Newly built bike won't start, help?

M

michaelbikin

Member
Here is my story... I have put my Chinese 66cc motorized bicycle kit on my mongoose mountain bike. Unfortunately, the regular chain that you use to pedal broke, and I have yet to replace it, so pedaling is not an option for me; but, I do have a pull start installed, which I have been pulling and trying to start for hours, and of course giving it a break for at least 20 minutes in between every 5 to ten pulls, in order to not flood the engine as I have been told. But I have yet to start it, one time I pulled it using the pull start and the engine started up literally for about 1 second only, and then died, but it was very loud... is this a good thing? Should I be pressing the prime button more? What setting should I have the choke on, should I change something with the carburetor?? Any help or feedback would be greatly appreciated.

Also, I saw a video about putting that rubber ring seal in the carburetor where it goes in the engine to prevent air leakage, will that help?

:-||
 
I meant loud as in I knew the engine started for a second, it sounded like revving the engine for only one second. Should I change my fuel ratio to one with less gas, I heard it makes it start easier.
 
Even broken in my bike with a long intake manifold is slow to start. One way I've found to wake it up quicker is to press the tickler and let some gas well up into the manifold..
For about 15 seconds! Yep, I hold it down that long and it starts better.
Some of em are just cold natured.
Try giving it more tickler time.
Also, get the pedal chain fixed. A broken in, well tuned engine can use the pull rope, but a new one in the rough needs to be pedaled a ways.
Or you could try having a friend give you a push, too.
Check your spark gap, too wide and it'll be even harder to start.
Hope this helps ya get it going.
 
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if carb is on tight, then no o-ring is needed

new engines often need some choke, but I suspect your idle screw may not be set right & there's no way to set it until the engine starts - unless you can hold the throttle at same time as pulling rope, you'll need someone to pull for you until you get it to start & then adjust the idle (note: once it tries to start, you'll need to turn off the choke quickly too)
 
I got it started! It was running loud for about 30 seconds, until I realized afterwards I forgot to turn the choke off... The engine seemed to be revving full throttle even though I wasn't touching the throttle, I think it might have been due to me not turning off the choke once the engine was running smoothly... Also, My throttle is somewhat broken on the handlebar and I am installing a brand new one soon. And, after the engine died I realized that the carburetor came fully off the engine, so I adjusted and tightened it back on, and I lowered the idle setting by unscrewing it because it seemed like it was idling too high.
 
Now that you can start it, the rest is easy.
Glad it's running, good job!
Loosen the carb clamp and press it onto the manifold firmly as you tighten it back up.
They need to be seated fully to close off the gaps in the flange on the front.
The throttle cable can be messed up where it goes through the guide and onto the plastic pulley doodad in there. I did that once myself.
Make sure your carb slide is moving freely all the way up and down, you should be good to go.
 
That "doodad" thingy is called a 'thimble', believe it or not. :) It also helps to trim away any overhanging casting flash where the cable barrel fits into it and the cable guides. I also lubricate that area with a light grease.

I like to seal the carburetor to the intake using a gasoline compatible sealer. The 'O' ring is a good idea however you must press the carb hard against it when tightening the clamp or it dosn't do any good. And you have to check it occasionally to make sure the carb is seated against it.

Tom
 
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Update: Haven't been able to get the bike started since with the pull start, which the pull start rope snapped and totally broke off. I am now going to replace the pedal drive chain so that I can try to pedal start it, and I am going to change the fuel mixture to one with less oil as I heard it will be easier to start... But... the thing is, I have picked up speeds numerous times in an attempt to start the bike by rolling down the hill on my street going up to about 15mph for about 100 yards and I have yet to start it at all or even hear any popping or any signs after several times trying it, do you think pedals will help it start more?
 
michaelbikin said:
Update: Haven't been able to get the bike started since with the pull start, which the pull start rope snapped and totally broke off. I am now going to replace the pedal drive chain so that I can try to pedal start it, and I am going to change the fuel mixture to one with less oil as I heard it will be easier to start... But... the thing is, I have picked up speeds numerous times in an attempt to start the bike by rolling down the hill on my street going up to about 15mph for about 100 yards and I have yet to start it at all or even hear any popping or any signs after several times trying it, do you think pedals will help it start more?
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No, if you got it up to 15mph and it still won't start it must be some other problem...check spark, gas, compression...look for air leaks around the head or intake.
 
michaelbikin said:
And how do I know if there is an air leak around the head/intake... And are you referring to the intake/black thing on the carburetor?
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No, the black thing on the carb is the air filter. It takes 3 things to get a motor to start, gas, spark, and compression. Compression can be checked by checking for air leaks. The most common places of air leaks are (1) around the head/head gasket, hold you hand by the side of your head while you crank it and see if you feel any air shooting out the sides around where the head gasket connects with the head, leaks can happen on all sides of the head (2) Check where the carb hooks into the intake, do you see any drops of gas leaking out? Spray a small amount of soapy water on the connection and crank the motor, it will bubble where the leak is. check that all the gaskets are sealed. Also, make sure you are getting a good spark, maybe try a different spark plug. Make sure the float is full of gas and gas flows through the jet. You could try cleaning the carb. too. Make sure the exhaust pipe is not clogged up with oil. If all that checks out, I don't know.
 
for an NT carb, a quick check is to take a piece of thin, safety wire and poke it into the ends of the slots in the carb mount - if it goes in, then the carb isn't on all the way
 
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