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Old 06-21-2015, 04:56 PM   #1
myCafeRacer OP
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Newbie with an R75/6 & issues

First, hello everyone. I am glad to be on the forum with you.
I bought a 1976 BMW R75/6 last week. I have developed an issue with fuel being expelled from my left Bing carb after shutoff with petcock closed.

The bike has 27,000 miles on the clock but has been sitting for years. The last owner had it safety checked but now I have to deal with the fuel being expelled. I have researched the issue a bit and have some ideas but what would the consensus be in what I should do first, the order I should investigate this.

In addition, there was a repair to the left valve head (threading for the exhaust). I get the odd fume leak from the point at which the exhaust pipe leaves the locking. Ideas?
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Old 06-21-2015, 05:36 PM   #2
Bigger Al
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Try turning the petcock off in the opposite side and see what happens. If it's still leaking you'll likely need to replace the gasket that lives inside the petcock. It's a not a tough thing to do, and the gaskets run about $10 US apiece.

Drop the float bowl on the offending carb, put a suitable container underneath, and turn on the fuel for a few seconds. Sometimes bits-o-junk can get stuck in the needle seat and this method lets a clear stream of gas wash it away. It might also be a good time to check your float level. Those are the easy methods. It could also be that you have a bad float or bad needle tip, and even those are not difficult jobs.
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Old 06-21-2015, 05:52 PM   #3
disston
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There are special tools for tightening the finned nuts on the exhaust. Many styles and different prices. You'll have to wait for somebody up North there to post a good option. Rarely is the tool from the dealer a good bargain on this one but ask them what they got. They might have an aftermarket variety. The OEM wrench is usually over $70 here.

You will need the wrench tho and after loosening the nuts to apply a fresh coat of antiseize they can be safely tightened. Antiseize must be applied to these threads now and again. A lot of riders do this once a year. It will save you the expense of having to have the threads repaired again.

It is the lack of this procedure that probably caused the original damage.

You say "fume leak"? It may be just some of the oily substance that Antiseize is made with. The important part of Antiseize is not the oil but the metal. They are made with Nickel and sometimes Copper but the carrier is the oily stuff. If it's not a real exhaust leak it's not a problem for now. Get an exhaust wrench before next year when you should reapply the juice.
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Old 06-21-2015, 07:51 PM   #4
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If the exhaust stub threads have been repaired, take a look at how it was done before you tighten them. Most of the repairs are done by welding the existing stub with aluminum, and they can be tightened normally, but one shop put a steel sleeve over the stub and retained the sleeve with pins. If this is the repair yours has, even a slight over-tightening beyond that shops recommendation will spin the sleeve on the head.
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Old 06-22-2015, 05:55 AM   #5
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Pic of the repair

Thanks for the responses. Here is a pic of the repair.
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Old 06-22-2015, 05:57 AM   #6
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Question

Is this type of repair common?
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Old 06-22-2015, 09:39 AM   #7
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Yup. A lot of shops will dress those welds to make it look factory, but that's a common fix.
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Old 06-22-2015, 01:33 PM   #8
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This repair is considered the better repair because it returns the exhaust port threads to their OEM mechanical configuration. The appearance is secondary. Some would not be happy with the looks. It wouldn't bother me a bit.

Other options include the steel threads pinned on. And a special nut fixture that changes the way the system works completely. Both of these options have disadvantages. Therefore the welded aluminum is the best.
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Old 06-22-2015, 03:25 PM   #9
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The pictured repair is one of the aluminum welded types. In this case, the original stub was milled off and a new one welded on. The other type consists of welding over the original threads and recutting the threads on a lathe. This requires a fixture to hold the head in the lathes chuck and rotating the head. Either way works, but the second repair is nearly invisible. Tighten away!-after confirming that the sealing rings are installed correctly.
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Old 06-22-2015, 10:18 PM   #10
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Welcome to the asylum!

Go to Northwoods Airheads and order yourself this exhaust wrench--great price and quality.

As for the leak at the header, once you have the exhaust nut wrench, spin the nut off and check that you have both the clamp and compression rings installed correctly.

In order of installation (in case you didn't know, apologies if you do):
1) Exhaust nut with fin end going on first
2) Clamp ring with flat side going on first
3) Compression ring with tapered side going on first. The tapered side will fit inside the tapered side of the clamp ring. The two together form a squared off ring.

These rings, along with the exhaust nut, form an airtight seal when everything's done right.

Good luck, and again, welcome. (And may the Sens, if that's your team, do better next season. I was pulling for them against the Habs. Hell, at least they made the playoffs, unlike my Kings).
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Old 06-23-2015, 04:08 AM   #11
disston
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Quote:
(2) For some Airheads there is BOTH a split ring and a solid collar that fit on the pipe, inside the
finned nut. To avoid you having to figure out how to assemble them, the split ring FLAT END goes next to
the head. The solid collar flat end faces the nut. This will put the two slanted surfaces towards each other.
From Snowbum's page on the exhaust nuts. Try as hard as we can we could never approach the detail from this one man.
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Old 06-23-2015, 07:40 AM   #12
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Aftermarket kickstand

Again, you guys are awesome. I will probably pickup an originally intact cylinder head (because I am that kind of guy, for better or worse).

I haven't taken off the float bowl for my left carb yet but that is coming up.

A previous owner installed this third kickstand.
I will remove it but I have a question. In the next photo (waiting for moderator approval) I am wondering about the length of the exposed thread after I remove the kickstand support arm from under the nut holding on my foot peg.
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Old 06-23-2015, 07:41 AM   #13
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more on the kickstand

After i remove the arm holding the stand, there will be a lot of extra thread showing out from the nut holding the peg ( see red circle). Is this normal?
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Old 06-28-2015, 02:28 PM   #14
Bill Harris
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That second sidestand is a Brown's sidestand, which is (in many's opinions) better than the factory stand. I'd keeo it and remove the factory s'stand.

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