I could only afford a 4 speed and those Ducs had 5 speeds. That guy beat me out of the last turn because he could down shift and I could not. I heard him reving the guts out of his Duc (they could turn 10,000 RPM) and he pulled me to the checker - I tried to draft him and almost re-passed him but came up short.
shit fire was that you? my apologies-- the usernames are new to me. no disparagement intended.
that's the whole problem with trusting theory. the O2 meter tells you only what is passing the sensor-- not what is present in the combustion chamber during the power stroke. my triumphs have a combustion chamber that spews unburned fuel down the pipe like a hose. to get an efficient burnable mixture in the chamber means i have to have liquid fuel running down the exhaust. so the exhaust sensor reads way rich when the mixture in the chamber is okay. were i to set the mixture by the sensor, my chamber would be lean.
I think there is a bit to be gained by using an advance curve which compensates for the change in rock-over time as the revs rise, as well as playing with different taper needles. I have never needed to bother about it. I rum fixed timing and the leanest taper Mikuni needles. I never believed in my Seeley 850 when I was building it in the 1970s, but it is easily fast enough. The steering geometry makes the biggest difference - getting on the gas so early coming out of corners, you get a lot more run up into the straights, so you are faster towards the ends.
The last time I raced, I was using a 4 speed close ratio gear cluster. I did not like revving the motor too high at the starts, so the bike was always slow off the mark. I was up in the lead bunch in two races. In the last I decided to go for it and risk being hit from behind if the gearbox gave up. I was with the leaders going into turn two, then rode under three of them and was in front when my motor stopped. I now have a 6 speed TTI box. But a 4 speed close box is fast enough as long as you use the standard commando first gear to get the bike moving off the start. The 4 spped close box was perfect everywhere, but risky when you use it in a clutch start, if you don't have the low first. Once you are rolling on most circuits, you never go back to first.
Weren't they semi factory teams and they had modern equipment and motor on you? The guy kinda sat back and at the end and used motor to get 3rd, to save "face" and stop from getting 4th to an old Norton. You did great in my book. CH
They may have been sponsored - or they could have been local racers - not sure. I made good time in the turns and road my ass off, but mags with radial tires and state of the art Duc technology was getting more and more difficult to keep up with. It was still fun. And if I'd had the bucks for a 920, better brakes and mags etc - it could have been better. In fact it was. Below is Ken Canaga's verion of the bike with all the best bits and with Rob Tuluie in the saddle it placed 3rd at BOTT on the same track a couple years later - the last time that Norton was on the AMA podium (with a couple other mono shock Duc riders of course). Rob Tuluie had nothing but praise for the way it handled. I remember I could lean it over into a bit of a slide and hold it there.
Looks like you need more resistors...interesting that you mention that. that 650 race bike runs a CR of 11.75, and after the first few runs at 38 BTDC, i took the head off and found this:
detonation was pecking the carbon off on the side away from the plug. i solved the detonation problem with 10mm plugs:
^^^this is the 1972 9 1/2-bolt (T140 casting) race head. i run a fixed advance ARD magneto at 30 BTDC, and it's been trouble-free. 10mm plugs.
this next one is the 1972 9-bolt (T120 casting) street bike with the boyer that sparked this conversation:
this one has 12mm plugs an th eboyer is currently set at 30 BTDC based on testing. the initial advance is therefore 8 degrees retarded, and i'll be trying sto solve the problem with one of these, that came in th email yesterday:
these are 470 ohms, 1-watt, 1 percent variance. i have another pack of 680-ohm, 1-watt, 1 percent variance too. US $6.99 per 100., so i have enough now to modify 200 motorcycle ignitions. these will restrict the advance range some fixed amount. if one were so inclined, you could also fit a 1000-ohm rheostat and experiment on advance curve reduction with a knob, too, but i wouldn't trust the instrument on a vibrating vertical twin
i did then, but i was running a pazon smartfire with an advance curve set to ordinary timing for a triumph, which is way advanced compared to nortons or BSAs. since then i've switched to fixed advance with this motor and run a magneto:
