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i gt a 107 has about 650 miles on build , an i had dyno again an it has lost 4hp an 6 tq i have rev perf self tuning system on it an fuel looks the same as before , what could make it lose power,at 1st it 102hp an 110 now 98 an 106
 

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I'm no tuner but a few things come to mind that could make a difference such as different Dyno, different Tech doing the tuning, different weather, different fuel and I am sure the tuner guys out there can come up with more reason. To many variables.

The real question is can you feel a difference and are you happy with how she runs?? If you cannot feel a difference and you are happy, no worries :)
 

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I agree with triplej as far as the cause for the difference. My question would be what cams did you go with and did you do anything else besides changing jugs and pistons? Power seems a little low for a 107 build.

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Any other symtoms besides loss of power? Smoke? Noise? Etc?
 
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What was the Temp/Humidity that day compared to last time it was tuned.Low tire pressure can also be a contributing factor.Also did he run it in the same gear.The higher the gear the better the number.
 

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Less than 4% difference?? I'd crumple up the 2nd chart, throw it in the garbage and ride away happily. Dynos are FAR from absolute, there's a whole raft of things that can cause that small amount of a difference, and motor problems are WAY down the list.
 

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Humidity, barometric pressure, air temperature, engine temperature, oil temperature, ethanol or non-ethanol gas, tire pressure, filtering/smoothing level on the computer that draws the graph, throttle technique, transmission gear...........the list goes on and any one of them can account for the difference you're seeing.

Fuel is a big one, and "race" fuels are the worst as most of them are junk unless they've been stored and handled just right.
"Oh but I was running 94 octane pump gas". Yep, that's great, how many people are buying that at 50 cents over regular and how long has it been laying in the underground tank??
"But my motor doesn't ping at all when I run that gas......" Well of course not, the crap won't even burn, how's it gonna ping??

Computer settings are huge, everything from the weather numbers entered to the calibration settings, to the filtering levels used to make the graph pretty.

Not trying to bust anyone's balls, just a little truth and education.
 

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Dyno your bike everyday for a week and you will have a weeks worth of different results.
Like others have said, every little detail makes a difference.
 
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humity was 34% on the good pull an 58% on the bad dyno,
a big part of the difference right there,but like another said,even the good pull seems low.our mildest 107" are doing at least a HP per CID.do you have any work done to heads?
 

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58mm?

heads were done by rev perf. got v&h power duall ,monster ovalls 58mm tb.
I'd be curious to know your reason for running a 58mm tb. You're losing velocity/cylinder fill/power with that big tb. Your stock 50mm with stock injectors is more than enough for your 107". If you would like I can give you contact info for numerous engine builders/tuners that do this chit for a living if you want a professional opinion. (Like Kirby from Vee Twin for one...what do you say Kirby?) You are not the first I have seen do this. I wish you well brother.
 

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same tech done the dyno, im wondering if i have broke a ring
Do a leakdown test.

Like others have said; 7 different days, 7 different results.

The original #s do seem a little down, but you have to keep in mind that the dyno is a tuning tool .

I can ride a motorcycle, but I never could ride a dyno chart...
 

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Discussion Starter #15
thats what harley recomened was the 58mm tb.their parts book says hp at a 100 or more use a 58mm tb,now i did dyno the scoot when i had a 45thous head gasket an the stock tb.and it was 98hp an 102tq ,and i put 30thous head gasket an 58tb an it went to 102 hp an 110tq, i dont no which one made the difference, but shop that built it just put 10to 1 pistons in it , i wished he had put 10.5to1 in but he didnt. it got 575 mackey cam, do you think a zipper system would help me get more out of it, because i cant tune the rev. perf.system
 
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