1976 R90/6 Problems

OK been leaning on the airhead site a lot lately and this post is kinda long but I felt a little back ground might help. First off I am retired and perform all my own work on my bikes, 2004 R1150 RT, 1996 R1100GS.
I always wanted a airhead and picked up a 76 R90/6 with only 23,000 miles on the clock. Problem was it had been sitting since 1988 but able to get it running with clean tank petcock and carb cleaning and new battery and tires. but it developed a pretty good oil leak that I decided to deal with. I installed new rear main seal, oil pump seal, and front gearbox seal, new axle boot, wheel bearing seals, clutch plate is good and while i had the gear box out I replaced the neutral switch everything is back together and decided to install Rick Jones Alpha ignition so far so good.
Tried to fire it up and neutral switch is not working and starter will only engage with the clutch pulled in even with the bike in nuetral, and seems to be running on only the left cylinder. I cleaned all coil and wire connections, new plugs and NKG caps installed, Valve clearance is good, Carbs are set to spec and will further tune once the bike is running properly. While running on one cylinder the S mark in the timing window shows a little low off center.
Any suggestions on the neutral switch and getting the right cylinder up and running would be great. The good thing is I am not seeing any oil seepage or leaking which was the fix I was after before these other problems arose.

willyb said:

Any suggestions on the neutral switch and getting the right cylinder up and running would be great. The good thing is I am not seeing any oil seepage or leaking which was the fix I was after before these other problems arose.

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For the neutral switch, it changed after 1976 from a normally open switch to a normally closed switch. Are you sure that you have the correct one? If so, does it test correctly electrically?

Regarding the left cylinder only - the two coils are wired in series, so that simplifies the electrical trouble-shooting. Swap the two high voltage leads to the plugs at the coils and see if now only the right cylinder fires. If so, look at the coil for a problem. If not, swap the entire plug wires left to right. If the problem moves, look at the coil wire for a problem. If not, look at the spark plug. If none of the above, look at carburetion.

Might want to try measuring the resistance from one spark plug cap to the other cap. Should be 20-22K ohms. If not, something is wrong...as Lee has said, that will help you isolate where the issue might be.

Thank You

Checked the spark this morning before I read your replies and left side shows strong arch but nothing on the right. I will check connections this weekend after I pull the tank but wires from left coil to the right seemed fine when I installed the Alpha ignition and the bike ran well before I started all the other work. As for the neutral switch I was not aware that there was two types until everything was put back together and it was not working I did notice that the electrical tabs either go straight down or out to the side and the new one has the side tabs so will have to check the old one when I get back to my shop this weekend. one step forward and two back if I have to change the switch again as it was so easy with the gear box removed from the bike.

willy, if your bike is fitted with the old metal-shouded BERU spark plug terminals (below) they are prone to corrosion.



Read > https://forums.bmwmoa.org/showthread.php?55485-You-know-it-s-going-to-be-a-long-day



Not "period correct", but I replaced mine with NGK caps; the resistor value is different but I've had no problems with them in the eight years I've been running them.

spark plug caps

I did install new NGK caps along with the Alpha ignition.

Well then, that ain't the problem.

If you high tension leads/coil are solid then a plugged main jet would be my next guess. Crud loosen when you did the cleaning perhaps?

For sure......DID YOU SWITCH COIL LEADS to make sure that the good cylinder follows when you switch sides????? If not, YES, now it's a fuel situation.......Good luck...Dennis

Pulled the tank and cleaned all the wire connections between the coils and still getting a nice spark to the left and nothing to the right. switched plug leads and spark followed to the right side and nothing to the left. So what is the best test for coil function although I can not imagine the coil is bad as the bike ran fine before the Alpha system install. I will check the plug in sections for the new ignition system although they seemed to attach fine when installed. Electrical system diagnosis is not my strongest talent so any step by step would be greatly appreciated as this is really frustrating. the carbs where cleaned well and working fine before all the other work was started.

Spark plug cap-to-spark plug cap resistance measurement. It's a static measurement and things could change once running, but it's a start.

I will give this a try tomorrow, I see from your earlier post 20-22 oms is what I should be looking for correct? and thanks again for your help.

willyb said:

I will give this a try tomorrow, I see from your earlier post 20-22 oms is what I should be looking for correct? and thanks again for your help.

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20000-22000 ohms or 20-22K ohms.

Not familiar with this "Alpha" electrical ignition system that you refer to. Are you using the original coils??? If that is the case, you can go to any '"import" junk yard and get some coils from a VW Beetle or the like. Just trying to get you a cheap way to check out the coil on the side that is not working...…...Then again, it could easily just be a connection or ground. Have you tried calling Rick at Motorrad Electric where you got this ignition system. Or if it wasn't him call where you got it for advice...………….Put the original back on and what happens???

Also have a R90/6 only 1975 model. With the -S- below center of window, sounds like ignition timing is delayed a bit. If the points look good and gap is good just rotate the points plate to bring the -S- back up to the center of the window. Have put around 600 miles on mine since last spring. Have been pleasantly surprised by performance once I worked through carbs, and timing.

willyb said:

Pulled the tank and cleaned all the wire connections between the coils and still getting a nice spark to the left and nothing to the right. switched plug leads and spark followed to the right side and nothing to the left. So what is the best test for coil function although I can not imagine the coil is bad as the bike ran fine before the Alpha system install. I will check the plug in sections for the new ignition system although they seemed to attach fine when installed. Electrical system diagnosis is not my strongest talent so any step by step would be greatly appreciated as this is really frustrating. the carbs where cleaned well and working fine before all the other work was started.

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If I read the above right. You swapped spark plug leads from the left coil to the right coil and had spark now on the right side but not on the left side. Sounds to me you found you problem being a bad spark plug wire or cap.

lmo1131 said:

willy, if your bike is fitted with the old metal-shouded BERU spark plug terminals (below) they are prone to corrosion.

Read > https://forums.bmwmoa.org/showthread.php?55485-You-know-it-s-going-to-be-a-long-day

Not "period correct", but I replaced mine with NGK caps; the resistor value is different but I've had no problems with them in the eight years I've been running them.

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Totally agree with Les. The biggest issues with any bike that has been sitting for as long as yours did, spark plug wires/end caps

willyb said:

I did install new NGK caps along with the Alpha ignition.

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So if you installed caps, how is that connection and the cables???...…….Did you check the resistance of those cables???

I will check out all suggestions again today and see if I can find a solution.

coils and plug wires test

checked plug wires with caps attached and am getting 4.93K and 4.66K resistance

Pulled the coils and have 1.2 ohms primary on each and 6.6K on one and 6.5K on the other for secondary
are the coils still usable

Looks like if you measure from cap to cap you'll get the requisite 22K ohms...I get that by adding up all of the individual ohms, leaving out the primary resistance. Doesn't mean the coils aren't breaking down in operation. Unfortunately, the only sure way to test this is to substitute known good parts...few people have coils just sitting around.