Hello everyone: I am pretty new to working on my bike--in that "just enough skill to be dangerous" phase. I am hoping that some people on here can point me in the right direction... I have a trip scheduled this Friday, and am trying to get the bike running. I have searched most of the airheads threads, but still have some questions. first, i have: 1977 r75/7, all stock except open pipe exhaust. Was professionally tuned 4000 km and 1 year ago. Tuned means: New points, new plugs, new condenser, valve adjust, oil change timing, air filter, oil filter. Many other things were done, but i dont think they are relavent for the current problem. Problem: The bike starts okay, warm or hot. it idles relatively rough, and coughs/hesitates at half throttle, when accelerating away from a stop for example. if i open up to full throttle, she coughs some, then kicks in full gas. Also, when going at a constant speed, there is some hesitation (like power cutting out) even though I am at a constant throttle. This problem just started in the middle of one ride-- one minute it was running great, and 10kms later, started running rough and all kinds of hesitation. What I have done so far: Checked plugs and plug gap. Plugs seemed whiteish, like bike was running too lean. Drained tank, replaced both original petcocks, fuel lines, and opened float bowls of both carbs. Tank is clean, petcocks were pretty gummed up with shit from 30+ years. carb bowls were clean. I opened the front cover and checked the gap of the points. I dont really know what pitted or corroded points look like, so i did not try to file them or replace them yet. turned the 6mm allen key clockwise on the alternator until the points opened, and reset the gap to .4mm. The advance unit seems to be opening and closing okay. I put everything back together. it runs better, but still seem rough and is exhibiting most of the same hesitation. Not near 100% performance. I have the clymer manual, and have read a lot of the information on tune-up, timing, etc. Questions: 1. When i took off the front cover, i did not unconnect the negative terminal of the battery. I have since read that it is easy to short out the diode board this way. Since I put the cover back on and have started/ran the bike... can the diode board be burned up? Does the diode board either work or not work, or can it be halfway broken? 2. There seems to be a lot of oil/grit/dirt inside the front cover. Is this normal? should this area be really clean, and can this dirt/grime contaminate the points or other parts? I am not running a tach cable, and some of the dirt could be coming through this port, but it seems like there is a lot of oil as well. 3. I have received some recommendations to just change out the condenser and points, and it should fix the problem. However, can points and/or condenser really wear out in 4000km? I dont want to throw in new parts, just to have them fail again if there is something wrong. 4. Clymer manual says to tune up the bike by doing these steps in the following order: adj valves, adj/replace points, check ignition timing, run compression test, replace plugs, clean float bowls, adj carbs and idle speed, sync carbs. considering i do not have the tools and knowledge to checking the timing or do a compression test, what are the chances this is the problem? 5. my plug wires seem to come off pretty easily. They dont really feel loose, but I can pull them off with very minimal force. Can it be that when i am going down the road, the plug wires are vibrating, causing the hesitation? I know this is a lot to arm-chair quarterback--i am heading back to the garage with the clymer manual and my tools tomorrow morning. I am determined to start working on this bike myself, and learn as much as i can... and any help anyone has on this problem would be greatly appreciated. Thanks, Rob
At 4000 miles the points can pit, the rubbing block can wear, the point gap can decrease and the timing can become retarded. AFAIK, the service interval on the points is 3000 miles. They last longer with a Points Booster, but still need to be regapped periodically. Un-Boosted points will oit, which can make regapping iffy. When regapping, renew the point cam lubricant. Recheck the timing, At 4000 miles/one year it's time for a tune up. First step in resolving this problem is a full engine service to eliminate variables. It's good practice to disconnect the battery before removing the front cover. It can be done if you have a deft touch and are willing to replace the diode board if the deft becomes clumsy. If you did zap the board, there would have been sparks and great fanfare. Disconnect the battery. What do you mean by "loose plus wires"? The plug caps are loose on the spark plugs? Replace them. NGK plug caps work well. If the wires are loose in the good plug caps, unscrew them, snip off 1/4" and screw them back in. BMW plug wires are stranded copper, not "carbon". Your problem may be carb-related, and maybe torn diaphragms. --Bill
Hello: i do not have anything to provide backpressure... could this be the problem? If so, any idea why it would work fine for 4000km, then start acting up? I have heard from different camps that say these bikes need backpressure, and those camps that say it doesnt matter...
Hey Bill: thanks for the reply! FYI, I am talking about 4000 kilometers, not miles, seeing as how I am in the land of the metric system, and I had the original speedo+odo converted to KM. Anyway, I will now always disconnect the battery before removing the front cover. I have never seen any sparks or fanfare when removing the cover, so i will assume the diode board is okay. I am more concerned about the amount of dirt/grime inside the front part, around the points and advance unit from what you say, maybe it is time to replace the points? I am not sure what to use for "point cam lubricant"... is this just a dab of grease to make sure the points move when the mounting screw is loose? For timing, i dont really have any way to check this... I have looked into making or buying a continuity tester to perform the static timing as described in the clymer manual... but can this really be off after only 4000km/2500miles? Also, for the plug wires, I mean that it is the plug cap that is loose. sounds like i need to order new wires, caps, the whole deal, from ngk. I will do this.
