needs help with an older bike

[xj650HO]

i have a 81 yamaha xj650 4 cyl shaft driver , up until last week she ran great and had lots of power , now while in 1st and 2nd gears , it seems like its not hitting on all 4 cyl , misses has no power for a few seconds , then it kicks in and takes off , the petcock has been giving me trouble , im thinking that it may be time for a new 1 , any other ideas? FYI once i hit 3rd its like a bullet and has tons of power

[pchast]

Is that a vacuum operated petcock. I had to pull mine apart and clean it. There was enough gunk in it to stop up the vacuum orifice...

Pete

[xj650HO]

yes it is a vacuum , i took it off last night , little gunked up and im replacing both the vacuum line and the gas line

[xj650HO]

ok got everything back on , also added a little seafoam , still missing not as bad , just a small hesitation in 1st and 2nd , funny thing is , was running great last week and now this

[pchast]

Are you running a fuel filter after the tank petcock? The bad news is that added seafoam and the old tank may have moved some of that gunk into the carbs. Just IMHO, I'm no mechanic myself...