How long has the poplar been split and stacked in the open? I'm a strong believer in moisture meters. It's the only way to know the moisture content of wood and it's the single most important factor in burning successfully. This Harbor Freight one is the cheapest around and has good reviews here. Try to get the wood to 20 - 25% MC before burning. You can also look on Amazon and ebay for a 2-pin meter. http://www.harborfreight.com/catalogsearch/result?q=moisture meter Here's what to look for with creosote: http://askthechimneysweep.com/2010/11/the-three-stages-of-creosote/ If you can at all swing it, installing a stainless liner would go a long way in making your experience a safer and more enjoyable one. If you're a DIY'er it doesn't have to be expensive.