1981xs400II Posted June 9, 2010 Share Posted June 9, 2010 OK, here is the problem. The bike (81 XS 400) now starts up no problem, all the lights work properly and for the first few blocks is a pleasure to drive. 3 blocks later I hit a stop light and the thing is now going crazy! The RPM's are at 5,000 and they wont go down! Its the devil!!!!! Does it not want to leave my home? Does this bike hate me?? Where the heck does that petcock lever go? Left, right or the middle? Is it related to the RPM's? What the heck is going on? Also, sometime the bike feels VERY powerful, then the next time I go to ride it seems to be at 70%?? Any suggestions??? Link to comment Share on other sites More sharing options...
Ebola Monkey Posted June 9, 2010 Share Posted June 9, 2010 OK, here is the problem. The bike (81 XS 400) now starts up no problem, all the lights work properly and for the first few blocks is a pleasure to drive. 3 blocks later I hit a stop light and the thing is now going crazy! The RPM's are at 5,000 and they wont go down! Its the devil!!!!! Does it not want to leave my home? Does this bike hate me?? Where the heck does that petcock lever go? Left, right or the middle? Is it related to the RPM's? What the heck is going on? Also, sometime the bike feels VERY powerful, then the next time I go to ride it seems to be at 70%?? Any suggestions??? Petcock: PRI: Prime, not vacuum operated, just OPEN On: Vacuum operated. Only lets fuel through when engine is running, if petcock is good. RES: Reserve, also vacuum operated, same as above, when you hit the reserve level go get gas. As far as the revving, check for air leaks in the carb holders. Also what choke setting do you have it on. Mine I start on full choke, then turn down to half for a few minutes, then off. If I leave it on half it will rev up to around 3000, and stay there after a while. Link to comment Share on other sites More sharing options...
1981xs400II Posted June 9, 2010 Author Share Posted June 9, 2010 Petcock: PRI: Prime, not vacuum operated, just OPEN On: Vacuum operated. Only lets fuel through when engine is running, if petcock is good. RES: Reserve, also vacuum operated, same as above, when you hit the reserve level go get gas. As far as the revving, check for air leaks in the carb holders. Also what choke setting do you have it on. Mine I start on full choke, then turn down to half for a few minutes, then off. If I leave it on half it will rev up to around 3000, and stay there after a while. Mine is reving at 5,000 with the choke all the way in. It seems to go down when it feels like it...then it will idle too slowly and stall? So, it should be on the on or res position most of the time? Thanks Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 9, 2010 Moderator Share Posted June 9, 2010 but also you may be able to tune the revs down by turning the pilot mixture screws anticlockwise which richenes the fuel mix! yellow on the diagram Link to comment Share on other sites More sharing options...
1981xs400II Posted June 9, 2010 Author Share Posted June 9, 2010 but also you may be able to tune the revs down by turning the pilot mixture screws anticlockwise which richenes the fuel mix! yellow on the diagram Can I get at that with ease? Do I have to do any dismantling? Thanks Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 9, 2010 Moderator Share Posted June 9, 2010 no, its on top of the carb as per diagram Link to comment Share on other sites More sharing options...
Ebola Monkey Posted June 9, 2010 Share Posted June 9, 2010 no, its on top of the carb as per diagram Drewpy, Isn't the mixture screw blocked by a brass cap on the 81? I know it is on the 82. Link to comment Share on other sites More sharing options...
dtmf Posted June 10, 2010 Share Posted June 10, 2010 Mine is reving at 5,000 with the choke all the way in. It seems to go down when it feels like it...then it will idle too slowly and stall? So, it should be on the on or res position most of the time? Thanks it should be in the on position all the time. it will let you know when you need the res . the 1st thing i did when this happened to me i pull'd the carbs and the carb boot's . then i resealed the carb boot's to the head. cleaned the carb's put them back on and resync'd them and was good to go Link to comment Share on other sites More sharing options...
Noah Posted June 10, 2010 Share Posted June 10, 2010 I would have to agree, it seems like a fuel mix issue, sounds like she runs fine then something heats up and starves her for fuel causeing the reving, you should definatly richen up the high speed needle, if you can easily get at it I would put a screwdriver in your pocket and take her out when she revs pull over and richen by 1/8th turn at a time till reving stops and she idles good again then ride some more if she revs again repeat, if this is obviously not working check for air leaks around the carbs, clogged fuel filter, degradded vacume line. as for the petcok leave it on PRI it will function normaly if not get a new one or rebuild it, rebuild kits are $25usd, could also be the vacume line to the petcok has a small air leak causing the problem, do not just open the petcok this is for draining fuel without removing the tank, in a bind it's okay to get you home but just leaving it there is a bad idea and you will soon figure that out for yourself when you go to get on the bike and realize that your tank contents are on the ground below the bike. Link to comment Share on other sites More sharing options...
