Minus the petcock...

If it's broken or just needs tweaked

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coffee_brake
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Minus the petcock...

Postby coffee_brake » Tue Apr 01, 2014 12:10 am

I honestly think I mistook it for a different model's petcock and tossed it out early this year.
The 1982 Nighthawk 650 petcock is a rare bird indeed. :( The part number is shared with only a few other bikes and nope, I'm not willing to drop over a hundred bucks just to still have old rubber parts. I've already converted the carbs to vacuum feed and I've removed the..uh..other vacuum thing, whatever it's called, that was on the carb rack. I still have it, I just wanted to keep it super-simple while I got the bike back on the road.

Now I'm looking at what I have left sticking out of the tank: an inch of threaded pipe with what seems to be a steel insert. Pretty beefy, really, even for vintage Japanese iron.

Could I tap it? It seems there's enough meat there to tap out to a smaller metric thread, drill down the shaft of a bolt that size, and cut off the head, attaching normal fuel line with a hose clamp from there. Then I'd use an in-line fuel valve instead.

The cost would be a tap and a bolt instead of a whole new petcock, which makes sense especially since I'd rather not use the vacuum fuel feed at all.

If I could only weld, the sky would be the limit. But all I have is a drill press.

I wonder if it would flow enough fuel? I've never tried a get-around like this one before.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

MiGhost
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Location: South Central Mitten

Re: Minus the petcock...

Postby MiGhost » Tue Apr 01, 2014 4:28 pm

The petcock from the 81 CB650C should work with your tank. The difference is the strainer bowl. At half the price.
16950-461-771 PETCOCK ASSY
http://www.partzilla.com/parts/detail/h ... 1-771.html

Most guys remove the vacuum shut off. No problems as long as you remember to shut off the petcock when not running.

The pipe looking piece inside the petcock bung is the in-tank filter screen. It is what makes the run/reserve action on the petcock work. You will get a new screen if you buy a new petcock.

It is nearly impossible to find a replacement tank for the $50 or so that the petcock will cost. Not to mention that the 82 CB650SC tank is nearly impossible to find in the first place. The 83-85 tank will not work as a replacement. I would not recommend trying to modify the tank bung.
~ Ghost

PD50 Carb Info
82 CB650SC Brake Caliper Info

Stable
Wayward Son:1980 CB650C, RestoMod Period Custom Touring
Bad Moon: 1983 XJ750MK Midnight Maxim, Full Dress Tour Deluxe w/ X-1 Fairing
Nemesis: 1983 XJ750K Maxim, Old School style chopper

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Tue Apr 01, 2014 10:26 pm

The threads on the tank are 20mm across. Isn't that larger than the petcock in your link will fit? The largest aftermarket petcock I could find was only for 18mm threads, as in 18mm across the OD of the bung sticking out of the tank. Mine measure 20mm across.
I'd LOVE to put an aftermarket unit like that one on it, but I didn't see any with large enough threads.

The filter is not in the tank, and the insert is made of metal. Unless the filter once upon a time had a steel base? I thought they were all brass or plastic, and press-fit into the stock petcocks...been wrong before, though.

Good call on modifying this rare tank. I was just thinking, if I were to tap the INSIDE of the bung, then the threads on there right now, on the OUTSIDE of the bung, would remain un-altered.

I would MUCH appreciate nailing down the actual size of this bung so as to source a petcock. I can't get my thread gauge on it, and I'm not very experienced with "eye-balling" thread size. I can only get the micrometers on it.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Tue Apr 01, 2014 11:07 pm

Yay, I found my other thread gauge! It shows a 1.0 thread on this bung. Here's some photos:
Attachments
CIMG3650.JPG
CIMG3650.JPG (151.38 KiB) Viewed 10595 times
CIMG3649.JPG
CIMG3649.JPG (138.86 KiB) Viewed 10595 times
CIMG3643.JPG
CIMG3643.JPG (87.58 KiB) Viewed 10595 times
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Tue Apr 01, 2014 11:08 pm

A couple more...
Attachments
CIMG3659.JPG
CIMG3659.JPG (128.87 KiB) Viewed 10595 times
CIMG3656.JPG
CIMG3656.JPG (124.51 KiB) Viewed 10595 times
CIMG3654.JPG
CIMG3654.JPG (133.54 KiB) Viewed 10595 times
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Wed Apr 02, 2014 2:56 pm

So...that ebay one won't fit, or will it?
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Wed Apr 02, 2014 9:20 pm

OK, well... :?


I asked a buddy who works on older BMW Airheads about a petcock they use, and he confirms it's 1.0 pitch and measures pretty close to the same. If he can get his hands on a used one, I think I can plumb it up.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

tcoop
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Re: Minus the petcock...

Postby tcoop » Wed Apr 02, 2014 9:38 pm

For the price this one might be worth looking into. The seller thinks its from an 82, would be worth sending them a message to verify.


http://www.ebay.com/itm/HONDA-NIGHTHAWK ... 0b&vxp=mtr
Ty
Current bikes
1980 CB650C - project
1983 Yamaha Venture
1978 YAMAHA XS1100E - project
1982 Yamaha XJ1100 - project
1982 Yamaha XJ1100 - Wifes bike
1983 Yamaha XJ750 MN Maxim - Also Wifes bike

cb650
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Re: Minus the petcock...

Postby cb650 » Thu Apr 03, 2014 5:44 am

that is on off a 83 or newer dohc.
Did you clean the tank out?!?!?!?!

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Thu Apr 03, 2014 8:22 am

Thanks for clearing that up.

I wish I knew if part number 16950-461-771 actually did fit.

A lot changes from 81 to 82, and this is the Nighthawk, with that one-year-only tank. It cross-references with the 1982 CB750C and SC, and CB900C,and the 83 1000 and 1100, but not the 81 of anything.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Thu Apr 03, 2014 8:23 am

Well, good old Sirius says they have one, but they say 22mm bungs...

http://www.ebay.com/itm/HONDA-CB650SC-C ... 88&vxp=mtr


It sure is a pretty unit.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Fri Apr 04, 2014 3:58 am

Just for the heck of it, I asked my brother to measure his '80 CB900C bung. Yep, 18mm.

I can't get the guys at Sirius to understand what I'm asking. They're marketing a petcock to fit this 650, but their listing (it's on Ebay) says it's for 22mm bungs. I've asked three different ways how this can possibly be, but they don't seem to get it.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk

jcasey007
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Re: Minus the petcock...

Postby jcasey007 » Fri Apr 04, 2014 4:26 am


cb650
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Re: Minus the petcock...

Postby cb650 » Fri Apr 04, 2014 7:03 am

Looks like the original except the screws. I would even get it but have a new one Jerry bought me already for a spare.
Did reply to OP's post on sohc4 too.

Yes take good care of the tank too. Its a bitch to find at all much less with out gold plating!!!!
Did you clean the tank out?!?!?!?!

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coffee_brake
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Re: Minus the petcock...

Postby coffee_brake » Sun Apr 06, 2014 5:12 pm




This can't possibly fit. It's for 18mm bungs. My tank has a 20mm bung.
Jenn in "Jaw-juh"
1982 CB650 Nighthawk


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