So my 2004 grizzly 660 just suddenly lost power. Went on a 10-15mile ride with some friends, stopped for about an hour, when I start it back up, it started bogging down an backfiring around 1/4 throttle. Give it full throttle and it just loses power. It’ll idle great, and go at low speeds up to 15mph until it starts acting up. Ran great everyday for the past month, and the entire cruise it did perfect up to that point.
What’s been done to it:
New Carb
New Spark Plug
New CDI Box
New Voltage regulator
Valves adjusted a few weeks ago
New K&N Air Filter just a few days ago

It does not have an in-line fuel filter on it, so I’m thinking it may have sucked something into the carb that’s blocking a jet. However, i was wondering of other possible causes before starting in on the carb. Will definitely be adding an inline filter after this regardless though.

 

Almost certain to be dirt in carb, that is the first thing to check anyway. One other problem with Yams is the inlet manifold is prone to cracks, which let air in, so if you have recently changed carbs you may have opened up a crack the manifold, that is more likely to give low speed trouble though.

 

Forgot to give an update yesterday, but as soon as i removed the gas tank, i saw the issue. Cheap after market carb was the problem, the vacuum chamber cover has a spring guide on the inside that was kind of riveted to the top of the cover, it had came loose an just fell in. There wasn’t anything to guide the spring, so just swapped out the cover with one from the old carb an problem was solved. Lesson learned on that purchase lol