TaoTao ATM-50A1 has stopped idling... {solved}

[djahd]

After unsealing, cleaning and tuning the carb, per this thread:

49ccscoot.proboards.com/post/340780/thread

... I had what I thought was an adequate idle. It would wander up/down a couple hundred rpm (by my ear, anyway) over time, but the idle mixture and speed screws were interacting as you'd expect and I could find a broad "optimum" setting for the mixture and a comfortable idle speed.

I took the bike out to test ride it today. Apart from it being my first time on a motorized 2-wheeler of any kind, it went pretty well at first. Then it started stalling occasionally at idle. By the time my practice session was done about 45 minutes to an hour later, it would no longer idle at all. I would have to start it, and keep the throttle in the low range of the needle in order to go anywhere. Tried tweaking the mixture and speed screws again in the field, and it turns out something has changed, such that:

Idle mixture screw has no effect, and it doesn't idle even with the idle speed screw bottomed out.

Start it and unless I rev the throttle, it will die within seconds. Any attempt it makes at idling is VERY slow.

Okay, I've got a couple of pieces of data that might be of interest, and I've started putting together a list of things to check or investigate...

I plumbed a mechanical vacuum gauge into the line from the manifold to the petcock. When running, the needle swings rapidly (at rpm speed) between 0 and 10 in hg, and up to 5-15 in hg at higher throttle. Is it normal for the vacuum to pulsate that severely at engine speed? I know on a car that wouldn't be so good. Are the vacuum levels adequate?

Beyond that, I've already pulled a few things I can check from searching the forum:

Spray carb cleaner (or propane?) around to see if the rpm changes due to a vacuum leak anywhere. I figure I can shim the throttle open enough to keep it running while I do this test. Does that sound like it will work?

Remove and observe the plunger on the electric choke thingy. Connect to 12v and it should extend after less than a minute, right?

Take the carb back off and check everything to see what has shaken loose, jammed or clogged all of a sudden.

Any other ideas? Corrections?

It seemed like I was getting reaaaallly close there for a bit. No way I'm turning it over to the nephew stalling at every stop.

It was also a real blast learning to ride this thing, despite the idle problem descending on me. I wore decent gear: full helmet, gloves, leather coat, hiking boots... so not totally unprotected. Managed not to fall or crash into anything. Got a good deal of practice starting/stopping, right/left turns of various radii... Even managed to coordinate the turn signals after a while.

I might just have to take the class, get my motorcycle endorsement and find something for myself!

Thanks,

Djahd

[FrankenMech]

Sounds like something in the fuel is clogging the carb or there is water in it. Clean it again and install a good fuel filter like:
www.amazon.com/gp/product/B0021Y2XQM

The paper and sintered bronze filters are no good.

Water in the fuel is a constant problem.

The pulsing vacuum is normal on a single cylinder engine.

[ratdog]

I would remove the air cleaner and look at the butterfly. When you adjust the throttle stop screw, you should se a difference in where the butterfly sits. When you back the throttle stop screw almost all the way out, the butterfly should be closed. Screw it in, and the butterfly should open. If this does not happen, you now know exactly where to look for the problem.

In order for your mixture screw to have any effect, the butterfly valve must be almost totally closed. My suggestion would be to screw the mixture screw in all the way, then back it out a turn and a half and forget about it. Use the throttle stop screw to adjust the idle from there. If you have movement of the butterfly when adjusting the throttle stop screw, and still can’t get it to idle, you may have a clogged polit jet. That would mean removing the carb and removing the jet and cleaning it with carb cleaner. Of course you would anso insert the straw into the passage and blow that clean. I think I would also replace the fuel filter while you have the seat out

[djahd]

I've managed to get the TaoTao idling again. It's running well enough now I just turned it over to my nephew.

FrankenMech said:

The pulsing vacuum is normal on a single cylinder engine.

Thanks for the reassurance. It makes sense, but I'd never seen it before.

Sounds like something in the fuel is clogging the carb or there is water in it. Clean it again and install a good fuel filter...

The paper and sintered bronze filters are no good.

Water in the fuel is a constant problem.

So I started by draining the carb bowl. Then I disconnected the fuel line from the carb, tested the vacuum petcock, pinched off the hose from the tank and pulled the fuel filter, then drained some fuel from the tank. Out of all of the fuel I collected, there was no visible trace of water or sludge. The fuel filter had some dirt in it, which I was able to rinse out with carb cleaner and compressed air.

