R75/5 not starting after a long days ride

Yesterday I made a day trip from Peoria Illinois to Davenport Iowa to attend the AMCA swap meet. This is purported to be the biggest meet in the United States. I rode my 1973 R75/5 and traveled with my friend Dan Bailey and his son Matt. All went well and my bike was running flawlessly. At the end of the journey I stopped at Dan's house to de-brief with those guys after the trip. When leaving to ride the mile or so home from Dan's house, the old /5 would not start. The starter would not engage. Gratefully, this model has a KICK STARTER and I rode on home.

Here is where the exercise begins. I thought it would be interesting to detail the incident here and let my fellow airheads offer up advice/opinions before I diagnose and correct the problem. The particulars of the incident are these; the red charging light is out and the starter does not engage when the start button is depressed. The bike DOES HAVE the starter relay "cricket" modification as described on Snowbum's web site.

What say ye?

So, key on and engine not started...the red light for charging is not on? That shouldn't affect anything, but that doesn't sound right.

Any sounds from under the tank? My first thought on these sorts of things is starter relay. Dirty/corroded contacts. Unplug/replug a few times to clean the terminals.

What does the battery voltage say while all this is going on? If the voltage doesn't budge when hitting the start button, that says the relay isn't latching. If the battery voltage drops way down, then something might be wrong with the battery or possibly the starter itself.

more clues

Kurt, I have not yet started to analyze this fault, but here is some more info. Normally, when I engage they main switch, the oil and charge light are on along with the neutral light when I park the bike in neutral. All day long I had these three lights until the last start when the charge system light was out. There was no sound from under the tank that I could hear from standing over the bike. Additionally, I did the "cricket mod" earlier this summer, so it seems unlikely that it would be corrosion since I cleaned everything off during that operation.

You mentioned that the alternator fault light did not illuminate... did the oil pressure and neutral light come on?bb Does the headlight come on?


BTW, the alternator indicator light and the starter switch go through the relay. Hmmmm

By you saying: "the starter does not engage" are you trying to describe you hear the starter motor "whirring", turning, sounding like an electric motor????...... If so, that is the bendix spring....... Or you depress the "start button" on the handlebar grip and there is no sound at all from anywhere??????? God bless......Dennis

Dennis, the start button yields nothing. I think Lew might be on to something here. I have to wonder about Lew's take on it because I was able to start the bike with the kicker and ride it home. My experience is that a failed relay might drop the ignition circuit. All this is yet to be determined. Thanks for the input. I will issue a full report when I get it all figured out. In the mean time, any ideas are appreciated. Looking at Lew's diagram, The charge light is involved with A fuse and the main switch and then tags to the starter relay. I will have to look into that circuit.

Thanks to all for the input.

Years ago, probably '88 or '89 seems like a couple a years ago. I was riding my '74 R90 to the Falling Leaf Rally in Bland, Mo. at the time and the starter switch quit working. The '74 starter switch is near identical to the /5's. Started the bike on the hill method or kick starting. Got to the rally at night, the next morning, got the chance to examine the switch. Took the 2 little screws out that held it in. Pulled the housing out and turn it over for a look. Nothing looked out a place. Got some contact cleaner from some where and cleaned all the contacts. Hooked it back up, tried starting it again, nothing. I had some extra leads with alligator clips. Clipped one end to a ground on the frame and started touching the 4 or 5 contacts on the underside of the switch. On one of them the bike started right up. Good. I wasn't paying attention, but a small crowd had gathered to watch and cheered when the bike started. Kinda embarressing. Then I pretended I was a great BMW tech, which I wasn't. Anyway I tye wrapped the switch in the open faced position. Wrapped the lead on the handle bar and left it. When I needed I ground it, then touched the contact and I had electric starting. I lost my turn signals, but it was a small price to pay to get the electric start. Hand signals work good in the daytime. Rode home with no problems. Got home, ordered a new switch; installed it and it worked like a champ. Still on the bike today. This might help you. Good luck with your fix.

It was the alternator rotor gone open. The battery read 12.3v when I initially checked it. The rotor probably went open right about the last time I shut the bike off before having to use the kicker. That would coincide nicely with a short running time on battery power only. When I saw that, the rotor became my prime suspect. I think I read on Snowbum's website that the original type /5 relay could dis-able the electric starter in certain circumstances. I swapped out for an extra rotor I had on a shelf and normal function is restored. That's the end of the story. Thanks to all for playing along.

James A...

I guess I'm missing it...how does a charging system failure cause the starter system to go completely INOP? If the failed rotor caused the battery become under charged, then I could see that. But you say you simply swapped in a good rotor and all works OK? You said the bike ran fine when kick started, so that must mean the battery was really alright.

Kurt, I think this is something unique to /5's.

With the original starter relay, there is a circuit that prevents an accidental starter engagement when the motor is running. Snowbum's article on the "cricket mod" details that the modification retains the so called anti-restart function as originally designed in the electrical system. I wanted to keep that feature and that is why I did not modify the wiring to utilize a more modern relay. I had seen this fault before on a different /5 that I used to own. I kind of knew what the trouble was when I initially posted the thread, but I wanted to get some additional input from our Airhead friends. If you could, maybe change the title of the thread to something like " R75 not starting after a long days ride", or something as such. It might be useful for members doing a search in the future.

All the best,
James A...

James -

OK, you're right about the special nature of the /5 circuits...not something that comes up all the time.

10-4...I'll change the title.