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Post by worzx on Aug 1, 2016 12:10:44 GMT -6
Thanks, I'll check it out!
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Post by worzx on Aug 1, 2016 11:49:01 GMT -6
Hi!
I have a 139qmb 50cc engine and I have a problem with it. I would like to perform basic maintenance steps before going any further in resolving it, since the source of the issue is unknown. The first thing I would like to do is checking the valve gaps. However, this will be the first time I'm doing it.
I've searched for several tutorials and guides over the internet, but I never found any information about the gasket below the valve cover regarding to this engine. As far as I'm concerned, there is only a rubber gasket below it. I've read that this does not need to be changed/replaced. Do I have to replace it every time I remove the valve cover?
My other question would be about the gaps. Will .003 at the intake and .004 at the exhaust valve be okay?
Thank you all for your answers!
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Post by worzx on Jun 29, 2016 17:16:27 GMT -6
could be a bad diaphragm in the petcock. you could gravity feed the fuel with an inline fuel shutoff, remove the petcock and block the vacuum source at the manifold. Thanks for confirming. I thought about just getting a manual petcock and just putting it somewhere, maybe above the filter and finding a right place for it. Do you think that is the source of the problem I mentioned? |
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Post by worzx on Jun 29, 2016 16:51:21 GMT -6
Hello all,
I have a Longjia LJ50QT-3M chinese scooter with a 4-stroke 139qmb engine. I am experiencing an issue where after few minutes of driving, the throttle falls back to idle and bogs down after I stop. I have to wait a few minutes then I can go forever. This happens randomly.
I had a tip that it might be an issue in the fuel system (petcock and fuel filter). Today I checked them. As far as I'm concerned, a vacuum petcock should only allow fuel flow when the engine is running and the vacuum in the carb sucks through the vacuum hose which connects to the petcock. However, I pulled down the fuel hose from the fuel filter and definitely got more fuel than what could be in the filter and the hose.
Is this normal?
Also, do you have any ideas about the issue?
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Post by worzx on Dec 2, 2015 4:27:01 GMT -6
Does it cause a random bog down like I have? As I said, it only hapopened twice, the first at summer and the second is a few days ago.
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Post by worzx on Dec 1, 2015 9:33:11 GMT -6
Hello!
I have a problem with my scooter. This occured only 2 times, but I wuold like to investigate and fix it.
So, the problem is that after a few minutes of riding, after stopping, the engine bogs down. It's not something like wrongly set idle speed, because it is properly set, so the engine slows down to idle as it should be, and one or two seconds after it reaches idle and I completely stop, the engine bogs down. This would not really be a big problem, but after this, I cannot start the engine with the starter, neither with the kickstarter. I have to wait a few minutes until it starts up. The first time, I was waiting for about 5 minutes then I could start, the second time, after 2 minutes of waiting I decided to move it home. I was pushing it only for 10 seconds, then I tried to start it, and it started up just as it used to.
I was getting some advices that the problem may be something with the mixture, especially the auto choke. Now, as I know it only helps to get a higher RPM at start to not bog down when it's cold. However, I think if it's completely broken and won't extend the needle, it would only cause constant higher RPMs, but correct me if I'm wrong.
Also, I read that this can be caused by the wrong adjustment of the valves. Does the valves have to be readjusted after some time? The scooter has 1300 kms, and I think if it sohuld be, it won't be this soon. The problem occured above 1000+ kms.
Can anyome help me with this problem?
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Post by worzx on Jul 15, 2015 14:34:27 GMT -6
Yes, I've been thinking about getting one, especially for temperature, but I think I'll go with an all-in-one if that's exist and I can get my hands on it.
The sound apears at the RPM which is right the maximum for the stock CDI. At the first run today, I did not event got it with the stock, but I immediately got it with the new one, and after that with the stock too.
Anyway, thanks for the help. I'll look into the CVT and the gears, and I'll write if I have progress.
Thanks for the help again!
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Post by worzx on Jul 15, 2015 12:54:28 GMT -6
Looks like you did not get my point, sorry, I'll try to explain it better. I don't blame the CDI because of the sound. I just want to know if higher rpms (which the new CDI allows) can cause problems like this in the future, because it revs more, and I assume the engine gets warmer and the materials are affected better. So basicly my point is that this problem is caused by the higher RPMs, or it would appear with the stock CDI, which won't even let the engine to that RPM where this appears if I don't drive it for a long time.
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Post by worzx on Jul 15, 2015 12:06:18 GMT -6
Okay, thanks, I'll check it out probably during the weekend. Also, I did not really found the source of the sound, I can only predict that it's more likely coming from the back end, somewhere near the wheel, or the back of the CVT. However, I'll check it out as I said.
Some more information about the noise, maybe it would help to determine the source: The whole chassy is vibrating as the sound "pulses". I can feel it on every part of it, including on the throttle lever.
About the CDI, I was asking if the high rpm can cause malfunctions like this. I mean, if I find the problem, fix it and replace something if I need to, is it possible that the high rpm will kill it again in that short time?
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Post by worzx on Jul 15, 2015 10:57:28 GMT -6
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Post by worzx on Jul 15, 2015 9:02:10 GMT -6
Thank's for the reply, I'll check the CVT. However, I would like to ask if something like that is caused by the CDI, so because of the higher rpm, and if so, what should I do to prevent it?
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Post by worzx on Jul 14, 2015 12:58:52 GMT -6
Thanks for the reply. I'll make a video if I can, until then, I'll try to get some more informations on it. Remembering back at first I thought something stuck in somewhere, I mean it felt like I'm braking the rear wheel (where a drum break is applied). However since the performance bottleneck applies at every rev, the sound is only at high rpms.
Since I was hearing on the left side when driving, I assumed something is wrong in the variator. Can something cause this in the variator? A washer maybe?
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Post by worzx on Jul 14, 2015 12:31:24 GMT -6
Hello everyone!
I would like to get some help with my 50cc 139qmb engine powered scooter. Today, bought a new CDI, the common blue racing one for the scooter. That was the only one the store had available which known it has no rev limiting. So I installed it, started up the engine, everything went fine, actually the engine started easier than with the stock one.
I took the scooter on a drive, it had better acceleration, top speed, so overally better performance. However after about 2-3 kilometers when I accelerated from a stop, a strange sound appeared. It appears when the engine is revving higher than with the stock CDI, this is about 50-55 km/h. The performance also got overally bad after this, basically about the one I get with the stock CDI.
I let the engine cool for 10-15 minutes, gave it another go, but the sound appeared at the same speed and it actually gets weirder in higher RPMs. When I got back, I installed the stock CDI and gave it a try. The scooter goes well with it, I mean it has about the same performance as it was before the new CDI, however the noise also appears here at high RPMs, when the CDI is limiting, but it is not that loud. Also it can be heard when the scooter is on the stander with both the old and the new CDI.
Description of noise: It is some kind of a high, sharpy sound, getting louder as the RPM goes up. It also kind of "vibrates", so it is not continous, it starts, gets loud in about 1-1.5 seconds then it disappears slowly, and it starts again. When I ride the scooter It is more louder and looks comes from the left-side, but if the scooter is on the stander it's hard to find it's source.
The scooter ran about 1000 km, bought it newly from a dealership.
Anyone can help me find the source of this sound and bottleneck?
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