Installing MikesXS Non-Vacuum Petcocks on Later Models

Robin, I believe what you have there is the '80-on single left side petcock for use with the BS34s.
 
Thanks for all this info 5twins. Now I know what to keep an eye out for to get a match for the other original. Would like to stay with rebuilt OEM parts if I can.
I hate the idea of using repops where I have to remember they operate in different directions. I just know that's going to lead to trouble. I've got enough to try to remember already! LOL
 
5T, yes i agree, When i checked the 78E parts manual it shows 2 part no's for the petcocks, (left and right).
 
Yes, last year for them. '78 was the first for the vac units.
 
All i Have...........you work it out

77-78-79 Parts manual
77-78-79-D-E-F- parts  Manualt51 51.jpg 77-78-79-D-E-F- parts  Manualt51 51.jpg 77-78-79-D-E-F- parts  Manualt53 53.jpg 77-78-79-D-E-F- parts  Manualt54 54.jpg
78E Parts manual........good clear diagram
78E Parts list086 086.jpg 78E Parts list087 087.jpg 78E Parts list088 088.jpg 78E Parts list089 089.jpg

78SE-79SF-80SG Parts manual...........some discrepancies where the part no doesn't match the Diagram???
78-79-80 E-SF-SG parts  Manualt066 066.jpg 78-79-80 E-SF-SG parts  Manualt067 067.jpg 78-79-80 E-SF-SG parts  Manualt068 068.jpg 78-79-80 E-SF-SG parts  Manualt069 069.jpg
 

Attachments

  • 77-78-79-D-E-F- parts  Manualt52 52.jpg
    77-78-79-D-E-F- parts Manualt52 52.jpg
    127.7 KB · Views: 204
Well, now THAT certainly blows a big hole in the side of the airplane !
RG, please share your empirical data on that statement.........

Hi 'dude,
FWIW the stock plastic filter towers do it too and as the stockers combine the gas taps' filter and reserve functions you are doubly SOL.
The problem is asyptomatic until you run onto what you thought was reserve to find it was already gone.
Happened to me 'way out in the boonies.
Took the 2 gallon reserve jerrycan from the sidecar and poured it into the tank.
Checked the tank when I got home by turning it upside down and shaking it.
Two little white filter towers fell out. Gawd knows how long it'd been like that.
 
No guarantee of original but these were on a 78SF I recently bought. The missing nipple is still in the fuel line. They are left/right handed.


DSCF9017.JPG DSCF9018.JPG DSCF9019.JPG
 
Last edited:
Is the missing nipple straight or 90°? I'm thinking the left one may be a newer replacement, right one original.
 
Well to add some to this thread as gggGary show us his guess it's only fair I'd show mine!

78 petcocks.JPG

The one on the left in above picture(right side of bike) is the one I'm having problems with right now. I have disassembled it and cleaned it real good but fuel dribbles out of the outlet in Run and Reserve with no vacuum applied. Apply vacuum and get a nice full stream. Also good stream in Prime.

I did replace the diaphragm assembly with one out of another petcock as the rubber had flaked off the diaphragm nearest the plunger with the oring on it.

I also have three other petcocks as shown below. They all appear to be for left side applications of unknown origin.
extra petcocks.JPG


Would I be way off base thinking I could just eliminate the problem petcock and run on the left one? Seems like it would work as the 1982 Heritage I have uses just one and the two carbs on the 1978 do have a jumper hose between them, or I could just use a TEE connection to feed them both from the petcock on the left.

PS if anyone thinks they could use one of the three in the bottom picture for some application I would be willing to sell for a little over shipping cost. They would need the internal parts replaced but levers and retainers are there
 
Did you replace the o-ring on the plunger and polish it's seat in the petcock body? That's what usually causes the leaks like you have (in "On" and "Res" positions without vacuum applied).
 
5t the nipple is straight.
Yes they run great on one petcock, on the manual petpcock resto I usually just turn on one, The 80 up bikes only have one.
I was looking at the 79 standard tonight and it also has both petcocks with the prime position straight back ie the valve is mirrored. I didn't look underneath to see if it has differences like the special above.
 
Last edited:
Did you replace the o-ring on the plunger and polish it's seat in the petcock body? That's what usually causes the leaks like you have (in "On" and "Res" positions without vacuum applied).

The seat looks perfect no pitting. The oring looked very good also. Just for kicks last night I found an oring in my oring kit that seemed to fit but that one still does the same. Even assembled parts into one of the other petcocks I pictured above and still the same result.

Might try some more today if no luck there I might just hook up to run on the left side petcock that appears to work fine for now and worry about it latter if everything else checks out on the bike. Sometimes what should be the simplest things on a project can sure cause many headaches!
 
I found several aftermarket kit makers sold the diaphragm plunger assemblies that are a bit short of the factory plunger they will never seat. Getting just the right size o-ring there is a pain, the one's in the red metric oring kit box are just a bit too big. #29 in that kit works a treat for the tank/petcock seal. I'm out, need to order more of that size.
 
Last edited:
I found several aftermarket kit makers sold the diaphragm plunger assemblies that are a bit short of the factory plunger they will never seat. Getting just hte right size o-ring there is a pain, the one's in the red metric oring kit box are just a bit too big. #29 in htat kit works a treat for the tank/petcock seal. I'm out, need to order more of that size.

Well that maybe what is/was the problem with this one. Last night I had noticed that if I held the plunger in against the seat the white plastic spacer between the two diaphragms while not clamped tight it did not have any free play either.

So as a test I put the diaphragm assembly on the end of a socket being careful to tuck the gas side down in the socket and the tin cup part of the vacuum side resting on the edge of the socket. Then will my tinny brass hammer gently tapped the center of the assembly. Could hardly see any distortion in the cup part but when I again held the plunger seated on the petcock I now had maybe 0.010 play in the white plastic spacer.

Reassembled the petcock and now when I applied suction to the fuel outlet nipple it held suction. So now it seems to be working as it should.

Bike seems to run pretty good for an engine that has not run since the late 1990's at idle it does have a intermittent popping in the right exhaust. Does not seem to have any hesitation when given gas. I did go through the carbs and was surprised how good they were from sitting that long. Tach is not working 100% sometimes it will go up to say 5,000 but just hang there when engine goes back to idle. All lights working and even the horn. Battery is bad and will not even crank it over with plugs out but did a quick check with volt meter and at part throttle it was showing 13.85 volts.
 
Back
Top