You may have skated by without damage, but don't remove your front cover again without disconnecting the negative cable to the battery. You can burn up either the diode board, or the main wiring harness by not doing so. If your plug wires are original, they could be bad. If the points gap closed up, the timing could be off.
We use the spark plugs with out the screw on tip on them that most of the rest of the world uses. Our plug caps have a pair of wires inside that grip the thread on the top of the plug. If you are using spark plugs with the round tip it may be removable or you may have plugs that don't have a removable tip. In which case you will have to get new caps at least, you may need wires too. Use the correct plugs and the caps will work. Our spark plug caps are rated at 1000 Ohms. Later models with electronic ignitions use 5000 Ohm caps. Either will work but the correct cap is 1000 Ohms. NGK makes a cap that works or you can still get the metal caps at a BMW dealer. The ignition Booster is a worth while addition to your bike. The points will last much longer. These points should not be worn out however they are probably pitted. So in your case new points are advisable because it is difficult to gap used points. You are probably setting the ignition timing with a test light? This is mostly used these days to get the bike running and then timing should be set at full advance using a timing light. Learn to set the points this way. In the future when the rubbing block wears you can adjust the timing by setting the point gap to return things to where they want to be. Our ignition systems are rather unique but to make them work properly you will have to learn the theory of how they work so you can practically make them work. The first thing to learn about ignition points, not just our bikes, is that the dwell or point gap will change timing but changing the timing will not change dwell. I double checked this so you can memorize it now. This will help if you understand the concept. When the points were new the gap was set using a feeler gauge. As they wear the rubbing block wears and the gap closes a little. Eventually this closing gap has changed the timing enough that they need attention. Some riders will adjust timing, thinking this takes care of the problem but they have not adjusted the gap and it can get so small they don't open at all. The correct thing to do with used points is adjust the gap till you have the original timing. I advise you to not ever use a file on ignition points except in an emergency. It will work if you have a Booster but if you have stock ignition it is problematic. Points cam grease is a thick grease applied to the felt of the points plate so it lubricates the cam and helps the rubbing block last longer. The OEM grease is not available. There are other Points Cam Greases available but if you can't find it use a small amount of some other thick grease. Use sparingly on the cam of the advance unit. The advance unit it self gets greased with a light grease that helps it function speedily. I do not disconnect the battery when removing the front cover. I live on the edge and I also have several spare diode boards in my stash. Some oil may be coming out the tiny hole the tach cable goes into. Maybe you can plug the hole with somethin? Clean the inside of the front cover. I can't sleep at night worried about how dirty these things get. If it is clean you may then be able to notice changing conditions. I polish the inside and the outside of my front cover with Mag Wheel Polish. If there is actual; wet oil inside the cover we will have to talk about you fixing the leaks up there. There are two seals, one behind the alt rotor and one behind the points plate that may need changing. Change the condenser every other time you change the points or even less but carry a spare working condenser with you. I understand it is daunting to have to get a whole bunch of new tools all of a sudden and all you wanted to do was ride this motorcycle. But you are going to have to get some if you don't want to spend all your money by paying for help. This is the time to buy a timing light. Get one that doesn't have any advance features. I will try to look some up later today on Ebay and give you an example of one that works. You are going to have to spend $25-$50 for a used item. It may be cheaper new at Harbor Freight. Get the magnetic pick up model. PS: You need mufflers.
There are only two problems with open exhausts: if they are two short you can draw cold air back to the exhaust valve, damaging the hot valve, and 9always) you totally screw up the tuning of the exhaust tract. it's not about back pressure, it's about length and exit profile. You end up making lots of racket and a whole lot less power. (seriously less). You are much better off with some sort of muffler (even the uber loud glasspacks I run) that is specifically tuned for the engine, that is, it fairly well preserves at least the pipe length. Do some googling on exhaust tuning to see what I mean. You can get all sorts of weird effects and trying to tune it out with other adjustments can be a fools errand.
