back fire when starting hot. By budvoss (Read 648 times)

[budvoss]

this is a new engine . after firing up cold it ran great. after it warmed up it would not idle. started backfiring when trying to start hot. I checked enricher, checked plug for spark and plenty of spark. I was tyeing enricher into 12 volts for try out and now I'm not sure if that is where it ties in . I am building from scratch and read somewhere that enricher should be tied in before rectifier.?? This sure sounds like an enricher problem but it grows when adding 12 volts... Any help on this would be greatly appreciated

[Bashan]

Your enricher runs right off of the yellow stator wire, if your building from scratch split the wire after it comes off of the stator, run a leg to the enricher, and ground the green wire on the frame. This supply to the enricher is rectified as all of the wires are simply by being plugged into the rectifier/regulator; it doesn't have to be before or after in the circuit. The enricher shuts off in ten minutes causing a leaner condition but would not cause massive backfiring like you describe......you might get a little popping. Mega-backfiring is way too lean or way too hot, or both. A bad coil will heat up after about 10 minutes and produce exactly those symptoms. Horribly adjusted valves will heat up and cause all kinds of problems. Vacuum leaks cause the mixture to be way lean and backfiring. If it was me I'd do the following:

• Swap out a good coil and see how it runs
  
• Check for air leaks everywhere, manifold, filter, air hose, vac hoses
  
• Make sure your A/F screw is 2 1/2 turns out just to rule that unlikely prospect out.
  
• Check your valve clearence.
  
• Check your air cut valve's integrity on the right side of the carb
  
  Rule those in or out and get back. Rich
  

[budvoss]

thanks rich, heres what i found. Keep in mind that i only had temp wires to get to run. When i hard wired the battery to scooter i forgot to tie in the charging circuit from rectifier. Now will start right up with no back fire. For some reason rectifier needs load of battery so it don't get any feed back I think lol. It wont idle longer than 1 or 2 mins but i still don't have an air cleaner hooked up yet and maybe that has something to do with the idle.

I did go over valve adjustment , variator, and carb before i installed motor. The engine came with new carb, cdi, coil, rectifier and all..

I take it the yellow wire off stator is low voltage ac and that wont matter ?? Just asking again before i do that
thanks again for your help

[budvoss]

disassembled carb again and ran my torch tip cleaners in the jet holes .One of the holes had silver metal in it. i think alum, anyways reinstalled and now motor idles like a charm. i did not run my cleaners in the jet holes on pre check just blew air. never again take that shot cut..lol
thanks for all the help guys