72clubman wrote:
i have the d4r83 in my clubman, 1100( LCB, 1.5inch su and airfilter) , and at the moment its set to 4 btdc, and it seems to have a huge flat spot under 3000rpm, i assume this is the dizzy having to much advance, can the d4r83 be modified easliy, so that you can have better power through the rev range. also has anyone else got the d4r83 to run well on an 1100, and what static timing do you have set.
I have run D4R83 and D4R85 on an 1100, and 1275, the difference is the 85 gives better low speed and lower midrange torque (when set at same max advance point of 30* BTDC).
If you have a flat spot just under 3000 I suspect it's carb related. With a cam of 270-286 duration, 2500-3000 is about where it is really getting onto the cam, and this can upset fuelling if it's not jetted/needled right.
With the twin HS4s on Barney's modified 1293, running #6 needles, too thick oil in the dashpots gave a flat spot effect when nailed (actually, it was going rich, but felt lean). Using ATF instead fixed it.
A decent A/F meter, either portable or during a dyno tune, will sort it out properly.
Money well spent.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
