Starter Frustation

[yourpalcal]

"I did notice a spark from an area of the choke cable that had worn to bare metal. It was sparking were it touched the gas lever. " That should not be happening. Do this: Follow and inspect the positive lead from the battery along the main frame to where it drops down to enter the engine housing just above and behind the diode board - actually through a 'u' shaped opening at the rear of the aluminum timing chain cover. Check to make sure that there is a rubber grommet surrounding the positive battery lead to isolate it from the engine through that opening. Next, make sure the grommet is intact and that the battery lead is not rubbing against the aluminum. Try the starter and watch closely around the starter solenoid where the battery lead terminates with a large ring connector on a large threaded pin at the back of the solenoid. If that connection is loose or in contact with the case or other connectors it will spark which equals a high resistance connection. It takes full battery voltage to activate the electromagnet which engages the starter gear and spins the starter motor. If someone replaced the starter recently, the routing, insulation and connections for the positive lead might be the problem.

You could be onto something here. I did notice some wear on the small red power lead wire near the connection to the battery. I may end up removing the plastic cover on the harness to fully inspect this wire. I replaced the engine wire harness but was hoping not to replace the chassis wire harness. Although I plan to keep this bike for a long time so it’s probably inevitable. I plan to do some more investigating this afternoon. Thanks for the tips!

 

[Na Cl K9]

The red wire at the battery is from the diode board and is responsible for providing current to keep the battery charged and maintains system voltage for ignition/lights/etc. The large black cable is a single run from battery + to starter solenoid. A small black wire at the solenoid activates the starter engagement gear and closes the circuit from the battery to provide current to spin the starter motor. I can see the grommet that is supposed to shield the cable from the engine casting. It looks quite worn. Check there first. The fuel tank is isolated from the battery by being rubber mounted. So in order to get a spark at the fuel tap from the choke cable it must be touching the frame somewhere AND voltage is present in the choke cable. For that to happen, when the starter solenoid engages power goes to the engine block instead of the starter motor. That’s one possibility anyway.

 

[FELAW]

no start

In the second picture, I see that the cable isn't connected tightly on the solenoid?

 

[lmo1131]

This is glaringly obvious. You're aware that the cable isn't tightened down, right?

 

[yourpalcal]

This is glaringly obvious. You're aware that the cable isn't tightened down, right?

Yea that picture was taken before I complete the install but good eye.

 

[yourpalcal]

The red wire at the battery is from the diode board and is responsible for providing current to keep the battery charged and maintains system voltage for ignition/lights/etc. The large black cable is a single run from battery + to starter solenoid. A small black wire at the solenoid activates the starter engagement gear and closes the circuit from the battery to provide current to spin the starter motor. I can see the grommet that is supposed to shield the cable from the engine casting. It looks quite worn. Check there first. The fuel tank is isolated from the battery by being rubber mounted. So in order to get a spark at the fuel tap from the choke cable it must be touching the frame somewhere AND voltage is present in the choke cable. For that to happen, when the starter solenoid engages power goes to the engine block instead of the starter motor. That’s one possibility anyway.

I’ll check that out. I plan to eventually go with an electric starter like the Dyna III but need to figure out why the original set up isn’t working. So frustrating!

 

[20774]

You probably meant electronic ignition like Dyna III. But you have a good approach...figure out why things don't work now. Points/condenser setups are pretty straightforward. Adding the "wizardry" of an electronic ignition only confounds the problems.

 

[69zeff65]

Ditch the electronic ignition?

I am no expert or "Guru" but almost every time there's a charging or spark issue with an Air Head the bike has had an "up grade" to the ignition system with an electronic pointless ignition. Thats another issue altogether and may spark (no pun intended) another thread such as "points or pointless" kinda like the oil threads. To address the sparking choke cables I would suggest you have a direct short in your starter circuit (12V) and (or) a very bad ground attachment on the bike. The original (factory) ground attachment on the /5 and later bikes is simply pathetic, it probably should have been an NTSB recall because it was so bad. Some people have made a secondary battery - to ground connection directly to a close by and better suited transmission stud.

The electrics on these bikes is surprisingly complicated to the point of being simple. Go back to completely stock and trace out the problem, its more than likely very simple and obvious until you have to figure out the effects of the aftermarket crap.

My '70 R75/5 is working OK for now but my Barn Find 90S is going to loose the Dyna III and go back to points just so I know it runs good.