hey Disston: thanks for the help... first things first--i will always disconnect the battery before removing the front cover from now on. you are right, it is time for me to figure out this timing thing. I really want to learn this stuff, and i like buying tools and using them as much as i do riding. I am a professional bicycle electronic technician for a living, and as much as I know everything about bicycles and their power measuring systems, i know almost zilch about motorcycles. This is what I am trying to change! Also, i am living in italy, so the little things like a Pep Boys or Harbor Freight are a lot harder to come by. anyway, i went to the electronics store today and bought the parts to build a continuity tester to test static timing via the method in my clymer manual. I know this might not be the best way, but: 1. the bike seems to run fine under full throttle, making me think the advance timing is okay, but the "S" timing is off. Can this be correct? Thank you for explaining the points dwell and how it affects timing. I understand: 1. put in new points, and set gap 2. set timing, via static with a continuity light... but also I am going to try to buy a timing strobe light tomorrow, but no idea what they are called in italy, or which one to get. 3. after the timing is set, go back and check the points gap, and readjust. is this right? Question on dynamic timing with the strobe light... Is this possible without a tachometer? Since I have no tach, how do I rev the engine to 2600--3000rpm as recommended in the manual? I know the first answer is, dont remove your tach, dumass... but now that this has happened? Just go by feel? I guess i can feel about 3000 rpm, since the bike idles at 1000, and redlines at 5000... shit, who knows. I will also try to buy some points cam grease, because with the dirt and oil inside the front cover, anything that was originally there is gone. Also, i have cleaned the inside of the front cover as best i can, and will reinspect for dirt entering after a few KM's. Also, disston, thanks for not busting my balls too much about running an open exhaust. The bike does have exhaust pipe running back past the passenger footpeg, and there was a short muffler installed, but the packing of this blew out pretty quickly. My plan is to replace this piece with a muffler that actually does provide backpressure and some semblance of noise reduction, but I was planning on this as more of a long term project--not a "this week" project. my plug wires are original. I understand what you are saying, and will make sure i order the correct wires, caps, and new plugs.
This is a link to an Ebay auction that is for the type of timing light you should get. I'm sure there is something comparable in Italy but I can't help you with the translation. http://www.ebay.com/itm/Sears-Craft...701?pt=LH_DefaultDomain_0&hash=item43bbdb564d Sorry I can only provide a link for now. The fact that the bike runs good on the static timing is a very good sign. If you have a friend with a timing light then check the timing with the light and see what it is at full advance. I'm sure if I was asked when you wanted to eliminate the tachometer I would have explained it is a stupid idea. If there is some way you can get it back then do so. A tachometer is an asset. The advance unit will advance till it stops. You rev the engine till the dot stays solidly in one place. This is full advance. 3000 rpm is a little above comfortable. What Plaka says about the pipes is true. Running with no mufflers can cause problems, such as, burnt exhaust valves. If you want the noise then do some research on exhaust systems. Maybe longer pipes are enough but I would be worried about it.
I started out with a 1978 Clymers manual and help from a buddy who had a R100RS, so some of my methods are not 100% in synch with the modern manuals: 1. My 'modern' Haynes and Clymer manuals talk about disconnecting the grounding strap before taking off the front cover. My '78 manual did not and I have taken the cover off ~ 2 dozen times with no incident. If I were more cautious, some liquid electrical tape would be used on the positive terminal to the diode board. I have to expect someone has fried their diode board with the front cover - or the manual would not talk about it; but it seems a bit overly cautious IMO. 2. There is likely a slight oil drip that collects crud. Clean out the cover. The points area of the front cover have (or should have) a rubber seal. 3. More than likely, the points may need to be adjusted. A good set of points will last a long time (much more than 4000 km). 4. Follow the Clymer manual steps. Adjusting the valves is probably the most important step in the tune up process. IMO, a decent (not overly expensive) timing light is very useful to check the advance and ignition timing and should be purchased. A compression test is not necessary for a tune up or diagnosing hesitation. 5. Plug wires can be replaced fairly inexpensively using NGK instead of Bosch. Unfortunately, high voltage leaking through plug wires an cause all sorts of weird symptoms. IMO, replacing the plug wires never hurts if they are suspect of causing problems - because they may be the culprit. In general, these airhead engines have two systems that must both work together: fuel and spark. Both fuel and spark have been blamed for causing symptoms due to the other. Generally, spark is easier to diagnose because it often works or not. However, when considering hesitation and rough running it could be fuel starvation/clogging or a leaky spark plug wire/cracked coil. If the symptoms can be repeated, there is a better chance to fix the problem; for example if the rough running can be made to occur with the bike stationary. If all else fails, a good technique is a methodical approach starting with the simplest to check. For example: disconnect a fuel line and check fuel flow with a stopwatch and container, followed by removing he float bowls and ensuring fuel flows freely, and make sure the fuel tank vent is not clogged or covered. Good luck!
right on, this style timing light is what i need to find. thanks for the ebay link--i will just go to sears' website to get as much pertinent info as i can, and head to the stores here. next paycheck will be mufflers, and the month after that will be a tach... god willin' and the creek don't rise. thanks again! tomorrow afternoon i dig in with my static timing and hopefully a timing strobe light. Also, thanks for the tips on the advance unit. This now makes much more sense to me...like "it doesnt matter much if you are above 3000 rpm, rev it until the dot stays in place, then rev it around to see the dots move." does this sound right?--like the only thing i am trying to do is seeing IF the ignition goes to full advance?
