TaoTao ATM50-A1 problems with starting, but idles fine By nivanov (Read 1,840 times)

[nivanov]

Hey everyone,
I recently changed the motor oil and gear oil on my TaoTao ATM50-A1 (3000 km). I've changed the motor oil enough times to not doubt myself, but with gear oil, I had to buy a new bottle of oil. For the first gear oil change, soon after the purchase, I used Mobil 1 75W-90, which has a clear side where you can see how much oil you've dispensed. I misplaced that bottle (from 3 years ago), so I went to buy a new one (still 75W-90 of course) which didn't have the clear side, so I eyeballed the amount, since the fill hole is vertical, and I couldn't get the funnel in to fill it. I eyeballed it by filling it and then letting it leak out in a vertical position - from what I've read, that seems to do the trick. This might not be the issue at hand, but I thought I'd mention it.

Anyways, here's the real problem. The scooter would have a TERRIBLE time starting, but once it starts, it has no problem idling, even after the choke stops enriching the mixture. I've recorded a video of me starting it:



I can get it started if I turn the throttle about 15% - any more or any less, and the engine just turns over without starting. However, once, the engine starts, I can let go of the throttle and it idles just fine. I've searched this forum and checked all the usual suspects: the vacuum line to the petcock produces suction, the petcock itself dispenses gas when suction is applied, the vacuum line is dry, and the carb is not leaking gas from the drain hose.

In addition to this problem, my scooter has been making a little more noise than usual while running, though it seems to not affect the performance at all. I've recorded another video where that sound can be identified, though it might be too subtle:



The noise in question is the higher pitch rattle that matches the engine RPMs. Before, the noise the scooter was making was of lower-pitch, the standard engine rumble.

[nivanov]

Another strange thing I noticed while trying to figure out this problem is that the scooter idles a lot better when it's off the center kick stand. As soon as the back wheel hits the ground (even if the scooter is perfectly upright), the idle RPMs go up. It still idles fine, but there's a noticeable differences in idle engine RPMs.

[Alleyoop]

If it starts better opening the throttle a little that means it needs more air for the amount of fuel it is sucking in. So First thing is check and clean out the air filter make sure it is not restricting some air.
It that is ok since we are having hot weather you could also Lean out the mixture a little by turning the FUEL RATIO MIXTURE clockwise. Try 1/4 turn clockwise and try to start it Just one hit if it does not want to catch turn it 1/4 more clockwise and hit the start button etc..
In hot weather the motors need LESS GAS, IN COLLER WEATHER they need MORE GAS.

The motors if adjusted right and everything working good should start with 1 or 2 hits of the start button. If you have to crank them like yours something is out of wack and it usually will be one or several of the following things:
1. To much fuel
2. To little fuel
3. Not enough air
4. To much air
5. Valves have tightened up and motor is loosing compression.
Alleyoop

Alleyoop

[nivanov]

As always, thanks for your advice, Alleyoop! I know how to do all those things except the last one. How do I check if the motor is losing compression?

[Alleyoop]

If the motor is loosing compression AFTER they get hot and the metals expand they do not want to HOLD idle and want to die unless you keep giving it throttle. Also after the motor is nice and hot when riding and coming to a stop they will want to die and you have to keep the rpms up higher than idle to keep the motor running.

The little rattling noise your hearing may just be the WEIGHTS after they get a little worn the will rattle around in their slots. You can pinpoint the noise by getting a funnel or a long screwdriver and hold it on the cvt cover where the Variator is and the noise will be amplified, you can use this method to find any strange noises you are hearing to pinpoint where it is coming from and then that helps identify the possible culprit.

[nivanov]

Great, thanks for the advice!

I don't think the motor is losing compression - the scooter idles just fine after it starts, whether it's cold or warmed up.

