Bill Wiegand
Member
Part One of this repair story appeared in the March 2016 issue of Owners News. You can find the digital version of that issue on this website .
While waiting for my parts, the next step was removing the throttle body assembly. In order to do that, I first needed to remove the throttle and choke cables, sensor switch that runs to the dash light that shows when the choke is engaged, fuel pressure regulator, throttle position sensor, and the six Allen head bolts that secure the three manifolds to the engine. I inserted paper towels into the holes beneath the manifolds to prevent road debris from falling inside. Once all was removed, the throttle body assembly slipped right out and I could vacuum 28 years worth of accumulated sand and debris from the top of the engine. Next, I slipped on rubber disposable gloves and used a brake cleaner-soaked paper towel to remove the black oily soot covering the throttle bodies. Always work in a well-ventilated area when spraying brake cleaner - it’s very toxic!
I wasn’t familiar with the one-time-use Oetiker clamps. I used a pair of tin snips to cut each of the six clamps. Once cut, the clamps sprung apart, making easy work of removing them from the throttle body and air plenum box. I took this opportunity to clean up the throttle bodies and butterfly valves. I planned to replace the fuel line that goes from the fuel pressure regulator to the rear fuel injector rail. The fuel rail had some rust spots, so I roughed it up with sandpaper and sprayed it with several coats of heat-resistant black paint.
About an hour before closing time, Melissa called from The Hitching Post saying my parts had arrived. I dropped everything and got them. I requested about two feet of fuel hose and was presented with an attractive gray hose that would compliment the gray color of my bike.
That evening I used my new Oetiker clamp tool to secure the new clamps to the new throttle bodies. I took it slow and successfully secured the new clamps to the new throttle tubes. I compared the new manifolds with the existing set that came off my bike and concluded the originals were still in good shape. Prior to ordering the parts, I’d asked Melissa about their return policy and she said I could return any of the parts purchased if they weren’t used.
The following afternoon, I reinstalled the three original manifolds to the engine base and the throttle body assembly. After installation, I discovered I routed the wires that connect to the fuel injectors behind the throttle bodies instead of in front of them. Dreading removing the throttle bodies again, I discovered the harness plugs into an accessible area on top of the engine. I also discovered the harness is secured with a thin wire that holds the plug in place. I tried using a very small flat-bladed jewelers screwdriver without success. After posting my latest challenge to removing the connector, Lee suggested I buy a set of pick tools from Harbor Freight. I found a set with long handles that allowed me to access and remove the safety clip. Once the plug came off, it took no time to re-route the electrical wires.
Now it was time to install my renewed fuel injectors. I followed the correct procedure of inserting all three injectors in the fuel rail and then gently but firmly pressing them in their respective holes on the engine. It’s important to coat the seals with engine oil to avoid damaging the O-rings. After installation, I reattached the electrical connectors to each injector securing with the thin safety wire clips and then reattached the three clips that secure the injectors to the fuel rail.
The next day, I cut my new gray fuel hose and installed it between the fuel pressure regulator and the two connection points on the fuel rail. About two years ago, I replaced the return fuel hose that runs from the fuel pressure regulator to the fuel tank, so I left that alone. After carefully installing the hoses and securely clamping them in place, I reinstalled my now mouse-free air box assembly and put the tank on the bike. I was now ready to start the bike, hoping not to see any fuel spraying from the reinstalled fuel injectors. I said a little prayer, asking for blessings from the BMW mechanical gods before pressing the starter button.
When I turned on the ignition and pressed the starter button, she cranked and cranked and sounded like she was going to start, but I quickly stopped when I noticed fuel spraying from the front left underside of the fuel tank. Fortunately there were no explosions or fires! Always keep a fire extinguisher handy when working with gas and electrical systems. Disappointed, I forced myself to walk away and regroup.
