1977 BMW R100RS Bing Type 94/40 Carburetor Rebuild-Refinish

This is the fourth set of Bing CV carburetors I’ve completely rebuilt. This is the link to the current work on the 1977 R100RS that uses the Bing 94/40 model of carburetors and specifically the 103-104 series used on the 1977 “CFO” engine version of the R100RS.

The previous rebuilds include the smaller 64/32 series used on the R75 series /5, /6 and /7, and the R90/6 bikes and the larger 94/40 series used on the later R100 model bikes. I documented the procedures of the earlier work in the following write-ups.

As is often the case, I found the o-rings were hard and brittle and in one instance I found two o-rings on the idle fuel jet! The internals were pretty clean so I someone cleaned the carburetors and for some reason added an o-ring instead of replacing it on the idle fuel jet.

I decided to shoot some short videos to demonstrate how I understand the way the Bing CV carburetors work. Each video covers one of the four major functions, or circuits, used in these carburetors. The operation of the model 64 and 94 CV carburetors is the same.

Constant Velocity Circuit Operation

Here is a short video showing how the constant velocity circuit works.

Main + Needle Jet Circuit Operation

Here is a short video showing how these components work in the main+needle jet circuit.

Enriching Circuit Operation

Here is a short video showing how the enriching circuit works.

Idle Circuit Operation

Here is a short video showing how the idle circuit works.

Here are some pictures of the completed carburetors.

Refinished Outside

Refinished Outside

Refinished Inside

Refinished Inside

Refinished Back

Refinished Back

Refinished Front

Refinished Front

Refinished Top with Added Rondel

Refinished Top with Added Rondel

1977 BMW R100RS Project: Remove & Repair Bodywork

I wrote up how I removed all the body work on this bike. I discovered a broken upper fairing bracket that was held on with only a hose clamp. There was a broken plastic boss with a threaded insert and numerous cracks and other damage to the fairing panels and side covers. I repaired all of them except for the top center panel that goes around the headlight. The damage was significant with a multitude of hairline cracks and I opted to buy a used panel rather than risk cracks showing up in the paint work after I tried to repair it.

Here are links to the write-ups.

I’m ready to start removing the forks and working my way towards the rear as I strip it down to the frame. Then I can see what other surprises are in store 🙂

Here are a couple pictures from the write-ups.

Screen Damage So I Will Replace It

Windscreen Damage

Drill Bit and Hammer Removing Center Pin of Windscreen Rivet

Tapping Drill Bit with Plastic Hammer to Drive Center Pin Out of Windscreen Rivet

Windscreen Removed

Windscreen Removed

Carefully Drilling Inside of Dash Rivet

Carefully Drilling Inside of Dash Rivet

Dash Removed From Fairing Panels

Dash Removed From Fairing Panels

Broken Upper Fairing Bracket Steering Stem Mount

Broken Upper Fairing Bracket Steering Stem Mount

Fairing Panels Removed

Fairing Panels Removed

Headlight Panel Badly Broken

Headlight Panel Badly Broken

Headlight Panel Lower Right Corner Badly Damaged

Headlight Panel Lower Right Corner Badly Damaged

Upper Side Panel with Large Crack

Top Left Side Panel with Large Crack

Top Side Panel Cracks Routed Out with Dremel Tool

Top Left Side Panel Cracks Routed Out with Dremel Tool

Top Side Panel Plast-aid Repair

Top Left Side Panel After Plast-aid Repair and Sanding

Bottom Side Panel Repair to Brass Insert Boss

Bottom Right Side Panel Repair to Brass Insert Boss

Bottom Side Panel Brass Insert Final Hole Size

Brass Insert Final Hole Size-5/16″

Bottom Side Panel Brass Insert Test

Testing Integrity of Boss & Brass Insert Repair

1975 BMW R75/6: Rebuilding Master Cylinder & Caliper

This bike uses a single ATE 38 mm caliper (as in the size of the piston inside the caliper, not the size of the caliper shell). In 1976 the ATE caliper was changed to a 40 mm model to improve braking. There was also a change to the master cylinder mounting system resulting in a single hole in the brake fluid reservoir that mounts on top of the master cylinder. Other than these small changes, the work I did applies to all the /5, /6 and /7 models of the ATE caliper and under-the-tank master cylinder.

You can read about how to do this work here:

I had occasion to work on both my 1975 R75/6 and someone else’s 1976 R75/6 at the same time, so there are some pictures of the markings on the 40 mm caliper and the different mounting systems (two hole and one hole) of the brake fluid reservoir.