This filter could be OEM for all I know. It's translucent plastic with what appears to be a plastic mesh filter element. It was easily cleaned. If it's original, I most certainly will swap it for a better one the next time I get the bike to work on.

The upshot is, however, there wasn't anything other than whatever was trapped in the filter to interfere with flow. It could have been enough.

Just to be sure, I also pulled the carb and reinspected my work.

ratdog said:

In order for your mixture screw to have any effect, the butterfly valve must be almost totally closed.

I double checked the butterfly was closing completely with the speed screw out and only slightly open with it fully engaged.

...you may have a clogged polit jet.

If there was anything at all I discovered inside the carb it was a little dirt in the pilot jet. Specifically, one of the atomizer holes in the side of the barrel was clogged so no light shone through. There might have been some dirt in the orifice, too, but it wasn't easy to see if it was a round hole or something else.

So I cleaned it thoroughly in hopes that it would help.

Whatever ultimately caused the problem, when I put it all back together it would idle again.

It's not perfect. When warm, the idle surges every little while, running up a few hundred rpms for 5-10 seconds before settling back. There's also less of an obvious peak adjustment for the mixture screw than I thought I saw the other day. Also, the idle is either pretty slow, or kicks way the heck up as you adjust the speed screw. It seems it's impossible to set it to an intermediate idle speed between the two... and I think the low idle speed is a bit slower than it ought to be, but I'm judging that without a tach.

I sprayed some carb cleaner around while it idled and didn't get any response, so if there's an air leak it's not a gross one.

With all that, I was able to ride it down to the park and take a few turns around the parking lot without any hesitation or stalling. Throttle response seems to be great all the way up, it's easy to start off, and it decelerates well when the throttle closes. No backfires or sputtering.

So, in the interest of letting my nephew get back on the road, I drove it over to his house and gave it back. The three miles or so at speeds of up to low 30-something mph all went off without a hitch. I didn't have any problems riding. It brought back memories of my bicycle riding days, interacting with the cars and drivers around me in much the same ways.  

All said, I've learned a bunch, managed to fix my nephew's scooter, began to learn to ride, and made my first purposeful trip on one. I'm sure I'm not completely done working on the thing, but at least for now he'll have a chance to use it to get around with again, until the next thing goes wrong.

I already have a few more questions to research and perhaps ask about.

I can't begin to say how much I appreciate the help this community has given me on this project. It's been simply awesome!

Thank you,

Djahd

[FrankenMech]

Those plastic mesh filters are about the best you can get. The one I listed is a plastic mesh filter. They can be cleaned by back flushing with carb cleaner.

Alcohol fuel (E10, E15) will cause the rubber fuel lines to crack internally which will spall off small particles of rubber that can plug carbs. The lines will eventually crack all the way through.

Good luck with everything.

[GrumpyUnk]

If it comes back, I would consider replacing the 'pilot' jet with a size or two smaller. When you cannot adjust the mixture well, and have the screw almost fully closed to get a decent idle, it may be feeding too much fuel. I have one like that and am going to install a smaller pilot to see what happens. As it is now, I find the idle to be weak, susceptible to variations and readily stalling if I goof with the throttle. To keep it running I have to have the idle rpm too high, IMO.
tom

[djahd]

Following up on this thread to report the final results...

Oct 16, 2018 11:28:45 GMT -5 GrumpyUnk said:

If it comes back, I would consider replacing the 'pilot' jet with a size or two smaller. When you cannot adjust the mixture well, and have the screw almost fully closed to get a decent idle, it may be feeding too much fuel.

Thank you, Tom. I did have a chance to tweak the carb again last weekend, and what turned out to work best and easiest was to undo one thing I did while I had the carb apart after it had stopped idling for us... I took out a second  washer I'd put under the main needle.

It seems pretty obvious now that I'd bumped the main metering a little too rich, swamping the pilot jet just as you suggest. Putting it back to the way I had it the first time around restored the same behavior I had then:  At a couple of turns out, it would slow down if I leaned it out any  more. At about 3 1/2 to 4 turns it peaked and would  slow down a little if I richened it any more.

With the mixture peaked, once again I can smoothly adjust the idle from way too slow all the way to starting to engage the clutch, or anywhere in between, using the idle speed screw. The idle is stable, now, without surging. Nephew reports it's running much better, without the tendency to stall or to bog down on initial acceleration that he had been seeing.

So, things are going about as well as I can ask for. Thanks again to the forum denizens who've offered their help and advice.

Djahd