TaoTao ATM50-a1 requires starting fluid and sometimes dies

[nehmo]

TaoTao ATM50-a1 requires starting fluid and sometimes dies

It has about a 1,000 km on it and so far has ran well. Now, however, it requires spraying starter fluid into the air intake to get it started. It also sometimes dies while riding down the road and needs to be restarted.

It still has the original carburetor and I'm considering replacing it as that is a common recommendation. I've searched around using "CARBURETOR 139qmb" and I get plenty of results. Which should I buy? What's the difference between the ones that have 18mm and 20mm (the opening?)?

Is this one (eBay giant_wave) ok? 
19mm one from Banggood.com
Could the problem also be the petcock?

Any help I appreciate in advance.

[ams417]

I'd start with a compression test on the engine. Just to rule that out. If it has good compression, move on to the fuel system. If it's has a vacuum peacock they can be an issue.

You can normally get a compression tester from the local auto parts store for a deposit. They give the deposit back when you return it.

[nehmo]

Once started, it usually runs perfectly normally. Then maybe it will lose power and die, but with fluid, it will restart.
I'm not familiar with small engines, but know when a car has bad compression, it never runs right. The exhaust color on the scooter is normal too.
I do, however, have a compression tester buried in my junk. I suppose there's no harm is doing the test, but I suspect the fuel system so much, I'm ready to try a new carburetor now. Lots of people recommend replacing the stock one anyway.

Is there any benefit in getting a 20mm carburetor rather than an 18mm?

[ams417]

I've chased a lot of issues related to compression before. I alway start there just to verify. The benifit to going to a larger carb would be to flow more air / fuel if you plan to add an after market pipe or a big bore kit. You might want to pick up some jets too for tuning.

[nehmo]

Oct 3, 2015 20:29:55 GMT -5 ams417 said:

"...You might want to pick up some jets too for tuning."

Jets? Wouldn't a new carburetor come with jets? 

[Deleted]

Yes, it would have jets installed but, maybe/probably not the ones your motor would require for proper tuning. That is why it needs to be tuned.

Bill

[ams417]

Oct 4, 2015 0:47:45 GMT -5 PirateLabs said:

Yes, it would have jets installed but, maybe/probably not the ones your motor would require for proper tuning. That is why it needs to be tuned.

Bill

Exactly. Chances of you buying a carb for your setup with the correct jet in it are slim. Just make sure the carb you pick has jets available for it. 

[nehmo]

I found this labor of love page on scooter carburetors. I understand the purpose of buying a few jets. You experimentally find the one that works best for your engine.
My choices 139QMB carburetors
18mm from scrappydogs $40
19mm from globalmotorimports $35
19mm from ezscootshop $35
19mm from ezscootshop $40
20mm from scooters_to_go $45
19mm (?) from infomarket40678 $28 (Intake Manifold side: 19mm (Outer Diameter) I don't think the others are measuring the outer diameter.
It looks like several of these sellers get their parts from the same big distributor, and they just resell the stuff on eBay. 
The 20mm one makes a good case for getting the larger opening. It's $5 more than most of them. I'm leaning toward that one.
Opinions? Please post. 

[kagetenshi]

Well, unless you are planning on a bunch of upgrades an 18mm should do the trick just fine. And you're less likely to get ripped off than trying to get a 20mm that isnt just a drilled out 18mm.

[Fox]

I am willing to bet that if your compression is low your issue is a tight valve. (no play at the rocker arm) Over time one or both of the valve tappets loses it's gap so there is always pressure on the valve stem. A tight valve is a compression loss because it doesn't allow that valve to close all the way so. It's one of the single most common occurrences with these GY6's. I have seen it literally a hundred times. It costs $0.00 to check and adjust the valves. If you have a compression tester then odds are you have a set of feeler gauges. It's easy to do and it will solve your hard starting issue.

I strongly urge you to check and adjust them.



I can also say with confidence that you probably don't need a new carburetor. Once you get the valves set it should fire up easily again but it may not want to idle right so you'll need to readjust the idle mixture screw on the carburetor you have. That is covered at this link:

49ccscoot.proboards.com/thread/429/idle-mixture-adjustment

Some carbs come from the factory with a sealed or capped mixture screw per E.P.A. directive. You can remove the cap to get to the screw. Here's info on that if you need it.

49ccscoot.proboards.com/thread/5148/unsealing-carbs-mixture-tamper-screws

Lastly, you need to know that valves and carb should be checked and adjusted at least twice a year or more to keep your scooter in top running condition. It also makes the scooter more reliable and adds to longevity. You can't gas and go forever with these Chinese scooter. They require vigilant upkeep. That's the trade off of the cheap sticker price.

[nehmo]

Oct 4, 2015 10:58:35 GMT -5 Fox said:

... issue is a tight valve...

Correct. There was no gap at all. I set both valves at 0.1 millimeter (0.004 inch). Now the engine runs better than when new.
Oddly enough, the videos I saw on the web all instructed you to take off the flywheel cover to see the timing mark. But there's a hole in the cover for the purpose. All you need to do is remove the plastic plug. It helps to first know what the mark looks like, but pic does that.




Also, 'course, you can see the position of the valves by looking at the exposed sprocket under the head cover.

But the project did produce a question for me. In the center of the pic below, you see a electrical connector with 2 wires, a green and a white.
This is unconnected in the scooter I have. What does it normally go to?

[90GTVert]

The last pic doesn't show up for me, but it's not uncommon for Chinese scooters to have connectors that go to nothing. Some even have bare end wires left in the harness.

[nehmo]

Oct 18, 2015 7:12:03 GMT -5 90GTVert said:

The last pic doesn't show up for me, but it's not uncommon for Chinese scooters to have connectors that go to nothing. Some even have bare end wires left in the harness.

Here's the image again. I'm not worried much about the connector. I realize products must have interchangeable parts in order to be mass produced, and that means the same part may be used in different models. So, it's possible this connector had a use in a different model.
I'll test the wires to see if either is hot or ground; they could be useful. I do plan to add a GPS tracker someday, and in the stool outside the bucket is a reasonable place for one.

[90GTVert]

Still broken. Here's exactly what I see :


And here's the link you provided to the pic, which also appears to be broken :
goo.gl/1kLuWr

At any rate, green is typically a ground. White is most commonly a lighting or charging wire. They could be anything though, because Chinese factories don't necessarily stick to the same colors all of the time.

[nehmo]

I compressed to 93KB this time. It's hosted on Google Photos, and I see it, but there has to be an explanation.