“Okay, what could be the problem,” I thought. A bolt of lightning floored me when I asked myself if that cool-looking gray fuel hose was rated for fuel injection systems. Our bikes require fuel injection hose with a minimum rating of 100 psi. I Googled the name on the fuel hose and discovered it was basic fuel hose used for carbureted - not fuel injected - machines! I was angry with myself for not remembering to specify that I needed fuel injection rated hose. This meant removing the fuel tank and air box again to access the hose connection points on the fuel pressure regulator that reside behind the air box.
It was just my luck that the dealer didn’t have fuel injector hose in stock. I drove to the local NAPA store and found fuel injector rated hose with a diameter compatible with the BMW hose. I replaced the gray fuel hose the proper hose, reinstalled the air box and tank, and tried again, but fuel was still spraying from underside the tank. I had to remove the fuel tank and air box again! It was time to press the pause button on the project, as I had to fly out of town the next day.
About two days later, I decided to reread the various responses I received to my post on the MOA forum when something hit me across the head like a two-by-four. Lee had said, “The fuel return hose between the Fuel Pressure Regulator and the tank MUST be the factory pre-molded hose, otherwise it WILL kink when the tank is moved forward into position.”
I hadn’t used the correct OEM fuel injection hose and surmised from all the times of removing and reinstalling the fuel tank over the years, I’d compromised the fuel hose where it was supposed to have a built-in bend. I searched eBay and found a NOS (new old stock) OEM hose for about $12. With the proper hose installed, the bike started but ran rough. After consulting the forum, it turned out I’d installed the air box improperly.
Lee provided me with the proper way to install the 90-degree hose that attaches from the air box to the intake air box above the throttle bodies. If you don’t do it the way I’m about to tell you, you’ll have an air leak and the fuel metering device will get a false reading and cause your bike to not run at all. Lee explains: “If that large 90 degree hose is not properly connected to the plenum over the throttle bodies, the bike either will not run or run like crap. When connecting that hose to the plenum, the air filter must be removed. Insure that the screw for the clamp is to the rear of the hose and pointed up for easy access. Use a flat bladed screwdriver with a long shaft to secure the clamp. This explains your difficulty! Before you finish tightening the hose clamp, push the air box lid as high as it will go up against the frame and wiring, as that will be its normal position. If tightened when hanging down against the bottom of the air box, it will have to twist to get to its final position and that would promote cracking.”
I’d installed the air filter and then clamped the lid to the air box and then tried connecting the 90-degree hose but this was incorrect and created air leaks. With the air box properly attached, I pressed the starter button and voila! My K 75 S roared to life and soon was purring like a kitten.
I took her for a test ride and rode her pretty hard. She ran like a jet! The one thing I hadn’t done since owning her was balance the throttle bodies. I’d never thought to do this because she always ran so good. When I attached my CarbMate throttle balancing tool to the throttle bodies, using the #3 cylinder as my reference point (aft on the bike), I discovered the throttle bodies were way out of balance. It didn’t take long to balance them up. I took a second test ride and she ran better than before!
With the long Minnesota winter approaching, I topped off the fuel tank, added a few ounces of STA-BIL, changed the engine oil, oil filter, and the gearbox and final drive oil before covering her up and putting her to bed for the winter.
My advice for any backyard mechanic is to do your homework before embarking on any repair project. Take things step-by-step and have a Clymer, Haynes or shop manual by your side. Many BMW dealers don’t support older bikes like mine, but the good news is they still carry the parts. It’s discouraging when things don’t go as planned and it’s easy to get frustrated; at least once or twice during this service I felt like setting my bike on fire! Seriously, though, when I created a quiet uninterrupted space, things came together. When I got stuck, I found taking a break helped me return to my project with a fresh approach.
For those of you who like to do your own wrenching, the MOA forum is an excellent place to get help from some of the most friendly and experienced BMW mechanics anywhere. I believe our forums to be underutilized by the MOA community and also to be one of the crown jewels of our membership. Additionally, I’ve developed some very solid friendships from the forum. Thanks to all who helped complete this service - case closed, no more K bike blues!
