Stumble, hard start, and backfire...

[vespajg]

All,

Last fall I posted about a small stumble with my 1971 r60/5 that eventually corrected itself. BIke has stock electrics. Now, it appears to be back and I'm looking to replace the capacitor per Jean's advice and maybe the points. Everything else SHOULD be okay (tune, carbs, etc. should be good) and the bike was, until a couple days ago, running like a top.

Symptoms are this: hard start, lots of backfire and burping, but improves when I get it up and running. Original thought was maybe some water in the tank. But an ISOHeet treated tank later and it still is having trouble. Twice when this occurred away from home, I was able to eventually get it started and make the run home, but it seemed a bit anemic. Ran all right, but felt like it was missing just a bit here and there. After being warmed up, though, it "seemed" to run better, which is counter to the "capacitor failing after heating up" that I've read about. Going to pull the plugs tonight and replace if necessary but I don't anticipate that being the problem.

Never messed with points but have a set of Noris points standing ready. Other than adjusting the gap, is there much more to replacing, assuming the timing is okay (it should be)? Or does replacing the points necessitate re adjusting the timing? Obviously, new territory for me and, yes, I've been to Duane's website. Just looking for a nod to the replacement task difficulty, not a dissertation on how the electrics work:). I think I have a decent grasp on that...or as best as I can after reading and re-reading...

Thx in advance...

~jg

PS - also looking to swap out battery cables...read a bit about aftermarket (more efficient) versus stock. I'm not going to make my own, so which ones should I buy?

[dwire]

Like your mention of the condenser (capacitor mounted by the points to reduce the points from arcing so...) the other thing that comes to mind is a bad coil (or two) but often they exhibit the opposite behavior too. I guess I have seen them both ways, but mostly it was they died when they got hot as the internals expanded and shorted out (worse)...

The points are a breeze if you have the dandy little tool the fabulous Duane Ausherman speaks about on his site (neither he nor I have any affiliation with the maker of said little tool...) If you do not, just be certain of a few things, don't mess up the kick starter trying to get the points on the ridge of full open. Also, don't even think about turning or tightening the screw on the end! One finger on your wrench is all that is necessary to hold it on - it will NOT fall off, but you'll be really sorry if you break that shaft off!

I suppose the timing could be off and the improvement is just you holding it higher up off idle, but I think you'd notice that. Have the carbs been rebuilt? You mention replacement. Is there something broken off of one that we don't know about? They truly are very simple to sit down and rebuild...

Battery cables, they will help with the electrical system all around, but won't make a sick bike suddenly not run "sickly" - IMO... Good investment cables are. Many of us make our own. If you are not going that route, there are likely countless places you could find something that "will work" but the stock brand cable having such a small connector on it to go through the speedo cable hold down, well you may have to look a lot harder for something like that; I never look at such things in stores anymore, so I have no idea what is available. The OEM ground cables (the only sort of "special" cable of the two) is still carried and affordable by many BMW vendors online and even off, so if you're not into home brewing one, consider just a simple stock replacement. BUT ALWAYS REMEMBER TO LUBE THE CONNECTIONS WITH GREASE! This is only to prevent corrosion, but that is the number one enemy on all connections anyway; save getting them caught up in something and ripped out!

To sort of reiterate here, are they stock coils? How old is the bike? hmmm... Also now that you've had the tank off, are you sure that none of the wires to the coils are touching the bottom of the tank, frame or anything else they should not be? Finally, I had a BITCH of a problem I created with some old NOS points I put in. No spark, and while a different topic we can cover elsewhere, when I pulled the plugs and saw there was a bit of anemic spark, but it seemed too purple/white/yellow to do anything in the combustion chamber. Spent half the day realizing, even after running a meter, test light up and down the whole thing numerous times, that since I had removed the front cover, that was the variable. I had inadvertently ever so slightly clamped that old fabric and fall apart rubber of the paints wire under its hold down clamp and got it partially shorted, or more like just bare in a spot, so things worked (so-so) with the cover off, yet did nothing with the cover on in front - such an easy fix I could not see the forest for the trees in front of me...

Others will chime in likely with far better advice than I can provide; 90% of my advice can only come from mistakes, not triumphs with my two example R75/5's... Good luck, wait for the pros to ride in and save the day.

[montmil]

The HEET treatment will not actually remove water. I believe the ingredients list includes alcohol which is hygroscopic. <http://en.wikipedia.org/wiki/Hygroscopy> In other words, the water is still there. Remove the tank and dump it out. Allow to air dry, then refit and refill. If you're suspecting water in the fuel, drop the float bowls and take a look. Water globules will be obvious in the float bowls.

When replacing the points, it's a nice idea to check timing. No guarantee it will stay in time or is already out of time. Easy task and will put your mind at ease.

When was the last carb overhaul? Could be some minor "grunge" blocking a jet or air passage. Deteriorating fuel lines shedding bits into the carbs?

If you have a "decent grasp"' on electricity then you understand that electrical circuits, like coffee and divorces, begin with good grounds.

[vespajg]

Many thanks for the replies. Re the carbs and hoses...should be in order. I think the hoses are only a couple years old at most. But worth looking into...

[Duane Ausherman]

You are taking the "shotgun" approach. If you were hungry, would you go out in the forest in the dark and start shooting, hoping to hit something? I don't think so.

Nearly everything can be tested, except the coils just aren't practical for most of us to test. So, test them by replacing them last.

You run a great risk of swapping out parts and having no idea what is going on.

I suggest more reading until you have some understanding of how the ignition system works. Then do one test at a time.

To start with you assume a lot with your statement of "Everything else SHOULD be okay"

[SteveD]

Many thanks for the replies. Re the carbs and hoses...should be in order. I think the hoses are only a couple years old at most. But worth looking into...

I had hoses less than 3 months old that shed a nice chunk that nested snugly in the main jet. Bike would start, but had no guts and felt like a single. It worked better the slower it went.

[vespajg]

Thanks for the metaphor, Duane. I intend to use your diagnostic algorithm, but, as airhead parts aren't available at the corner store and I don't share your encyclopedic knowledge of airheads, I ordered what MIGHT be needed. That way, the repair won't take three months while I wait for parts with a ripped down bike in my garage during the precious summer months in Oregon. Jean suggested the capacitor last fall and I know your opinions on that replacement. Regardless, it's simple and worth a shot since it only takes a few minutes as will popping in a new set of three dollar plugs. Reading the board instructs that often repairs seem to work for no apparent reason. Maybe that's the case here, maybe not. As for why I say things SHOULD be in top order otherwise...my bike is lovingly cared for when things get out of my comfort zone by a very reputable airhead mechanic who last treated her in June. I think it's safe to say, from my perspective, that it SHOULD be running well given the work that was performed and the overall condition of the bike. But certainly, something else COULD be wrong.

Steve - I'll check the hoses, but it seems to be a bit too intermittent to be be a clogged carb...but you never know.

[dwire]

Yes, check once, twice and then again. Your problem could be a potato or banana stuffed in one (or both) of the pipes; we don't know that; these are only things you can determine on your end. Once you are able to supply the real geniuses here (NOT I) with information, over 9 times out of 10, someone will either recognize the issue and help speed your repair and cut the costs of unneeded parts, labor and frustration, or will know where to start you off in the BMW "My Bike is stumbling and not running right" BMW diagnosis flowchart, as most have been there; Duane and his service personnel on a daily basis while the bikes were new and as they matured. "Most" everyone else has EXCELLENT advise for you as well mostly (not all, but mostly) from a different angle - common issues that happen when people like us want to ride a bike that is 40+ years old; I think Duane states he retired after two weeks of owning his dealership as he was so good at what he did...

(Just kidding Duane, but we both know you are a shining example of a success story in so many things you've done and have been involved with; you often don't give yourself enough credit for such things and I am not at all just speaking BMW's here...)

[Jean]

Hi, vespajg...I've been away for a while but got on just in time to see this!!
Duane NEVER wants to replace the capacitor, but I have learned to suspect it whenever something goes wrong once the engine has been running for a while and things get warm. Pushing a '77 RS up a hill is a great teacher. I haven't experienced hard starting or backfire (when?) if the capacitor was bad...bad is usually shorted, BTW. How did you lastset of points look when examined? a capacitor that's not doing it's job at all (open) will result in points that have a pit on one side and a mountain of metal on the other due to arcing when they open.
Do you have the coils connected correctly? It does make a difference. Terminal 15 should be on the "hot" side and terminal #1 should go to the points. Since the coils are in series, terminal #1 of one coil should be connected to terminal #15 of the other one...
So, how long ago was it running OK?

[vespajg]

Oh, I know...I've been on here for ten +/- years now, so I recognize and appreciate the helpful advice and knowledge!