bswinn Posted June 10, 2010 Share Posted June 10, 2010 Alright I hate to beat a dead horse....and by dead....I mean nothing left but bones since all the flesh is LONG gone. It's just that I've spent HOURS reading through these forums about carb issues/information and can't seem to nail down what I need to know. The bike. 1977 XS400D. The carbs. Mikuni BS32 I think. The issue. Cold bike, pull the slide choke or enricher or whatever all the way out. Start bike. Revs spike and then slide the choke in half way and revs go down and then spike again. Choke is all the way in now and revs seem to be okay around 1500. Take the bike on the road and hit a stop light. Revs hold steady at 3000+. The only way I can get them down is to hold the brake and let the clutch out and bog the engine down. It'll stay at 1500 for a bit but then shoots back up to 3000+. What I've tried. Adjusting the idle speed screw that lies between the carbs. This doesn't seem to do squat. The idle mixture screws are out about 1.5 to 2 turns. Balancing doesn't seem to work at all. When I think it's balanced and I rev up the engine the balance is WAY off and wont go back even at a steady idle. What I've read. If the idle mixture screws are making the mixture too lean it can cause a high rev. If this is the case is there some way of adjusting the mixture screws so that they are at a good level? Broken carb holder boots can cause a bad idle. But I have brand new gaskets and boots on it so I doubt it's this. Lack of a good filter (letting too much air through) can cause a high idle. If I decide to put new filters on then I would have to buy pods and rejet the carbs. Does anyone know the correct jet sizes for a poded carburator on this bike? Could this also be due to bad float levels? I adjusted them to what is in the haynes manual, but the manual contradicts itself with two levels. Does anyone know the correct float level and where exactly it's measured from? I know these issues have been hammered to death and I apologize for making yet another post about this. But it's riding season and this is the last thing I need to get done on the bike. I have the bike out and running but I know the carbs aren't adjusted correctly. Any help would be greatly appreciated. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 10, 2010 Moderator Share Posted June 10, 2010 can't touch this....... 1) the carbs are 34mm, you didn't read properly did you!! 2) don't overtighten the intake boots onto the cyl head as they can bow leading to air leaks, use the correct torque 3) try enrichening each pilot mixture screw ANTICLOCKWISE say another 1 to 2 turns and see what happens 4) I inadvertantly forgot to tighten the intake jubille clip on carb to intake which sucked in air, i blame OG for that one! 5) try spraying wd40 or such arounf the intakes, any change in engine revs indicates an air leak 6) float height is 26mm NOT 32mm as per haynes Link to comment Share on other sites More sharing options...
HoughMade Posted June 10, 2010 Share Posted June 10, 2010 I agree with everything Drewpy says. This sounds like a lean idle issue. Assuming no intake leaks (good advice of what to check above, you need a richer idle mixture. I have my idle screws at about 3.5 turns out and it revs easily and returns to 1200 rpm idle quickly. I know what the manual says, but those settings are aimed at passing emissions tests, not at good performance. Link to comment Share on other sites More sharing options...
bswinn Posted June 10, 2010 Author Share Posted June 10, 2010 Thanx guys. I'm gonna head out and adjust those mixture screws right now and see what happens. If they ever successfully clone a human being I'm gonna make sure they clone Drewpy so I can have my own copy here at home whenever I run into an issue Link to comment Share on other sites More sharing options...
bswinn Posted June 15, 2010 Author Share Posted June 15, 2010 Okay...my bike is the magical mystery bike. It's a walking contradiction. That or I know nothing about what i'm doing. I adjusted the idle speed screw to JUST on the verge of stalling the bike. That means it's either tacking at 3000 or stalling. I assume that this means that the butterfly valves are only SLIGHTLY open so the bike will actually run. The idle mixture screws are anywhere from 4.5 to 6 turns out. They started at 3 when I first started this thread. The bike is STILL running at 3000 RPM and the plugs are carbon fouled (light powdery black coating) after running in idle fro 10 to 15 minutes. I've searched and this means that the carbs are running too rich correct? So I'm at a loss now. The idle mixture screws being turned anticlockwise make the mixture richer (more gas)? If this is the case then I must have to go the opposite right? Screw them clockwise to make the mixture leaner? But wont this cause the RPM's to go up? Link to comment Share on other sites More sharing options...
armyofda12mnkeys Posted July 11, 2010 Share Posted July 11, 2010 So I'm at a loss now. The idle mixture screws being turned anticlockwise make the mixture richer (more gas)? If this is the case then I must have to go the opposite right? Screw them clockwise to make the mixture leaner? But wont this cause the RPM's to go up? yes, screwing it clockwise will make it leaner... (if its a carb with the mixture screws towards engine versus back of the carb which i believe it is) hmmm not sure about rpm's. i dont think it really messes with the rpm's when i mess with the idle screws. it just stalls if i goof on the setting. Get a Colortune 14mm spark plug to play with if you got $50 to spend... I like it as you can literally see whats going on in there (spark plug has clear casing you can see through). and get the mixture correct when it turns burnsen burner blue ... then mess with the throttle-stop screw to optimize rpm's at idle. Link to comment Share on other sites More sharing options...
junununu Posted October 13, 2010 Share Posted October 13, 2010 recycling an old topic. I'm basically having the same issues as the OP. I enrichened the mixture and used the balance screw enough to get it to hold at 1200-1300 idle. I also screwed the throttle stop screw all the way out and just in enough to where it doesn't die(I hope I did this right), but I'm still having the high idle issues. I'm still running a tank of seafoam as we speak, but its not done yet, I'm afraid to go anywhere because my kickstart also is shot, but thats another post. The electric start also doesn't start with a bit of throttle to it, if that helps in the diagnosis. why does the idle come down when the front brake is pulled all the way in? when parked at my house, the idle also comes down a bit when i turn my lights on(sometimes). Link to comment Share on other sites More sharing options...
OllieB Posted October 13, 2010 Share Posted October 13, 2010 recycling an old topic. I'm basically having the same issues as the OP. I enrichened the mixture and used the balance screw enough to get it to hold at 1200-1300 idle. I also screwed the throttle stop screw all the way out and just in enough to where it doesn't die(I hope I did this right), but I'm still having the high idle issues. I'm still running a tank of seafoam as we speak, but its not done yet, I'm afraid to go anywhere because my kickstart also is shot, but thats another post. The electric start also doesn't start with a bit of throttle to it, if that helps in the diagnosis. why does the idle come down when the front brake is pulled all the way in? when parked at my house, the idle also comes down a bit when i turn my lights on(sometimes). Have you replaced the small O-rings that are found at the base of the idle mix screws? These get hard and deformed and will leak air causing just what you describe. Same symptoms with my bike. After I installed a set of new idle mix screws and O-rings, engine behaved as it should with idle mix screws set at about 3 turns out. Link to comment Share on other sites More sharing options...
Recommended Posts