Home Forums Gear Horses and ATV's Yamaha Big Bear 400 Down On Power

I contacted my son , who works as a mechanic and a place that sells motorcycles, snowmobiles, and quads. And probably won’t have an answer until tonight.

I appreciate it. I messed with the pilot screw a bit today. Making it more rich *may* have made it start easier, but it still ran poorly when cold. When warm it was too rich and kind of fell on its face. Leaning it back out made it run better. I tried a cold compression test but the meter didn’t have have the appropriate adapter. Just holding it on there have a poor seal but still yielded over 90 PSI. I’m guessing compression is probably ok.

So you have a $50.00 carb from Amazon, probably made in China, and you have obvious air/fuel ratio issues. What does that tell you?

That’s the conclusion I’ve arrived at too…time to rebuild the original carb. It’s just weird it only does it when dead cold.

I had a 2000 Big Bear. Finally had to replace the carb in 2018 or so. Ran fine after that. If you are having cold start run problems, you have a choke problem. The old Big Bear is still running fine over at a neighbor’s place. Only problem with that is if it ever acts up, he brings it and parts to me to fix. Luckily, those old Big Bears are almost indestructible.

I'm no mechanic, but have a 2000 Kodaik 400, that just underwent major electrical overhaul. CDI box, rectifier, evrything short of harness and stator. Unlike yours, mine was sputtering at high end, or would die unexpectedly. Lucky a work buddy figured it out, he likes tinkering, he has race machines and such.

Have an 03 Big Bear. It's been almost trouble free. Had to rebuild the carb and change out the fuel valve.

I’m moving slow over the holidays, but I have the factory carb on the bench and see it has a torn diagram. That would explain the poor high end. I’m going to rebuild it and swap it back in. I’ll post up when I do.