1981xs400II Posted June 10, 2010 Author Share Posted June 10, 2010 I have to be honest here. I don't see any adjustment screws other than one that looks to be a throttle adjustment of some sort. I actually monkeyed with it last night and amazingly the bike ran good! No high idle, no stalling...I actually was confident to take a 5 kilometer ride! I definitely have to investigate the carbs further as I dont see adjust screws (at least from the sides) as I have had on previous bikes. Link to comment Share on other sites More sharing options...
armyofda12mnkeys Posted June 11, 2010 Share Posted June 11, 2010 I have to be honest here. I don't see any adjustment screws other than one that looks to be a throttle adjustment of some sort. I actually monkeyed with it last night and amazingly the bike ran good! No high idle, no stalling...I actually was confident to take a 5 kilometer ride! I definitely have to investigate the carbs further as I dont see adjust screws (at least from the sides) as I have had on previous bikes. Here ya go if not sure of where to find the adjustment screws (correct me if Im wrong hehe): Show the carb from the Left side of bike, Lower Left side, Right side, Someone else's right side with the 'limiter cap' on idle mixture screw(s) Link to comment Share on other sites More sharing options...
1981xs400II Posted June 11, 2010 Author Share Posted June 11, 2010 Apparently either I am missing parts or this isnt the original carb. I dont see an idle mixture screw anywhere? I think I can see the balancer adjuster screw. Sorry for the crappy pictures but I had to use my Blackberry. Link to comment Share on other sites More sharing options...
armyofda12mnkeys Posted June 11, 2010 Share Posted June 11, 2010 Apparently either I am missing parts or this isnt the original carb. I dont see an idle mixture screw anywhere? I think I can see the balancer adjuster screw. Sorry for the crappy pictures but I had to use my Blackberry. hmmm, does seem like the same carb from the markings/MK label. Are you missing Idle Mixture screws lol? Can someone else confirm Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 11, 2010 Moderator Share Posted June 11, 2010 i got a pair of the DOHC carbs and they are recessed inside the "yellow" in the diagrame. It could be that there is also a thin plate across it to stop peeps fiddling, just needs to puncture it with a nail and lift it out. Link to comment Share on other sites More sharing options...
1981xs400II Posted June 11, 2010 Author Share Posted June 11, 2010 i got a pair of the DOHC carbs and they are recessed inside the "yellow" in the diagrame. It could be that there is also a thin plate across it to stop peeps fiddling, just needs to puncture it with a nail and lift it out. But what about the idle mixture screws? They both seem to be missing? Should I go get a couple and put them in? Are they actually missing or not suppose to be there? Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 11, 2010 Moderator Share Posted June 11, 2010 But what about the idle mixture screws? They both seem to be missing? Should I go get a couple and put them in? Are they actually missing or not suppose to be there? so you looked inside and all there was, was a hole? yep you need those screws, I'd pull the carbs first and checked the screw's tips wer'nt snappped off in de hole! Link to comment Share on other sites More sharing options...
1981xs400II Posted June 11, 2010 Author Share Posted June 11, 2010 so you looked inside and all there was, was a hole? yep you need those screws, I'd pull the carbs first and checked the screw's tips wer'nt snappped off in de hole! it sure is odd that both screws are missing (as pictured above)...and that it seems to be running quite well? I am going to a shop at lunch and have it looked at (I need some other parts anyways). I will let you know what they say. Thanks Link to comment Share on other sites More sharing options...
Ebola Monkey Posted June 11, 2010 Share Posted June 11, 2010 There should be screws in there. They are the spots that drewpy pointed out, but if they are untouched they will be plugged with a brass plug. The plugs are pretty thick, and you have to drill a hole in them then use a screw, or something to pull them out. You have to be very careful though because the mixture screws are very close. If you get goofy with the drill you can mess up the mixture screws. If the plugs have been removed the mixture screws are recessed pretty far. Have you actually removed the carbs, and looked?? You can't see the screws without removing them. If you have a flathead screwdriver that will fit in there you should be able to feel them, and adjust. It's a pain in the ass though. They are in the spots with the arrows. Link to comment Share on other sites More sharing options...
1981xs400II Posted June 11, 2010 Author Share Posted June 11, 2010 There are working screws in there. I was told by the mechanic that there were two versions of the screws. Long and short..dont know if thats true or not but thats whats in there. He also said that the longer version of the screws were like $60 buck each! I have yet to go and check it out online but I am guessing if I needed them I could get them cheaper. Turning the screw clockwise or counterclockwise...what exactly does it do? Thanks Link to comment Share on other sites More sharing options...
Noah Posted June 11, 2010 Share Posted June 11, 2010 they are the idele mix screws also known as low end or low speed needle, counter-clockwise will unscrew it so the fine tip pulls out of a small hole makeing it bigger so more full can flow, this is richening the mix, which in turn should help with your high rpm idle which is a sign of a lean idle mix, if you have a problem with bucking, sputtering or some other fuel issue at high rpm you need to adjust the high speed needle screw on each carb, good luck. from what I can tell not a long and short screw rather a small redesign of the carb where they resesed the needle screw rather then having it open. Link to comment Share on other sites More sharing options...
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