Zeff

 

[yourpalcal]

I am no expert or "Guru" but almost every time there's a charging or spark issue with an Air Head the bike has had an "up grade" to the ignition system with an electronic pointless ignition. Thats another issue altogether and may spark (no pun intended) another thread such as "points or pointless" kinda like the oil threads. To address the sparking choke cables I would suggest you have a direct short in your starter circuit (12V) and (or) a very bad ground attachment on the bike. The original (factory) ground attachment on the /5 and later bikes is simply pathetic, it probably should have been an NTSB recall because it was so bad. Some people have made a secondary battery - to ground connection directly to a close by and better suited transmission stud.

The electrics on these bikes is surprisingly complicated to the point of being simple. Go back to completely stock and trace out the problem, its more than likely very simple and obvious until you have to figure out the effects of the aftermarket crap.

My '70 R75/5 is working OK for now but my Barn Find 90S is going to loose the Dyna III and go back to points just so I know it runs good.

Zeff

Zeff,

It’s currently completely stock with the points and such. I was only saying I eventually want something low maintenance like the Dyna. Your ground comment could be the issue. I replaced the original ground wire and it turned over for a brief second on the first try then went back to clicking. How can I add an additional or improve the ground connection?

 

[52184]

Zeff,

It’s currently completely stock with the points and such. I was only saying I eventually want something low maintenance like the Dyna. Your ground comment could be the issue. I replaced the original ground wire and it turned over for a brief second on the first try then went back to clicking. How can I add an additional or improve the ground connection?

That sounds like a dying battery or, in light of your choke cable sparks, a short that is bleeding off current from the starter circuit.

Best,
DG

 

[69zeff65]

I have seen one once before

The ground connection to the speedometer cable bolt is a very weak and bad idea. I have seen a ground cable that was made a little longer and attached to the transmission mount stud off the back of the motor. If I were to make that cable conversion I would make it some type of quick disconnect also, some times its advantageous to be able to quickly pull the ground strap off.

 

[FELAW]

no start

Is the relay you bought from EMs electronic or mechanical? I got the "clicker" when I burned the contacts on a mechanical one when I didn't unplug the battery charger when I tried to start the bike. As a test I'd swap out the new relay for the old but first making sure the contacts close when 12 volts is put across them. if it turned over once when you tried to start it, that sort of tells me you have it wired correctly.

 

[yourpalcal]

I am about to just suck it up and take it in to be looked at by the local mechanic. I have inspected every wire, cleaned all connections and replaced both the power and negative battery cables. Fortunately, the kick starter works so I can ride it up to the shop. As for the spark, I think that originated from the smaller red wire near the positive battery terminal. It had frayed and was touching the frame.

On another note, I was inspecting the left switch for the horn and high beam and it needs to be replaced. There is a large crack in the thumb button and the spring is coming out. The plastic is too flimsy to repair. How difficult it is to the new switch connect? I noticed the replacement ones have open wires and no connectors. Will this require soldering onto the relay board?

Also, I noticed this lovely oil leak from the clutch when I was inspecting the neutral switch connection. One more item to fix but it's an old bike and bound to need some repairs.


Thanks again for all the advice. You all have been great!

 

[surfdad1060]

Check the teeth on the flywheel itself.

 

[yourpalcal]

Problem solved with starter but high idle

After checking and triple checking all the wires, connections, relay, etc. I decided to change out the battery. The one in it was not very old and tested ok but it was all I haven't changed out. I ordered a Westco battery after reading good reviews and sure enough the bike cranked right up. So pleased!

The issue now is the idle. It started around 3500 then stayed around 4500 with the choke. Then went up to 5000 without the choke. Perhaps its a sticky throttle cable or one of the carb slides sticking??

 

[20774]

Certainly sticking slides could be an issue...easy enough to see. Could be hung up throttle cables, the ends not seated properly where they enter the carb. Could be sticking advance mechanism.

 

[ebeeby]

+1 on load testing the battery. A multimeter can show plenty of voltage that is just a surface level. Load testing (you can get these from Harbor Freight for $20) reveals all.

Apparently, the "testing" at the store was not Load Testing.

 

[yourpalcal]

Certainly sticking slides could be an issue...easy enough to see. Could be hung up throttle cables, the ends not seated properly where they enter the carb. Could be sticking advance mechanism.

After a little inspection I found the issue with the high idle. It seems the left side carb is missing something. See if you can spot it:

Right Side:
View attachment 72463

Left Side:
View attachment 72464

Unfortunately, BMW no longer sells the idle screw and spring and no dealers or eBay sellers had it in stock. Luckily, our Forum Liaison Kurt's "Resource and Links" page listed Bing Carburetor company in Kansas. I called their sales team and the gentlemen I spoke had both the screw, spring and o-ring in stock and mailing them out this morning. Thank you Kurt!

I should have this bike on the road very soon.

View attachment 72462

 

[20774]

Sweet! Glad you tracked things down! Your experience might help someone down the road.