Bicycle Motor Spark Problem?

[deacon]

You definitely have an air leak. When you have two problems at once like that it makes you crazy. If you want to check it coat the outside of all the connections with a serious glob of bearing grease. You can always clean that off later. Then if it runs better, take it off one connection at at time. Then you will find the one that is bad and can figure out how to stop that leak. Beating that little beast is half the fun... Well it is when you look back not at the time.

Good luck and our weather is getting bike friendly.

 

[Bikeguy Joe]

I'd change the needle to a leaner setting if it runs bad until WOT.
Start at the second from the top.

BTW, what exactly is a "premium carb"?

 

[deacon]

Joe is probably right these guys know more than I do. I was thinking it would be air most likely because the carb didn't fit the manifold.

 

[buttburn]

Its supposedly the Premium carb offered by GruBee's 48cc kit. Has a built in choke cable and a mixture screw along with an idle screw. The new NGK plug looks light brown, I'd be scared to run it leaner. But I will try it since you know far more than I do about these engines. The carb has a built in shim but it isn't close to being tight once I torque it down till it's at the point of stripping. So I used electrical tape as a second shim and it snugged up.

It's like the bike is sluggish and is misfiring until I get fed up and pin the darn thing for a while. Then I can pull the clutch and start off from a stop and it will pull all the way to peak rpms pretty well.

I bought the stock happy time carb and big intake manifold from revolutionarycycles on ebay for $50, jeez. Little bit steep to test the waters on, eh?

 

[Bikeguy Joe]

Now hold on.....

Maybe the bottom end mix is too rich and the top end mix is fine.

I can't comment on adjusting this since I'm not sure whaty does what on that particular carb.

If the mixture screw is for the idle mixture or low end, go ahead and make it a LITTLE BIT leaner. Don't mess with the top end (needle)

 

[Bikeguy Joe]

From your description, it does sound like it's loading up and once cleared out, runs O.K. for awhile.

The plug should be chocolate brown, but that's if it is running good all the time, in all ranges. If you "clear the plug" by running WOT, you could be getting a false reading.

Also, does the mixture screw turn in for leaner, or out for leaner? Contact grubee for the answer, as there are both kinds.

Where is the screw set at now? Gently turn it in until it stops while counting how many turns it take to turn in.

DO NOT TIGHTEN IT LIKE A REGULAR SCREW.

Should be around 1 1/2 turns.

BTW- how much choke do you need to start it, and what throttle opening do you use when starting it cold?

 

[Norman]

If your engine is brand new it won't run real great until its broken it some but if the plug looks tan at wot then you are in the ballpark. I have a new Dax engine it had 2 base gaskets under the cylinder I think they equaled 0.070 in thickness I made a base gasket that I thinks was 0.050 thick and its improving as it breaks in I'm tempted to mess with the exhaust pipe so it will breath a little better. My neighbor rode it and wants it so bad the can taste it I'll maybe sell him it. I don't need and can't ride 3 bikes. Its a good circus act to ride 2 at one time Bob does a pretty good act doing that when he gets enough O'doulls in him, very entertaining .

 

[Ilikeabikea]

Norm, you know I don't mix motorized bicycles and O'Douls. Dangerous combination...................

 

[Norman]

Wait a minute you mean its me???? That does that!!! and worse.