I've managed to tear into the bike in the garage while waiting for the waters round Brisbane and environs to recede a bit. The intake rubbers were my target, as the bike has exhibited some vibration at certain rpm (3200 and about 4100-4500) that became slightly annoying on the longer open road cruises which have dominated my life over the past six months or so. As I said before I've gathered up the necessary bits and got cracking. I'd previously checked ignition timing, wheel balance, throttle body sync and general frame to engine and gearbox bolt tightness. I'd observed a slight hairline crack in one of the rubbers and verified a potential leak by using a propane bottle pointed at the rubbers with the engine running (no flame) and observed a mild fluctuation in the idle. The bike now has over 100kms on the odo and the rubbers looked original from the outside. It was time.
My experience was much the same as Ned's and I won't bore you with the details about how to get stuck into the fairing panels and such because you've all got different models. Suffice to say that the tank and fairing panels have to come off to make it easier to access the bits. I use a special fuel clamp on the fuel hose to avoid leaks. Remove the two fuel hoses from the tank or the fuel rail. It's a good idea to run the bike prior and unplug the four-wire connector that clips to the underseat computer to avoid having excess fuel under pressure when you do slacken the clamps to the fuel lines. The bike will stop after a mo' when the fuel pressure drops. I also bag and tag all screws, clips and smaller components to make it easier when reassembling the pieces. I also have a pad and biro to draw myself a map of vacuum and fuel hose routing, or just for reassembly notes. You may not get to it the same day and coming back into the garage after a lay off and realising the maze of pieces before you don't all look familiar is a sinking feeling. All back together and what's this extra bolt or spring or clip for? I hate that.
Once you can see the things you're going for it's best to start removing the airbox halves by unscrewing the band clamps and fiddling the airbox pieces out and away to the right hand side. The top half which contains the L-Jetronic housing can be left to dangle, though I wired it up to take strain off the electrical wiring leading to it. The bottom half has two Allen head bolts holding it to the block inside. Take out the oil bypass hose. Remove the fuel pressure valve from the back of the throttle bodies by unscrewing two Philips head screws. Unscrew the TPS from the end of the throttle bodies. It's easy to set it up again later on 8V models. Take out the accelerator cable by loosening the cable's chain and gear at the right hand handle, then freeing the small barrel at the TB end. Remove the 'choke' cable in a similar fashion, at the left hand side handle control, take off the plastic cap and remove the large screw holding down the thumb control. The cable end pops out easily. Remove the injector rail and carefully wiggle the injectors out of the cylinder head, being extra careful not to drop any debris down the holes leading to the intake valves. I stuffed a small piece of clean cloth into each hole after carefully cleaning out the rubber and dirt that accumulates there. The injector seals, as Ned or others have said, might be 'welded' to the aluminium head. Mine were and had to be gently rocked back and forth until they broke free. Unscrew the clamps that secure the rubber spigots to the cylinder head - you might have to jump round to the right hand side to access one or more of these screws, depending upon how they were attached by the P.O. or the factory, if original. Tilt the entire upper airbox and throttle body set to the left and wiggle it out from under the frame, sliding them a bit toward the back of the bike once the throttle bodies are free of the rubber spigots. It's a tight squeeze but having taken off the bits at the back it comes out fairly easily.
All four of the upper rubber sleeves had visible hairline cracks and one was split right through, falling apart in my fingers when I pulled it free of the airbox upper. The lower spigots were in better nick except for one which had a visible crack in it. They've all been binned.
Clean the throttle bodies with carburettor cleaner and a soft toothbrush, being sure to squirt some of that juice into all of the fine orifices. It's amazing how much accumulated gunk there can be on these faithful old soldiers. I lubricated the return springs, throttle and 'choke' cable arms, and replaced the old vacuum caps with newies too.
Now you can begin the task of removing the upper airbox from the throttle bodies and giving the whole mess a good cleaning. I used carburettor cleaner so it does not attack the rubber bits, leading to potential swelling, like brake parts cleaner might. The upper rubber sleeves are clamped down with one-time-use clamps that come off fairly easily with a twist of an appropriate tool like the pinch clamps I used in the photo. Perhaps BMW have a special tool but I didn't bother with it. I'd bought the proper sized clamps to replace them with and because they are a small width they may not be easy to find generically. Some people have used cable ties (zip ties) with success. The uppers are 50mm and the lowers are 48.5mm. This is important because the rubbers are stepped to fit their respective housings. The lower spigots use thin width screw clamps and are reusable, but I bought new ones just in case too. The throttle bodies were covered with dust that had attached itself to the grease and oil that accumulates over time. I used an old toothbrush and gently cleaned out and thoroughly hosed down with carbie cleaner the TB set, including the air screws and vacuum holes. Surprisingly, with a good eye and some fine thickness gages I could see and measure that the throttle body butterfly plates were opening at about the same rate as one another in the early stages.
