1973 R75/5 Problem With One Carburetor Running Rich

I found the right cylinder was running rich, but not the left.

Right Spark Plug-Can You Say SOOTY

Right Spark Plug-Can You Say SOOTY

So I started from the beginning.

  • I checked head torque at 26 Ft/Lbs. Nothing was loose
  • I checked the valve lash. Spot on.
  • I checked the jet needle position. Correct at #3 just the same as on the left.
  • I checked the main jet and needle jet sizes. Correct sizes and matched the ones on the left. O-rings are in good shape and not torn or brittle.
  • I checked fuel depth in the bowls. They are the same on both float bowls; between 19 and 20 mm. The fuel level is correct on both sides.
  • I checked the timing. It’s spot on and there is no ghost image. The timing advances smoothly.
  • I switched the spark plugs and rode the bike for 50 miles. The original left plug, now in the right cylinder, is sooty and the original right plug, now in the left cylinder, is fine. So, there is no issue with the plug, plug cap or plug wire.

If it’s sooty, it’s rich. So, what’s going on that causes only the right side to run rich?

The, valves, timing, jets, needles, spark plugs, wires and caps are fine. There is no obstruction in the air tube feeding the right carburetor. The crank case breather isn’t showing any more oil than normal, so it’s not getting a lot of oil mist into the right carburetor. I mulled this problem over for several days with no new insight as to what to try next.

A couple days later I was at coffee with some friends and was chatting about this problem when an idea hit me. What if the slide isn’t going all the way up at full throttle? If that’s the case, the vacuum will be higher than normal at higher engine speeds. A higher vacuum means the fuel delivery is going to be higher than normal but the air volume will be lower than normal. That certainly would create a too rich condition and sooty plugs on one side, but not the other.

I take the air tubes off both carburetors and push the slide up on the right side. It won’t go all the way up.

Right Slide Can't Go All the Way

The left one goes all the way up.

Left Slide Goes All the Way

So, my hypothesis is correct. The rich condition is caused by the right slide sticking.

But what’s the cause of that?

I updated these carburetors with springs (not originally used on the /5 carburetor, but added to later versions). These help smooth out the transition from idle to mid-range.

Spring Installed

As I look at the spring, it looks like it can get caught on a pin that protrudes inside the air well the spring fits inside of.

Pin Inside Slide Where Spring Goes

I can get the spring to hang up on that pin. When I do, the spring is cocked and then snags on the split washer under the screw that holds the plate onto the diaphragm. That stops the slide from moving.

Diaphragm Screw & Lock Washer

I think this “cussedness of inanimate objects” is what stopped the slide from going all the way up.

I install the spring and make sure it isn’t hung up on the pin. I also loosen the screws holding the plate that secures the diaphragm and push the split washers outward so they aren’t protruding into the air well.

After I put the carburetor back together, the slide moves freely. I’ll take the bike for a ride when it warms up and see if I have fixed the problem. I’ve grown accustomed to not concluding I’ve fixed something until I take a longer ride and the problem doesn’t reappear. ūüôā

Repair Stripped Cylinder Head Stud Threads in the Engine Block

The first sign of the problem was this bike would not idle well. I thought the carburetors got dirty and all I needed was to clean them. But, before I started on that task, I decided to check the valves and I found the left intake valve lash was 0.012 inches instead of 0.004-0.006 inches. Hmmm …. how did that tappet get so loose?

Before I reset the valve clearance, as I always do, I torqued the cylinder stud and head bolt nuts to 25 Ft/Lbs. But, one stud just spun.  Bummer. That means the threads in the engine block are stripped.

It turns out a friend of mine, Dick, had the same problem on his 1972 R75/5 a couple of weeks earlier. I contacted him and learned he made arrangements to rent a jig to repair his stripped threads from Northwoods Airheads. So, we jointly repaired our stripped threads in “Brook’s Airhead Garage” when the jig arrived.

This write-up is based on the work we did on both bikes.

Here is a link to a video of how to use the Northwoods jig to drill out the damaged threads, tap new threads for a 20 mm long M10x1.5 Heli-Coil insert, and install the insert.


Coffee with Craig

During the recent rebuild of “Grover”, my wife’s 1973 BMW R75/5, I wanted to restore the original Windjammer II fairing it came with. The Windjammer was designed and sold by Craig Vetter who has long been associated with motorcycles, fairings and fuel economy. So I was pleased to find he and his wife maintain a web site and store for his fairings¬†with what¬†I needed to repair it.