While waiting for my parts, the next step was removing the throttle body assembly. In order to do that, I first needed to remove the throttle and choke cables, sensor switch that runs to the dash light that shows when the choke is engaged, fuel pressure regulator, throttle position sensor, and the six Allen head bolts that secure the three manifolds to the engine. I inserted paper towels into the holes beneath the manifolds to prevent road debris from falling inside. Once all was removed, the throttle body assembly slipped right out and I could vacuum 28 years worth of accumulated sand and debris from the top of the engine. Next, I slipped on rubber disposable gloves and used a brake cleaner-soaked paper towel to remove the black oily soot covering the throttle bodies. Always work in a well-ventilated area when spraying brake cleaner - it’s very toxic!
I wasn’t familiar with the one-time-use Oetiker clamps. I used a pair of tin snips to cut each of the six clamps. Once cut, the clamps sprung apart, making easy work of removing them from the throttle body and air plenum box. I took this opportunity to clean up the throttle bodies and butterfly valves. I planned to replace the fuel line that goes from the fuel pressure regulator to the rear fuel injector rail. The fuel rail had some rust spots, so I roughed it up with sandpaper and sprayed it with several coats of heat-resistant black paint.
About an hour before closing time, Melissa called from The Hitching Post saying my parts had arrived. I dropped everything and got them. I requested about two feet of fuel hose and was presented with an attractive gray hose that would compliment the gray color of my bike.
That evening I used my new Oetiker clamp tool to secure the new clamps to the new throttle bodies. I took it slow and successfully secured the new clamps to the new throttle tubes. I compared the new manifolds with the existing set that came off my bike and concluded the originals were still in good shape. Prior to ordering the parts, I’d asked Melissa about their return policy and she said I could return any of the parts purchased if they weren’t used.
The following afternoon, I reinstalled the three original manifolds to the engine base and the throttle body assembly. After installation, I discovered I routed the wires that connect to the fuel injectors behind the throttle bodies instead of in front of them. Dreading removing the throttle bodies again, I discovered the harness plugs into an accessible area on top of the engine. I also discovered the harness is secured with a thin wire that holds the plug in place. I tried using a very small flat-bladed jewelers screwdriver without success. After posting my latest challenge to removing the connector, Lee suggested I buy a set of pick tools from Harbor Freight. I found a set with long handles that allowed me to access and remove the safety clip. Once the plug came off, it took no time to re-route the electrical wires.
Now it was time to install my renewed fuel injectors. I followed the correct procedure of inserting all three injectors in the fuel rail and then gently but firmly pressing them in their respective holes on the engine. It’s important to coat the seals with engine oil to avoid damaging the O-rings. After installation, I reattached the electrical connectors to each injector securing with the thin safety wire clips and then reattached the three clips that secure the injectors to the fuel rail.
The next day, I cut my new gray fuel hose and installed it between the fuel pressure regulator and the two connection points on the fuel rail. About two years ago, I replaced the return fuel hose that runs from the fuel pressure regulator to the fuel tank, so I left that alone. After carefully installing the hoses and securely clamping them in place, I reinstalled my now mouse-free air box assembly and put the tank on the bike. I was now ready to start the bike, hoping not to see any fuel spraying from the reinstalled fuel injectors. I said a little prayer, asking for blessings from the BMW mechanical gods before pressing the starter button.
When I turned on the ignition and pressed the starter button, she cranked and cranked and sounded like she was going to start, but I quickly stopped when I noticed fuel spraying from the front left underside of the fuel tank. Fortunately there were no explosions or fires! Always keep a fire extinguisher handy when working with gas and electrical systems. Disappointed, I forced myself to walk away and regroup.
