mtnmason Posted August 27, 2008 Share Posted August 27, 2008 hi all - soooo... the 77 xs400d that i picked up with less than 6k on the odo. is just about road ready. When i roll off of the throttle the engine sometimes wants to tach up to about 4000. Sometimes it will do this sitting still in nuetral after i have given it some gas. it will also do this on the road when i pull the clutch approaching an intersection. The only way i can get it to die down is by twisting out the idle adjustment screw on the carb. Then of course I have to twist it back the opposite way to keep it from dying on me. But then - sometimes i will pull up to a stop sign and the rpms will fall off as they should. What explains the eradic behavior? I will say that I have installed a new throttle cable and I have taken the carbs off and they appear to be virtually spotless. What gives? Could it be a float level problem? Any help would be very dear. Link to comment Share on other sites More sharing options...
billfrombyron Posted August 27, 2008 Share Posted August 27, 2008 My 360 is damn near doing the same thing. I found that I need to replace the intake boots, your mileage may vary. I will watch this to see if someone has a better suggestion than that. -Bill Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 27, 2008 Moderator Share Posted August 27, 2008 What gives? Could it be a float level problem? Any help would be very dear. Thats what i'm thinking too! Link to comment Share on other sites More sharing options...
mtnmason Posted August 28, 2008 Author Share Posted August 28, 2008 thanks for the quick response guys. i've looked at my boots and they seem to be intact. perhaps i will remove them next time i pull the carbs off for a closer inspection. keep up to date with me on this, billfrombyron (texas?) and maybe we'll find the fix. btw- are you using the adj. needle to get the revs down as well? again, thanks. Link to comment Share on other sites More sharing options...
mtnmason Posted August 28, 2008 Author Share Posted August 28, 2008 thanks for the quick response guys. i've looked at my boots and they seem to be intact. perhaps i will remove them next time i pull the carbs off for a closer inspection. i meant the carb mounts - not the intake boots. i know the intake boots are fine. i may be a newbie but i dont wanna sound like a dumb*ss Link to comment Share on other sites More sharing options...
Cy Welch Posted August 28, 2008 Share Posted August 28, 2008 thanks for the quick response guys. i've looked at my boots and they seem to be intact. perhaps i will remove them next time i pull the carbs off for a closer inspection. keep up to date with me on this, billfrombyron (texas?) and maybe we'll find the fix. btw- are you using the adj. needle to get the revs down as well? again, thanks. Also make sure the idle mixture is properly adjusted. The symptoms you describe are a sign of being lean and the idle cranked up to compensate. Adjust the mixture screws out until the RPMs stop going up and then back in just a little bit (adjust each carb a little and then do the other). Then adjust the idle (or even while doing this), if it's lean you will be amazed at the difference. Link to comment Share on other sites More sharing options...
christoph21 Posted August 28, 2008 Share Posted August 28, 2008 Yeah. Cy's right. This is a pretty common thing i find among these ~30 year old xs400's. Heck, Cy answered this very question for me aways back. Link to comment Share on other sites More sharing options...
billfrombyron Posted August 28, 2008 Share Posted August 28, 2008 Hm, I will try that myself this evening or maybe tomorrow whilst on CQ duty at the barraks. 24 hrs of nothing but time, though no internet... And no its Byron, IL.....the communist state, the state that brought you barak hussane obama, may he loose the election. Im currently at Fort Campbell, Ky until I get my walking papers this month or early next month. -Bill Link to comment Share on other sites More sharing options...
sschering Posted August 28, 2008 Share Posted August 28, 2008 Hm, I will try that myself this evening or maybe tomorrow whilst on CQ duty at the barraks. 24 hrs of nothing but time, though no internet... And no its Byron, IL.....the communist state, the state that brought you barak hussane obama, may he loose the election. Im currently at Fort Campbell, Ky until I get my walking papers this month or early next month. -Bill I have the same bike and just finished going through the carbs.. Almost all the parts are avaliable from Mikes XS http://www.mikesxs.net/ We have a earlier model of the BS34 carb used on the 80-up XS650 I'd recomend checking to be sure the diaphragms are not torn. to do this look in the intake side of the carb... push up the needle slider and then cover the oval hole on the top of the intake with your finger.. let go of the slide.. if it holds they are good. Also be sure they slide smoothly and don't hang. If you do take the sliders/diaphrams out be careful with them.. a new set is about $120 a pair. while you have the bowls off to check the float level you might take the time to pull and clean the pilot jets. these are located under the brass plugs right next to the main jets. also clean out the passages for the pilot jets and needle screws while you are at it.. If you open the throttle and look inside from the motor side you'll see 4 small holes in the roof.. the closer one is the passage for the needle screws, these are also called the pilot screws the 3 others are for the pilot jet circuit. You might see posts about the pilot jets being under rubber plugs but that's for the 80-up carbs.. Ours are srew on under brass caps. They also talk about removing a pressed in cap to access the pilot screws.. the 77 carbs didn't hide the pilot screws so don't go pulling out any plugs looking for em. the 80-up BS34 rebuild kits don't work for our carbs.. they changed the needle/seat design. Link to comment Share on other sites More sharing options...
mtnmason Posted August 28, 2008 Author Share Posted August 28, 2008 And no its Byron, IL.....the communist state, the state that brought you barak hussane obama, may he loose the election. -Bill Oooooh. Sorry Bill - damn those rotten America haters. Try visiting ol' Virginny sometime. despite our democrack governor we're usually pretty red through and through. To everyone else - thanks aplenty for the help. Guess i'll yank the carbs off once again this weekend (hopefully for the last time for a while). Happy riding. FALL IS ALMOST HERE!!!!! Link to comment Share on other sites More sharing options...
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