I had a question about what adhesive was used to attach the headlight bracket to the fairing and sent a note to Carol Vetter, his wife. In short order I was in an email exchange with Craig. I thought at the time how cool it is to be able to get information directly from the designer of the Windjammer 40 years later.

When I got done with the fairing repair and paint work, I send him a link to these write-ups.

Last week I got a note from Craig saying he would be coming through Colorado on his way back to his home in California and would I like to get some coffee.  And yesterday, I got coffee with Craig Vetter.

Chatting with Craig Over Coffee

Craig Vetter

What Craig Has Been Up To

Craig has documented the work he has been doing to build ¬†“The Last Vetter Fairing” in his quest to boost fuel economy and mileage for motorcycles. He had been in the mid-west at a mileage competition, the 2014 Vetter Fuel Challenge¬†at the AMA Vintage Days, but the weekend before we met,¬†someone stole his trailer with the bike in Kankakee, Illinois. The good news is the bike was recovered but the bad news was the trailer is still missing and he was now returning much later than he had anticipated, but he was still willing to stop and chat with me.

I rode Grover over to a Starbucks near the intersection of I-76 and I-70 where Craig would be arriving so he wouldn’t have to detour far from his route.

We talked about his goal for energy efficiency, a long time passion, and his efforts to “learn what I don’t know” to design and make available a motorcycle fairing that can double fuel efficiency. So, does¬†anyone really care enough about conserving fuel on a motorcycle to want a fairing that doubles the mileage? ¬†He admitted it has been a struggle, but he¬†believes¬†the need for energy efficient gasoline powered bikes is¬†inevitable as the cost of oil exploration continues to rise with the corresponding hike in gasoline prices at the pump. The near term opportunity lies in¬†the emergence of electric powered motorcycles since they¬†need more range between recharges and that matches up with a well designed, cost effective, slippery fairing that cuts drag enough to double the¬†range of any electric powered bike.

As you might expect from a man who built a successful company, sold it and then¬†continued to work on projects to¬†extend the limits of what is possible for motorcycle fuel efficiency, our conversation was fast, wide ranging and equal parts observation, questions and guesses about what the future could be. ¬†It was the best hour of coffee drinking I’ve spent in some time.

We took some pictures of the old (Grover with a Windjammer II, circa 1974) and the future (The Last Vetter Fairing) that span 40 years of Craig’s thinking, learning, testing and trying in the parking lot at Starbucks.

40+ Years of Vetter Technology

Craig Vetter Surrounded by 40 Years of His Innovation

Criag and his "Last Fairing"

Only 16 HP, 70 MPH, and Over 100 MPG

Me Holding Grover's Hand

Me Holding Grover’s Hand

One of the stories Craig told me is whenever he rides the bike or trailers it, it’s almost always a women who will stop to ask him what it is, but not men. We both think men are reluctant to ask because¬†they are uncomfortable¬†admitting they don’t know what it is (sort of a corollary to the “men don’t ask for directions”¬†syndrome), but women are genuinely curious and are not so encumbered. He jokes with me that if the women is older he will tell her “It’s really a chick magnet” which always gets a chuckle before he tells her the rest of the story and why it matters.

And then as he is about to leave, a lady drives by the two of us and leans toward the passenger window of her car¬†and asks, “What is that?”

A Curious Bystander

“What is That” From a Women Passing By

Craig looks at me and just smiles. He tells her what it is and before you know it she is out of her car and the two of them are talking about fuel economy, how to get 100 MPG on a motorcycle and why he believes this matters.

Then, after saying good bye to her, he tows The Last Vetter Fairing out of the parking lot and heads west on I-70 toward home. As I fire up Grover, I realize rebuilding this old bike opened a door for me to get a cup of coffee with one of the icons of motorcyling. The old airhead engine runs that much smoother as I head back to work.

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. ūüôĀ

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.

1973 BMW R75/5 Rebuild: Grover’s First Ride Around the Block

The rebuild is finished and I documented the final assembly process in this write-up.

On the Fourth of July, “Grover” was ready for his first ride since he was stored away seven years ago in my friends barn.

Out of the Barn

Grover On His Way to My New Shop 18 Months Ago

Here¬†is a short video of the first 3 mile “around the block” ride on Grover. You can’t see the s&*$ eating grin on my face, but it’s there ūüôā

Here are some photos I took before the ride when I took the bike out of the shop for the first time in 18 months.

Side View

Side View

Front Side

Front View

Rear View

Rear View