Starts up and Runs but will not accelerate By briankeith79 (Read 42,329 times)

[briankeith79]

I got a problem for ya biker guys, I bought a moped in 2008 and its been good ever since. In the past year or so, Its just been sitting while Ive been trying to diagnose the problem and Im stuck as hell.

The moped will start up and idle fine, at times, but it will not accelorate without dieing in the process. At first I thought it was the carborator, so I purchased a brand new one from Partsforscooters.com and put it in. It still does the same thing, Starts and idle's but will not throttle to higher speed without dieing. I read about checking the valve lashes. so I popped the valve cover, head gasket off and check the clearances. I saw they were tighter than should be, about .001-.002 .   I adjusted them too a .004, pieced it all back together and put valve cover back on. Still same issue.    During all this process, If I had a air cleaner or air filter on it, it will not start at all to even idle, just sits there and cranks over with no stable running. So I took the air cleaner, air filter off. Right now, it will sit there and idle but not throttle with NO air cleaner on the carborator.  Seems like putting an Air cleaner or filter on it only chokes it out even worse, it wont even idle then, it will idle without the air filter no problem. 

Any one else have an idea of what could cause it too not throttle up, besides even start with an air filter on it?  It use to run fine but now, im at a loss. I plan on buying a new moped anyways soon as I get my tax return here in a few weeks anyways, already picked one out, but in the mean time, I would like to fix this problem and have two mopeds, so I can teach my wife and son how to ride one safely without having to worry about wrecking my new one when I get it. Im not letting noobs ride the new moped when it comes... lol  haha  ya right.

[Deleted]

A plugged fuel filter or bad petcock comes to mind. Take the fuel line off the carb and put it into something to contain the gas. Trace the vacuum line from the petcock to the T adapter and remove it from the adapter. When you suck on this line, you should get a good flow out of the fuel line.

[twowheeler]

Rats nest in the airbox? Could be almost anything. Vacuum leaks maybe? Petcock? Fuel filter? New lines? Spark plug?

[twowheeler]

Rats nest in the airbox? Could be almost anything. Vacuum leaks maybe? Petcock? Fuel filter? New lines? Spark plug?

Old crud in a gas tank will tarnish a brand new carb right off the bat.

[briankeith79]

Airbox was cleaned out from dust and debree, the filter looked clean, even used soap and water to clean the sponge, allowed it too dry, it never started up with the airbox connected still. Spark plug is brand new, recently purchased. Fuel filter is also brand new, its a clear model, you can look into the fuel filter and see the filter metal still clean looking. Most of the hoses are replaced with new fuel line hoses, the green clear ones from a motorcycle shop. The carb is still clean, checked it out before. the main jet and idle jet is still clear. The petcock under the fuel tank flows when I suck on the hose to allow it too open.

Any other ideas guys??

[twowheeler]

Gotta be electrical at this point. Coil? CDI?

[briankeith79]

Not sure on the coil, I did the Ohm test on the 50cc manual I found for 139QMB motors, coil seems to be ok. the coil is standard that came with bike, the CDI was replaced last year with those Orange high performance ones. Im not sure if that would make a difference from using a stock cdi to a high performance cdi besides reaction times I would think. Would electrical be an issue from not allowing it too throttle up too a higher RPM ? but allowing it too Idle at least?? And this is all still with the Airbox not attatched, because when I attach it, it wont even start then at all

[Deleted]

Check to make sure the two nuts on the intake are tight and no cracks in the rubber. It doesn't take much air to throw the mixture off.

[briankeith79]

I disconnected the air intake lastnight, looked inside it. Didnt seem to find any cracks visable to the eye.

[Deleted]

Strange as it sounds, I had loose spade clips on my coil's power wires once, did the same thing you described.

[Alleyoop]

Appears just to be a fuel delivery problem. Have you adjusted the carbs Fuel Ratio Mixture.
At this point since it only runs without an air filter on it means it is getting to much fuel with the Air Filter on it. So PUT THE AIR FILTER BACK ON and Turn the Fuel Ratio Mixture screw Clockwise until it stops AND count the number of turns it took to close.
Then Turn it out Counter Clockwise 1/2 the number of turns it took to close. So it if tool 3 turns Clockwise to close then turn it COUNTER CLOCKWISE 1 1/2 turns and try that(WITH THE AIR FILTER ON IT).
Alleyoop

[kz1000st]

Spray the carb and intake manifold with WD-40 and see if it works. If it does you have air leak somewhere.

[briankeith79]

I tried that already the fuel mix ratio, its still set on the 1.5 turns its suppose too. so does this problem sound like its wanting to run with airbox off cause its not getting enough air or too much air, not enough fuel or too much fuel?? with airbox off and its running sounds like its getting more fuel in intake then it should basicly ?

[Alleyoop]

with airbox off and its running sounds like its getting more fuel in intake then it should basicly?

That is what I said, to much fuel. Now you say the fuel ratio screw is out only 1 1/2 out from the closed position???
Let me ask this DID you put in bigger carb or PILOT JET?
What size carb is on there and is this a 50cc or 150cc?
Alleyoop

[briankeith79]

yes the screw is only 1.5 times out from fully closed position.

The carb I have in it now has been used in it for about a year without problems prior to this unique situation. This is the current carb Im using in it now. www.partsforscooters.com/151-222__QMB139__Carburetor__20mm Its the type 2 carb.

The carb that came with the moped in 2008 was a carb without an Accelorator on it, a type 3 carb. www.partsforscooters.com/151-224_Carburetor_qmb139

The type 2 card Im using on it now Ive been using for over a year. almost 2 years with no problems prior to this situation.