Originally Posted by 5-7HEAVEN
Bob. Mike, both engines share the same large automobile fuel filter. It is transparent; when I prime the fuel lines I can see the air bubbles flow through the filter and into the Happy Time reserve tank. If it was defective both engines would have high-speed stumbling.
I just replaced both sparkplugs. Since I use the bike every day there is always fresh gas in the tanks.
If the fuel filter has some age on it I'd still replace it just to be sure ... shouldn't cost much. Seems like it might be possible for a partially clogged filter not to let enough fuel through to run both motors at high speed.
But, as someone else said, it's starting to sound like the carb may need cleaning. Here's a way to check ... when the back engine starts to falter, try choking it a little bit. If it picks up speed with this richer mixture it may indicate that the carb jets need cleaning and/or the air mixture needs adjusting. This would at least confirm that it's probably a gas problem.
Hope that helps ...