Inherited a 1979 XS650 Bobber build which is in progress. It has a Harley peanut tank on it with all the vacuum hoses blocked. No gas/carb problems with the old air box attached but when it was removed and cones were installed first the left carb started spewing gas then the right. I have rebuilt several Keihin CV 40's but never fooled with Mukuni's. Have checked out the Tech. section on this site and have no problem with taking these carb's off and apart but I sort of live by the KISS principle. So, I was wondering if anyone else has experience with this or a similar problem and has a fix/suggestion before I go exploring?
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Carbs spewing gas
- Thread starter OldGuy
- Start date
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- carburetors
Ironsled77
XS650 GRAND HACK
check float level
Never had the bowls off of these. Easier to do off the bike or can be done in place with care?
Hi and welcome to the forum. It can definately be done with the carbs on. What I do is take a phillips bit like you would use in a cordless drill, and with a 1/4" wrench and a mirror you can pull the screws. Its a bit tricky at first, but can be done. I would recommend pulling the needle and seat, on the BS38's the seat is removable (10mm I believe) and I take a q-tip with some rubbing compound, that you would use on buffing out paint. Put the q-tip in ur drill and clean/polish the seat and needle. Had gas gushing out of mine last week, and this cured it. Make sure there is a filter on the bike. My peanut tank has it on the inside, but I still get settlement in my bowls. May install an inline filter to see if that gets more of it.
bassgoat1979
XS650 Addict
Did you try to to tap it firmly with a screwdriver handle to the bowl? If it doesn't work the float valves (needles) are shot, I think it's easyer to pull the carbs. Saves me a lot of cussin and only adds about 15 minuets to the job. Gives you a chance to check the boots out too and clean them good.
bloodthirstysystem
XS650 Addict
the floats have a hole and are sinking OR the float level is way off OR the float needle is stuck and not stopping the gas flow
take em off, might as well clean them out while you're at it
take em off, might as well clean them out while you're at it
These carbs DO NOT have float valve o-rings do not replace what does not exist. Only the BS34 series have float valve o-rings. Those (nearly always) need to be replaced.
Pull the carbs, it's not that bad and if you don't you will a little later anyways.
Pull the carbs, it's not that bad and if you don't you will a little later anyways.
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bassgoat1979
XS650 Addict
I would get kits and do everything unless you like pulling carbs.
pamcopete
Ride.Enjoy.Life is Simple
OldGuy,
Some of the after market cone filters block the vent for the bowls. Try removing the cones and see if you still have the problem.
Some of the after market cone filters block the vent for the bowls. Try removing the cones and see if you still have the problem.
Sundie
Jabroni
78/79 float valves do not have o-rings. They screw in. They don't even have rubber tips on the pins.
I would take them off the first time to get the float bowls off. They probably need a good cleaning anyway. And the screws may need some grunting to get them to release, which is impossible with the carbs still on the bike.
Get the kits (which include the main and pilot jet) and a new z2/502 needle jet/needle and a needle jet o-ring. Rebuild and clean. It's totally worth it to bring the carbs to a known point.
Your carbs (if they really are 78/79) should have an E or F stamped on the bottom of the float bowls.
I would take them off the first time to get the float bowls off. They probably need a good cleaning anyway. And the screws may need some grunting to get them to release, which is impossible with the carbs still on the bike.
Get the kits (which include the main and pilot jet) and a new z2/502 needle jet/needle and a needle jet o-ring. Rebuild and clean. It's totally worth it to bring the carbs to a known point.
Your carbs (if they really are 78/79) should have an E or F stamped on the bottom of the float bowls.
bassgoat1979
XS650 Addict
Yes the aluminum needles don't get grooves and the brass seats never get pits in the seat area. That is why they don't sell replacements becuase they never go bad. In reality they go bad more often that is why they switched to rubber tips on the needles. If you are spewing gas and never have been in the carbs befor it is either a float valve sticking or a bad needle and seat. I guearentee you that is you say the needle and seat look good, you will be in for a headache in the very nerar future if not as soon as you fill them up with gas, just replace them. If you don't have $40 for the bike, I would sell it, I will cost more than that to keep it going. I run a small engine repair shop that includes bikes and atvs and the #1 repair is carbs. If I ever try to use the needle ant seat agian it seems the job comes back in a week. (even aluminum needle carbs!!!) Cheap insurance IMO.
Even if the air filter blocked air jets and vents it wouldn't leak gas just from putting them on.
If you rebuild them and clean them completely you won't have a issue (don't mess with the floats hieght they worked before!!!) you will be happy. If you want to try to just get it working, good luck!
Even if the air filter blocked air jets and vents it wouldn't leak gas just from putting them on.
If you rebuild them and clean them completely you won't have a issue (don't mess with the floats hieght they worked before!!!) you will be happy. If you want to try to just get it working, good luck!
Sundie
Jabroni
uh, i was only mentioning that the seats don't have an o-ring as a correction. But +100 points for crankiness.
By the by, blocking air jets *will* cause excess fuel to be sucked up into the carb body, the same way that if you have a hole in the side of a straw, you can suck up more liquid with the hole covered than open.
By the by, blocking air jets *will* cause excess fuel to be sucked up into the carb body, the same way that if you have a hole in the side of a straw, you can suck up more liquid with the hole covered than open.
Also the running engine vibration will loosen years of Cr#p from the tank that immediately heads down to fuggle your carbs.
Too all of you that posted a reply to my question, I thank you. They provided fuel for thought. The carbs are off, doing a clean and rebuild, then I'll see what happens. Floats weren't taking on gas and were still on factory setting plus or minus. Float needles look good along with the holder. Doesn't look like they have had a rubber "O" ring at the base of the tip nor can I find a diagram that shows that they should have an "O" ring. A lot of gunk in the circuits but really these carbs are pretty straight forward. I'll be back if this isn't the cure. Thanks again.
bassgoat1979
XS650 Addict
For shizle. Throw a filter on there too if you don't already have one.
Sundie
Jabroni
Just to re-iterate - The only o-ring that BS-38's have is around the needle jet. Which should be replaced while you're in there. It's a $1.25 part.
bluebikerblan
Geezer
- its a lot easier to pull the carbs and gives you a chance to clean them and check the boots
- could replace the screws with allen heads- makes it a lot easier for next time
Since you mentioned that you were not yet familiar with Mikuni CV's, I would encourage you to follow INXS advice re pulling them off the bike....at least this first time, mostly just to familiarize yourself with them, clean em up etc. There's a great carb guide available on this site.Next time around perhaps for the "left on the bike" quickie. Best, Blue
Sundie, It was the BS34's that have the o-ring on the float valve and pressed in held with a screw and clip. The BS38's have a screw in valve seat with a copper sealing washer.
Changing the Phillips head screws on the top cover and float bowl to Allen head screws is a good idea. Makes removable much easier on or off the bike.And if you do strip the heads, there is enough head to get a pair of Visegrips on to get it out.
Changing the Phillips head screws on the top cover and float bowl to Allen head screws is a good idea. Makes removable much easier on or off the bike.And if you do strip the heads, there is enough head to get a pair of Visegrips on to get it out.
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