BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

Saw on Autolight's website that the platinum AP3923 plugs are supposed to be gapped to 0.025" for the 01'-03' R1150Rs. Just set mine, will get back after I run it. That is a significantly smaller gap than for the stock plug. Had the plugs gapped to 0.034" up to now, and even with that gap it ran a lot better!

So what I noticed is that I can now cold-start my bike with just the choke with the Autolights, with the OEM NGKs I always had pull the choke and turn the throttle to get it to start.

That's the plug and gap I'm using. Works good.

Were there any issues with the gaps at .034" ? I ask because I remember reading an article many many years ago. It was found at that time that a gap of 035" was much better for ensuring the combustion process. Fewer misses and fouling. The reason gaps for motorcycles were set to .024" in those days was because the coil couldn't fire across a gap that was wider reliably. They just didn't have the voltage. The fix was to replace those coils with some that were of a much higher output voltage. I have not seen any output voltage numbers for these coils, but if they are 35,000 volts or more, they should be able to handle the larger gaps. Which also means they can work more reliably.

The original design of the R1150R single plug combustion chamber performs better with a slighter larger plug gap as it allows a longer duration flame. For this application single electrode plugs perform well in the .031” to .034”.

One of the improvements I done for our R1100R was to install Autolites, with cut-back ground electrodes. This opens the spark up to the chamber allowing a better burn. Smoother idle and less surge were two benefits. The gap was .030" This is a race bred performance trick from way back, that happens to help the boxers.

I would imagine if you could find a dual ground electrode plug in the right heat range and height it would perform much better then stock.

John

After 11000 miles one of my Autolite 3923P blew the platinum tip out of the electrode and killed the engine like turning off the key. After much investigation and assistance from several members of this board (thanks again Boxermania and Iowabeakster and Cycelrob!) the cause was finally determined, and I was surprised to learn that neither plug would fire after just the one blew it's tip, since both plugs are in a series circuit which the blown plug could not complete.

I can not recommend platinum tipped plugs for high compression engines. And the lesson learned is If your bike suddenly quits, try replacing the plugs!

Sunbeemer wrote:After 11000 miles one of my Autolite 3923P blew the platinum tip out of the electrode and killed the engine like turning off the key. After much investigation and assistance from several members of this board (thanks again Boxermania and Iowabeakster and Cycelrob!) the cause was finally determined, and I was surprised to learn that neither plug would fire after just the one blew it's tip, since both plugs are in a series circuit which the blown plug could not complete.

I can not recommend platinum tipped plugs for high compression engines. And the lesson learned is If your bike suddenly quits, try replacing the plugs!

The plugs can not be in series (just think about it). I had a R75 that had a bad plug cap that prevented the plug on one cylinder from firing, it ran on one cylinder without a problem.

owldaddy wrote:Were there any issues with the gaps at .034" ? I ask because I remember reading an article many many years ago. It was found at that time that a gap of 035" was much better for ensuring the combustion process. Fewer misses and fouling. The reason gaps for motorcycles were set to .024" in those days was because the coil couldn't fire across a gap that was wider reliably. They just didn't have the voltage. The fix was to replace those coils with some that were of a much higher output voltage. I have not seen any output voltage numbers for these coils, but if they are 35,000 volts or more, they should be able to handle the larger gaps. Which also means they can work more reliably.

The gap of 0.025 was from the Autolight website for my model year bike, so I assume that gap is the optimal setting for their plug on my bike.

One needs to take the OEM recomendations as "guidelines" merely because not two engines are alike, or are operated alike or reside in the same environment, or the fuel is the same and the list goes on. Find what works for you and stick to it.

R1150Rclean said,

The plugs can not be in series (just think about it). I had a R75 that had a bad plug cap that prevented the plug on one cylinder from firing, it ran on one cylinder without a problem.

I'm not familiar with the ignition system on that bike. Maybe it's not the same as ours?

I related what I learned while trying to fix mine.
Full details available here:
viewtopic.php?f=2&t=18394
and here:
viewtopic.php?f=2&t=18377
and especially from what the venerable Cyclerob wrote here:
viewtopic.php?f=2&t=15601&p=138351&hili ... es#p138351

The cheapie single coil twin fire ignition system, common to most all even firing motorcycle engines and some cars, fires TWO sparkplugs at the same time every 360 crankshaft degrees. If either one of the plugwires is ungrounded, i.e. hanging in the open, neither sparkplug will fire. The secondary hi voltage circuit is a series circuit between the 2 plugwires. One sparkplug fires the right way, the other one fires backwards . . . . from the ground electrode to the center electrode. It works and it's cheap to make because there's only 1 bigger coil and 1 trigger unit. If you unknowingly break that circuit using powder coated fins, you have a "Do Over".

Sunbeemer wrote:R1150Rclean said,

The plugs can not be in series (just think about it). I had a R75 that had a bad plug cap that prevented the plug on one cylinder from firing, it ran on one cylinder without a problem.

I'm not familiar with the ignition system on that bike. Maybe it's not the same as ours?

