HondaMan -
I know your'e talking about 550 and 750's (in this old thread) but just curious what would you recommend for a 350F?
I just installed Dyna S, Dyna 5 Ohm coils and Accel 8.8 plug wires yesterday and I'm running the NGK's DE8A at .030 gap.
I think that situation depends a little on your riding style? The 350F/400F bikes are super-winders, running for the 10K RPM mark every time they get the chance. This implies a colder plug could be helpful, if it is always ridden that way. But, most of us live in areas where either the speed limits are low enough or the traffic heavy enough that we can't keep the revs up as much in day-to-day riding, lest we just overheat things.
When I had my shop, it was in a small town surrounded by wide-open 2-lane roads through the hills and river valleys, with 65 MPH speed limits until the 1973 Congress clobbered all that with their 55 MPH sledge hammer. These bikes were designed to do...that. Today, we have cold gasoline that will not lube the top end, so going to a hotter plug to increase combustion power causes more stress on the rings and valve guides.
My solution (there may be others) has been to warm up the combustion a little bit, and then add top-end lube in one form or another. This can be done by slowing down the spark advance curve a little bit (trim off 1/2 turn of the spark advancer spring(s) so the burn takes longer at lower RPM and increases the startup heat as you roll through each accel-shift sequence, and the lube helps to clean the piston tops and keep the rings and guides cooler. It was, during the 55 MPH era, hard to keep the D8E(?) plugs clean, even with this technique, and the D8ES-L and the X24ES-U saved the day. Today, unless you're tearing down the road in the 5k RPM-plus range on a regular basis, the colder fuels will not heat up the D8 heatrange, and plug fouling will result. The slower spark advance only helps up to 4k RPM ranges, after which the combustion cools off again and is controlled by plug heat and mixtures. Hotter = more power and MPG, cooler = less complete combustion, carbon buildup, and less efficiency. This is one reason why the "ugly" (say some) Vetter fairing, with lowers, generates the highest MPG on these bikes (always has) and the longest engine life: it encloses much of the engine and evens out the heat across the cylinders, even at hiway speeds. (Craig was pretty sharp...). But today, the ethanol in the gas boils in 100-degree traffic with the lowers, because the carbs get too hot. So, I pull off the lowers and increase the plug heat withthe X24ES-U plugs to balance things out again.
One neat thing about running these plugs that I haven't [yet] mentioned: they let you target the octane to make the bike run the best. For example, with D7E plugs in a 750, you'd better be running premium most all the time, as it will get hot from the plugs in [even] commuter traffic. The premium will burn further down the stroke and spread that heat out into more fins. If you switch to D8EA plugs, it is best to run low-grade fuel to heat up the head more with the shorter burn time, in the hopes of keeping the top end cleaner. If you go in-between with the D8ES-L or X24ES-U heatrange, you can run midgrade most of the time, premium on hiway trips, an regular in cold weather or pure in-town riding, and control the heat yourself. That's what I do.
Has anyone noticed, this looks like an oil thread?
