Hard to start but runs good - atm50-a1

[techbilly]

My 2018 tao tao atm50-a1, riden 4000 miles, takes several minutes to start. Each try it fires once or twice which releases the Bendix. I let the starter stop, then repeat this for maybe 5 minutes until it finally keeps running and runs great. If I try opening the the throttle, the starter stays engaged but it makes no attempt to fire. I have adjusted valves, replaced carb, plug, hoses, fuel valve, CDI. Compression is 115 psi, maybe that's the problem? Thanks for any advice.

[Zino]

If you dont run seafoam in the winter and she sat for a long time with old gas

pilot jet will gum up
You can boil it in vinegar and use a fine wire to clean it out

[GrumpyUnk]

On the occasions you get it running, have you adjusted the new carburetor idle mixture and speed? It seems to me that those must be set and adjusted so when the engine fires with the byvalve allowing fuel & air to pass through, the engine base idle circuit is also functional. The combination is what allows the cold engine to run. I think.
The temperature sensing valve in the byvalve will slowly cut off the mix it was providing, and transition to the idle mix. So... the idle must be set up properly for hot running.
There is a tiny pinhole in most carb float bowls that fills a vertical tube cast into the float bowl with fuel at all times. If the pinhole is clogged, the byvalve will have no fuel....... bazinga, gotcha.
The tube fills, and the byvalve uses that fuel along with air coming in at the air inlet(opening around 9-10 o'clock) to mix with the fuel metered from the tube cast into the float bowl. No fuel could be a problem.
It can happen to new carbs also... If you drop the float bowl, there should be fuel in the bowl, AND in the little tube. If not fuel in the tube, it will be muy difficult to start.
A helping action in most would be to cycle the twist throttle several times. Each cycle should squirt in some fuel via the accelerator pump. Some do not have one, and I have not looked to see how they work...
tom

[techbilly]

Thank you for this. I have not tried adjusting the carb. It behaves exactly as the original. You could be correct, but I tend to eliminate carb. problems at the moment. I have tried pumping the throttle before trying to start but it doesn't seem to help. It's main idle setting is fast enough for it to keep running well when it starts and seems to be quickest way to start. My original description should have said "backfire-like firing" releases the Bendix. I'm trying to be open to anything, but now I'm inclined to focus on 1. is 115 psi sufficient compression when other bloggers say it should be 175 psi and 2. if so what might cause too much spark advance or something to make it kick out the Bendix, considering that I changed the CDI and nothing changed?

[geoffh]

Most pilot jets will block easily you need to clear every passage way in the carb I do this with copper wire, air and water ,a spray with carb cleaner won,t clear the tiny tubes.

Geoff

[techbilly]

So I'm hearing it's still the carb, even a new carb from Amazon, adjusted as delivered and getting the same results. As of now, I plan to re-read the above recommendations and try them, easiest first.

[FrankenMech]

'New' carbs can often be surplus leftovers from a scoot manufacturer's production run or even a lot of defective rejects sold on the surplus market. Only buy carbs from reputable scooter parts distributors. Carbs and parts purchased from eBay and Amazon are often just surplus parts of unknown pedigree. Caveat emptor.