Some pictures from this write-up are below.

Master Cylinder & Fluid Reservoir Mount Under Gas Tank

Master Cylinder & Fluid Reservoir Mount Under Gas Tank. Note the Evidence of Brake Fluid Leak.

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve

Earler Two Hole Master Cylinder

Earler Two Hole Master Cylinder

Master Cylinder Piston Assembly Removed

Master Cylinder Piston Assembly Removed

Removing Top Hat From Master Cylinder Piston

Removing Top Hat From Master Cylinder Piston

Master Cylinder Rebuild Kit Parts

Master Cylinder Rebuild Kit Parts

New Master Cylinder Piston with New Rubber Seals Installed

New Master Cylinder Piston with New Rubber Seals Installed

Master Cylinder Installed on Frame Tube

Master Cylinder Installed on Frame Tube

R75/6 Caliper Seal Kit - Source: MAX BMW

R75/6 Caliper Seal Kit – Source: MAX BMW

Caliper Showing Piston and Dust Seal

Front Face of Piston with Center Hole Surrounded by Rubber Dust Seal

A Blast of Compressed Air Removes Piston

A Blast of Compressed Air Removes Piston

Dust Seal Installed in Large Groove in Piston

Dust Seal Installed in Large Groove in Piston

Pulling O-ring On Eccentric Pin With Pick

Pulling O-ring On Eccentric Pin With Pick

Movable Pad with Flat Face of Pad Pointing to the Front

Movable Pad with Flat Face of Pad Pointing to the Front

Fixed Pad Secure with Wire Clip

Fixed Pad Secure with Wire Clip

Caliper With Painted Metal Line Installed

Caliper With Painted Metal Line Installed

1983 R100RS Rebuild: Diagnose and Replace Failed Neutral Switch

When I bought the bike in January 2015, the neutral bulb didn’t light and the starter motor wouldn’t work unless I pulled the clutch. I need to figure out what is going wrong in the starter circuit and the neutral switch. I wrote up the work I did here including how I diagnosed that the neutral switch failed and how to replace it:
This write-up makes use of some short videos to show what I do. I’m experimenting with how to use video clips to explain things better than just pictures and text can.
There is a longer video at the beginning in which I explain how I use the Haynes wiring diagram and Bob Fleischer’s material to figure out how the neutral and clutch switches work in the starter switch circuit.
I’ve heard fellow Airheads tell me electricity is confusing and a mystery. So I thought maybe showing how I try and figure out how components work from the wiring diagram when I have a problem may be of some value.  Here is a direct link to that video.

Here are the other short videos I shot that are included in the write-up.

Here are a few pictures from the write-up.

Neutral Light Not Lit

Neutral Light Not Lit

Printed Circuit Contacts for Neutral Switch

Printed Circuit Contacts for Neutral Switch

Neutral Bulb Pins on Printed Circuit

Neutral Bulb Pins on Printed Circuit

Neutral Switch with Grunge

Neutral Switch with Grunge

Degreased Bottom of Transmission and Engine Oil  Pan

Degreased Bottom of Transmission and Engine Oil Pan

Prying Out Center Engine Mount Spacer

Prying Out Center Engine Mount Spacer

Old Switch Ready to Remove

Old Switch Ready to Remove

New Neutral Switch and New Washer/Spacer

New Neutral Switch and New Washer/Spacer

New Neutral Switch with Plast-Aid Applied to Prevent Leaks

New Neutral Switch with Plast-Aid Applied to Prevent Leaks

Neutral Light Works Now :-)

Neutral Light Works 🙂

1973 BMW R75/5 Rebuild: Using Plast-aid To Attach Electric Connector in Windjammer Fairing

After I took my first ride on the bike, in parking it I had occasion to turn the handle bars all the way to the left and heard a loud “cracking” noise. I kept the stock turn signal stalks on the fork tubes. It turns out they hit the wiring harness connector that I had repaired as I describe here.

46 BMW R75/5 Repair Windjammer II Fairing, Strip Paint-Reattach Fairing Wiring Connector

Now I know why one of the stalks had the tube the turn signal would mount on bent upwards, so when I straightened it, I set myself up for this surprise. 🙁

I originally used a piece of ABS from the fairing repair kit Craig Vetter supplies as an internal bracket to hold the end of the white plastic connector inside the fairing and tried Epoxy Plastic adhesive to attach it on the inside of the fairing.

