outlined, only this time instead of following step 4 (running the starter motor manually with a screwdriver connection), press the start button instead.

Do you get spark at the spark plug?

What these tests do is determine if you "engine dies" problem is due to not having any ignition spark. Note that we are testing this with the starter button pushed, and with the starter button released - the two conditions where your engine runs, and doesn't run. There is a lot of info to be learned in these tests. Take your time and do these tests accurately. Repeat them to make sure they are consistent. We need good data to figure this problem out. Good data will point the way to the solution, and bad data always points down blind alleys.

 

OK change of plans....the first atv has a broke starter mount,so off to atv #2.I looked at for a few minutes tonight and its not getting fuel.I pulled carb off and will clean it out good.then will check for spark like you posted.will probably be monday or tuesday before I get back to it.I get to work all weekend.thanks for all the help and advise man.