spark plug size?

[masterx1234]

hey guys im sorry if this has been asked before but i did search the forums and found nothing... ok so i just changed the spark plug in my 49cc monster scooter engine, but now i can barely go over 23 mph according to my bike computer, so whats the big deal? the guy at the hardware store said the new plug i bought was made especially for small two-stroke engines. so please does anyone know of some compatible high performance spark plugs for this engine that will allow me to achieve my normal 34 mph again? and also i have completely ruled out an air leak or carb problems, i have changed every gasket a month ago and it had ran perfectly at 34 mph with the old spark plug, and also when examining the spark plug theres only a slight difference in the distance of the spark on top of the plug, ive attached a picture explaining more.

 

[Dave C]

That looks like a chain saw plug.

http://www.motoredbikes.com/showthread.php?t=31731

These are the right crossreferences for different manufactures of the Chinese plug. For some reason the NGK's seem to work better than most. Especially the Irridum or platinum plugs.:helmet:

 

[motorpsycho]

the first problem is that you got it at a hardware store. Those guys don't know what's good....they're just talking the basics when you're looking for a spark plug. they're used to selling plugs for lawnmowers, weedeaters and chain saws where they all operate at the same rpm all the time.
The reach on the plug you have looks too short. The problem with that is that the electrode may be up inside the spark plug hole and not down right on top of the piston like it needs to be. You could be losing combustion because the plug reach is too short.
you need to go to an autoparts store, and get an ngk plug with the right reach, and the right heat range.
Now, i don't have any experience with a monster scooter engine, so i am assuming that they are similar to the chinese happy time engines. the plugs for the h.t. engines have more reach than the plug you have shown.
it could be that you did get the right reach plug, but it could be that you picked a bad manufacturer. if that plug does have the right reach, you need to cross referance it with an ngk. My reccomendation is to stay away from champion plugs as well as autolite plugs, but that's just my opinion.

 

[masterx1234]

the spark plug on the left (ngk) was the one that came with my motor, and any spark plug longer than that one would hit the piston.

 

[motorpsycho]

the spark plug on the left (ngk) was the one that came with my motor, and any spark plug longer than that one would hit the piston.

well then maybe the replacement plug that you got is just a poor quility plug and it could also be the wrong heat range.
Mybe that small difference in the reach is why it doesn't run as good?
I really have no idea now because i assumed that your stock plug had a longer reach than both of the ones you are showing.

 

[GearNut]

Did you correctly gap the new spark plug to your engine's specifications before installing it?
Spark plugs are not correctly gapped from the factory.
It also could be a bad spark plug right out of the box.