Hi there, I have a 1974 Yamaha 125cc enduro motorcycle thats having some issues starting. I've taken it in a few times to get running but with all the time I have now I was hoping to get it going again myself. Im not very mechanically inclined but have done a few things. Before I had put it up for a few weeks, it was having issues dying down when I rode it, it would then start on fuel reserve, but just rev up and then die. Now it won't even start with reserve on. I know the carb is getting fuel so maybe its an air intake issue? One of the screws that attaches the carb to the engine is quite stripped and I can only get it about 1/3-1/2 in tightly. The other screw goes all the way in though and secures the carb quite well. The rubber clear tubes also fell off the carb and I lost them, but they were the ones that just led to nothing, just hanging of, do I need these perhaps? Other than that, the spark plug is fine and I have cleaned the carb a couple times. The air intake tube is clear and the filter is fine. What am I missing? When I first purchased it, it wasn't running so I took it in and its "points" needed to be adjusted. Could this be the issue again? Basically what would be some troubleshooting steps to find the issue at hand?

Hi & welcome [if you're new]. Bit difficult guessing the issue but still sounds fuel related from what you describe. A video would be good if possible--well mainly for the audio part. I see reading it again that you cleaned the carb but wonder if there's still something missed. www.partzilla.com/catalog/yamaha/motorcy...74/dt125a/carburetor Looking at the pic in the link [if its right] the main jet is in the side mounted holder in the bowl, so just double check its clear. In fact take it out & check there 'is' a constant fuel flow into the bowl [& out the mainjet holder hole]. There is a little Oring in there that seals the bowl in the center onto the holder thingy--But, the problem sounds opposite to if that wasn't sealing as would go rich, very rich. Other possibility is the left side crank seal has popped out but think by your model they had a retainer plate on that side & the right side. [I'm assuming yours is an electric start model as ours in NZ were mostly kickstart only but did have a few electric models. I'll leave it there as getting interrupted here. Oh & check the fuel cap is breathing. Easiest way is to run the fuel hose into a can & let it run for a while & see if it keep flowing constant. Could remove the float valve seat & make sure nothing is behind it but a blow through with the air should be good enough. You mentioned the bolts holding the reed inlet/manifold on but if the bolts are tight they should be sealing even if some are short on thread. Good luck.-from NZ downunder.

Having one of the two screws stripped that hold the carb to the manifold is very likely a problem. Likely the source of a fairly decent air leak.