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2006 Yamaha Bruin 350 - Running Issues


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Hey everyone. I have been poking around this site for awhile and I am in need of yalls assistance. I have a 06 350 bruin. It has sat in my parents garage for about 2 years and was never started. I got it home, put fresh fuel and plug in it. It would start and run great but it wouldn't idle unless choke was on. Also when you were moving and let off the throttle it would make a pop noise down by the carb area. I thought it was a dirty carb so I sprayed some carb cleaner in it and didn't help.

I removed the carb, tore it down and cleaned it. I removed the jets spraying carb cleaner and compressed air thru them. I removed the float as well and cleaned. I drilled out the plug that covers the air/fuel mixture screw. I read where the spec is two turns from fully seated. So that is where I set it at. Before I did that, I removed the screw and spring and cleaned that bore out as well.

I reassembled and now I have issues. It is very hard to start, choke or no choke, and when you do get it started, you have to hold the throttle at 3/4 way to keep it running. It will run very rough at 3/4 as well. With the air filter off, while trying to start, it is blowing a lot of fuel back out into the air filter and the plug is getting fuel fouled very bad. I removed the carb again thinking I messed something up or got the float stuck but everything looked fine. I put the carb back on the second time and it didn't change a thing. I assume its something I did since its not running like it did before I tore down the carb. Can anyone please help? Thanks a lot.

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check your valve clearances ... that would make it hard to start and push fuel back thru the carb ...

I was thinking about checking that but I figured if its running worse after I cleaned the carb, then I thought it was something I did. Also, with the plug removed if I hit the starter it will blow my finger off the hole.

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  • 3 months later...
  • 4 weeks later...
  • 1 year later...

Almost certainly valve lash and/or burnt valve(s). My friend has one. His was doing the same thing. Adjusted the valves, found the intake valve lash at 0mm (held a bit open). Additionally, rocker not flush to the top of the valve (gap larger on one side than the other). After the valve adjustment it runs a lot better but is still lean (runs better with a bit of choke) and small pops (backfires) when backing off after high rpm. Also took the carb off. All jets clean, carb in good shape, not dirty...no issues there. It now easily runs good enough to ride...but still not quite right. I am 95+pct sure the remaining issue is slightly burnt valve as the valve-to-rocker-not-flush issue, popping, and lean condition are classic indicators of this.

They are notoriously under-powered (heavy to start with). Folks ride them and you get high rpm for extended periods. Over time this results in burnt valves (especially when the high school kids are riding the crap out of it for years).

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  • 2 months later...

I am having almost the same problems and I recently adjusted my valves and it ran great except for at full throttle. So, I pulled the carb and found some debris in the main jet. Put it back together and now I can't get it to run. If I pull the diaphragm with the needle it runs.

It's running really rich and I can't figure out why. I've pulled the carb and checked it at least 5 times and can't figure this one out. Any help would be greatly appreciated.

Sent from my SM-N920P using Tapatalk

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