VL Spark Plugs Different Heat Range

[downunder vl]

Has anyone successfully used different heat range plugs in their V model. I mean a different rated plug front to rear cylinder. If so what brand and numbers.

[T. Cotten]

Downunder vl!

If your cylinders do not burn the same, juggling plugs may only mask a problem.

Have you bubble-tested your manifold?

....Cotten

[downunder vl]

Hi Cotton, I have tested both the inlet nipples and the manifold/nuts. I pressure tested through the manifold at assembly before attaching the carb and also tested it running. I thought the same as you and then I saw a thermo temperature video of a VL which showed the same sort of difference from front cylinder to rear.

[T. Cotten]

Downunder Vl!

I have seen thermal imaging of modern v-twins that display hotspots on the front cylinder. My best guess is that is where the most heat is drawn ("driving force" is what I was told in school), as it gets the most wind.
It may or may not be an indicator of internal temperatures.

How differently do your plugs burn?
Please remember that plugs only show symptoms, and not a cause (unless so hot they pre-detonate...).

And I must ask: has either cylinder had a plug thread repair?
An insert can insulate a plug.

....Cotten

[downunder vl]

Hi Cotton,

Neither cylinder have had a plug repair.

Front cylinder has the rim of the plug black with the colour graduating to grey at the electrode. When the front cylinder is like this the rear plug is fully black. It doesn't foul city or country riding but if I could improve it I would like to.

The floats that you sent out to me are working great, thank you. My M21 and M31 are both set up with them and one of the others has a mates carb doing well. I have mentioned you to others here so I hope you have sent more out here.

Regards Phill

[Steve Slocombe]

Dear Phill, on the VL the front cylinder runs hotter than the rear and a black plug at the rear and a brown one at the front sounds normal to me. Old time riders like Connie Schlemmer recommended a Harley No 4 plug in the front and a No 3 in the rear.

[downunder vl]

Hi Steve,
Thanks for the input. I have been looking for original plugs as you mention in your book but haven't been able to pick any up yet. Until I can locate them what I'm looking for is a modern equivalent of a 3 and a 4.
Regards

[23JDCA 808]

I found POSSIBLE equivalents on the Internet using Google:
http://www.sparkplug-crossreference.com/convert/hd/3-4
http://www.globaldenso.com/en/produc...ce/1023_1.html

[downunder vl]

Thanks Bill, but if you look at the Global Denso they recommend the same plug for both the Harley 3 and 4. This is what has slowed me down in doing something, finding two different heat range plugs. I was hoping to use the experience of someone who has done it before and made it work. I know there are plenty of switched on VL owners over there. That's why they ride V models. Thanks again.

[Steve Slocombe]

You could try NGK A7 in the front and NGK A6 in the rear. These still seem reasonably easy to find.