Any inductive timing light. I have an old Sunpro that has done me forever. Also get a tach/dwell meter. This will serve as a tach and will also reveal your dwell. If it has a two cylinder setting that is ideal. Otherwise you multiply or divide the four cylinder reading--I forget which. If you come across a Fluke 88 automotive meter for under $100USD, score it. Must have all the original cables and the manual. You wanna test it in person. I would avoid flea bay. Get a relationship going with a regular automotive place.
Stan, super info! thank you so much. Quick question... i think my rubber seal around the points area is pretty roached. Are these easy to come by, or are they some super-rare part? Also, tomorrow i will pull the tank and look at the coil for cracks... but what am i looking for? somewhere i read that the cracked coil would have electrolytic sludge coming out... short of having some sort of testing unit, is this the best way to test if the coil is cracked? I bought some heatsink paste today to put under the coil... but where am i supposed to put it? Between the coil and the frame of the moto...? Anyway, thanks again... i feel like this problem should be easy to fix, but i am a foriegner in a foriegn land, and i'm pretty short on experience with this moto. But, i am excited to dig in. ciao, rob
Right on, thanks Plaka! i have now printed out some stats for an inductive timing light, but THANK YOU for mentioning a tach/dwell meter. shit, i never even knew something like that existed! this sounds like EXACTLY what i need to figure out the RPM when setting the timing. and yes, here in italy it is even more important than other countries i have lived to have a good relationship with a regular moto/auto parts store. i have a place in mind where i will go tomorrow with some cranky old dudes that will give me the stink-eye, but it might just be the right place. rob
Just be respectful and maybe mention you need to learn a lot and you are in there because you have heard experience abounds. You don't put heatsink paste anywhere but under certain electronic ignition modules. You do use a very thin smear of silicone dielectric grease inside the spark plug wire boots, both ends. Makes them easy to put on and off and keeps moisture out. Heat sink paste is often a very heavy silicone grease combined with zinc oxide (it it's white). You may as well try it, won't hurt. Cracked coils have cracks in them. "look mommy, that man has a crack in his coil". Y'know. Check the coils with a meter for continuity and resitance. If you are getting nice fat blue sparks, the coils are fine. Run them. Ditto check the wires for resistance and continuity while wiggling the ends. I make my own wires, Used to use Packard 440 wire, switched to copper core silicone. No resistance and I use resistor plugs. This horrifies some gurus. Bike runs fine anyway. I do check the plug resistance. You can run without any resistance but you get a better spark if some is present. Also noise suppression for any electronics. Running a zero resistance system it used to by mildly amusing to pull up next to some boom car at a light and listen to my ignition through their amps. Points must be unholy clean before running the motor. Wet a slip of paper with rubbing alcohol and draw it through the closed points. If you want to learn a ton, buy this book: http://www.amazon.com/Keep-Volkswag...&sr=8-1&keywords=how+to+keep+volkswagen+alive You are dealing with half a VW engine. A great deal of knowledge and all the shop tips, tricks and techniques transfer over. You will learn more about tune-ups and fault diagnosis on a flat air cooled carburated engine for $20 than you can get for any amount of time here. Also buy the bing manual which is exhaustive on the carbs. And maybe the charging system manual from Mottorad Electric which will cover all that stuff.
Rob, Here is a link to Motobins with the points rubber protection hose and the BMW part number: http://www.motobins.co.uk/displayfinal.php?q=07700&topsearch=1&go=GO Here are some plug wires from them as well: http://www.motobins.co.uk/displayfinal.php?q=70080&topsearch=1&go=GO Unfortunately, cracked coils can be hard to spot. Removal and carefully cleaning should reveal if there are cracks. All things considered, these older (original) Bosch coils are good quality. I am still using my originals from '78.
The twin 6 Volt round Bosch coils seldom have problems. Looking for cracks look for leaking fluid coming out of the coils. They are filled with an oily substance.
Whoa there. You don't need heat sink paste. That's only used on post '81 models with electronic ignition, and even there I think the need for it is a bit overstated. Second, cracked coils don't really ooze anything. They just have a crack on them somewhere. Normally this isn't much of a problem until it rains at which point you might notice a weaker spark (stuttering, especially under load). As for testing the coil, you can measure resistance across the windings, but this is not definitive as bad windings often have failures of an intermittent nature relating to heat, their mood, phase of the moon, etc. Best is swapping in a known good coil (or set of coils) to eliminate that possibility.
