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Old 08-22-2010, 12:51 PM   #1
drooartz OP
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Talking Observations on my first real airhead ride

Took the new '73 R75/5 out for my first airhead ride today. Put just over 100 miles on it, going over my favorite local mountain pass road -- Wolf Creek pass, a bit over 9000' elevation.



Bike definitely has a fueling issue (PO did tell me about it). Quite a few times the bike would feel like it was out of gas -- tank was full and both petcocks were on. Sputtered and hesitated. Carb rebuild, as well as cleaning out the tank and petcocks probably in order.

Where's a good source for cab kits for the Bings?

Other than that, it was a very pleasant ride. Bike is definitely slower than my old '07 Bonneville, but not by a whole lot. I'll wind up a bit slower over the passes, but still plenty fast to enjoy the ride. Those big drum brakes really do work just fine for my riding style. Never felt like they were not powerful enough for me.

So a happy first ride all around. I'll get safety inspection done this week so that I can get my permanent plates. I'm feeling good about this bike -- with a bit of work it should be a nice rider.
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Old 08-22-2010, 01:24 PM   #2
Jinx
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Before diving into the amusement park that is carburettors, make sure the fuel tank is doing two things:
  • The petcocks are clean (specially if they have internal screens) so fuel can flow freely

  • The Tank is venting. If the vent isn't letting air in, fuel can not flow to the carbs

Quote:
"...NOTE: The fuel caps and venting means for the tank varies by year/model, but it is common to have an early Airhead run out of fuel.... stumbling, loses power, etc......and the problem will be the tank vent...or the cap.

This is provable by loosening the cap and hearing a whoosh of air entering, and the bike then runs OK (within 10 seconds). Stumbling from this vacuum problem usually happens more quickly with a fuller tank. Fuel cap cork seals are replaceable. So is the black surround on the later caps..."

Source


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PS - Bike is a beauty
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Jinx screwed with this post 08-22-2010 at 01:30 PM
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Old 08-22-2010, 01:46 PM   #3
Chad M
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Quote:
Originally Posted by drooartz
Took the new '73 R75/5 out for my first airhead ride today. Put just over 100 miles on it, going over my favorite local mountain pass road -- Wolf Creek pass, a bit over 9000' elevation.



Bike definitely has a fueling issue (PO did tell me about it). Quite a few times the bike would feel like it was out of gas -- tank was full and both petcocks were on. Sputtered and hesitated.
I second Jinx. Did the bike present the same problems under similar conditions, ie: under load, climbing, around a left hand sweeper, etc..? If you can't find a pattern, perhaps electrical isn't out of the realm, ie: condenser, failing spark plug or poor connector at the cap etc. I have had the sputtering carb thing, and it was relatively easy to diagnose, ie: under load, every time. I found a small beetle in my float bowl plugging up the main when I was accelerating hard. I think taking apart your new old bike is part of the experience, it's yours now and you'll need to find out what makes her tick. Have fun!
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Old 08-22-2010, 01:58 PM   #4
Bigger Al
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Nice looking bike!

You can get the carb kits directly from Bing:

http://www.bingcarburetor.com/bmw/bmwcvkits.html

Snowbum's site can be kind of tough to wade through, but there's a ton of great information to be had there.
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Old 08-22-2010, 02:00 PM   #5
Wirespokes
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When it feels like it's running out of gas, lift up the gas cap. If you hear a whooshing sound and it suddenly runs fine, you'll know the cap vent needs cleaning.
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Old 08-22-2010, 02:04 PM   #6
Hawk Medicine
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Quote:
Originally Posted by drooartz
Took the new '73 R75/5 out for my first airhead ride today. Put just over 100 miles on it, going over my favorite local mountain pass road -- Wolf Creek pass, a bit over 9000' elevation.

Bike definitely has a fueling issue (PO did tell me about it). Quite a few times the bike would feel like it was out of gas -- tank was full and both petcocks were on. Sputtered and hesitated. Carb rebuild, as well as cleaning out the tank and petcocks probably in order.

Where's a good source for cab kits for the Bings?

Other than that, it was a very pleasant ride. Bike is definitely slower than my old '07 Bonneville, but not by a whole lot. I'll wind up a bit slower over the passes, but still plenty fast to enjoy the ride. Those big drum brakes really do work just fine for my riding style. Never felt like they were not powerful enough for me.

So a happy first ride all around. I'll get safety inspection done this week so that I can get my permanent plates. I'm feeling good about this bike -- with a bit of work it should be a nice rider.
I'm glad that you're enjoying your new/old Airhead! They're great bikes and you're living in a place where you can enjoy yours in its natural element. Bravo!

