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Crank Position Sensor
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Old 08-01-2007, 09:00 PM
BLB350
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Default Crank Position Sensor

Riddle me this Mr. Mike. I lost my crank position sensor (CPS) last week. Upon installing a new one, I now find out that my timing is too advanced and/or running lean. For the last year and a half (2000 FXD w/ two front heads, now 110 ci) I have been running just about as much advance in the motor as my SE adjustable ignition will give me (curve 1 with 5 degrees advance). At 10.3 static compression (9.3 CCR) I thought that this much advance was a little strange, and have been running 135 main jets in my two HSR45s (you "coached" me on the jetting, as I was freaking out about too small jets). So I get the bike going again, haven't changed anything but the new CPS, and it's detonating really bad. I'm now on curve 3 (more retarded with respect to curve 1) and am slowly advancing timing up from there. I may be able to fatten up jets also. So here's the questions: Why would changing out my CPS cause my engine timing to need to be changed? When the old Hall sensor was working, could it have been giving a "poor" reading resulting in too much advance? Where the timing is now (curve 3) makes much more sense to me based on experience at this compression ratio.
As before, I remain indebted to your willingness to help me. Your knowledge and experience are rare.
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RE: Crank Position Sensor
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Old 08-03-2007, 09:00 PM
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Mike Mike is offline
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Default RE: Crank Position Sensor

In theory it should have no effect as it is used to establish engine cycle when used with the Cam sensor and the cam sensor sets all the timing events. On EFI bikes the opposit is true, the cam sensor establishes cycle (on those so equiped) and the CKP does the rest. It could be that TC carbureted bikes use the same stratigy. If I had to theorize with no proof, I would say that the new sensor may have increased coil dwell time (conversely the weak sensor was not allowing for full coil saturation/dwell) and therefore increased spark energy. That would then mean the motor will want more jet or go lean with the original jetting. The advance timing you've been running was likely trying to make up for a weaker spark which would also be lazier on the burn, requiring more lead. Our experiance with bigger motors and the Dyna ignition modules is that they typically have made the best dyno numbers on the lowest/most retarded settings. We've even been in the position of wishing for even more retarded curves (I realize that Dyna offers programming software for this but the dyno time has not been available to learn and experiment, and that same time is hard to digest for customers when asked to pay). We actually had a similar problem with our XB racer using the ICT ECM. The coil firing time was so close to the CKP initialization point (two missing teeth on flywheel) that we would burn the coil driver in the ECM. It took their engineer and an Osciloscope to figure that one out. Your situation would be the reverse of this, but this is what I'm basing the above on.
Mike
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