XS400 carb issues

[atticus]

I need help. I have a 1979 XS400 that is only running on one cylinder, the right cylinder isn't firing. It has good compression and good spark i just don't think it's getting fuel. I've pulled the carbs off the bike and pulled out all the jets and so forth and cleaned EVERYTHING. The right cylinder is still not running and now the left cylinder is back firing and dying. I'm a new rider and not very familiar with carbs. Any ideas anyone?

[bikerphil]

Make sure you are getting good unrestricted fuel flow from your petcock. Are the floats set at the correct level? Are the carbs absolutely clean, meaning...did you spray carb cleaner thru every passageway making sure there are no obstructions? Did you remove the pilot jets too and not just the mains? Try some new plugs if yours have been fouled before. HTH

[cywelchjr]

I need help. I have a 1979 XS400 that is only running on one cylinder, the right cylinder isn't firing. It has good compression and good spark i just don't think it's getting fuel. I've pulled the carbs off the bike and pulled out all the jets and so forth and cleaned EVERYTHING. The right cylinder is still not running and now the left cylinder is back firing and dying. I'm a new rider and not very familiar with carbs. Any ideas anyone?

Idle circuit is still clogged or you have a vacuum leak. With it running spray some starting fluid or wd-40 around the carb boots and see if it makes any difference. If it does fix the leak (replace or seal the boots), otherwise you still need to clean the idle passages.

[soccer4m]

try this

HI, I have had a few xs400's. The carbs are pretty simple pieces. Just try again to flushout all the jets, always have a GAS FILTER inline with the tank-very important to keep the crud out. Another trick is to pull the plug, check it for color, squirt some gas in the hole and quickly put plug back in. Crank it over and it should quickly fire for a second or two. If it does then your firing is ok, then onto the carbs. Probably your float is not working properly. Check both carb floats to see if they are the correct and SAME height when raised, and freely moving up and down. Blow through the fuel line to see if both carbs have free passage to the float needle, if not, then blow through some carb cleaner and flush out. Try blowing through with carb rightside up and upside down. ONe way the air goes through easily, the other the float should close off the flow,now go clean one more time, blow lots of carb cleaner through the passages and good luck, let us know ,,,,regards, Mike in S.Diego

[soccer4m]

almost forgot

Almost forgot some other points, the carbs need to be synchronized. There is one screw that does this. THe bike has to be running, so the carbs should be cleaned and gas flowing ok first. Get a repair manual for the bike,,,Ebay has lots of them, read the synch. section. Basically, hook up a carb synch tool,,,Ebay has them or JC Whitney, to the carb vac tubes, get bike running, at high idle, and turn screw until both gauges, one on each carb, are equal readings. Then both carbs are flowing equally. Also,,,,,,,CHECK YOUR VALVE CLEARANCE! Maybe prev. owner didnt adjust properly. Use a feeler gauge and check the cylinder that is not right. Also, switch spark plugs to see if one is malfunctioning, and check that they are correct for that bike, use manual. You will get it going, they are very foregiving bikes, and easy to maintain once adjusted .....Mike

[atticus]

Ok, I've reset the floats in the carbs (they were both set wrong) and I've sealed up the vacuum leaks. The right cylinder still isn't running right, in fact it's blowing smoke now. Could the valves be out of adjustment?

[atticus]

Oh and also, I've heard of two different settings for the floats, 32 mm and 26 mm. I set mine to the 26 mm, was this right?

[soccer4m]

valves

Hey Atticus,,,yes, check the valves carefully. Follow the manual and leave slightly loose with the feeler gauge. Also, check the points to make sure they are adjusted with the right gap and not worn out or pitted. It could be blowing smoke because of the above, or the rings are shot on the piston. Adjust the valves, points, and put in some fresh thick oil, maybe 30 or 40 weight which will not blow by the rings as bad. Also, if there is gas in the oil from flooding or leaking needle in the carb it will blow oily smoke from the exhaust. So,,,,,,,check valves,,,points,,,,,and drain the oil asap. Stick a long skinnny branch in the oil filler hole until it reaches the oil. Pull it out and smell it and feel it. If is smells slightly like gas or is thin feeling you have gas in the oil. You can also try lighting the stick with a match and if it burns you have gas in the oil. Anyway,,,,,narrow down the problems one by one. The carb float setting is in the manual but 25 cm sounds about right. As long as both floats are adjusted the same, both carbs should act the same. Try screwing in the mixture screws to see if each one is turned out equally. If one is way off one will run too rich. Regards, Mike in S.Diego

[DJinNH]

I need help. I have a 1979 XS400 that is only running on one cylinder, the right cylinder isn't firing. It has good compression and good spark i just don't think it's getting fuel. I've pulled the carbs off the bike and pulled out all the jets and so forth and cleaned EVERYTHING. The right cylinder is still not running and now the left cylinder is back firing and dying. I'm a new rider and not very familiar with carbs. Any ideas anyone?

I wish you weren't all the way across the country. My girlfriend's landlord has a 400 Special sitting in his back yard that he wants to give away. It's in pretty sad shape but you could probably get some internal parts out of it.

Don (New Hampshire)

[atticus]

That would be nice having a free parts bike. So, I got curious and decided to do a carb swap. my wife's bike is an identical XS 400 (which runs like a champ by the way) so I pulled the carbs off and installed them on my bike. And guess what, my bike runs great. Anyone know where I can get a set of carbs for a 1979 XS 400 that are in good shape?

[soccer4m]

try ebay

Hey Atticus,,,good news for you that the other carbs worked, which eliminates lots of other possible problems. I would suggest EBay for the carbs, and or get a rebuild kit for yours from Carb kit capital, or partsnmore, or any carb rebuild kit supplier. There should be a few on Ebay at any given time. Good luck, Mike in S.Diego