Also: Wolf Creek pass is one of my favorite roads in the whole world! Rolling up that mountain, flat-out heading East, is a huge thrill and one that should give a good rider, on a good bike, a huge sense of accomplishment, without threatening anyones life.

Drain and clean your tank, clean the petcock screens and then blow the petcocks out with air. When thats done, add a couple of plastic filters between the tank and the crossover. You'll need to replace the filters once or twice yearly and the tank gets drained and cleaned at the end of each riding season. I like to store my bikes with the fuel system drained and the tank lid and petcocks disconnected and open to let air circulate. No rust that way...

Make sure your tanks venting. Next time the bikes goes into "Sputter Mode" crack the tank lid and see if the sputter goes away. If thats the culprit, clear the cap's vent and you're home free..

I buy most of my parts from Chicago BMW because I like the service and the 20% discount, so thats where I got my carb kits. MUCH cheaper than Bing but Bing is the place to buy alcohol proof floats and I'd recommend em.

Lastly:

If you like that drum brake, fine. Lots of people do but when you have time, read through your shop manual and then make sure that your brakes are operating at 100%. If your brakes are like everyone else's, you'll need to clean everything up and install new shoes, front and rear.

Lastly, lastly: Be very careful with those drum brakes in wet weather! They are very difficult to modulate in the wet and if not wary, you'll reach for some front binder, it'll grab and put you on your ass, sliding down the road wondering what happened. Sorry but you now own a bike that uses late 1950's brakes!

Other than that, ride fast and take chances!

PS: Once you get into the Airhead world you'll discover ways to make your bike at least as quick as your old Bonnie! Thats a very nice looking /5. Good score!!
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Hawk Medicine screwed with this post 08-23-2010 at 09:05 PM
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Old 08-22-2010, 02:04 PM   #7
Bill Harris
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A good source for BMW parts is Hans Lowe: http://bmwhucky.com/ Check the filter screens, petcocks, carbs, venting. Check the vacuum diaphragms. Problem sounds fuelish...
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Old 08-22-2010, 03:04 PM   #8
drooartz OP
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Rides like Wolf Creek are one of the reasons I love living in the Utah mountains. The riding is great right from my front door.

Thanks all for the ideas. The problem with the sputtering is under load. I will drain out the tank and clean everything, and will grab a Bing rebuild kit. I must admit, they look a lot like the SUs on my Bugeye, so I should feel right at home.

I did try opening up the gas cap while riding, as I've had that venting issue before on other bikes. Didn't seem to solve the issue. Will probably get the bits to rebuild the cap seals anyways (given the bike's age, *all* the seals will need some attention soon).
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Old 08-22-2010, 04:12 PM   #9
rufusswan
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Quote:
Originally Posted by drooartz
they look a lot like the SUs on my Bugeye, so I should feel right at home.
They are, but don't try puttin' any damper oil in'em
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Old 08-22-2010, 04:15 PM   #10
Frank06
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At 9,000 feet altitude your bike will be running fairly rich I would think... maybe float levels are a bit high? Go down one size on main jets?
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Old 08-22-2010, 04:24 PM   #11
Lornce
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What Jinx said.



And Snowbum's a great source of info and amusement.

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Old 08-22-2010, 04:33 PM   #12
coastranger
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are those the right crbs for that bike ? maybe its the angle of the picture

aside from that eubmw carb kits are the best deal running. both diaphrams, all gaskets and o-rings for like 30 bucks
you can then supplement them with needles etc elsewhere, have used several times on several bmw's and never a problem
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Old 08-22-2010, 06:53 PM   #13
drooartz OP
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Quote:
Originally Posted by coastranger
are those the right crbs for that bike ? maybe its the angle of the picture
Carbs are Bing, labeled 64/32/13 and 64/32/14 (left and right). No idea if these are the proper carbs.
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Old 08-22-2010, 07:27 PM   #14
goatroper
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From the pictures, at least one previous owner has loved it enough to spend some $$. Repairing negligence is never cheap, but if someone else has made appropriate prior "investment", you may be a winner.
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Old 08-23-2010, 07:59 AM   #15
Renner
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64/32/13 & 14: those are the right carbs.

Concerning the fuel delivery issue and resultant stumbling: I would suggest you try a few miles without the "VW" style paper inline filters as the added restriction, though minimal, can result in the symptoms you describe.

I don't use inline filters on my /5. With a clean tank and the petcock mesh screens I find no debris in my float bowls during periodic maintenance.

Bing also sells inline mesh filters which function well with lower pressure differential across the filter requirements.

Really good to hear you've had a chance to take it out for an extended ride, except for the part where it's slower than your not-so-old Bonnie.
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