1979 xs 11

[boots06]

What is wrong with my carbs? I have cleaned them tuned them and adjusted them to spec and yet they still leak fuel out of the carb mouth. Do I need new needles and seats and where would I buy these.

[TopCatGr58]

Hey there Boots,

If they are leaking, then the most common reason is that the float needle valve and seat are not sealing properly. HOWEVER, a often overlooked problem can be that the upper "T" VENT tubes are not properly vented, either the "T" itself is clogged, the hose is clogged, or 2 carbs vent hoses are "T'd together with just a single vacuum hose barb but not an actual "T" that will allow the bowls to actually vent/equilize pressure, or even the ports on the AIR BOX that the vent tubes are supposed to be connected to....the airbox ports can also be clogged....again not allowing them to actually vent=LEAK!

SO...if you are sure of your vent tubes, then the needles and seats are not sealing. There are techniques to POLISH their sealing surfaces with a little metal/chrome polish on Q-tips for the seat, and some very fine 1000/1200/2000 grit wet/dry paper on the needle tips. ALSO, are the springs on the needles still working/springy?

Other problems...are the floats actually floating...they can have pinhole leaks that are hard to see....putting/submerging them in almost boiling hot water can reveal pinhole leaks via bubbles seen when submerged. There's an adjustment tang on the side of the float to keep it from dropping too far when the bowl is empty, otherwise they can get caught and hang, also can hang up on the bowl gasket, as well as the float pin itself if it's not spinning easily within the float.

It's suggested to do a bench test or at least turn them upside down and try to blow into the fuel supply hoses with the float bowls off with just the weight of the floats against the valves, then lifting one at a time to verify that you can blow thru, but will again stop when you let the float back down.

If you want to get new needles/seats, aside from a few places like Partsnmore, or Z1enterprises, find a guy named GeorgeFix on ebay, he'll treat you right. HTH!

T.C.

[boots06]

Carbs

Cool I will try your recomendation's and see what happens. Thanks.

[DGXSER]

even the ports on the AIR BOX that the vent tubes are supposed to be connected to....the airbox ports can also be clogged....again not allowing them to actually vent=LEAK!.

Another thing to watch out for, in similar concept, the 80-81 air boxes look identical to the 78-79 air boxes, both Standard and Special models (except MNS) used the same air box. However, in the 80-81 models air boxes, the nipples were never drilled for those vents to connect to. They are there, just no hole through them, and no brass nipple inside. So, someone could swap the air box, hook the vents to it, and never have any "vent".

[boots06]

Carbs

Thanks guys. Turns out that both vent lines had some gummy gunk in them not sure what it was but I replaced both and it stopped leaking.

[scalded dog]

had to change my airbox, on 79 special, the box I have has the nipples for the vent hoses, but are not drilled open I wonder if I can drill a hole in the nipples, and would it work properly. Thanks, 'Dog

[skids]

It should work OK if you do that.

[scalded dog]

Thanks Skids. Later 'Dog

[natemoen]

had to change my airbox, on 79 special, the box I have has the nipples for the vent hoses, but are not drilled open I wonder if I can drill a hole in the nipples, and would it work properly. Thanks, 'Dog

Just keep an eye on them. The factory holes had a brass tube running through them, si that added some strength.

[scalded dog]

Thanks Nate, good idea. Will be checking ebay for another stock airbox. Later 'Dog

[trdriver71]

you could probably use the brass inserts from air brake fittings to put in the nipples after you drilled them out.

[DGXSER]

Truly, I would not worry about the nipples. The vent lines are not going to put any stress on the nipple. Its pretty hard plastic. Now, you may want to be carefull when removing and installing carbs.

If it gives you comfort, get any type of metal tubing, copper, brass, even steel will work for this, and put it in there, I would epoxy it in though to be sure it does not vibrate out.

[natemoen]

I agree. Not worth finding a new airbox. Just worth noting and thinking about when messing with the carbs.

[scalded dog]

Thanks guys. Looking forward to a great riding season. Later 'Dog