R90/6 stalling at speed

[fritz_r90]

Apologies in advance if I'm asking a stupid/already answered question. I've searched other forum posts quite a bit, and I've not found anything that seems to address my situation, so here goes:

I'm having a relatively infrequent but stubbornly persistent issue with my R90 trying to stall out at random times (usually at speed). Typically the stall is preceded by some very slight hesitation/jumping that feels like very subtle lurches. If the lurching worsens, the red battery charge light illuminates in time with the lurching; occasionally this will ultimately lead to the bike stalling (but not always -- it's probably stalling out only 10-15% of the time). This has happened in a variety of gears at a variety of speeds -- from low speed in 2nd/3rd gear to 65 mph on the highway. Not sure whether this is relevant, but there is an occasional popping that accompanies the lurching, and very infrequently a backfire.

The battery is only ~6 months old, and the charge has been solid at all times. I have taken apart both carbs, replaced gaskets and O rings, cleaned the jets and the float bowls, and re-set the floats -- the jets were a bit dirty, but otherwise I saw nothing of note there. I did find the ground bolt to be a bit jiggly, so I replaced that -- the ground wire still moves a bit if you pull on it, but it's more firmly stationary than it was.

I'm still fairly new to this, and I've definitely been learning as I go with this bike. Probably there is something very simple that I've overlooked or that I just don't know yet (I'm actually hoping that's the case). Any suggestions for next steps?

 

[20774]

Welcome to the forum! My first thought was that it was possibly the fuel cap is not breathing and it's building a vacuum inside the tank. You said it happens at low speed as well, so that probably rules out the cap. But you could consider safely loosening the cap when this happens and see if the problem goes away.

Then you say that the charge light comes on. Sounds like you might be losing electrical power. That jiggly ground bolt doesn't sound good. If you lose a solid ground, the ignition is going to shut down. I wonder why it's so loose. You might want to consider an appropriate washer at the connection just to take up some slack. You should be careful with this bolt...it's easy to strip the threads which makes things interesting in terms of finding another ground. Also check the bolts at the battery terminals.

What type of ignition do you have on the bike? Stock points/condenser or something newer? I suppose something wrong with the timing could be a problem, but that would only make the bike run rough, not necessarily causing the charge light to come on.

I'd look closer at the grounding of the battery.

 

[stevenrankin]

My first thought is a bad ground. Kurt is 100% correct that common bolt for speedometer cable and ground is prone to stripping. I can't tell how badly stripped it is from here or if it can be in fact fixed. The bolt itself has a breather hole in it so not any bolt will fit. I confess I am pretty blank when it comes to heilicoils and their uses, so I can say for certain one will work or not. Now the good news is that is not the only place you can attach the ground strap. With another perhaps longer ground wire, you can ground anyplace on the engine or transmission. A bit of ingenuity goes a long way.

OKAY, Kurt also mentions the battery terminals, yep, I have been caught there with a loose ground.

Other than the ground strap, it sounds like an electrical issue so next step after securing the ground would be to do a thorough inspection of the various connections in the ignition system. It could just be due to a corroded plug on the ignition switch or the starter relay. Yeah it is a pain to trace wires, at least most terminate in the headlight shell were they are pretty well protected.

Last time you changed the points did you accidentally pinch the point wire in the front engine case? LOL, I have done that.
A long list of things to check, if you are near Rochester NY I would be happy to have you stop by and give you a hand, If not, I know an airhead shop nearby. Good luck and hunting, St.

 

[PGlaves]

The first thing I would do is find a substitute bolt to which I would attach the main ground battery cable; a good location on the engine case or frame. It has been too long without an Airhead for me to remember the best location but look around and find one.

 

[stevenrankin]

LOL, Paul I am still riding an airhead and I for the life of me can't point out a good spot either. I suppose I should quit being lazy and take a look for the fellow. Hopefully he can save the threads on the existing spot.
St.

 

[PGlaves]

LOL, Paul I am still riding an airhead and I for the life of me can't point out a good spot either. I suppose I should quit being lazy and take a look for the fellow. Hopefully he can save the threads on the existing spot.
St.

I failed to mention that a longer ground cable might be needed, or not. Maybe the bolts where the rear subframe attaches to the main frame.

 

[kinterridge]

+1 on Kurt's, Steve's, and Paul's replies I'd add why not try a wiggle test on the suspect ground while idling. Does sound like a ground issue.

 

[fritz_r90]

All-

Many, MANY thanks for the kind and helpful responses. I sheepishly acknowledge that it hadn't occurred to me that even a little bit of wiggle in the ground could be such a problem. In any case, I've added a washer to the anchor and took a brief run around town, and so far so good -- no symptoms, no problems. I'll post again if the problem resurfaces -- meantime, thanks again, everyone. I really appreciate the guidance.

 

[omega man]

I’m a fan of “star” washers in a “bad ground” situation. Even better if the surface can be cleaned. Even better if the “star” washer is stainless.
Hopefully you have it solved and are good to go.
OM

 

[stevenrankin]

Adding a star washer is a good idea for that spot. Hopefully you have solved your problem.

LOL, I chased a bad ground in the system for a year, bike would hiccup then gradually reached a point were it would quit. I never found the exact smoking gun spot but believe me all the grounds got a good going over. Thank God I can do the work myself. St.

 

[20774]

Best to use a wave washer...generally BMW never used star washers. I think they tend to cut into the aluminum.

 

[pauls1150]

True, but in this case, Fritz needs to lose the jiggle (a star washer would generally be a little thicker) AND ensure a reliable connection.