2wheel newbie Posted April 9, 2010 Share Posted April 9, 2010 My neighbor recently bought a 1981 xs400SH, it was running when he bought it. One morning it wouldn't start, so he asked me for help, I'm a car mechanic. I've never worked on a motorbike before, but on a 30year old carb'ed Yamaha, how hard could it be? I grabbed my battery jump pack and got it started. He took it for a quick spin up and doun the street, he came back pushing it and when it went over the curb, gasoline poured out the air filter boxes. I grabbed a drain pan and drainded the tank, I told him that the carb floats were probably stuck wide open. I told him I could easily fix that. I took the carbs off the bike, took them inside, to work on, removed the float bowls, the floats and the float needles. Both needles had rips in the rubber tips. I stoped by the library for a book on Yamaha XS bikes to supplement the Haynes manual that came with the bike, and went to the bike shop for new needdles and seats ($90 ). I put them in, adjusted the float level to 32mm like the books said, put it back to gether with new gaskets. Before I put the carb back I fliped the rubber boot/carb holder thingies so that the vacuum ports pointed up (previous owner replaced them w/o gaskets when he replaced the carb with another one). I reconnected everything, set the fuel tap to PRI, pulled out the choke all the way, started it up. Then it stalled when I put it in 1st choke position and gave it even a little bit of throttle. Wouldn't fire at all with the choke all the way in I went back to the bike shop for advice, they looked at the carbs and tolled me the anti-tampering plugs on the pilot screws were gone and the screws were all the way in. He backed them out 1 1/2 turns. I looked online and MikesXS(dot)net says: "Suggested setting position of the normally hidden mixture screw is 2 1/2 to 3 turns out from bottom." I tried starting the bike at 1 1/2 turn from bottom, 2 turns, and 2 1/2. Would not start at any those I tried. My neighbor had the original carb with the anti-tamper plug still in place, I used a drill and tap to remove them, and the right carb had the needle at 4 1/2 turns. I could'nt find out the left side, the drill went in too far, toutched the needle and turned it all the way in. I swapped the screws with the ones from the old carbs (after soaking them in cleaner over night) and turned them out 4 1/2. Still wouldn't fire. When ever I pull the plugs out, they are damp, but not soaked. I pulled the spark plugs out and held them against the cylinder head. I didn't see a spark jump the gap. After reading the wiring diagram and testing every componant, I replaced the TCI box with a used one ($50), now I get spark, but it seems weak, both coils read 3 ohms on the primary, but I'm not sure how to measure the secondary. Do I remove the plug wire, leave it on but unscrew the spark plug cap, or measure it with everything on? I've also done a valve adjustment, oil change (crankcase was full of gas), put in a new used starter solenoid, new fuses, charged the battery several times with my car batt charger, and gapped the spark plugs to .6mm to help the spark jump the gap. I need advice, I'm about to pick this thing up and throw it in the dumpster. Link to comment Share on other sites More sharing options...
2wheel newbie Posted April 11, 2010 Author Share Posted April 11, 2010 Never mind, I got it running by sanding off a rather thick layer of build up that looked like metal (but was actually soot) from the spark plug electrodes and hooking it up to my car battery charger and using the 260 amp Start Boost setting. Setting the mix screws to 4 1/2 turns after it had warmed up had it running perfectly. Now I just need to put in a new voltage regulator for the charging system to work. Link to comment Share on other sites More sharing options...
sdhynds Posted April 14, 2010 Share Posted April 14, 2010 Never mind, I got it running by sanding off a rather thick layer of build up that looked like metal (but was actually soot) from the spark plug electrodes and hooking it up to my car battery charger and using the 260 amp Start Boost setting. Setting the mix screws to 4 1/2 turns after it had warmed up had it running perfectly. Now I just need to put in a new voltage regulator for the charging system to work. Nice work - Going thru a lot of the same stuff on my bike. I admire your patience and restraint as I have wanted to pick mine and and toss it in the dumpster several times as well Link to comment Share on other sites More sharing options...
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