I related what I learned while trying to fix mine.
Full details available here:
viewtopic.php?f=2&t=18394
and here:
viewtopic.php?f=2&t=18377
and especially from what the venerable Cyclerob wrote here:
viewtopic.php?f=2&t=15601&p=138351&hili ... es#p138351

The cheapie single coil twin fire ignition system, common to most all even firing motorcycle engines and some cars, fires TWO sparkplugs at the same time every 360 crankshaft degrees. If either one of the plugwires is ungrounded, i.e. hanging in the open, neither sparkplug will fire. The secondary hi voltage circuit is a series circuit between the 2 plugwires. One sparkplug fires the right way, the other one fires backwards . . . . from the ground electrode to the center electrode. It works and it's cheap to make because there's only 1 bigger coil and 1 trigger unit. If you unknowingly break that circuit using powder coated fins, you have a "Do Over".

Draw out a "series" circuit and try to figure out how both plugs are in series, versus a parallel circuit which is what it really is. For them to be in series, the current has to go through the left plug first to spark it and then the current would have to travel through the engine to the right plug and then spark it.

Here's a novel idea. Look in your owners manual and get whatever plug is recommended and set the gap accordingly then go for a ride and call it good. There isn't enough difference in these engines to matter and none of us are that sensitive that we can tell a difference in performance one way or another. That presumes that things such as stick coils are working properly and valves are within adjustment spec and so on. Spark plugs in good condition be they NGK, Champs, Autolite, etc. just aren't going to perform with any discernible difference. Any difference you perceive is between your ears. I thought there might be something to this AP3923 business until I thought about it then common sense got in the way and with some troubleshooting and much thought I finally determined my problem was a high impedance from the built in RF shield and the HV pin of one of the stick coils and maybe both. The solution was two new coils and cut the center pin of the 3 pin connector that connects to the coils thus removing the potential path to ground. Who needs this RF shield that is there to prevent radio reception interference anyway?

Jammess wrote:Here's a novel idea. Look in your owners manual and get whatever plug is recommended and set the gap accordingly then go for a ride and call it good. There isn't enough difference in these engines to matter and none of us are that sensitive that we can tell a difference in performance one way or another. That presumes that things such as stick coils are working properly and valves are within adjustment spec and so on. Spark plugs in good condition be they NGK, Champs, Autolite, etc. just aren't going to perform with any discernible difference. Any difference you perceive is between your ears. I thought there might be something to this AP3923 business until I thought about it then common sense got in the way and with some troubleshooting and much thought I finally determined my problem was a high impedance from the built in RF shield and the HV pin of one of the stick coils and maybe both. The solution was two new coils and cut the center pin of the 3 pin connector that connects to the coils thus removing the potential path to ground. Who needs this RF shield that is there to prevent radio reception interference anyway?

Well I could "not" start the bike with NGKs set to 0.032" using only choke, had to turn the throttle and have choke on max. With the autolites I can start the bike using only choke.

R1150Rclean wrote:

For them to be in series, the current has to go through the left plug first to spark it and then the current would have to travel through the engine to the right plug and then spark it.

I think you've got it...the ignition wires are connected to each end of the secondary coil winding in the ignition coil completing the HT circuit.
You could test this by pulling one plug wire off and seeing if the other cylinder fires, but you run the risk of frying the Motronic.

Well I could "not" start the bike with NGKs set to 0.032" using only choke, had to turn the throttle and have choke on max. With the autolites I can start the bike using only choke. [/quote]

If this be the case then all I can say is your bike is very different from mine. My machine starts fine on just the choke, which is only a fast idle device and nothing more, on NGK or AP3923 plugs. No difference and no need to roll on the throttle. Spark plugs just ain't the magic bullet unless the plug in question has a problem of its own then all bets are off, obviously.

Jammess wrote:Well I could "not" start the bike with NGKs set to 0.032" using only choke, had to turn the throttle and have choke on max. With the autolites I can start the bike using only choke.

If this be the case then all I can say is your bike is very different from mine. My machine starts fine on just the choke, which is only a fast idle device and nothing more, on NGK or AP3923 plugs. No difference and no need to roll on the throttle. Spark plugs just ain't the magic bullet unless the plug in question has a problem of its own then all bets are off, obviously.[/quote]


Had that problem from the beginning with the NGKs, and found out by accident that the autolites did not need the throttle roll with the choke. I agree, that a plug should not change it, but it did.

OK, if the NGK and the AP are both new, have same heat range, are both non-resistor, and are gaped the same then you will not be able to discern any performance difference in operation of your machine, period. Oh, forgot to mention both plugs installed with new crush washer and tightened properly. There simply are no mysterious forces at work here.

Jammess wrote:OK, if the NGK and the AP are both new, have same heat range, are both non-resistor, and are gaped the same then you will not be able to discern any performance difference in operation of your machine, period. Oh, forgot to mention both plugs installed with new crush washer and tightened properly. There simply are no mysterious forces at work here.

As I said, they were not gaped the same, NGK 0.32 per spec, AP 0.25 per spec
And did I mention I can now pull a wheelie in second gear and my gas millage is now 100 mpg, amazing plug