Mini bike won't start

[Dimeman]

I just built a mini bike from scratch. It has a 6.5 hp engine. I had just completed the build and was out on my first test run when the engine crapped out. Had it running for about 20 minutes with no issues. Just won't restart. Engine is about 3 years old and has always started. I was not in use for the last three years. The gas was in there for those three years. ( I think) I had it running prior to the test run for the last three months. Every now and then I would start it and leave it running. It would idle but when it was at full throttle it was not smooth. It sounded like the rpm's were going up and down. Any advice on where to start to get her going again?

 

[KartFab]

Clean all the varnish that has accumulated in the carb out, clean out gas tank, fuel line, and change oil.

 

[bob58o]

I know I had a decent post somewhere, where I laid out a universal plan of attack for "MY ENGINE DOESN'T START".... Lemme look.

But KF's suggestions should be done, no matter what.

Same for every engine doesn't start question....
Does it try to start???
Did you recently have the camshaft out?

I'm tired... so this might not be as universal or complete as it could be, here's what you get. LOL

1.) Make sure there is a spark. Take out plug and put wire back on. Lay against the block and pull the cord. Look for spark. If no spark then check ground wire, (EDIT: also Kill switch wires), then coil gap, then try a new plug. If still no spark, then maybe need a new coil.

2.) Make sure fuel is getting to the carb and in the bowl. Check the line. Check the bowl. EDIT: Check the filter.

3.) If all the above seem ok, You can spray carb cleaner or starting fluid though the carb with the slide open and try to start it. If it starts and dies or tries to start, then you probably need to clean the carb (EDIT: or lines, tank, or fuel filter... because you have identified a fuel delivery issue).

4.) If it still doesn't try to start, take off the valve cover and make sure everything looks hunky-dory in there. Is the lash set correctly?

5.) If can't find anything wrong and still won't start...Take off the flywheel and check for a sheered flywheel key.... The timing is probably off due to a sheered key.

6.) If key looks good.... Check compression. Can do this earlier is the diagnosing too. Pull spark Plug an put thumb on hole. Pull cord. Check for pressure. ... Compression test. Leakdown Test. New Head gasket. Hone Cylinder. New Rings. Valve Job.....

By the time you get through all 6, you should have identified the issue.

 

[Dimeman]

Thanks for your help. I will give it a try and hopefully I can get it running.

 

[Dimeman]

I took apart the carb and cleaned it inside and out and dumped the old gas. Started right up but ran really rough....just like before. I played with the choke and it ran a lot better. I still have the choke open a smidge to make it run that way. Took it out for a spin and it was working perfect. I copied the guidelines from this you tube post. Thanks again for your help. https://www.youtube.com/watch?v=KiWItZSJfPs

 

[OzFab]

Unfortunately, that's a basic or "general maintenance" clean; your carb may need more work than what you see in this vid; eg: "spray through the orifices with carb cleaner to dislodge & remove all dirt" doesn't always work; general practice is to poke through said orifices with thin wire or a tip cleaner...