Topic: relocating petcock bung

[75modrat]

So I am almost finished with my cafe project (1975 cb750k). My buddy and I are nearing paint but we just noticed a major/minor problem. The P.O. used a non stock tank (among other things). The tank was mounted high of the frame with a bracket. We thought this was done to facilitate his faux-chopper look. Once we lowered the tank to the proper position, we realized that the petcock bung is right on top of the carbs. When you twist the throttle the carbs almost hit the bung without the petcock on. We are thinking about trying to do an inline petcock or something. Maybe use an elbow fitting off the bung and go from there. Has anyone else encountered anything like this? Any ideas? Thanks in advance.

Frank

P.S. Dont want to have to weld on the tank if we dont have to.

[.RJ]

P.S. Dont want to have to weld on the tank if we dont have to.

I'm afraid thats what you're going to have to do - I tried to fit a CB500 tank to my frame, and ran into the same issue.  Ultimately it didnt work out as the rear of the tank where the carbs fit is *just* too narrow (by a few mm) to get it all to work.

[75modrat]

Crap! But thanks.

[754]

You could use a 90 degree fiting and a ball valve in line, if you have pipethread. a lot of tanks though have a british pipe thread..19 TPI.. you may have to rethread the bung or fiting..

[754]

Those square petcocks with the red handle, I had rethreaded one on them to that british thread on my lathe.. to fit a tank with clerance problems. I think it was a 90 degree one.

[75modrat]

So then it is possible, though difficult to find proper threads?

[754]

To answer your question, you probably have the brit threads (one on each side) or a pipe thread.. try to find out which.

Some after market tank use the british fuel taps which usually go straight down...

You can mod an amazing amount of parts if you have a machinist you can afford, that wants to do it..

[75modrat]

I think its an old honda tank (but could definately be wrong). It had a gas cap latch but was broken off long before it got to me. we lead filled the area to make it look like the latch was never there. However the tunner underhead is huge (it only holds about 3 gallons of gas) and it doesnt mount the cb's do (with the rubber things on the frame and just slide the tank onto them). How do I find out if its a pipe thread? Just get a metric nut the diameter of the bung?

[754]

I was thinking you were talking chopper tank, but now am not sure what you mean. Can you post a pic, if we can ID, someone will know the thread it has.

Does it look like an insert welded in with internal threads?

[75modrat]

Dang it! my project is in my buddy's basement (I live in an apartment so it really works out). I wont be over there again for a few days but I will try to take some pics of the tank to see if someone can help ID. What do you mean by internal threads? There is one bung on the the left hand side of the bike (sitting on the bike). The threads of the bung are on the outside. Am I missing something or am I just burnt out from sitting in this class (Administrative Law)?

[754]

Now I know what you mean, after about 75 or 76 most bike went to that setup.. if you figure it is a factory tank it will be easy to determine size, an adaptor could be made, but it may be tricky.