One cylinder running

[jp9094]

Took a ride to do some shopping and while on the highway at 50mph my 83 r65ls started running poorly. Turns out was only running on the right cylinder. Switching spark plug leads gets the left cylinder to run. Suspect failed coil. The coil was replaced 7 years ago for, I believe a Bosch dual coil. My question is how is this mounted?  Am I correct in my surmise vis a vis the failed coil? Enquiring minds want to know!

TIA

[Bob_Roller]

Remove the fuel tank and it's mounted with two fasteners ,
Is it a red and black coil ??
When you swapped the ignition lead, did you just take the lead and put it on the right cylinder spark plug or did you swap the leads on the coil .
I'm looking at a wiring diagram right now, it looks like if the coil fails, it should effect both cylinders .
Before replacing the coil, do a continuity test on the right cylinder lead, should get around 5K ohms .
Or swap the ignition leads at the coil to see if the problem follows the original right cylinder lead .

[jp9094]

Bob,

Thanks for the advice. Have done as you suggested, and the spark plug lead is good. Were it so simple (and inexpensive) to fix!
The current coils are Bosch dual towers with the red ends. Have ordered a replacement, and hope to be back on the road soon.

Thanks to all

[georgesgiralt]

Hello,
I doubt the coil has failed, but you never know... In the mean time, if you have a car wreck yard near you, ask them for a dual output coil from a car. Fiat Punto comes to my mind but plenty had these.
Check that their primary have not a too low resistance in order to keep your ICU running and you are good to go.
Cost a couple of Euros for me. Cheaper than the gas used to go there....

[jp9094]

Have replaced the coil and now have a big fat spark to the left (non running) cylinder. Still cannot get it to fire. Now suspect the carburetor is at fault. When I turn on the gas, it runs out of the overflow ie. floats not sealing. Have unshipped the left carburetor and run some carb cleaner through it. Will now return to the parking and remount it. Wish me luck!!

TIA

[jp9094]

Still no luck. It is now worse than before as I now have gas running out of the black plastic side plate that has Bing written on it!!. The question is now; Buy a used replacement or try a rebuild myself?  Am I missing anything? Please let me know.

Best regards to all.

[georgesgiralt]

Hello,
To fire a petrol engine requires a set of conditions.
First, the engine and components must be sound. You checked the ignition, so that's good (provided that the ignition timing is set properly).
Next, check the valve train : proper gap at both cylinder with proper timing (do not forget to turn the crank one full turn when changing the cylinder under test... Do not ask me why I know)
Then, check the carbs : proper setting and functioning.
If these steps are followed, no reasons why the engine won't fire.
IMHO you should check all the steps above asking for help if you need it to set each step properly.

[Barry]

Still no luck. It is now worse than before as I now have gas running out of the black plastic side plate that has Bing written on it!!. The question is now; Buy a used replacement or try a rebuild myself?  Am I missing anything? Please let me know.

Best regards to all.

I think you need to address one thing at a a time.  The immediate problem is the carb overflows and that can only be either the float valve is not sealing, or the floats are grossly too heavy.

To check the float valve, turn off the fuel petcock and remove the float bowl. You going to spill a little fuel so have something to catch it. Now hold the float up with your finger until it's parallel with the carb flange and turn on the fuel.  If the fuel still flows and can't be stopped by raising the floats a little higher then the float valve is leaking either because there is some dirt in there or the rubber tip is worn.

If the float valve seals ok then the fault lies with the floats. They can get too heavy over time until the point comes where they no longer float.  If you can weigh them, they should be approx 12-13 grams, By the time they get to 15 or 16 grams they need to be replaced.

What ever else you do you have to sort out this flooding problem first.

[jp9094]

Thanks for all your replies. I actually rest the valves only a month ago, and the other cylinder runs fine so do not think it is a timing problem. As I have had this in the back of my (admittedly tiny) mind for awhile, I have bitten the bullet and have organized for a Siebenrock 860 upgrade and carburetor rebuilds with a reputable BMW dealer here in the US. As a consequence, I will be off the road until early February. I will let you all know the result in the new year.

Happy holidays to you all,