James in Atlanta

I find some knock off air filters for $14 HERE. I was thinking about picking up a pair. I put in new spark plugs and the new fuel filter today, and the bike ran beautifully for a few hours I also noticed I have a 2 into 1 exhaust, and after reading the forums here I don't think thats standard. Am I correct in that assumption? Mine is a 1980 XS400 (special I think?). Would the bike run well with new exhaust without rejetting the carbs? Again, the idle screws still have caps on them, so nobody has touched those. I won't know for sure about the jets until I take the carbs off in December. I guess its more for my curiosity and to make future plans if I ever decide to change the air filters. Thanks for the suggestion OllieB, I'm trying not to add any aftermarket stuff if I can help it, at least not while I'm on a poor college kid budget.

I found pictures of what the air filters are supposed to look like, and I think the ones I have are almost unusable. The metal on the sides of the air filter are not attached so the whole things falls apart if you touch it. I think this is why its hard for me to attach them to the hoses. I saw some pics where others have used a different air filter in lieu of the stock filters and boxes, but it sounds like the carbs have to be rejetted for this to work. This may be too much work for me at the moment, so I might try and find some original replacement air filters. One problem at a time though. Once I get the air filters properly connected, I'll get back to you if it is still having problems idling. The previous owner said he cleaned the carbs out well, so I'm going to avoid doing it myself for a few months if possible. I should have more time for such a task in December. Thanks all!

It seems the air filters have a mesh cage connected to a metal cylinder. The metal cylinder part sticks out of a hole in the filter box, and this is the part that connects to the hose leading into the carbs. The rubber between the carbs and the engine and between the carbs and the air filters looks brand new, so I assume they were recently replaced. The air filters look home made, but with the original cage. The metal cylinder on the cage was wrapped with black electrical tape, so there was no way in hell they were going to fit inside the rubber. I removed the tape, but I still have a hard time pushing the metal into the rubber. It seems to be an extremely tight fit, and the metal part of the air filter retreats into the filter box when pushed making it even harder to connect. I think the rubber intakes may be a size too small? Did the intakes and air filters I described sound normal, or has something been 'ghetto rigged'? I unscrewed the battery box between the two air filter boxes to make this task easier, but that was rather annoying. I got the left air box connected solidly, and the right one still lets air in at the connection so I will work on it tomorrow. It ran great today after I fixed this. It idled around 1600 which is high (should be 1200 I read). I ran it around the block for about 30 minutes and I had no loss of power all the way up to 8000RPM. The idle didn't stick when I made it to a stop sign, so its some improvement I think. There 'was' an inline fuel filter, but I managed to break it yesterday :-/ I will get another one, it looks the K&N one I saw on a previous thread. I am trying to avoid removing the carbs because I live in an apartment and management gives me dirty looks when I work on the bike, but if I have to I have to. The idle screws still have the metal plug from the factory, so I will have to drill those out to access the screws. If the bike is running, what are the downsides of having it idle a little high? Thanks for your suggestions, I am not only new to the XS400, but this is my first motorcycle.

Just bought a 1980 XS400, and it runs...sometimes. It cranked today relatively easily with the choke all the way out. I let it warm up for a few minutes, then pushed in the choke. It seemed to be idling around 1400. I ran it around the block for about 30 minutes and it was fine. Went home and turned it off. About 20 minutes later I started it up again, but it was having a hard time idling. RPMs dropped several times before it just died. I kick-started it , and revved the throttle. When it dropped to idle, it would die again. Sometimes when it was trying to die, I revved the throttle, but that just made it die quicker. I adjusted the idle stop screw between the carbs so it would idle a little higher, but I had to drop it back down because after revving the throttle it would stay at 3000RPM. The air filter boxes are very poorly connected to the carbs. I tried to make a secure connection with the clamp on the rubber hose to the box, but the metal shaft sticking out of the box kept getting pushed inside the box. So, the boxes aren't really connected to the carbs. Air can enter the hoses directly to the carbs and bypass the air filter boxes. Is this the reason the bike dies while idling, or do I have a more serious problem? Also, any suggestions on the air filter boxes? Are they supposed to do this, or are mine screwed? Thanks for any suggestions!