It purrs, but does not run

[Kiwi]

Ok, this isn't my first motored bicycle, but it is the first one that is giving me this much trouble.
So... I start pedaling, then let go of the clutch, and the motor purrs, but provides no power.
If i twist the throttle, it makes a little but louder purr.

I have tested the spark, and i could see it.
I replaced the magneto, spark plug, and CDI with one i know to work.
There is fuel in the carb bowels.

Any suggestions?

Thanks

 

[Al.Fisherman]

Sounds like the choke to me. That is the same thing I get with a FULL choke. Just for S&G, remove the carburetor /or air filter and while looking into the throat make sure the choke is operating correctly. Have you had the magnet in the coil off? They can go on two ways. Wrong way ...incorrect timing. What kind of compression are you running? How strong is the spark? Condition of spark plug? How did you check it? Disconnect the kill switch if you have it hooked up. Are you sure fuel is getting into the combustion chamber?

 

[motorpsycho]

if you have spark, air and fuel it should run...but if the spark is not storng enough, it will not run.
i would spray a small shot of starting fluid into the carb. and see if it fires.
if it does, you have a fuel problem. if it will not run on starting fluid, then i would say that your spark is too weak. you could also have a major air leak somewhere or a bad head gasket.
even tho there is fuel in the bowl, that does not mean that it is getting into the cylinder.
check to make sure your choke is off as al said.
also, check to make sure that your spark plug is not wet and fouled out after trying to start it (when you just get the purrrr noise.)
the noise you are hearing is the piston going up & down, sucking air into the carb. and pushing air out of the exhaust.
if your plug is wet, then you are obviously getting fuel into the cylinder.
i don't see how disconnecting the kill switch would help, because he says that he has spark. if the kill switch is bad or hooked up wrong (grounding out all the time), there would be no spark at all.
i had a similar problem when trying to run a headlight hooked to the white wire. the motor would not run, but i had spark, fuel and air. as soon as i disconnected the headlight from the white wire, it fired right up. the headlight was drawing too much voltage from the mag. to provide a strong enough spark to fire the fuel.

 

[Al.Fisherman]

Depending on how the kill switch is hooked up could possibly be a problem. If the switch is grounded at the throttle, it might get grounded with a twist of the throttle..not likely, but as you know we have seen stranger things happen.

 

[motorpsycho]

Depending on how the kill switch is hooked up could possibly be a problem. If the switch is grounded at the throttle, it might get grounded with a twist of the throttle..not likely, but as you know we have seen stranger things happen.

true, that is a possibilty. as we all know, ANYTHING can happen with these things, and i have seen some strange things.