It seems that adjusting the mixture screw is kind of an ongoing thing as the temperature changes during the season. On my carb (and I think on all stock carbs), the screw was sealed (I drilled out the cap) and the screw itself was not slotted (I slotted it with a dremel). However, the screw itself is still located on the side of the carb and isn't really accessible via the little door under the seat, like the idle screw.

Is there a carb that has that screw relocated so it's more easily accessible? I'm thinking of replacing the stock carb. While I'm at it, I might as well get the one with upgraded jets. Do you know of a replacement carb that would fit that criteria? I've read that japanese carbs are more expensive but way more reliable, but I can't find any, since I don't know the exact brand. I've found this one:

smile.amazon.com/49cc-Scooter-Carburetor-Stroke-Upgrades/dp/B002QBNH9W/ref=sr_1_5?ie=UTF8&qid=1441312834&sr=8-5&keywords=50cc+carburetor

...but I'm pretty certain it's still China-made and the mixture screw isn't any more accessible.

[Alleyoop]

Yes they are made in China, but all the carbs work the same way whether it costs 99.00 or 25.00 for the same carb. They do not have many parts that can go bad really just 1 or 2. Also the Fuel Ratio Screw are always on the Left Side of the Carb except some bigger carbs 30-32 some have it UNDER the Intake if you think yours is hard to get at you should try one on a 250+ scoot it is a bear to get at to adjust. Some guys just loosen the clamps rotate it just enough to get the screwdriver on the screw adjust it and straightening it out again and re-tighten the clamp. But that is not a good way, you want the motor to be running to adjust it correctly the other way your just guessing.

On yours you can stick your hand under the left panel over the CVT with a screw driver and look down from under the seat to get the screwdriver in the screw to adjust it that is how I get at mine(HEHE).

[nivanov]

OK good to know! Once again, thanks for all your help!

[cyborg]

Alley has pegged it again,,,I think it's a combination problem,,,air filter dirty ( you need more air ) and the valves are getting tight

[nivanov]

I ended up buying that carb on amazon with upgraded jets as well as a new air filter that plugs directly into the carb instead of having a pipe lead to a filter box like it does on stock.

In terms of valves getting tight, could you guys point me in the right direction of how to fix that?

[scooter2]

Sept 4, 2015 15:22:51 GMT -6 nivanov said:

I ended up buying that carb on amazon with upgraded jets as well as a new air filter that plugs directly into the carb instead of having a pipe lead to a filter box like it does on stock.

In terms of valves getting tight, could you guys point me in the right direction of how to fix that?

Search youtube for "adjust scooter valves". It's pretty easy once you get the idea. If you have a manual, you can look up the proper gaps. Usually .003" - .004"

[Alleyoop]

Here you go how to adjust your valves on your 139QMB motor:
Alleyoop

[nivanov]

So I replaced the carb, and the scooter started, but slowly, as always. I noticed that the spark plug coil (or shroud, whatever you call it) was shaking quite a bit when the engine was running. I gently touched it and the scooter died instantly. I think maybe the coil isn't sitting well on the spark plug, or maybe the spark plug itself got loose - that would certainly ruin the compression! Unfortunately, while I was ducking around, the battery died from all the cranking, so now I have to wait for it to recharge a bit. I'll post an update once this problem is solved!

[Alleyoop]

If the boot cap was shaking maybe it is just loose on the COIL WIRE. The boot caps screw onto the COIL WIRE so try screwing it on the coil wire CLOCKWISE. It could also be that the Clip inside the boot cap is broke and is not holding onto the spark plug threaded tips, if so you need a new BOOT CAP.
Alleyoop

[nivanov]

Oh no, the whole spark plug was wobbling. That explains everything - the engine was indeed losing compression, though not because of the valves. After I installed the new carb, the scooter started running very loudly, so I replaced the new air filter with the old one - that one seems to hold the carb at a slight angle to the manifold, which was the source of all the noise (not the original rattle - that was just the spark plug/shroud). I'm going to install the new air filter without touching the manifold and calibrate the mixture / idle. Thanks for all the help and support!