TaoTao ATM-50A1 plumbing questions... {SOLVED}

[djahd]

Hello,

My nephew's scooter is a 2015 model with about 3k miles on it. The previous owner dumped it in a collision with a car, causing a fair amount of scuffing and some breakage of cosmetic bits. I'm well on my way to putting it back together, but I may need to undo some "tweaking" the other guy did to the engine before it'll run right again.

My Main Question:

Has anything changed in recent years about the way the vacuum plumbing is SUPPOSED to be?

As received, there is a hose running directly to the fuel valve from the intake manifold and there is NO tee and line to the carburetor. On the carburetor, there is one port on the (rider's) left side of the carb. It came with a short piece of hose that is molded with a 90 degree bend in it and the end is cut off at a slant... and is open to air.

With this arrangement, the bike starts and seems to run pretty well. You can adjust it for a low but steady idle, but it takes as long as 15 seconds to return to idle after you rev it at all. It just roars along for a long while before it SLOWLY settles back down to idle speed.

I'm not sure the idle isn't too low, as I don't have a tach, but if you crank the idle speed screw up, it doesn't change much until you reach a point where it suddenly gains a LOT of RPM. This carb is one of the ones that's otherwise locked down, so I haven't looked into any other settings.

2nd Question:

I patched together a tee and hoses to hook it up the way the videos say it's supposed to be... and it barely starts, doesn't like to stay running, doesn't respond well to the throttle, and stalls after a not very long time.

If this is the way it's supposed to be plumbed, then what next? Carb rebuild? Any thoughts or ideas?

Thank you!

Djahd

[gsx600racer]

There should be a auto/vacuum petcock on the bottom of the fuel tank



or one installed remotely on the frame of the scooter.



On both petcocks, the fitting that looks like the 90 degree bend is the vacuum side and that connects to the intake.

The other is the fuel side and that goes to the carb.

[djahd]

Thanks, gsx600racer.

I have the vacuum petcock mounted on the left side frame. The motor definitely gets fuel when that's connected directly to the manifold the way the previous owner had it. No problems staying running, but issues with slow return to idle.

As soon as I connect vacuum to that port on the carb, everything changes and the engine doesn't want to run.

Things I can/will do then:

Test the vacuum petcock by disconnecting the fuel line from the carb and routing it into a jar; apply vacuum to the diaphragm with a pump. I would expect to see fuel start flowing, and stop again when vacuum is released, right?

Make sure the fuel filter isn't clogged.

If the above are okay, do we start looking at the carb? I'm thinking the carb started crapping out on the previous owner, and he jury-rigged something to keep the bike running rather than fixing the actual problem.

Thanks,

Djahd

[djahd]

I just tested the vacuum petcock and it acts just like it's supposed to. Doesn't leak. Pull a vacuum and fuel flows out as fast as the fuel line can handle.

Somebody, please answer my main question:

Do the videos on the Taotao ATM-50a1 showing vacuum hose routing still hold true?

90GTVert's un-crating and pdi videos were done in 2013, and any others I've found showing vac hose routing have been of similar vintage, and I want to make sure there's been no design change before 2015 when this bike was built.

If true, then I have to put the plumbing back to original and start debugging from there.

What say you?

Thanks!

Djahd

[FrankenMech]

Leave the 90° bent tubing alone. It is an atmospheric vent for the carb. It is not connected to anything.

There is one vac line from the intake manifold to the vacuum petcock.

There is a crankcase vent from the valve cover to atmosphere or the air filter assy.

I don't know if your scoot has an EGR system.

[djahd]

Oct 7, 2018 14:27:33 GMT -5 FrankenMech said:

Leave the 90° bent tubing alone. It is an atmospheric vent for the carb. It is not connected to anything.

There is one vac line from the intake manifold to the vacuum petcock.

There is a crankcase vent from the valve cover to atmosphere or the air filter assy.

That is EXACTLY how the scooter was plumbed when we got it. THANK YOU for confirming that, Mr. FrankenMech sir, so I don't waste effort on outdated info. That's what I needed to know.

I don't know if your scoot has an EGR system.

As far as I can tell it doesn't have EGR, but just a PAIR system exactly as in 90GTVert's video, here.

