Q on petcock rebuild

Took the bowl off to see if some crud was causing the slight gas drip on the garage floor. With the petcock in the off ( yes off, horizontal) position, gas poured from the carb at the very proper rate. Pushed the float up while I dumped gas from the completely full float bowl and replaced it. With the petcock off, on, pointing front, pointing rear, the gas FLOWS. So i guess I'm rebuilding the petcocks.

As i look at the parts fiche, it seems there could be four likely culprits: #5 the gasket ring, #7 O-ring, #8 compression spring, or #11 gasket (the one w 5 holes)

I haven't taken the petcocks off yet to inspect, but I wondered if you guys had any thoughts on what to look for. I suppose it'd be cheap and easy enough to just replace all four parts. None of them list at more than a few dollars, but hey, why not save the price of a coffee?

Also am I right in thinking I've got to either drain the tank or somehow clamp the fuel line below the petcock, remove the tank w petcock and first length of hose attached, and set it upside down in order to remove the petcock?

Thanx, as always.....or in my case about every 300 miles. The rate at which i'm replacing rubber stuff.

Just a thought, but worth asking- did you have both petcocks turned off? If you have the crossover line, it will feed both Carbs.
Jim

I'd consider replacing just #7 and 11...the other items typically don't wear out. As for #5, I think what you really want is #12 strainer. BMW now sells a tall strainer with fiber gasket attached at the bottom. Used to be you had the sealing gasket (#5) and a separate little strainer...I still have that arrangement on my /7. But I'd get #12, also.

Use a little silicone grease on the o-ring and the obvious moving parts. That will allow the petcock to move easily.

If you haven't drained the tank in awhile, this would be a good opportunity to flush all the crud, water, etc., out of the bottom of the tank. Ride the bike until you just go on reserve, then drain the remaining gas into a small container. Look at what comes out. You can reuse the top portion of the gas if you want.

The large nut holding the petcock onto the tank mates two different threads - left and right handed. To put things back together, you'll want to get the nut started on both the petcock and tank side at about the same time and then draw the two together by turning the nut. Try not to tighten too much...get a feel for how tight they are when you take it off. If you get some leaking after reassembly, you can't give the nut another nudge.

I found disassembling my R90/6 petcocks that the threads behind the handles had been staked with a small punch & had to be forced a little bit. I ended up making a wrench/screwdriver from a short length of 1/2 inch conduit. Otherwise the "screwdriver" slots get buggered up dealing with the staked area. Use some anti-sieze on the threads and on the rubbing metal surfaces when putting it back together. I don't think it is necessary to restake the threads.

The wrench can be made in a few minutes with a hacksaw & a file.

Last time I checked, a complete new petcock was $25. (Just for reference, of course.)

thanx

lkchris said:

Last time I checked, a complete new petcock was $25. (Just for reference, of course.)

Click to expand...

That thought occured to me too, but so far a bit of tapping w the handle of a screwdriver seems to have stopped the overflow. Tho in the spillage there was still a fair bit of fine orange flake from the tank, tho' I cleaned it out a few months ago. Might be worth repeating the process.

Thanx to all you guys who responded. Now can you do something about all the rain predicted for this week?

lkchris said:

Last time I checked, a complete new petcock was $25. (Just for reference, of course.)

Click to expand...

Yeah.... this was the route I took recently. New ones from Bob's - then sold the old ones on ebay for the same price I paid for the new ones. This was obviously less than the price of a rebuild kit and my time. Just a thought.
Murph

I recently replaced mine. I found the factory coating in the gas tank had come off and was causing significant problems. It was worth draining the tank to get it cleaned out.

Just a dumb question? Have you tightened the outside nut? It does come loose from time to time. If does not do it, I would replace them both with new ones. My food for thought....

dont remeber seeing what year your bike is, but if your gonna replace them , get the newer ones with the big strainers that fit into the tank, also the outlet comes out to the side. Most of the ones I ran into with the drain straight down have a little tiny filter in them which plug real fast if you have any junk or flaking in the tank

I switched my 78 to the newer ones

Isamemon said:

dont remeber seeing what year your bike is, but if your gonna replace them , get the newer ones with the big strainers that fit into the tank, also the outlet comes out to the side. Most of the ones I ran into with the drain straight down have a little tiny filter in them which plug real fast if you have any junk or flaking in the tank

I switched my 78 to the newer ones

Click to expand...

Mine's also a '78, but having drained the tank once I think the po had already replaced 'em. I'll 2ble check when I do it again.

Once again thanx to all corespondents. Some year when I get a little more travel time during rallye season it'll be fun to meet more of the forum gang.

26667 said:

Some year when I get a little more travel time during rallye season it'll be fun to meet more of the forum gang.

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You don't absolutely have to wait for rally season if you ride north. I'm up here along Lake Michigan if you want to take a 'putt' with another '78 RS rider. Ever get to Road America?

535is said:

You don't absolutely have to wait for rally season if you ride north. I'm up here along Lake Michigan if you want to take a 'putt' with another '78 RS rider. Ever get to Road America?

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I have been to RA and of course loved the track and the races, but I almost always work weekends w mon/tues. as the days off. ( tho' sometimes i get called to work then, too) Busy is good, isn't it? Happened to have a week off earlier and made it to the Madison rallye and had a great time w several cheesheads who just sort of waved me into their area because one of them liked my '78. One guy, Rich fromCedarburg turned out to be the guy from whom I almost bought a newer RS. Great roads over there, too.

So thanx so much for the invite. I'm trying to finagle my way to the Dells rallye, but my son's b'day bash may have to be that weekend. la guerre.
I'd like to check out kettle moraine, mindoro cut and some of the other rides that were discussed around nat'l time. So i may be out and about in Wisconsin (you have to go to Missouri to find good riding in Illinois) btw Aug 31 and Sep't 9. It's hard for me to plan, but I'd love to hook up, have you show me around, and admire your scoot.
Ride safe, C.R.