75/6 from non-runner to runner: Bing rebuild

[Porge]

Thought instead of keeping on with my buying thread, I'd start another with what I'm finding with the bike.

First up, I've mentioned the horn blaring when the key is on. That kinda killed any ideas of cranking her for extended periods. I've disconnected, but as I was doing think I've found the leak to earth. Have noted, and will try a dry run at some stage.

When cranking her over, she's got a fat spark on both jugs, but dry plugs. The fuel lines are old, and starting to crumble on the lowers. From the T junctions up, they're newer, or at least have weathered better.

Have removed the LHS carb to clean up. Have found a couple of interesting things. Firstly, the screws on top of the carb.


Two of them had cammed out pretty badly at some stage - maybe before she was laid up? Anyhow, I reformed filled he bottom part of the threads with some WD40, and left it for a few hours. I then tapped the best fitting screwdriver in place with a light hammer, and the good ones let go. I screwed them back in to just tight, and had a go with some heat from my wife's brulee torch, and then reformed the slots with a large punch, used lightly. This kinda closed the slots up. I then hammered the right driver in, and success! Past experience has taught me to replace. Should I go hex head?



The diaphragm...hmmm....Looks okay, but appears to be a bit large for the carb. There also appears to be no locating tab on it. Replace? Thoughts?



Next to have a crack at was the starting circuit. Is the Haynes manual wrong...or has the PO somehow reversed the assembly?



Apart from that, it was uneventful. The pilot jet was blocked...the main was a little varnish-y. And I didn't manage to squirt myself in the eye with carb cleaner!

[melville]

The cold start parts are marked with "L" and "R" on the end of their shafts where they bear against the carb body.

The tab on the diaphragm is on the bottom and not very big--maybe 1mm deep, 1mm wide, and about 8mm long IIRC.

I was able to find some stainless inhex flattop screws at my local hardware store and I'm quite happy with them, although if I were to find some convex topped screws they'd look so much cooler.

[Porge]

Cheers Mel,

I've done the other carb since, and found the cold circuit is the same. My point was more that in the Haynes, the mechanism would be back to front. Note that the 3 venturi are absent on the Haynes pic.

I just watched the Chris effing Harris vid - they're right. I think as so far as I've watched

Love his down to earth approach.

[Rob]

I installed the hex-head screws on my R65 when I had it.
Function over form.

[Porge]

Haven't been able to get to the shops to get more fuel hose. In line filters? Yea or nay?

[Porge]

Oh...rhs carb main jet holder is locked solid. Brulee torch time!

[Rob]

I always liked the look of the braided fuel line like it came with in 1979, but be prepared to replace it every 3 or 4 years.
There are types that are much more durable, but I didn't mind renewing.
I suppose this is one of those rare cases where I chose form over function.

On my R65, the petcock (exited at 6 o'clock) had two filter screens - one over the intake tubes inside the tank, and one at the bottom of the petcock right above where the fuel line attaches.

I never felt the need for an inline filter. Again, I didn't care for the look. I also drained my tank in the off-season and let it vent until it was completely dry before closing it up. That is harder to do with my current, fuel-pump equipped fuel injected gas-and-go bike.

Others will tell you to go with the modern fuel line (for modern junk fuels), and the inline filter.
I won't argue with them.

[Duane Ausherman]

You shouldn't need inline filters, as the petcocks have filters in them, or should. If you use inline filters, check the flow rate to be sure that the filters flow enough fuel. Many don't.

[Rob]

You shouldn't need inline filters, as the petcocks have filters in them, or should. If you use inline filters, check the flow rate to be sure that the filters flow enough fuel. Many don't.

It is a good idea to measure the number of seconds that it takes to fill a fixed volume container from each petcock. Record it for future comparison. An Everbest will flow 100 cc of fuel in about 12-15 seconds with a half full tank. Only when it would get up to around 20 seconds would I remove the petcock to investigate it further. A full tank will flow more fuel than a low one, so take that into account in your flow measurements.

Notice the appearance of normal flow, as you need to be able to recognize it. Later when you have some high speed problem, you will be able to easily check to see if it is fuel flow related. If you pull the fuel line off often and let the fuel flow freely, you will eventually learn to see what is "normal" and what is "too little".

If you think that you may be seeing less fuel flow than you want, here is a quick test. Remove the lower end of the fuel line at the petcock that you want to check. Use air pressure to try to blow any dirt upwards and back into the fuel tank. Be sure to clean out both main and reserve positions. Now test the flow again. If it has improved, then you have just proven that the fuel flow system was clogged up. You haven't fixed anything at all, only temporarily relieved it. This might get you home, but you must drain and clean the entire fuel system soon.

http://www.w6rec.com/duane/bmw/petcock/index.htm (scroll to near bottom)

[Porge]

I'd actually checked that one out recently!