Formal Introductions From a New Airhead

[0m3nc0w]

Hi there guys and gals, my name is 0m3nc0w, pronounced "omen-cow"



It's a nickname with a long story that I won't go into here. Anyway I'm a new '78 BMW R100/7 owner. I sold my last bike 8 years ago when my wife got preggo with our first girl and honestly never thought I'd really ride again. She recently inherited a motorcycle and I've been getting the bug again. Next thing you know a neighbor a couple blocks away is wheeling this bike out to the end of the driveway and putting a for sale sign on it.

I pull over and offer him his asking price before he has the 2nd piece of tape on. I asked him if he knew how much the bike was worth and he said he looked it up but wanted to get rid of it in the next two days as he was moving. So I gave him a $20 downpayment and was back in less than 15 min. with the $2480.00 balance.



I know right? Seems like a good deal. Come to find out it's 1 owner, 18K miles, never ridden in the rain, no rust, always garaged, new tires and looks pretty good to boot.

I've put a couple hundred miles on it and it seems to run perfect except one thing... When I get it on the freeway and get up to speed in top gear and it hits 4K RPM it starts to bog down like someone is pinching off the fuel lines. The tone of the exhaust changes like it's loosing power and it won't accelerate any faster. I should also mention this is intermittent, it doesn't always happen, it depends on the day.

Now the really weird thing is that in every single lower gear I can take it up close to redline and it won't exhibit this behavior. It will only do this in top gear on the freeway somewhere around 60+ MPH that this happens.

I have an appt. to have it looked at in a month but I thought I'd just ask on here because you all have been so wonderful at answering all of my questions that I have posted so far.

So, does anyone have any idea what would be causing this and why it would only happen in top gear at freeway speeds?

[Major Softie]

So, you're not just saying you're a thief, but also that you're proud of it.

It's only displaying this behavior under more of a load. Leaking diaphragms can exhibit this symptom. Possibly coils, but they usually aren't as load sensitive as rpm (and heat) sensitive.

It also could be genuinely running out of gas - that can also be load sensitive. Restricted fuel flow could create such a symptom.

[montmil]

I agree with the Major. One of my Airheads exhibited the same symptoms. No issues until high gear and asking the Bings to pull a high vacuum. New diaphragms cured all. Tiny pin holes and/or all but invisible cracks will cause this. Your description of the problem leads me to believe it's not a fuel flow problem but that's an easy check.

Beautiful bike. Where do you hail from?

[SteveD]

Classic buggered diaphragm symptoms.

[SteveD]

Wilkommen Mr Cow.
Classic buggered diaphragm symptoms.

[ME 109]

Holed diaphragm should exhibit symptoms in lower gears as well, with a wide open throttle.
Low float bowl fuel level on one carb is also a likely culprit.

[Kurt in S.A.]

Nice bike. I don't think I've seen that color before...I like it.

Where's the battery? And has the front rim been replaced? Can't tell from the picture, but it doesn't appear to be the reinforced variety.

http://bmwmotorcycletech.info/19inchrecall.htm

Kurt in S.A.

[0m3nc0w]

Hi Kurt,

I think it's a custom paint job. When the tank is off there are hints it used to be red. The front wheel is the original OEM that was never replaced when the recall went out. I spoke with my local BMW dealer and the service manager (that has been with BMW for >20 years) told me that while there were a bunch of bikes that exhibited minor cracking there has never been a reported instance of catastrophic failure. He recommended I NOT replace the wheel and just inspect it carefully every couple hundred miles for any evidence of cracks.

Apparently BMW had a special run of replacement wheels manufactured for this recall and when the wheels ran out they ran out, and folks had to then pony up for a wheel. I'm thinking about writing BMW in Germany to see if this is really factual as I thought a recall was a recall and they didn't expire. But what do I know... and this service manager seemed really knowledgeable.

Oh and the battery is one of those little lithium polymer jobs that slip in under the seat. I like the way it looks being able to see the whole airbox. There is a significant size difference:

[Kurt in S.A.]

Interesting...thanks for the update. As for the recall, I'd be interested to hear what you find out. My understanding, only by reading what has been going on, is that BMW is obligated to get all these wheels off the road. It's a national recall and apparently will never close. Sure, there has been limited evidence of cracking, but I'm not sure I would want to be the exception...front wheel locking up is not fun. BMW would have known how many wheels were produced and it would see logical (to me) to have an equal number of the new wheels produced waiting for customers to come in for them. I've heard where there are issues with 2nd/3rd owners of bikes with these wheels having difficulty proving the lineage of the bike...and that a dealer might refuse to exchange because of that.

Kurt in S.A.

[0m3nc0w]

OK I've contacted BMW at:

BMW Group
Archive, Collection, Classic Brand Management and Historical Information Service
Moosacherstrasse Straße 66
80809 München

I immediately received an auto-reply letting me know they are on it and I'll post when I hear something back.