berend2712
XS400 Member
Hello fellow xs400 enthousiasts,
I had a thread earlier with some issues I wasn't able to resolve, and unfortunately they still haunt me. It seems to be a fairly common problem: when the bike is warm, it won't idle properly, which means I have to keep it revved at about 2-2.5k rpm, taking a lot of attention when I ride. The problem seems to get a lot worse if the bike gets warm, after about 45 minutes of riding or so.
Since the last time I posted, I managed to fix all the holes in the exhaust. There was quite a big gap in one of the mufflers, so I figured that would be a large part of the problem, but alas, it seems to have gotten even worse now.
As I understand all the posts here, I'm probably dealing with a lean condition in the idle circuit, due to a vacuum leak or maybe incorrect idle screws. The fuel setup on the bike is all stock as far as I can tell. Problem is, one of the idle screws is stuck and stripped and I will take them out at some point, but I'm a bit apprehensive to, because I'm afraid I'll do more damage than I'm fixing. So before I go in, I would like to rule out other possibilities. The one that wasn't stuck was set at 1.5 turns out, so I assume the stuck one is as well.
I have extensively checked for air leaks, and I'm quite certain the boots, throttle shaft seals, and vacuum ports on the exhaust and the air intake aren't leaking (wd40 spray test). I did find some pinholes in the carb diaphragms, but the slides do stay up if I put my finger on the intake port. I think the pinholes might be the cause of the leak, but as far as I can tell from the diagrams, the vacuum is not connected to the idle circuit, so it couldn't be the cause of the leak.
Also at higher revs the bike performs fine, which makes me think that the problem is in the idle circuit only. Carbs are clean (although I don't know what hides under the stuck screw). Haven't synced the carbs yet, but the exhaust pressure seems very equal and the fine test is something you do after all is fixed anyway right?
Sorry for the long read, lot of information, but I can't decide what the important bit is
Do any of you have suggestions for what I should try to fix first? Diaphragms or mixture screws? Any other things I should check?
Cheers
Berend
I had a thread earlier with some issues I wasn't able to resolve, and unfortunately they still haunt me. It seems to be a fairly common problem: when the bike is warm, it won't idle properly, which means I have to keep it revved at about 2-2.5k rpm, taking a lot of attention when I ride. The problem seems to get a lot worse if the bike gets warm, after about 45 minutes of riding or so.
Since the last time I posted, I managed to fix all the holes in the exhaust. There was quite a big gap in one of the mufflers, so I figured that would be a large part of the problem, but alas, it seems to have gotten even worse now.
As I understand all the posts here, I'm probably dealing with a lean condition in the idle circuit, due to a vacuum leak or maybe incorrect idle screws. The fuel setup on the bike is all stock as far as I can tell. Problem is, one of the idle screws is stuck and stripped and I will take them out at some point, but I'm a bit apprehensive to, because I'm afraid I'll do more damage than I'm fixing. So before I go in, I would like to rule out other possibilities. The one that wasn't stuck was set at 1.5 turns out, so I assume the stuck one is as well.
I have extensively checked for air leaks, and I'm quite certain the boots, throttle shaft seals, and vacuum ports on the exhaust and the air intake aren't leaking (wd40 spray test). I did find some pinholes in the carb diaphragms, but the slides do stay up if I put my finger on the intake port. I think the pinholes might be the cause of the leak, but as far as I can tell from the diagrams, the vacuum is not connected to the idle circuit, so it couldn't be the cause of the leak.
Also at higher revs the bike performs fine, which makes me think that the problem is in the idle circuit only. Carbs are clean (although I don't know what hides under the stuck screw). Haven't synced the carbs yet, but the exhaust pressure seems very equal and the fine test is something you do after all is fixed anyway right?
Sorry for the long read, lot of information, but I can't decide what the important bit is
Do any of you have suggestions for what I should try to fix first? Diaphragms or mixture screws? Any other things I should check?
Cheers
Berend