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Old 08-10-2004, 09:11 PM   #1 (permalink)
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Cams and "rough idle"

I have not built a v-twin engine, just some big block chevys years ago. Loved the "ticking" sound of one them idling. My question(s) is: is this what the 'rough idle' is in comparison. What causes the rough idle.

All right, what cam or other factors create the best sounding engine?
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Old 08-10-2004, 09:40 PM   #2 (permalink)
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The rough idle is caused by overlap; that time when both the intake and exhaust valves are open at the same time. Generally, the more radical the cam is, the more overlap it has. A stock Twin Cam carbed cam has 2 degrees of overlap, an Andrews TW26 has 20, a TW37 has 32, an SE 203 has 35.
If you're buying a cam for sound, that's the wrong reason.
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Old 08-11-2004, 01:53 AM   #3 (permalink)
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I agree, if you are buying a cam on sound alone, more than likely you will be severely dissappointed in it's performance on a street engine.
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Old 08-11-2004, 06:28 AM   #4 (permalink)
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Talking Rough idle

My bike has had the bore size increased, the compression increased and the duration and lift of the cam increase. I would not say it has a rough Idle, it's a fuel injected bike. It does have a definate lope to the idle. Anyone who knows what a twin cam sounds like knows mine is not stock. My build was done for mid range torque, a pleasent side effect is the better sound.

If you put a big cam in for the sound and do not modify everything else to take advantage and optimize the cam you will be very unhappy with performance. The overlap in the cam is to help deal with increased compression.
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Old 08-11-2004, 09:02 PM   #5 (permalink)
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Thanks. NAH! I knew it was overlap. Just thought I might get some interesting responses. I would not make performance modifications to achieve a better sound. If I really wanted better sound I would go buy a trailer and pack the home stereo in it with an AC generator and maybe put on some good ol Led Zeplin.
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Old 08-12-2004, 12:07 PM   #6 (permalink)
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Murphdog--interesting info on the cam overlap. I just put in 203's 35 degree Overlap.. Am I correct in assuming that if more overlap causes ruff idling, it also causes missing/sputtering at slow crusing speeds and my dealer was correct in telling me that my bike now misses because the cams wannna get up and go? Is the 203 a higher perfromance cam then the Andrews you mentioned?
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Last edited by Bluescb; 08-12-2004 at 12:09 PM.
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Old 08-12-2004, 12:25 PM   #7 (permalink)
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Blue, your dealer isn't in Greenville, SC is he? I've had mine back three times complaining about the idle with 203 cams. "Perfectly normal", they told me, "you should hear the radical ones". Other people have told me their's don't idle any different than stock with 203's.
Mine does sputter some at steady low speed, below 2000 rpms. It doesn't cause me a problem, though, and I've gotten used to it.
I'm no cam expert by any means, but I think I would try the TW26 if I had it to do over (stock compression with big bore). I may try them anyway if I decide to keep the bike a while longer...it's almost 2 years old now and I can hear a RK calling me . I'm told the TW37s are a little soft down low with stock compression.
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Old 08-12-2004, 01:13 PM   #8 (permalink)
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Fayetteville, NC...our dealers went to the same school of "if you don't know what the hell is goin' on, tell 'em "Its a Harley--its normal!" Man, I'd like a nickel for every time I heard that. You know, if you think about it, if you take a highly engineered item like a TC88 powerplant and start swappin' out MAJOR parts like cams, exhaust, intake....you really can't expect to run perfect without some major dyna tuning/Powercommander stuff.. I put in a 95" and 203's to get more low/mid power and I got it..the trade off is spittin' at slow speeds. I spent my last dime on the Build---PC will have to wait.
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