“Okay, what could be the problem,” I thought. A bolt of lightning floored me when I asked myself if that cool-looking gray fuel hose was rated for fuel injection systems. Our bikes require fuel injection hose with a minimum rating of 100 psi. I Googled the name on the fuel hose and discovered it was basic fuel hose used for carbureted - not fuel injected - machines! I was angry with myself for not remembering to specify that I needed fuel injection rated hose. This meant removing the fuel tank and air box again to access the hose connection points on the fuel pressure regulator that reside behind the air box.
It was just my luck that the dealer didn’t have fuel injector hose in stock. I drove to the local NAPA store and found fuel injector rated hose with a diameter compatible with the BMW hose. I replaced the gray fuel hose the proper hose, reinstalled the air box and tank, and tried again, but fuel was still spraying from underside the tank. I had to remove the fuel tank and air box again! It was time to press the pause button on the project, as I had to fly out of town the next day.
About two days later, I decided to reread the various responses I received to my post on the MOA forum when something hit me across the head like a two-by-four. Lee had said, “The fuel return hose between the Fuel Pressure Regulator and the tank MUST be the factory pre-molded hose, otherwise it WILL kink when the tank is moved forward into position.”
I hadn’t used the correct OEM fuel injection hose and surmised from all the times of removing and reinstalling the fuel tank over the years, I’d compromised the fuel hose where it was supposed to have a built-in bend. I searched eBay and found a NOS (new old stock) OEM hose for about $12. With the proper hose installed, the bike started but ran rough. After consulting the forum, it turned out I’d installed the air box improperly.
Lee provided me with the proper way to install the 90-degree hose that attaches from the air box to the intake air box above the throttle bodies. If you don’t do it the way I’m about to tell you, you’ll have an air leak and the fuel metering device will get a false reading and cause your bike to not run at all. Lee explains: “If that large 90 degree hose is not properly connected to the plenum over the throttle bodies, the bike either will not run or run like crap. When connecting that hose to the plenum, the air filter must be removed. Insure that the screw for the clamp is to the rear of the hose and pointed up for easy access. Use a flat bladed screwdriver with a long shaft to secure the clamp. This explains your difficulty! Before you finish tightening the hose clamp, push the air box lid as high as it will go up against the frame and wiring, as that will be its normal position. If tightened when hanging down against the bottom of the air box, it will have to twist to get to its final position and that would promote cracking.”
I’d installed the air filter and then clamped the lid to the air box and then tried connecting the 90-degree hose but this was incorrect and created air leaks. With the air box properly attached, I pressed the starter button and voila! My K 75 S roared to life and soon was purring like a kitten.
I took her for a test ride and rode her pretty hard. She ran like a jet! The one thing I hadn’t done since owning her was balance the throttle bodies. I’d never thought to do this because she always ran so good. When I attached my CarbMate throttle balancing tool to the throttle bodies, using the #3 cylinder as my reference point (aft on the bike), I discovered the throttle bodies were way out of balance. It didn’t take long to balance them up. I took a second test ride and she ran better than before!
With the long Minnesota winter approaching, I topped off the fuel tank, added a few ounces of STA-BIL, changed the engine oil, oil filter, and the gearbox and final drive oil before covering her up and putting her to bed for the winter.
My advice for any backyard mechanic is to do your homework before embarking on any repair project. Take things step-by-step and have a Clymer, Haynes or shop manual by your side. Many BMW dealers don’t support older bikes like mine, but the good news is they still carry the parts. It’s discouraging when things don’t go as planned and it’s easy to get frustrated; at least once or twice during this service I felt like setting my bike on fire! Seriously, though, when I created a quiet uninterrupted space, things came together. When I got stuck, I found taking a break helped me return to my project with a fresh approach.
For those of you who like to do your own wrenching, the MOA forum is an excellent place to get help from some of the most friendly and experienced BMW mechanics anywhere. I believe our forums to be underutilized by the MOA community and also to be one of the crown jewels of our membership. Additionally, I’ve developed some very solid friendships from the forum. Thanks to all who helped complete this service - case closed, no more K bike blues!