It's said that cleanliness is next to godliness. I hope that makes the bike run better!
The alu cylinder head needed a good scrubbing (stuff the intakes with rags) as there was a bit of corrosion. After the intake spigot surfaces were made clean and smooth I screwed down the new rubbers using a tiny dab of non-silicon sealant and tightened them to spec. These are 6mm Allen heads in soft aluminium and don't need more than 8 NM or 6 ft/lbs of torque. Position the clamps but don't tighten them as later on you will need to be certain they clear the area around the throttle bodies like the throttle cable arm and other bits. Replace the rubber on the airbox top half and position the pinch part of the clamps facing the bike's left hand side, but don't snug them just yet. You will see why when the bits are all back on. Slide the upper airbox half back onto the TB set and wiggle the assembly back into the new intake spigots, being sure you don't squash down the edges of the new spigots. A very small dab of grease on the inside of the rubbers works a charm here, lubrication being the essence of making pleasure in our lives. It's a wiggly, fiddly thing to do, but with patience and a few curses of praise to the Teutonic gods, you should get the whole mess fitted back into place. Now with the ancient pinch clamp pliers tighten the clamps, after you've made sure the airbox half and the TB set are resting comfortably and lined up correctly. Mine had to be forced a bit to be aligned. Now work out the best position for the screw-type clamps to be in and tighten them down. Replace the TPS and adjust the it 'til you hear a click (you can come back to this later on by just setting the screws so they don't fall out), replace the fuel pressure valve and vacuum hose, vacuum caps and fuel lines. Install new o-rings on your fuel injectors, both upper and lower ends, replace the fuel rail (a tight squeeze, this) against the injectors and bolt it down, being sure the top o-rings don't squash out and distort and that the square retaining clips attach to the injectors and the fuel rail correctly. Again, a small dab of fuel soluble grease works a charm for allowing the injectors with new, fat o-rings to slide into place.
The 'hundred year old' tool makes a comeback! Those eight clamps aren't easily pinched tight any other way.
Refit the accelerator and 'choke' cables, being sure you get the full range from open to close, adjust 'choke' cable freeplay, be sure the clamps are tightened sufficiently once again and in the correct position so as not to interfere with the workings of the cables, and replace the airbox halves and be certain the large clamps are tight after giving the lower airbox half a thorough cleaning out, renew or reuse the air filter, fit the oil bypass hose (I replaced mine - had tiny cracks in it visible only by pinching it - a potential air leaker), and refit the fuel lines. Refit the computer and any other items except for the side panels and such just yet. There is always something you want to re-check before buttoning up the works and realising you need access to that little tiny thing way down the bottom under that thing that's right in the way and your big fat hand is too big for the space you've got left! I set the TPS by switching on the key, making sure it was not holding the throttle plates open, and listening for the click when I opened the throttle. I fine tune it once I've taken a test ride. With battery connected and all components given the once over I levered the thumb control, pulled in the clutch lever, and pressed the starter button. It lives!
I've never had my bike start instantly and settle down into a such a smooth, steady (but slightly faster than before) idle. I believe this to be because the old, perished rubbers allowed air leaks and are now tight and sealed up. After a five minute warm-up at idle I gave the throttle a coupla quick blips. She revved up nicely but consistently hesitated a tad, but the throttle snaps back to idle like never before. I was careful to route the throttle cable in the most direct line under the tank and around the airbox. I moved the TPS a notch and tried again a few times until the hesitation was gone, so I tightened the screws to the TPS. Reaching for my electronic syncro tool I realised the 9 volt battery was flat, it was time for a beer, and a bit late as my music was still playing at daytime volume in this quiet neighbourhood. I closed the garage door, turned off the music, switched off the lights and went inside for the night. Man, my legs ached from the all day up and down (I don't have a workbench for the bike) and the strain from the cement floor. I needed that beer. Today I am checking the throttle bodies for sync and refitting the panels. I've been away working all week and a nice ride will do me a world of good.
Later that day...a cuppa tea and a 9 volt battery for my syncro techno gizmo in hand and I've warmed the bike to operating temperature. The idle is smooth and unhesitating. I whack the syncro thingy onto the individual vacuum ports and discover that #3 is just off the others a smidge. A blade width of the screwdriver or two anti-clockwise and she's spot on, inline like a good citizen. A few good revs and she settles to a nice steady, sewing machine idle of about 1000 rpm +/-. At revs the TB's are goose stepping in unison like old pros in a marching band. Synchronising them is a bit more complicated and I'm feeling glad I don't have to touch 'em. The feel on the road is good, smoother and crisper than it's been in yonks. The vibes have dissipated. I like a definitive fix.
Next up, sloppy timing chain.
Leaky Intakes - rough running Mon Nov 08, 2010 5:25 pm
tiny Sony camera with close up lens, just right for a single paw operation. Even fits in the pocket, sorry, pouch. 
