I bought this bike a couple of years ago. 23,000 miles on it and it was bone stock. Since I bought it it detonates, or something similar... usually when it is cold outside like under 45 F degrees.
I have a lot done to the motor now

Ported heads, 5 angle valve job, andrews 27 cam with 155lb crane springe, s&s lifters, rockers, pushrods, etc., .080 off stock deck height (.065 shaved, .015 under head gasket) with flat top, .010 over wiseco pistons, with balanced rods by DarkHorse, Whole bottom end was completely blueprinted and rebuilt by DarkHorse, cycle shack slip-ons with the baffles bent lower (more open pipe), arlen ness big sucker with 3" element, DynaTech 2ki ignition module still on dual fire, I believe, a hair over 10.5:1 compression (which doesn't seem right, thought it should be less) and the timing and carb tuned to fit the mods.

Keep in mind, this bike has done this since I bought it stock and as much as that engine has been modded and I figured it would go away. Plug chops show very nice burn, combustion chamber is very nice, not a lot of build-up on the pistons, valves resealed, and no leaks with the leak down. Manifold prted and polished and running a stock, rejetted and tuned carb (I believe in the cv carb, haha)... So with as much of a picture as I can paint of my engine, anybody under the opinion that maybe cooler plugs would help? And this happens as a muffled pop (a completely powerless stroke when rolling back on the throttle after decelerating... like to turn a corner) and the carb was filthy after 12,000 miles.

 

Since I bought it it detonates

you did extensive shaving and compression increases with a short duration cam and the noize is still in it < i would expect the sound you now have would be detonation --

and what was making sound 2 years ago was different unless you used a decible meter to track the sounds -- johnjzjz

 

Same noise, same place, same exact response from the throttle, and happens exactly like it always did. Just take my word for it... this has happened since the bike was stock.

 

Detonation happen when the octane in the fuel is not high enough (because of high compression) or to much advance. Weight is a factor too, lighter bike can take more advance than a heavy bike. See if you can buy some race gas (110 octane), and see if it still does it. You might have to adjust your V.O.E.S switch. Check out the link below.

http://www.mklsportster.com/xlvoes.htm

 

Hey thanks Little... This is what I was looking for, ok so lower heat plugs are out... dumb idea.
I just had the bore, pistons and bottom end done this winter. I am wondering if maybe it's just the gas from sitting for months. I noticed it goes away as the weather warms... maybe that has something to do with running old gas out of the bike and, at the same time, gas stations going to their warm weather formulation. But I run 93 octane... should I try a booster?
I have a short duration cam with very high flow intake (heads ported specifically for this). The bike, the power, etc are exactly what I was going for. I can stand it up... there's no question about the power. It's just that damn detonation that has pestered me from day 1. But I guess I can experament with fuel and mixtures

 

The gas additive don't work. You might have to call a auto race shop to find out where you can buy 100+ plus octane gas. Here in Minnesota we have some station that sell 110 octane gas. But you just want to run it to see if that's the problem. Because it about $7 a gallon. Like I said check your V.O.E.S switch adjustment and check out that link. When I built my bike I have about 10 1/2 to 1 compression and I was have detonation problems, I adjusted my V.O.E.S and that help out alot. But my bike is vary sensitive to the gas I put in it. I run premium (93 octane) and that work OK.

 

Yep, I read the link and then did a little more research. My bike was tuned on a dyno but that doesn't mean the voes was adjusted. The timing and jetting were all done and my chart is awesome and my numbers are way beyond what I hoped for. But from what I read, the voes is done, as you said, and after the bike is already tuned. That is what I am understanding anyway. Thanks, brother.

 

Which retard setting are you on the Dyna 2ki ? With that much CR you should be 3-4 curve and maybe add 6" VOES. Dyna 2k ignition can be tweaked just for your bikes set up with a wire dn load.

 

retarded 3 degrees

 

I found another article on the V.O.E.S. switch. It work like a switch to turn your advance on. The higher the inches of mercury the more it delays it to advance time timing, so you need to find out where your V.O.E.S. switch is set, and then set it higher in inches of mercury.