mdsims Posted March 31, 2009 Share Posted March 31, 2009 Bike: 77 xs400 Just got the carb rebuild kits in the mail so I put everything back together, threw the tank on and she started up first kick. sounded good, even firing. was running high though, about 4500 rpm. I figured it was just blowing through some extra fuel and getting warmed up and would tame down once warm. no such luck. not sure what that means or what I could do to fix that. any opinions? also, upon reassembly of the carbs, the choke rod no longer holds in the out position. it used to have two positions, in and out. now if I pull it out and let go, it just springs back in. maybe I missed something when reassembling the carbs? Link to comment Share on other sites More sharing options...
mdsims Posted March 31, 2009 Author Share Posted March 31, 2009 So I checked the float levels. I measured and they were quite low, 24mm, so I adjusted per the haynes manual (to 32 +- 1mm) and set mine at 31mm. Now I can't even get the bike to start. Seems like I'm fighting this beast at every step. Link to comment Share on other sites More sharing options...
mdsims Posted March 31, 2009 Author Share Posted March 31, 2009 In addition, sometimes the engine forces air back through the carb. I just got it to idle down to roughly 1600-2000 rpm. when I go to tun on the lights, then engine bogs down, slows, sputters a bit and tries to die. It's quite odd. the engine seems like it wants to run, but something just isnt set rightor there is something I'm missing. Link to comment Share on other sites More sharing options...
Ttaskmaster Posted March 31, 2009 Share Posted March 31, 2009 Have you made sure the air/fuel mixture is set correctly? Usually this kind of tuning is done by a mechanic with equipment and so on, but you can get it approximately right with a Colortune kit. the choke rod no longer holds in the out position. it used to have two positions, in and out. now if I pull it out and let go, it just springs back in. Dunno about your specific bike, but my Dragstar does this also. Always has. I have 3 positions; Off, Half and Full choke. When the engine is mostly warm the knob pops back in to half choke. When it's properly warmed, it pops all the way in. If I then hold it out, the engine either stalls or revs like a motherf**ker, so I try not to do that Link to comment Share on other sites More sharing options...
Moderator drewpy Posted March 31, 2009 Moderator Share Posted March 31, 2009 the haynes 32mm is wrong, its 26mm +/- 2.5mm you will find all of the above problems will disapear!! you have left your balls on the floor!! there are 2 tiny balls in the front carb bodies which are held against a notch in the choke lever by tiny springs. best get your magnifying glasses out Link to comment Share on other sites More sharing options...
mdsims Posted April 5, 2009 Author Share Posted April 5, 2009 It runs!! and I rode it around the block for a bit. I adjusted the float to 26.5mm and the thing still idles very high. I used the idle adjustment screw once it was warmed up and i slowly backed it all the way out with not much change in idle speed at all. There are times where the bike will idle around 1800rpm but the second she gets any throttle, she'll rev back up north of 3500. other than that the engine sounds great, the mixture seems not too rich, not too lean, pleanty of power when you open her up. Just this darn high idle. any suggestions? and I rewired the tail light and winkers due to some frayed wiring, works wonderfully now. Link to comment Share on other sites More sharing options...
Madison Motorsport Posted April 5, 2009 Share Posted April 5, 2009 The choke should be connected to a bi-metallic strip which auto-closes it to half setting once the engine warms up a little. Don't know if that helps you in any way. Link to comment Share on other sites More sharing options...
JimR Posted April 5, 2009 Share Posted April 5, 2009 In addition, sometimes the engine forces air back through the carb. I just got it to idle down to roughly 1600-2000 rpm. when I go to tun on the lights, then engine bogs down, slows, sputters a bit and tries to die. It's quite odd. the engine seems like it wants to run, but something just isnt set rightor there is something I'm missing. The Mixture is well wrong .. but I guess you have turned down the idle screw or adjusted it, as after work to the carbs this will alter, what you need to do is check the ign timming & valve clearences then connect vaccum guages to the take offs balance them then turn to the mix screws, with all the previous adjustments do the idle will alter so you will need to adjust this at every step of the way. The mix screws need to be screwed in fully home (lightly) and turned out until you get the highest idle, then adjust the idle down & check if the bike cuts out/slows down when you put the lights on ... then just tweek the screws until switching the lights on or off makes no difference. Regards Jim Link to comment Share on other sites More sharing options...
JimR Posted April 5, 2009 Share Posted April 5, 2009 The choke should be connected to a bi-metallic strip which auto-closes it to half setting once the engine warms up a little. Don't know if that helps you in any way. Not on an XS400, just a good old plunger choke with 2 grooves in it and a spring wire behind the rubber cap on the plunger which dropped into the grooves and held the choke full on or half on, back in the 80's the only Yamaha's the had bimetallics were bikes like the SA50, CV80, MJ50, BL125 and other bikes of that ilk Regards Jim Link to comment Share on other sites More sharing options...
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