Topic: cb750 fuel petcocks

[octagon]

hello i'm new to the forum and owner of a 76 750k that hasn't been running awhile.
it's basically in good shape, seems to have had a bad voltage regulator and overcharging problems. some electrolyte had boiled out of the battery, 10, 15, and 20 amp fuses were in the fuse holders. the po removed the coils (maybe while troubleshooting) and also somebody did some creative wiring. anyway some of that is sorted out and the bike cranks and runs well at this point. still have to rebuild the front brake master cylinder and work on the caliper. 
unfortunately the gas tank bottom is more like a shower head than a tank bottom. looked around for a replacement and noticed there are two petcock designs - are these petcocks interchangeable? from searches i learned about left vs right location of the petcock, but its hard to tell from pictures how the earlier model petcock actually attaches to the tank. the 76 petcock on my tank is in great shape and i'm wondering if its useable on an earlier tank.
thanks for any info. 

[ekpent]

The earlier pre 75 tanks have a two line outlet petcock that is mounted on the opposite side of the 75-76 tank. They are held on by two screws where the 75-76 are screwed on to a bung fitting off the tank. The petcocks are NOT interchangeable,but an earlier tank petcock combo can be used on a later bike,you just need two fuel lines not one.

[octagon]

great to know - thank you - so stay with the same tank/petcock combination.
it's a shame the way water gets in there and wrecks the bottom of a tank. so many of them seem to be like that. i'm thinking of cutting the bad places out of the bottom of my tank (carefully) and making patches from sheet metal off an old volvo, and taking the patches and the tank to a metal fabricating place to be welded in. if somebody good does the work, that should be a reliable fix.
i tried jbweld, which my opinion is a very good product, and prepped everything carefully, and followed instructions, etc.
it worked, but on the first hot day the sun beat on the tank a few hours and the pressure created forced gas past the bond between metal and epoxy.   

[ekpent]

On repairs like that where you try and patch holes from the bottom, if your saving a nice stock paint tank for instance,then its best to put in a couple of "fluffy" coats of Red-Kote tank sealer in there also, so you not only seal it from the bottom but from the inside of the tank also and create a gas free barrier. .

[Hinomaru]

great to know - thank you - so stay with the same tank/petcock combination.
it's a shame the way water gets in there and wrecks the bottom of a tank. so many of them seem to be like that. i'm thinking of cutting the bad places out of the bottom of my tank (carefully) and making patches from sheet metal off an old volvo, and taking the patches and the tank to a metal fabricating place to be welded in. if somebody good does the work, that should be a reliable fix.
i tried jbweld, which my opinion is a very good product, and prepped everything carefully, and followed instructions, etc.
it worked, but on the first hot day the sun beat on the tank a few hours and the pressure created forced gas past the bond between metal and epoxy.   

Welcome to the forum!

Along with the tank repairs, you should not have any pressure building up in the tank as the gas cap is vented to prevent this. Check the vent hole to be sure it's not clogged or restricted as it should freely flow air in and out. The white arrow in the pic shows the location of the vent hole.

(click on photo for a larger image)

[traveler]

I agree....if the tank is really straight, then the bottom can be saved by coating the insides, and some have had some luck using JB Weld on the holes from the bottom.  Might be a good idea to have the bottom sandblasted to get all the rust out first.  Just my .02

~Joe

[greasy j]

if you do change out the tank and petcock...

you can use one on the other side, you just have to reroute your fuel line. and if you get the screw onto bung type there are lots of replacements for cheap.

and if you reline it, make sure you get COMPLETE coverage. lots of times people miss a spot, then it starts to peel, because it has a lifting edge. good luck.

[octagon]

from forum posts it seems like recoating the inside gets such mixed results, and there doesn't seem to be any one brand or method that stands out. that's got me a little worried about recoating.
checked the tank cap and it wasn't venting. 

[greasy j]

as far as recoating, it can be a really good thing or really bad thing. you just have to be very thorough if you do it. make sure you completely prepped the tank and that it is completely covered and you'll be fine. people get bad results because they didn't prep it thoroughly, missed a spot or it's too thin.