Topic: Petcock Query

[Skonnie Boy]

Howdy all, recently got a '73 750.  Have managed to put in new coils, remove an uncooperative spark plug, but noticed a leaky petcock as I was just about to put everything together and ride after a two week hiatus.  My question is, is ANY leaking from a petcock OK?  It was in the "off" position and as I lifted the tank to put it back on the bike, a rather noticeable amount of fuel dribbled out.

Actually, as I type this, I think the answer is becoming pretty apparent.  Some postings I've read have had some great tips on using rubber washers instead of fiber washers.  But is it OK for there to be a MODERATE amount of leakage from the petcock, given that I'm carrying it around and there's 3/4 of a tank of gas in the tank?  Just curious.  Any advice would be much appreciated.  THX ALL.

[kslrr]

No, the petcock should not leak at all.  Just imagine that the gas is sloshing around while you are riding and getting gas onto you or a hot engine when you stop.

[jabbadeznuts]

No amount of leakage is acceptable. I'd just go ahead and use rubber o-rings/washers.

[rhinoracer]

WHen you say leaking in the off position, do you mean to the carbs or to the outside of the petcock?

[USN20]

This eBay rebuild kit (or one similar) will take care of any unacceptable petcock leaks:

http://cgi.ebay.com/ebaymotors/Honda-CB-750-K-CB750-750K-petcock-rebuild-mount-kit_W0QQitemZ300093988120QQcategoryZ35597QQrdZ1QQcmdZViewItem

[bryanj]

If you are talking about the two washers under the heads of the screws holding the petcock on they MUST be there and they MUST be hard fibre OR something i have discovered here in UK known as a "Dowty Washer" which is a thick aluminimum washer with a rubber "insert" on the inside diameter and these are available in various sizes, you need 6mm. Over here, if i buy 100 i can get them for 40pence each plus tax thats 94p per pair or about $1.85 so by the time you factor in $2.50 for postage and envelope its cheaper for you yanks to bite the bullet and buy the Honda ones, You might find the sealing washers at a hydraulic supplier who does valves and fittings a s well as hoses.

BE ADVISED "ordinary" fibre washers are too thin and too big on the outside diameter to work

[Skonnie Boy]

Leaking to the carbs, or rather to the fuel tubes.  Nice trickle to both lines from the petcock.  Only happens when I pick up the fuel tank, though there was a strong odor of gas when I had it on the bike with the petcock in the open position as well.  Thanks for all the links, will update.  Looks like I've got my weekend project lined up.

Looks like I've been demoted fom Newbie to Visitor.  That's terrrible, ha.  Oh well.

Thanks, all.

A

[GoatBaSS]

Mind that cig!

[doug_id]

If you are talking about the two washers under the heads of the screws holding the petcock on they MUST be there and they MUST be hard fibre OR something i have discovered here in UK known as a "Dowty Washer" which is a thick aluminimum washer with a rubber "insert" on the inside diameter and these are available in various sizes, you need 6mm. Over here, if i buy 100 i can get them for 40pence each plus tax thats 94p per pair or about $1.85 so by the time you factor in $2.50 for postage and envelope its cheaper for you yanks to bite the bullet and buy the Honda ones, You might find the sealing washers at a hydraulic supplier who does valves and fittings a s well as hoses.

BE ADVISED "ordinary" fibre washers are too thin and too big on the outside diameter to work

Yep, I finally solved the same problem with my petcock by getting the washers direct from honda and then really tightening down the mounting screws hard......drip is finally gone!   

[bryanj]

I will happily go out and buy a lot of the Dowty Washers if enough people want them, in UK its cheaper than Honda and about even for you in USA. Also i use allen head cap screws instead of the  posi screws.

[Skonnie Boy]

Looks like washers might be just the tip of the iceberg.  The main fuel feed tube is cracked from top to bottom.  Not sure if this makes a difference, but it surely cannot be good.  Hope I'm not on the hook for another petcock.   

[TwoTired]

The internal stand pipe separates the main from the reserve fuel supply.  A cracked pipe reduces teh separation.  It is possible to replace the stand pipe pressed into the petcock.  Just have to find the right size tubing.

However, if you a talking about the output tubes being cracked, you will have to replace those pressed in parts or replace the entire petcock.

Cheers,

[Skonnie Boy]

Sorry shoulda been clearer, it is the stand pipe which is cracked.  Might be able to replace that, assuming I don't need to solder it on.  I'm guessing some sort of sealant on the cracked pipe wouldn't be helpful, as the gas will eat away at it or become contaminated by it? 

[TwoTired]

It's your call.  I don't like to put anything in the tank that wasn't intended to be there.  And, certainly nothing I wouldn't like to see bits of in my carburetors.

Lots of people like to do experiments with their bikes.  Some of the experiments turn out to be reliable. How are your engineering skills?

A cracked stand pipe just means you have no reserve setting on your petcock.  When you're out of fuel, the soles of your shoes wear faster.

Cheers,

[Skonnie Boy]

Nah, think I'll just fill up early and often until I either fix or replace the petcock.  Considering the crap I found in the screen, I'm not eager to add carbs to the list of things I need to clean.  That's next month's project.

On a completely unrelated note, a friend of mine spilled gas all over his tank in the act of removing the petcock (wow, what are the odds?) and seems to have mucked up the clearcoat a bit.  His clearcoat is more like clear-lacquer or laminate due to the thickness of its application (previous owner's fault).  What's the best way to fix some of the damage, given that little bits of terrycloth are now embedded in the clearcoat?  The paintjob on the tank is not one he'll likely keep for long, as it resembles a retarded cubist soccerball (see pic).  Any opinions/advice?

Fearless in confronting my stupidity, and that of my friends...

A     

[TwoTired]

Wait a week for it to re-harden and use poilishing compound on it.