Well first off i have a 400EX big bore 440 with fmf powerbomb header and White bros E-series slip-on. I took the spark arrestor off my pipe because i heard a dinging inside. I found that the guts of the pipe were tore up. The metal mesh tube was just flopping around inside the pipe with minimal packing around it. It's loud as heck now but I don't really care, i just don't wanna hurt my bike. Is this harmful to the wheeler? My dad always told me that back pressure helped cool your valves but this was referring to automobiles. I don't think this applies to wheelers but should i put the spark arrestor back on for some back pressure? I don't fully understand the exhaust so I need some opinions so I can learn. Anything will be helpful. Thanks in advance guys.

 

ok, the theory of burning valves is partly true, but only if you have a very short exhaust, like on a car if you had no pipes on it after the headers (or no headers at all) or if you just had the header pipe on your quad, and nothing else. if the exhaust is too short, sometimes colder air will get sucked back into the engine on deceleration and can warp the valves, but if you still have the whole head pipe and silencer on, i highly doubt you're gonna have that problem. as far as the spark arrestor, it's always a good idea to have it in (illegal to ride without one up here in minnesota) just so you arent responsible for started 50 acres of farm field on fire. it will also add some back pressure to your exhaust, some backpressure can be better than none at all, especially for low end power.

the only thing i would be worried about after that, is if the exhaust is flowing significantly more than when it was new, the jetting might be slightly lean now, and that could do some damage. Just pull your spark plug once in a while and check it, if its gray or tan, you're ok. blistery white is bad

 

Ah, thanks quicksilver that shed some light on the subject. I just purchased a dynojet kit about 2 weeks ago. I installed the 165 main because i felt a 170 maybe to large for my atv since its not camed. I guess i can step up to the 170 if my airflow increased. Sounds like I'm going to be able to get off without spending any cash! I make it a habit to check my plug regularly I've found that one thing that an atv has in common with your automobile is that the plug is the tell all for you engine.

 

YES check the plug cause i lost some of the baffles in my sled and it melted the one piston really fast.