Topic: whats the next step colder plug?

[eurban]

I am going to try a set of colder plugs in my 836 hot rod . . . Stock NGK plug would be the D8EA.  What would be the next step colder plug ?. . . The D9EA??  The Clymer lists a D10E plug as the NGK colder plug but this info is a bit dated.  I may eventually try some fancy irridium plugs but for now I sticking with non fancy ones.  Thanks

[eldar]

D9 is colder and d7 is hotter.

[scondon]

eurban, on the advice of another member here I switched from D8EA to D9EA and the bike is much happier. I used standard NGK plugs while I dialed in the carbs and have since switched to Denso Iridium plugs. The Denso's have been in for a year of daily riding and I pulled them one time just to inspect and clean them, they have not degraded a bit and I'm very happy with them.

[eurban]

Thanks for the info guys.  Scondon, is the engine with the D9eas in it a performance build (larger displacement/higher compression)?  If so, did you find the need to back off the spark advance as well??  Thanks

[scondon]

Thanks for the info guys.  Scondon, is the engine with the D9eas in it a performance build (larger displacement/higher compression)?  If so, did you find the need to back off the spark advance as well??  Thanks

  Engine is a 836(Wiseco) with a well decked and ported head, Megacycle125/65 cam, Kerker Exhaust w/med. comp. baffle, Dyna 3.0 coils, Dyna S ignition, and Dyna 8mm suppression wires.

   I have not been able to fully dial out pre-ignition. I am using stock '78 carbs with raised needles(shimmed) and 120 mains. Pre-ignition occurs when transitioning from idle circuit to mains(about 1/8 throttle) and can be minimized by rolling the throttle hard from a stop, thus causing the accel pump to squirt extra fuel. Only happens when the bike is good and hot. Over richening of the idle circuit has not helped. I have also retarded the ignition to the point of barely running at idle with no good effect.

   The head was decked a couple of times and I think I may be running a much higher compression than the advertised 10.5:1
The colder D9ES plugs certainly seemed to help more than anything else.

[eurban]

Scondon-  Thanks for the info.  I hear detonation only very rarely and it is more in the mid to upper throttle ranges when driven hard.  From what I understand, just cause you don't hear it (particularly on an aircooled) doesn't mean its not there.  Glad to hear that the colder plugs helped.  Have you examined your plugs closely for tiny specs of aluminum on the insulator?  Thats what got me started down this route.  For your situation you might be able to shim the acelerator pump spring (inside the fuel supply bowl)  The carb set (78F) that I currently have on my bike actually came with something like 140 mains and a washer shim on the acel pump.  Not sure what monster they were being used for!  You should  also make sure that you have no gap between the pump rod and the mechanism on the throttle.  You also could try experimenting with contouring the shape of the slides and or needle for a richer mixture but you would certainly need some extras and need to have some idea what to do.  I personally have no idea what makes a slide richer or leaner but I know that they are available for some carbs.  A more sophisticated Dyna 2000 ignition would probably help both of us out but I'm not quite ready to lay out the $ yet.  Thanks again.

[scondon]

    Thanks to you too,eurban. I've been planning on "monkeying" with the accel pump so your ideas are a great help. I did have some pre-ignition in the 3/4 throttle range, but shimming the needles took care of that. Seems most of my detonation troubles have occured from slightly lean mixture coupled with the very hot environment of the  combustion chamber. The D9ES plugs took out at least part of the source of high heat.

     I have found aluminum build-up on one of my plugs(#2). I had the engine apart after 1500 miles and found that the ridges on the very top of the piston side had worn smooth on just that one bore and I swapped in a new piston/rings at that point, but problem remains. Bike has had several different carb sets, plugs, leads, etc.. but #2 always gets the hard deposit on the plug. The iridium plugs collect far less deposits. Those deposits can certainly contribute to detonation once they get hot.

     My theories on why just the one bore have ranged from improper cylinder boring to worn rod bearings to pre-ignition on just the one cylinder. For now I'm content to just ride the piss out of it, and after 15,000 miles of daily riding I haven't holed the piston or had any power loss. At some point I will have the engine apart to correct all the new leaks and possibly new primary chains and main/rod bearings(skipped those on this engine). I hope to find some visual/measurable explanation at that time.

[eurban]

Scondon- Another thing you could try is putting a D10 plug in the #2 and perhaps #3 cylinders.  This would be a a relatively cheap and easy thing to experiment with although you would probably want to set aside the irridium plugs temporarily . . . . .