Chinese scooter problem.. (Longjia LJ50QT-2L)

[cptego]

So, I own a VGA Digita (Longjia LJ50QT-2L), and I have a minor problem. I was out scooting a couple of weeks ago when the engine died on throttle. Couldn't start it up again. I then changed the spark plug, and the scooter once again would start up and run fine. After driving about 50 km though, the engine died again during throttle, couldn't start it up again. Then, a couple of days later, the scooter now starts and runs fine again. Any idea what the problem could be?



I was thinking about cleaning/adjusting the carburetor, but unfortunately, I don't know a thing about scooters. This is the carburetor in it:

 

[90GTVert]

You may be running lean and soft seizing. When they soft seize the piston expands more than the bore and the engine stops until it cools. Sometimes they start right back up, sometimes it takes a few.

I think starting out by cleaning the carb is a good plan. If it looks clean, consider installing a larger main jet and/or moving the needle clip down a spot to richen the mixture depending on what throttle position you're having issues at. Main jet for 3/4-WOT, needle for 1/4-3/4 throttle.

Make sure all connections around the air box and carb/intake a secure. Check the condition of the fuel lines and filter.

4 vids in this series that may be of some use :
www.youtube.com/watch?v=UipC6DLD-EE

More help including a couple of cleaning articles :
49ccscoot.proboards.com/board/12/carburetor-intake-tech

[humanshield]

You can check for a "soft seize" by immediately trying the kickstarter when it stops. You have to do it quickly because it will cool quickly once it stops running. If the kick starter feels harder than normal to move or doesn't move without a lot of force, the motor is seized.

The electric starter may also not work during the seize.

A compression check would be a good idea. Seizing tends to lower compression.

You could also have a vacuum leak causing the fuel flow to be inadequate to keep up with the engines demand for fuel. Could be as simple as needed a new fuel filter.

I always try to tackle these types of problems by first narrowing it down to a fuel issue, mechanical issue or electrical issue.

[cptego]

Thanks so much guys, I'll see what can be done, my own lack of expertise is probably the biggest problem I'm having right now Been reading about how to tune the carburater and other things so I can fix this problem. You guys think it could possibly be moisture in the spark plug cap? I've read that this in particular can be a problem with this model. Was thinking about ordering a silicone plug cap..

[humanshield]

If you've discovered that moisture has been the problem with that particular one, I would say you have a fairly good shot that that could be your issue too.

But, if you dry it out and it's not raining and you don't go through puddles I don't see how it could happen again on a dry day?

[cptego]

Mar 31, 2015 14:05:49 GMT -5 humanshield said:

If you've discovered that moisture has been the problem with that particular one, I would say you have a fairly good shot that that could be your issue too.

But, if you dry it out and it's not raining and you don't go through puddles I don't see how it could happen again on a dry day?

Well, where I live, it rains alot, and a scooter that dies out when it rains is pretty useless here. I guess someone would only discover this issue in a cold and rainy climate, and the scooter is chinese made, so the manufacturer probably did not consider this. People are saying that I should get a silicone cap and wire. I'm getting a fuel filter too, since they are so cheap. Also going to clean the air filter, and as mentioned, attempt to clean and adjust the carburetor. 

Oh, and someone also said that there has been some problems with defective stators not generating enough voltage with my model..

[humanshield]

Ok. if you're in a very rainy climate I could see how that might be a ongoing problem. Although people ride their scoots in damp rainy weather with no problem. Your scoot probably has a typical QMB139 motor so it really shouldn't have any problem with that more so than other scooters I would think unless the design directs water to the spark plug lead?


Try removing the gas cap next time it stalls and see if you're maybe getting a vacuum in the fuel tank preventing fuel from flowing.

Also next time it stalls and wont start, (after you've done as I suggested earlier and made sure it wasnt heat seized), remove the fuel line leading to the bottom of the carburetor and see if fuel flows freely from that line that feeds the carb.
That should tell you if you have a fuel supply problem.

If not.....

Carry a spare spark plug with you and next time it stalls, immediately disconnect the spark plug lead from the engine, connect it to your spare spark plug and lay it on the engine then crank the engine over with the electric starter and observe if the spark plug is sparking a nice bluish white spark.

That will determine if you're having an intermittent ignition issue.

There are a lot more things it could be but this is a start and will hopefully narrow the search.

[cptego]

Thanks, you have been very helpful. I will do all of that. The scooter is only a year old, and although I was aware that it's a low quality scooter, I did expect it to perform better.

[benny]

interesting. this same model number scooter here in australia is called a MCI riviera.

[humanshield]

Mar 31, 2015 19:26:11 GMT -5 cptego said:

Thanks, you have been very helpful. I will do all of that. The scooter is only a year old, and although I was aware that it's a low quality scooter, I did expect it to perform better.

Well, they pretty much all have the same motors.  The rest is copied or done by individual Chines or other firms.  They design a frame or work around an existing frame then make plastics and hardware for their specific version.

What I'm getting at is that with a little patience and know how, you can resolve these issues.

It's just a matter of actually discovering exactly what the issue is sometimes. 

Do try a better quality spark plug cable and boot.  And also the things I suggested and above all, PLEASE report back on your findings and if any of the suggestions DO (or DO NOT) help.

[humanshield]

Oh, you mentioned one thing earlier that now has me thinking about the air filter....

Make sure it stays dry. I'm wondering if it's possible your air box design is allowing water to enter the air box. If so, and you have a paper air filter , it could clog enough to restrict the airflow enough to cause the problem you're having.

Just a thought.


Ok, gotta run out to a scooter service call to make a few beans.
Talk at ya later,

[cptego]

I got a question about the carburetor, I'm reading this page and I don't really understand the terms "high jet" and "low jet", is that another way of saying idle and mixture screws?

[humanshield]

Does your carburetor have a H and L adjustment screws?

I think your scooter may have come in a 4T and a 2T configuration from what I've read?
Is yours a 2 stroke?

[cptego]

Apr 1, 2015 8:20:15 GMT -5 humanshield said:

Does your carburetor have a H and L adjustment screws?

I think your scooter may have come in a 4T and a 2T configuration from what I've read?
Is yours a 2 stroke?

2T. And it doesn't look like it has those L and H screws, judging from the pictures..

[90GTVert]

That site is for goped type scooters. They use piston port engines and some carbs for them have high and low speed adjustments. Our carbs are not like theirs. You should have an idle mixture screw to adjust idle to maybe 1/4 throttle mixture as well as a pilot jet. The pilot jet shouldn't need to be messed with unless you can't get the idle mixture right. A main jet in the bowl is for 3/4 to wide open throttle. It is not adjustable, but must be swapped when tuning. A needle controls mid throttle and it has a clip that can be moved up or down to lean or richen the mixture in that range. All of that stuff is shown in the vid series I linked to earlier.