Thread: Motor stumbles

I finished the 1971 Trail 70 early this summer for my son. I repainted stuff, replaced stuff, bought some new stuf and it came out nice! He has been riding it quite a bit, but just last week it started acting up. It idles fine, but when you turn the thottle at all fast, the motor stmbles and if you go slowly to full throttle, it gets worse and starts to miss.
When I refreshed everything at the beginning and went through the ignition, I replaced the points and condensor, ingition/ alternator coil and plug. The previous owner had installed a new carb and I replaced the air filter. When I was done, it started on the 3rd kick and it ran great until now.
What are the things that I should check -and in what order?
Thanks, glen

Take out your plug and see what it looks like. If its wet and oily you are running too rich and possibly burning oil which would mean new rings. If it looks burnt you are running too lean. Its better to be running too rich then too lean. It may just need a new plug if you never changed that.

The plug was a little ritch. I replaced it and it still won't go past idle. Is is possible that when I put in the new points, I didn't set them right and they worked ok for a while and then were either to open or not openning enough. Or is this more likely a carb problem? It has a replacement carb, that doesn't appaer to be too used. This all happened pretty quickly -it ran great and then when right to this problem. Again, it will idle fine, it just stumbles bad or stalls when you open the throttle? Thanks, Glen

I guess I would start by recleaning the carburetor. Take it apart and reclean the jets and look for light through each of their holes. Then I would double check the settings of your idle and air screw and set them like I have said in previous posts. The only way to find out about your points setting is to check it. Look to see if they are just beginning to open when F mark reaches the notch on the casing. It does not look like the problem is going away by itself so you will just have to recheck everything and go from there.