My 300 is loping only at idel and I cant figure out why, its strang because sometimes it runs fine I can drive it 20 miles and no loping but then out of the blue it will start loping to the point where I think its going to die at stop lights ect I was thinking it was a valcum leak but I cant find any, other then that it runs fine no hesitation or miss, any more questions just ask thanks

 

I'd try to "catch it in the act" and get as much information as you can in the fault state. In particular, I'd check timing and throw a vacuum gauge on it during the time in which it's running poorly. I might even go so far as to remove the air horn from the carburetor and check the fuel level in the bowl.

 

Carb could be loading up. Did you spray carb cleaner on the gasketed surfaces to see if the idle raises? Has your fuel mileage suffered?

 

Well today the engine was running like a top drove it to work, but on the way back just as I pulled it in the driveway it out of now where almost died I put the clutch in and sure enough she was a loping like mad, kind of odd right?