Idle fine dies during acceleration

[zemuz]

I've got a TaoTao (VIP) 2012; GY6, 139QMB 50cc scooter that keeps giving me issues.
Got it second (third?) hand from a previous owner who had said that it worked fine until it just sat for 3 years taking up space.

Got it home and I did an oil change, drained fuel, changed fuel filter, changed air filter, new plug, new battery and did a new OEM  carburetor and got it to start up and run.

After a few adjustments with the small idle screw? I was able to keep it on and seems to have a constant idle right around 1700rpm.

Rides just fine, slow is slow off a start... have to get like 3000rpm when sitting on it for it to start going but figured this is typical for a 50cc

The issue I'm having...
Will be riding fine, usually at full throttle and cap out around 6000rpm and 35-40mph on flat. I'll come up to a stop light and have to stop for a short period of time. Come to a full stop, scooter get's settled into it's idle than when it's time to take off again give it some gas and it just dies. This happens either by a slow start or going into full on. To get it to start back up I need to give it full gas while running the starter and it gets back on and starts going. If i keep the brake on and throttle held at around 2500-3000rpm I can avoid the stall out. I have to do a rolling stop at a stop sign to prevent the same condition or it has to be very abbreviated, like a 1-2 second full stop.
This seems to be the same for either cold or hot engine

Thoughts on what I can check to correct?
I'm looking at replacing the valve in the fuel line in case there is a little build up in there; also plan on upgrading the piston to 47mm for the extra start power and hopefully top end, but would like to have it running as expected first as a baseline before doing that work.

[scooterpimp]

Have valves been checked or ajusted lately?

[GrumpyUnk]

I would be looking at the carb, given that it runs ok at high speed. If the idle is solid, no evidence of wanting to die, then take a look at the flat metal arm attached to the throttle linkage. It should start to push on the vertical rod sticking up from the carb immediately when you start to open the throttle. The rod operates the squirter that takes care of mass difference between air and liquid fuel, causing improper mixture due to inability to accelerate at the same rate. As you open the throttle, look into the carb and observe the tube sticking into the airflow area from about 3:00 o'clock. It should spiff out a bit of liquid fuel on each movement of the throttle linkage. If not, accelerator pump is clogged or inop.
tom

[zemuz]

Scooterpimp - I haven't checked the valves yet; will add that to my list to check/try

GrumpyUnk - Thanks for your reply and detailed explanation, this will make it easier to track down and check.


You would think a new OEM carb would just work with just a slight adjustment on the idle screw.

[kagetenshi]

I have the same make, model, and year scoot. The OEM carbs come jetted lean most of the time. I also found that raising the needle in the carb helped with the stumble on acceleration from a stop. If the needle isn't adjustable you can find very small washers roughly 1mm thick that should be able to fit over the needle but not slip through/obstruct any other parts in the diaphragm. Hope that helps some.

Side note. That year taotao was notorious for being shipped with a 63cc instead of a 49cc motor. It might be worth measuring your cylinder before doing a bbk. I would think that 9cc extra wouldn't do too much for the money.

[ratdog]

My first thought is that this sounds a lot like a “lean surge”. Because the new carb would have come with its own jets, there is a possibility that you are jetted too lean. As mentioned, raising the needle should help some. I’d be looking at the main jet in the old carb and in the new carb. If the old carb has bigger jets ( larger number) it might be worth cleaning them up and switching to the larger jets.

In case you haven’t already read the procedure for adjusting the mixture screw, here’s what you want to do... get the bike warmed up and set up on the center stand. Now adjust the throttle stop screw until you have the lowest speed idle that the bike will still run at. Now go to the mixture screw adjust the mixture screw to get the highest idle and you have the mixture set as best as possible. You may want to go back to the throttle stop screw and increese the idle slightly so if you make a sudden stop the engine dosent die.

If you do decide to join the BBK crowd, I’d go up to the 50 mm piston. Hopefully you are only doing this once, why not look for that extra tourque?

Might also be a good idea the Check for air leaks. Easy way is to set the warm motor running and spray some starting fluid or carb cleaner around the intake manifold and engine side of the carb. If your sucking air, the engine will speed up when you stray