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Loss of power 100s

seaswood

New member
Lost power on hwy at first it was just a slight intermittent power loss.
Then it would go away almost like water in gas, checked float bowls did not see any water.
Had been riding in rain for two days?

If any one has any ideas, was low on oil but not out of oil & had just added oil when this started.

Was heading north on 81 in Virginia when this happened.
Presently bike runs but not like it should be.

Craig
 
Check the coils,plug wires n plug caps. Recently,my R100/7 acted like water in fuel on way home from work. Turns out,my right plug cap was bad.
 
Reply just spoke with Craig and got him some #'s from the anonymous book. Here's some info he gave me that may or may not help.

Started after a fuel stop (new bike to him, just bought it today and riding it home)

Earlier today they discovered the locking gas cap was locked a there is no key so they had to drill the cap to get it open.
 
Check that your tankbag is not sealing so tightly against the top of your tank that the fuel cap can't vent.
 
If the trouble started right after a fuel stop, that would shout "bad gasoline" in my ears.
 
Torn carb diaphragm?

some more info would be helpful. Low, mid or high speed power loss? Or all the above. Won't accelerate as should, or won't hold speed as should?
 
umm, doesn't the tank vent thru the gas gap lip area to underneath the tank, not above it?

No, it vents right through the cap. You might be thinking of the overflow drain. If you get too much fuel or water gets around the cap, there is a hole and a drain line to the bottom of the bike. The hole at the top of the cap is actually connected to the bottom of the tank via an enclosed pipe through the tank.

BTW...I don't see where the OP mentioned anything about a tank bag. Maybe it's an assumption if he's on the road. :dunno
 
No, it vents right through the cap. You might be thinking of the overflow drain. If you get too much fuel or water gets around the cap, there is a hole and a drain line to the bottom of the bike. The hole at the top of the cap is actually connected to the bottom of the tank via an enclosed pipe through the tank.

BTW...I don't see where the OP mentioned anything about a tank bag. Maybe it's an assumption if he's on the road. :dunno

thx. haven't looked at my airhead's tank in a while. it's in "project" status.
 
Broken

Torn carb diaphragm?

some more info would be helpful. Low, mid or high speed power loss? Or all the above. Won't accelerate as should, or won't hold speed as should?

Spent the day yesterday draining fuel, changing plugs.
Did not get to try bike with different plugs wires yesterday before trials started on point!
And that took a while to adjust point decided parts were needed.
So awaiting to hear back from Salem BMW.
I am hoping gambling on plug wire as changed plugs no change.

After a gas stop there was an intermittent loss of power, initially just a blip I could feel it would go away.
Then return 5 10 minutes later eventually the interval became continous.
Lost idle & top end power still could drive bike well sorta.
Shop says one side is not heating up. Plug wire maybe.
With luck.

Was Ottawa wifi range yesterday.

No tank bag the drain hole appeared to work, added fuel cleaner for water no change.
 
I didn't get, but are you still running points and condenser or electronic.

What you are describing sound eerily similar (if I remember that far back) to what my /2 did. Turned out to be condenser.

It would work fine till it got warm, and then completely quit when hot.

took me a while to figure out.

I wonder about valve settings as was mentioned, my /2 also would run fine until it got really warm (very warm/hot weather) and a lot of city stopping from red lights, etc) and it would run rough and be extremely hard starting. Turned out to be valves. I added a .001 or .002 to gap, and solved the problem completely!

Other than the junk Bing carbs, that engine ran like an electric motor after that.
 
I had a condenser "POOCH" a few day's ago with about 1500mi of duty. Similar problems, could not figure out the root of the problem till my mechanic narrowed it down. I should have left the old one in there. Do we really know where these parts are made today??:uhoh I don't remember having to change condenser's but every few years.
 
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If it is a 100 with emission stuff it does vent from underneath the seal lip of the tank cap via a solenoid into the air filter housing.

Is that what you had in mind, bikerfish?

/Guenther
 
I didn't get, but are you still running points and condenser or electronic.

What you are describing sound eerily similar (if I remember that far back) to what my /2 did. Turned out to be condenser.

Ran fine until it started cutting out, plug wires tested bad are coming from BMW, condenser, points are being changed also. The wires are shot condenser & points may be at fault also so.

I was interested in a pre can ignition bike chance I took seller had basically not done anything! Go figure.
Just trying to git it home so I can go through it all.

Thanks for the input, thoughts!
I believe this is a pre emission stuff 78s has only a single vent to r side carb, if that is correct?
 
I believe this is a pre emission stuff 78s has only a single vent to r side carb, if that is correct?

Yes it is a single vent from the breather to the right carb. The '78s (most of them anyway) are subject to EPA (aka emissions) constraints but maybe not in the way you're suggesting. No fuel vent lines or solenoids, no external pipes back to the heads, etc. The timing on the '78s were set back in order to make them run a bit leaner...it got worse over time.
 
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