Autolite 3923 plugs

[red102]

Gotta love this forum. On your advice, I took out the Bosch plugs & installed the Autolites. What a difference $3.28 made in the way my R1100RT is running. It's like a different bike now. They took out about 90% of the surging I had.

Thanks to all who advised me to try the Autolites.

[red102]

Why would changing to these plugs make so much difference in the way the bike runs now?

[redryder]

The only thing I can think of is that the extra electrodes provide better ignition to the fuel/air mixture. Just a guess on my part though. Evidently, the clue bird hasn't landed on anyone else's shoulder either.

[Paul Mihalka]

I think what makes the difference is the size of the spark gap. The Autolites are gapped at .32". The original plugs use much smaller gaps. The Bosch 4418 plugs some people use have a huge gap, over .40". Having more then one electrode still gives you only one spark, jumping from the electrode that is closest to the center.

My impression is that to generate a spark for a larger gap the coil has to build up to higher voltage before it jumps the gap ("hotter spark"?) and that would fire a lean mixture better than a lower voltage spark. Just in case, I'm not a engineer and I did not sleep in a Holiday Inn Express (except at El Paseo)

[red102]

I think what makes the difference is the size of the spark gap. The Autolites are gapped at .32". The original plugs use much smaller gaps. The Bosch 4418 plugs some people use have a huge gap, over .40". Having more then one electrode still gives you only one spark, jumping from the electrode that is closest to the center.

My impression is that to generate a spark for a larger gap the coil has to build up to higher voltage before it jumps the gap ("hotter spark"?) and that would fire a lean mixture better than a lower voltage spark. Just in case, I'm not a engineer and I did not sleep in a Holiday Inn Express (except at El Paseo)

Would the gap for the Autolites be the same as the stock plugs? I gapped the Autolites at .030.

[Paul Mihalka]

Would the gap for the Autolites be the same as the stock plugs? I gapped the Autolites at .030.

I thougt the Autolites have a stock gap of .32, and .30 is about the same. I don't know what the gap is on the original plugs, but I think it's smaller. Because I'm a heretic, and because I think that large gap = no surge, I gap my Autolites to .40 when new, which I think is the largest gap specified by BMW. The gap grows a bit with use, but not too much.

[red102]

Would the gap for the Autolites be the same as the stock plugs? I gapped the Autolites at .030.

I thougt the Autolites have a stock gap of .32, and .30 is about the same. I don't know what the gap is on the original plugs, but I think it's smaller. Because I'm a heretic, and because I think that large gap = no surge, I gap my Autolites to .40 when new, which I think is the largest gap specified by BMW. The gap grows a bit with use, but not too much.

Thanks for your input Paul. I'll regap mine & give it a whirl.

[smiller]

My impression is that to generate a spark for a larger gap the coil has to build up to higher voltage before it jumps the gap ("hotter spark"?) and that would fire a lean mixture better than a lower voltage spark.

I think that's kind of reversed... the higher voltage isn't so much the objective as is a larger spark gap. A larger gap will light off a lean mixture more reliably, which is the main reason most automobile manufacturers went to high-energy ignition systems back in the 70s-80s. Higher voltages allowed the use of larger spark plug gaps for the increasingly lean mixtures of the time.

[SWB]

The Autolites are gapped at .32". The original plugs use much smaller gaps. The Bosch 4418 plugs some people use have a huge gap, over .40".

 

Paul. ... The manuals I have indicate .8mm (0.0315in) to 1.0mm wear limit (0.040in). I assume that BMW engineers consider the ideal gap to be .8mm, not the higher figure.

 

But I guess the precise gap isn't all that important if your bike runs better at the higher value.

[Andy A]

Can these plus be used in an 1150RT as well?

Thanks,

[redryder]

Just in case, I'm not a engineer and I did not sleep in a Holiday Inn Express (except at El Paseo)

 

 

You may be on to something Paul. What's the statue of limitations for a Holiday Inn Select?

[ACsRT]

yes 3923's or AP3923's are applicable for the 2002 - 2003 R1150RT

See Autolite.com - theres a PDF link on the lower Left Side under the parts catalog tab

[Andy A]

Thanks Andy. I'll take a look at their site.