So, what remains are the original problems:

The engine returns to idle VERY slowly after you rev it at all... many seconds of roaring along before it gradually slows and then drops to idle.

The idle is basically unaffected by the idle speed screw, before what I assume are higher jets taking over, and while it's fairly stable, seems to be too low to my ear.

What's the easiest way for me to put a tach on this thing for diagnostics? Can I pick up a rpm signal anywhere? I have a multimeter with a frequency counter feature, if that's of any use.

What could be the problem with the slow idle recovery? I think some of the basic tuning tutorials are in my future...

Thank you for your input.

Djahd

[FrankenMech]

EGR = PAIR

Basic carb tuning is required based on your other symptoms. Idle speed is not important, just as long as the rear wheel isn't trying to turn.

[GrumpyUnk]

Two thoughgts. EGR is Exhaust Gas Recirculation, causing some amount of spent mixture to be metered into the combustion chamber. PAIR is Pulse Air Injection Reactor(?). Not sure on the last R word. The only thing PAIR does is allow some air to be 'pulsed' into the exhaust from atmosphere to mix with the exhaust gas. There should(may) be some sort of catalyst in the muffler that depends on the excess air so injected to perform a bit of exhaust gas 'cleanup', making sure anything unburned is exposed to O2's, and in a hot space(inside the muffler/exhaust pipe/etc). To my knowledge there is no path into the combustion chamber for exhaust gas. FWIW.
I would suspect the slide is binding up and not returning to its lowest position after throttle close. That would allow free passage of a lot of air at least as far as the throttle plate. If the throttle plate is not adjusted 'closed' enough, it will run faster with free access to more air. Check that the slide moves freely, and falls back into place when released(from being held open).
I am chaing a similar problem, such that the rpms increase as soon as I close the idle mixture screw to the almost fully closed position. I *think* I am into the low end of the 'middle speed circuit', leading to a non-quality idle, and wandering rpms. Thing is, I noted that the throttle plate was almost a tight fit in the venturi before installation. Dunno if I can back it off to get a lower idle. Pilot is a #33.
I think ratdog posted a link to a PDF describing how the carbs work, which I downloaded and printed. I do not have the link.
tom

[djahd]

I'm happy today!

Using 90GTVert's video on unsealing the stock carb:

www.youtube.com/watch?v=MLpkf2LINzo&index=8&list=PLm3-Rt5jsolvEQcIl1CMZGW5Yj_kP4Wjc

And the HowTo on carb cleaning from the tech library:

49ccscoot.proboards.com/post/190143

And finally the 49ccScoot.com Scoot F.A.Q. on "How do I tune the carburetor?"

www.49ccscoot.com/faq/carbtune.html#again

... I have managed to unseal, clean, re-assemble and tune the carb at least well enough it no longer hangs at high RPM when you rev it.

I haven't counted the turns yet (I will, before I button things up!) but it's obvious the idle mixture is richer. While I had it apart, I added one washer under the C-clip on the needle. Between them, it's enough richer to solve the idle hang and have a decently stable idle.

I've also dealt with many other little things, like taking apart the fuel sender and flexing the contact fingers out a bit to eliminate intermittent readings; lubing up the kick-starter so it returns; replacing and bleeding the front calliper and checking the rear brakes; welding the package shelf mounting bracket back together; installing the new tail-light assembly the previous owner was kind enough to supply... And putting the poor tortured skin panels back together, even to the point of gluing little hooks and tabs and bosses back on where they were broken.

All that's left is the engine compartment front cover and the seat bucket, and it's ready for a test ride. Hopefully, it'll run well enough to give it back to my nephew.

GrumpyUnk: I think this carb was pretty clean inside. Everything that was supposed to move was moving great. It seems it was adjusted too lean and/or whatever cleaning I did accomplish made things better.

So, again a big THANK YOU to FrankenMech for confirming how the plumbing is supposed to run, and nudging me in the direction of basic tuning to solve the RPM hang problem. And to GrumpyUnk and gsx600racer for their thoughts and input.

This has been a fun project. I can see the addiction potential!

Thank you,

Djahd

[pinkscoot]

The hanging idle is usually a sign of a lean condition or a sticky throttle cable