Is your 2-stroke BACKFIRING? This could help ...

[BrewCityMusic]

Hi Kids !!! Over the last month or so while everyone is getting their carts dialed in for the season, I have noticed an above-average number of posts asking about backfiring issues with Marathons, so I thought I'd throw this post together so there's a searchable solution for those with questions.

The most common cause of backfire is the lack of a spring on the throttle cable, from what I've seen (and experienced) ... Quite often, these springs get lost, etc when the carb or cables are adjusted/serviced, and running without it is a common cause of backfiring. The spring goes between the "arm" on the carb and the cable stop that is used to adjust the throttle. What happens is that without this spring, the butterfly has a hard time completely closing when you let off the gas pedal, and while you are coasting or while the engine winds down, the carb continues to draw fuel into the engine while there is no spark. This loads up inside the motor, and when you hit the pedal again, it ignites !BANG! - which isn't good for your piston, rings, seals, etc - just bad JooJoo all around.

Here's a pic of the spring as it should be installed - in a pinch I have used the spring from a clicky-pen, but the actual spring should be a tad bit heavier (I bought an assortment of small springs at Home depot for $2.99 and experimanted until I found the correct one, roughly 3/4" long and just under 1/4" diameter) ... You want to adjust the cable stop using your ears as well as your eyes - you want the spring under tension when the pedal is NOT depressed, and you should adjust it so that when you depress the pedal, you want the carb arm to NOT move until *just* after you hear the pedal microswitch "click" - this ensures that the carb butterfly is closed until AFTER the ignition kicks in - that will solve about 80% of the 2-stroke backfire issues people are having:



SO - You've obtained, installed, and adjusted your springy-thingy, and you're still backfiring? OK, the number TWO cause of backfire is a leak in the exhaust gaskets, generally at the junction of the cylinder and pipe, but can also be caused by a leak where the pipe meets the muffler... Gaskets are only a couple of bucks a piece, so if you're backfiring due to a damaged or missing one, it's best just to replace them both. Clean the surfaces thoroughly before installing, and a little high-temp gasket goo isn't a bad idea (just a little bit to seal, you don't want to goober it up TOO much or you'll actually create a weak spot) ...

While these aren't the ONLY causes of backfire, they generally are the "prime suspects" - and are easy fixes that should likely be performed before delving into a huge hunt for the problem. Hope this helped some people out, and if anyone wants to add to this that would be GREAT !!! Happy Carting