My 1981 R65 has run very well for the last 10 years.... until a month ago.
I had been riding the bike, and stopped at a Lowes to do some shopping.
Tried to start the bike, but during cranking the ignition caught and it ran briefly and then misfired.
I tried cranking it several times, and then it mis-fired and blew off the left carb.
Here is what I have done so far now:
I assumed that my problem was ignition timing related..... Maybe my ignition system was going bonkers and igniting the fuel at the wrong time.
So... I did several checks and thought the spark was weak and intermittent...
So I put in a new battery .. the old one was from 2004.... great battery but time to go.
No change... bang! off goes the carb....
Maybe hall effect sensor in bean can is going nuts and firing off the thing at the wrong time.
Rebuilt the bean can and replaced the hall effect sensor.
Also put in a new ignition module.... and put in new bean can wiring and igniton module wiring.
New Plugs and new spark plug wires.....
Checked the coils on my Dads Coil tester... they are fine.
Thought maybe the back firing through the carbs perhaps blew holes into the diaphram... checked those.... NO holes.
So.... after putting all the ignition system back together today.... THE SAME DAM THING happens...
Crank the bike.... it tries to run at idle... but when I open the throttle back 1500 RPM... BANG ... left carb blown off...
Also checked my valve clearances on both sides.... perfect....
I used a timing light to see where my timing was... and it showed correctly at idle with the "S" Mark in the window... the bean can is working because when I did increase the throttle I could see the spark advance...
Where do I go next?
That may simply be how the Coronavirus exhibits in an Airhead. 👿
Take the other carb off and do a compression test on both sides. It's got to be firing when the intake valve is open. If there is trash holding the valve open, then...
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Hi Again.....
More info.....
I thought maybe the left cylinder itself had a problem.... So with the blown off left carb dangling.... I connected my dummy external test spark plug on the left cylinder so I could watch the spark while I ran the right side of the engine.
I started and ran the engine on the right cylinder only.... and it RAN... AT IDLE .... but when I tried to increase the RPM past 1500 (when the GEN lights goes out) the engine ran roughly and worse the faster i went ... and stalled. (Did not blow off the Right Carb... but it did backfire a little)
As I did this, the dummy spark plug on the LEFT cylinder would spark nicely and evenly AT IDLE .... but again.. when I increased the RPM it started to go intermittent ... firing evenly at IDLE.. and then as I opened the throttle... the spark would start getting visibly rough.. with lots of "dead time"....
SO..... I reconnected the left spark plug... and put the left carb back on..... and started both sides again....
And the engine stayed at IDLE nicely.... and then I put the STOBE light sensor onto the left ignition wire to check the STATIC IDLE setting on the BEAN CAN.
The "S" mark shows in the inspection window at IDLE ...... and as I slowly increased the throttle up to 12-1300 RPM I could see the timing mark advance corectly... So I think the bean can is doing it's job.......
BUT again... at 1500 RPM (just when the generator indicator light goes out) the stobe light flashes just like the Spark Plug did.... it is steady flashing at IDLE... but at 1500 RPM the STROBE flash starts going intermittent with "short dead spots" then the bike stalls..... AND IT JUST DARES ME TO throw off it poor little left carb again.
So.... I am thinking maybe I need to start going through all the wiring to see if some kind of voltage problem is out there in the ignition circuits?
Maybe an "almost" short or open is going on that is limiting the voltage to the coil or ignition modlule? Maybe the coils are getting just enough voltage to operate at low speed... but cannot get enough to charge up at faster firing times? Maybe they arent getting enough juice to fully charge at higher speeds?
My last major component to replace is the Bean can itself..... maybe it has a mechanical problem that replacing the Hall Effect sensor would not fix? I do have a spare on my 1984 R100RT... I just hate tearing into it an operating bike (don't want to down it if I don't have to)
Anybody else have this kind of thing happen?
Oh.. and I do not have the Corona Virus... and nobody else has touched the bike.
Clark of the South
ABC #4099
Ok guys ... Here is the post mortem.....
The problem with my R65 is that the BEAN CAN..... the one that I overhauled with a new Hall Effect sensor ................. IS BAD!
Once I overhauled the bean can... the bike still ran very badly at any RPM past 1500 and would backfire and stall.
I then suspected the ignition module..... So I replaced THAT..... Still ran bad.
Suspected the ignition module to coil and hall effect sensor cable... replaced THAT... still ran bad...
Suspected the coils.... tested them..... perfect.... (but I put in new ignition wires and spark plugs just to make sure) ... still ran bad....
Thought maybe the ignition switch or the kill switch was providing bad power to the system... so I bypassed these by powering the coil and ignition module directly from the battery.... STILL ran bad.....
It just could not be my overhaul job on the bean can.... but that was all that was left to verify...
SO... I took the R65 bean can off..... and took my known good bean off my 1984 R100RT .... and put the suspect R65 bean can (with the brand new connector and brand new sensor) onto the 1984 R100RT......
When I ran the R100RT with the suspect bean can.... the same symptoms occurred to this bike...
The bike would run fine at idle... but once the revved the engine past 1500 it started running very rough... and would stall.
Also, when I used the strobe light to look at the sparking cycle... at idle... I could see where sometimes there was a slight "drop out" of the signal....
At idle this did not cause the engine to stop or hesitate... I assume because it was not that critical at this RPM...... BUT at higher revs I could see definite strobe timing gaps when the engine miss fired....
So..... My thinking now is that the "square molded" wire that goes between the chassis connector and the Hall Effect sensor has some kind of intermittent continuity in it.
I did not check the conductance of this wire when I rebuild the unit....(installed a new hall effect sensor and new molded connector only!)
This type of thing HAS been a known problem on the R1100 bikes.... a bad/crumbly internal shorting of the hall effect sensor cable itself.
I also noticed that the original connector on my 1984 R100RT is cracked and crumbly (just not as bad as my 1981 R65 bike was)... so I am suspect that it too has a very short time to live.
So..... what to do next.
I could find some good small sized three conductor wire and rebuild both units again..... OR I could spend the money and get rid of the bean can and go completely electronic ignition. So no more worries about the mechanical advance wearing out.
Anyhow.... what I SHOULD have done... if I had more experience with this kind of work... is to build the little hall Effect sensor test rig that I found on line... and TEST the stupid thing BEFORE tearing apart the bike and buying lots of parts that It appears that I did not need.
Hope this narrative will help others if it happens to them.
Thanks for listening...
Clark of The South
ABC #4099
1981 R65,
1984 R100RT
1971 R75/5 under restoration
1988 K100RS
1999 R1100RT-P
1987 325i Convertible
2002 330ci
You think I can get a parts discount on account of all the BMWs I own?
NOT!
My first impression was that something was misfiring in the ignition. Lots of experience with low voltages causing erratic sparks with EI. But I could not see how it would happen only on one cylinder.
Still can't.
Glad you're happy and back on the road.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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