Jimbozcrazy Posted March 28, 2010 Share Posted March 28, 2010 Hello, I'm the owner of a 77 XS500 C and cant figure out what gremlin is plaguing me. The bike runs wel enough when it's cold, but once it warms up develops a very high idle (this starts low and gradually gets higher (3500-4500 rpm) as the bike gets warmer/hotter). Once the bike gets fully warmed up or hot, it starts to bog down and requires almost WOT to get it moving at all. Once it starts doing this, it wont idle at all, like it's not running on both cylinders. If it stalls, it will easily start right back up, but RPM's must be kept very high (3500-4500 RPM) to keep running. This problem occasionally clears up for a minute or or so, but once the bike is hot, the problem is there intermittently until the bike cools off for a couple or three hours. Does anyone know what may be causing this? Any help at all would be MOST appreciated! Thanks! James Link to comment Share on other sites More sharing options...
Moderator drewpy Posted March 28, 2010 Moderator Share Posted March 28, 2010 weak fuel mixture Link to comment Share on other sites More sharing options...
Jimbozcrazy Posted March 28, 2010 Author Share Posted March 28, 2010 Ok, weak fuel mixture... Carb is clean, all passages seem to be unobstructed. Would incorrect idle mixture screw adjustment cause this? Or should I go directly to larger jets? I could also lower the c-clip on the needle. The bike is completely stock with the exception of individual air filters, instead of the factory air box. Now.... Please pardon me while I ask a real dumb question.... Float level? Would this cause my condition? The reason I'm asking is the only adjustments I've made on these carbs since I got the bike is the idle mixture screws (were completely closed when I got the bike) and float levels (raised them), thinking the bike was starving for fuel. Thanks! James Link to comment Share on other sites More sharing options...
turrican64 Posted March 28, 2010 Share Posted March 28, 2010 Ok, weak fuel mixture... Carb is clean, all passages seem to be unobstructed. Would incorrect idle mixture screw adjustment cause this? Or should I go directly to larger jets? I could also lower the c-clip on the needle. The bike is completely stock with the exception of individual air filters, instead of the factory air box. Now.... Please pardon me while I ask a real dumb question.... Float level? Would this cause my condition? The reason I'm asking is the only adjustments I've made on these carbs since I got the bike is the idle mixture screws (were completely closed when I got the bike) and float levels (raised them), thinking the bike was starving for fuel. Thanks! James Did it do this before the float level change? If not... 1. Any aftermarket filters will require a jetting change. 2. A rough estimate would be 1 1/2 turns out on the air screw. 3. Clip could go down the needle...better making it too rich than too lean IMO. If that helps, you need to fatten your jetting up. So go ahead and try it if the above don't work If this doesn't fix it up...maybe an air leak? Link to comment Share on other sites More sharing options...
Jimbozcrazy Posted March 29, 2010 Author Share Posted March 29, 2010 eh, it was a $100 basket case before... Negative on the air leaks, checked and rechecked several times. The floats were WAY off, I fixed that this afternoon. Might need to fatten up the the jetting, but this seems so much worse than just the jetting. I'm starting to think it's a coil. I checked the header temps once the bike started acting up again this afternoon. Left side (riders perspective) was 135 degrees, while the right side was 180 degrees. Like the left side wasn't even firing. Both sides are completely even when the bike is running right, but when it starts acting up, the left side cools off. Checked the plugs, just replaced them, doesn't look like one side is obviously more fouled than the other. Gonna replace the coils, check the air screws, and order some new jets i guess. Thanks guys, I'll keep ya posted on the outcome. Any other ideas, please feel free to chime in and let me know the error of my ways, God knows, I'm no expert at this stuf! Link to comment Share on other sites More sharing options...
Paulwhite Posted March 29, 2010 Share Posted March 29, 2010 id say try and get an airbox for it that would b ur easiest fix. because it has differant filters, there isnt enough suction so to say to suck the fuel through the jet. plus they say if ur rejetting the carb then u need to put differant air filters on plus put a new exhaust on with more flow. so as i said if you want to get it working the easiest way then try and get the airbox and go from there, then you will have a better idea of what could b up with it. plus lack of a good mixture could result in one cylinder running hotter than the other. plus all what you are discribing points to this. so try and set ur fuel mixture as rich as you can get it then see what happens, worse case senario it will start ok then bog down and stall when you put the power on. have you tried reving it with the choke on? thats an easy way to see if ur mixture is too lean, if its running ok with the choke on then cuts out with it off then you know its lean. hope this helps. Paul. Link to comment Share on other sites More sharing options...
Jimbozcrazy Posted March 29, 2010 Author Share Posted March 29, 2010 Big help Paul! Thanks! I have the original air box, I just gave up on getting it on the bike. Trying to fit that thing around those cables was hard enough, then the freakin thing fits SOOOOO tight, I couldn't get the darn thing on . So I decided to just put individual air filters on it instead. I'll re-apply my efforts on the air box again, as this truely seems to be the easiest fix because I have the parts on hand. Again, the only mystery to me is that the bike runs so darn well until it gets hot, then like a light switch.... BANG, runs like crapola. Reguardless, I'll try the stock airbox again as I am out of ideas. Just in case this doesn't fix it, are the coils from the XS650 the same as the coils for the XS500? Mikes XS has the 650 coils (but of course are currently out of stock). Thanks! James Link to comment Share on other sites More sharing options...
Jimbozcrazy Posted March 29, 2010 Author Share Posted March 29, 2010 Almost forgot another symptom... it does indeed act lean Paul. The RPM's hover a bit (between 1.5k and 3.5k) before returning to 1k after reving the engine and releasing the throttle (when the engine isn't fully warmed up). Been doin a ton of reading on lean/rich symptoms, and this one keeps hitting me square in the face. The hovering effect gets progressivly worse as the engine warms up. The idle keeps creeping higher and higher as well. If I set the idle at 1K with the engine cool, after it warms up, it wants to idle at 3-4k RPM. Eventually, it wont run at all below say about 4k RPM and acts like it's it's running on only one cylinder. James Link to comment Share on other sites More sharing options...
Jimbozcrazy Posted March 31, 2010 Author Share Posted March 31, 2010 Ok, Thank you all for the help and assistance, hope this post helps someone else out there too. Lean condition confirmed! The fix, however, was rather unorthodox. I still couldn't get that darn factory airbox on, so.... I wrapped duct tape around the individual filters until I acheived the desired result. I cant figure out how to post a pic of this, but soon as I can figure it out, I will for anyone wanting to see it. The tape wont be on there long, I'll soon be rejetting and putting aftermarket pipes on anyway. Link to comment Share on other sites More sharing options...
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