ABS Patch Attached with Epoxy to Fairing Wire Connector

ABS Patch Attached with Epoxy to Fairing Wire Connector

ABS Plastic Patch Epoxyed Across Connector Hole in Side Pocket

ABS Plastic Patch Epoxyed Across Connector Hole in Side Pocket

The ABS patch separated from the inside of the fairing wall.

Plasti-aid(R) Multi-purpose Repair Plastic

I read in Motorcycle Consumer News a short article about Plasti-aid, a product produced in Estes Park, CO which is at the entrance to Rocky Mountain National Park, and a nice ride from my house along the front range of the Rocky Mountains.

Plasti-aid Kit-Large Size

Plasti-aid Kit-Large Size

Dale Greenawal, a fellow Airhead who lives in Boulder, told me he wanted to fix a broken fairing lug that attaches the lower part of his R80-RT fairing to the frame, and wanted to know if I have any ideas. I told him about Plast-Aid and that it sounded interesting, but I hadn’t used it yet.

So, Dale called the company and spoke to the owner, Randall Amen. Randy invited him to come up and take a tour of his operation and talk about how it can be used. When Dale invited me to come along, it was a no brainer. I had the week off and was finishing up Grover in preparation for the first ride around the block. The ride from my house to Estes Park is one of my favorites up Coal Creek Canyon and then along what is called the Peak-to-Peak Highway. So Dale, my wife and I set out on a day ride to the Plast-aid HQ.

When we arrived it was lunch time. Randy came over as we got off our bikes and said they were having lunch at the restaurant next door, the Mountineer. So, we had lunch (good food) right next to the Plast-aid’s office/factory, and then got a personal tour with technical background and tips about how to use the product from Randy. His wife and daughter (wo)man the front office while Randy handles the R&D and manufacturing.  Dale and I were nerding out and even my wife was thinking of several problems she faced at home where Plast-aid could be a solution.

Randy was very gracious and gave all three of us free samples. So, a few days later when I heard that “crack”, I decided it’s time to try Plasti-aid.

Securing Windjammer Electrical Bulkhead Connect with Plast-aid

I removed the gas tank as I decided to remove the turn signal stalks from the front forks rather than bend one of them. I put some towels along the frame tubes near the rear of the tank and the removed the wing nuts securing the rear of the tank.

Protecting Frame Tubes when Removing Gas Tank

Protecting Frame Tubes when Removing Gas Tank

I put another towel on the front of the tank and then carefully lift the rear over the bolts and slide the tank back. Then I lift the front past the steering head chrome cover. This is not so easy with a full tank and 5.8 gallons.

Protecting Gas Tank From Steering Head When Removing Tank

Protecting Gas Tank From Steering Head When Removing Tank

Then I removed the fairing and carefully put it on the work bench.

I put some Plast-aid powder in the supplied mixing cup (the cup is made from a plastic that Plast-aid doesn’t stick to, so it’s easy to clean up and reuse).

Plast-aid Powder in Supplied Measuring Cup

Plast-aid Powder in Supplied Measuring Cup

I add a little liquid to the powder and stir with a popsicle stick (included in the kit). I want a pancake batter consistency. I let the mixture sit for a bit so I can mold it. I use a small paint brush and paint some of the Plast-aid liquid around the edges of the electrical connector. Randy said this is a good idea when you mold some Plast-aid and want to attach it to another piece of plastic. The liquid component softens the part a bit to ensure a tight bond to the molded Plasti-aid when you attach it.

By now the Plast-aid is acting like taffy. I take it and make a rope of it in my hands and mold it around the plastic of the electrical connector. I press that into the hole in the fairing filling the gap between the fairing and the electrical connector with Plast-aid. I dab a bit more Plast-aid on the edge of the fairing and over the top of the Plast-aid filling the hole and then hold the electrical plug steady for a couple more minutes.

After Applying Plast-aid In Its Moldable State

After Applying Plast-aid In Its Moldable State

Plast-aid gets hot as it sets and then cools off when the reaction is about done. I wait for it to start cooling and then let go of the plug. Wow. It’s solid as a rock.

I remove the turn signal stalks from the fork tubes and mount the faring on the bracket. Then I install the tank using the cloths to protect it and the frame tubes. I plug the wiring harness into the Plast-aid repaired connector inside the fairing and check out the electrics. It’s all good and the connector seems nice and solid.

The next morning, I check everything again before I go to work. The connector is Rock Solid and I don’t have an ABS plastic patch inside the pocket of the Windjammer to snag stuff on.

I’ve got some other ideas of where I can use Plast-aid. It will stick to metal as shown in one of the videos on the Plast-Aid site. I’ll post more about my experiments with Plast-aid when I get that far.