1981 CB750C with leak

[pistonjocky]

I have a 81 CB750C that leaks out of the overflow tube on carb 2.  I  was told that the carbs needed to be rebuilt, and the cheapest place around me was $350.  I found a rebuilt set of carbs for $150, so I bought them and installed them.  Carb 2 was still leaking out of the overflow tube.  So I compression checked cylinder 2 to see if the valves were seating all the way, and they are.  I also bought a new needle and float for it and installed them, but it still leaks.  I am out of ideas.  Any help???

Thanks

[liljohnnie69-2]

As unlikely as it sounds you still have a float/float needle problem unless the floatbowl drain screw is backed out or the overflow tube is cracked.Make sure you check to see that the floats aren't cracked and half full of gas.Buy a can of carb cleaner,remove the carbs,remove the bowls from the offending units and spray out the seat pocket thoroughly.Check overflow tubes and sealing gaskets and note if there seems to be too much sediment in the bowls,if there is your problem is coming from your gas tank and you will have to clean it out good and seal it with a good tank sealer
http:/http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2000794/c-10101/Nty-1/p-2000794/Ntx-mode+matchallpartial/N-10101/tf-Browse/s-10101/Ntk-AllTextSearchGroup?Ntt=gas+tank+sealer
 Sorry the link is so long.There is probably something i've missed but this is a forum and i'll leave something for the next guy or gal.
     

       liljohnnie69

[gonebiking-2]

Hear is simple little trick I learned. Before stripping the carbs off the bike, give the offending carb bowl a couple of gentle taps with a small hammer. I know it sounds stupid , but thats what I have done every time I have had a carb that leaks out the over flow rubber tube. Its usually a microscopic piece of dirt in between the needle and seat, and this gentle tap on the side of the float chamber usually does the trick. If it doesn`t solve the problem, off with the carbs and sort out the problem.

[pena750f]

I have one, more stupid than that. I was going through my float bowls adjusting the floats, when I noticed one valve wasn't placed in the same way as the others. The other three were installed wrong by previous owner. You want to be sure they are in correctly and adjusted properly. As with the other replys they need to be free of debris and the overflow tube needs be cheked for cracks. Those are about the only reasons I know of why this would happen.

[gonebiking-2]

So I assume that you now have the problem with the leak sorted out and no more leaks??? Amazing how people with a little bit of knowledge can turn a simple problem into a nightmare !!

[barnstormer44]

Liljonnie has some good info for you.  If you see any rust at all in your tank, get a POR 15 tank sealer kit for about 40 bucks and you will have it right.  Make sure you take out the screen in side the tank, as soon as you get the petcock off the tank, and follow the directions to the T.  I didn't know the screen was in there, and I sealed it up.   I had a hard time getting all the sealer to drain also,, so I used a clear tube and flashlight,, sucked it out being careful not to suck it up too far before blowing it out.