Assuming he does replace it, what does he do when the replacement exhibits the same thing (as it probably will)?
I suggested a way to determine an oil control problem. Perhaps he has not checked yet.
You make a good point if the replacement 6.5 does the same thing, but I've bought two of the 6.5s, both the old models, and they both burned pretty clean. If he has any problem, he should return it regardless with these mass-produced China engines. They make so many of them so fast, that some come out different than others, (somewhat defective) and you want the best.
I do find adjusting the screw on the carburetor helps if they do smoke some, as a 2.5 I had smoked, but it was just too rich from the factory, and after adjustment it burned clean too.
I know on Motoredbikes.com forum that used new 6.5's on their bike-trailers never reported smoke either. Mine only smokes when cold, because it's had the $hit beat out of it from accidents and crashes, dirty oil sometimes, high RPM with low oil at 50mph, nasty dirt roads, and bumping all the time with no suspension.
Abused to the max, but never smokes constantly.
However, I would return one if it continued to have constant white smoke, as I've had two that never did that. Rgvkid here on this forum had a new 6.5HP engine shoot a constant blue flame, and he returned his engine to HF, and the replacement ran fine with no smoke or flame. Ask Rgvkid about his 6.5 clone, as he's reported it's been really good running and clean burning, and he's very pleased with his 6.5HP Lifan engine now.
The only reason I mention returning that engine to the OP, because you want to get the most for your money, and not just deal with whatever they sold you. You want the best, no matter if you spend $1 or $5,000.
I really wish I returned my first engine because it always leaked a bit of oil out of the oil seal, and after damaging and replacing it, the new seals leak too, but I didn't worry about it when I originally bought the engine when I
should have returned it, but then when I worked on another 6.5 for a friend, and a 2.5, none of them leaked out the seal or smoked (after some adjustment burned clean), and that further reinforces why I believe if the engine is brand-new, it should run leak-free and smoke-free. I just want to be considerate to the OP by saying he should get the most for his money, and get a decent engine that you don't have to worry about too much for a while, as they are fairly maintenance-free when they are new, other than regular oil changes.
Also these engines are made in China, very mass produced, and even though they are great engines, I'm fully aware the poor Quality Control issues with some of these clones, so you have to make sure you get a good one first, and it will be dependable for a long time.
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