Runs rough at higher rpms

[80sDweeb]

Just got this '97 YFM350 last week. Was running great, son having a great time on the trails near our house. Quad was sitting out when a sudden thunderstorm came through. Next time he tried it, it started and idled great, but ran rough and stumbled at higher rpms under power. Revs fine while sitting (just thumbing the throttle) but taking it out, bucks and stumbles. Doesn't die, though.

At first I thought it could be water in the fuel, but nothing showed up. Now I'm thinking the rain may just be a coincidence, but still don't know what might have changed. Is there some place moisture can cause trouble in the ignition system?

I'm probably going to have to pull the carb and take a look inside, but if anyone has any thoughts, I'm all ears. Since it idles OK, I'm wondering if something happened with the main jet (what, I don't know.)

Thanks,
Scott in Snowflake, AZ

 

[Truck Norris]

My carb needs cleaned way more often than it should. I have this problem often and a carp clean usually clears it right up. I don't know why but I need to clean it monthly or learn to ride it in the mid rpms because of how but it is when it's revving. I'm not sure why the carb is so finicky. I use ethanol free fuel and it never sits long without being ran.

 

[bomber315]

mmmmm as usual its hard to diagnose things like this over the internet but what is the air filter and or airbox like? if it somehow filled with water then that obviously is your problem... i could also be any number of connections, but they are generally fairly water tight and water generally doesnt affect them anyways (in my opinion)

 

[lbjamm]

Check everywhere for water entry. Carb, filter, Stator, Connectors, CDI or rectifier.