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Author Topic: jetting for 970 motor  (Read 1645 times)

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Offline cbr954

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jetting for 970 motor
« on: July 12, 2014, 02:40:13 pm »
I just built a 970 with a F2 head.  Running the stock 78 carbs for now till I get enough money rounded up for some Mikuni RS carbs or find a set of webers that wont cost an arm and a leg.  I know jetting has a lot of variables but wondering if anyone has a base line for 970 size motor with the stock carbs.  Right now I have 145 mains, two .020 shims under the needles and 40 idle jet.  It still feels like it is lean when I run at 70mph cruise speed.  It seems to accelerate good through the rpm range but  I dont seem to be getting any color on the new plugs.
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Offline dusterdude

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Re: jetting for 970 motor
« Reply #1 on: July 12, 2014, 03:04:15 pm »
I bet that thing is a monster


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Offline Old Scrambler

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Re: jetting for 970 motor
« Reply #2 on: July 13, 2014, 10:06:43 am »
I like to tune from the rich side of things to just right............if your plugs are clean, your exhaust-tail should also be clean.  Have you tried a plug-chop?  If you see any sign of a 'bead' on a plug........any color..........including deep inside with a 'looking glass'.........your lean......and heading for trouble. 

Nice motor build............what cam?
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Offline cbr954

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Re: jetting for 970 motor
« Reply #3 on: July 13, 2014, 10:40:31 am »
I like to start rich also but I didn't know where to start to be rich with this motor.  I thought 140 mains would be rich but there not.  The biggest I have is 145 and it still isn't noticably rich.  I have put .055 of shims under the needles also to get the lean out of the mid range.

It has a megacycle 125-75 cam,  I thought this thing might not idle that smooth but it runs about as smooth as my dads stock 750
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03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline Jim F

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Re: jetting for 970 motor
« Reply #4 on: July 15, 2014, 09:01:28 am »
Can you get it to a dyno just to do an air fuel run and see where your at?

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Offline Bill/BentON Racing

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Re: jetting for 970 motor
« Reply #5 on: July 15, 2014, 03:45:40 pm »
+1. Have some 150's also some 170's mains. ;D
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Offline cbr954

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Re: jetting for 970 motor
« Reply #6 on: July 15, 2014, 04:56:51 pm »
Unfortunately there are no motorcycle dynos anywhere close except for during ralley week but they only want to do a run or two just for people to brag about there hp...or lack of, they dont want to spend the time for tuning.
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03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline Jim F

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Re: jetting for 970 motor
« Reply #7 on: July 15, 2014, 05:42:54 pm »
well take it out on the highway and get it up to speed
pull the clutch in and kill the motor
check your plugs

(Be sure to take your plug wrench)

not the best way but
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2002 RC51 1000 (SP2)
1983 GS1100EC Suzuki
2002 998 Dukati (Customers Bike)
1992 KTM500 2 stroke
1975 CB750/836 Honda
1978 GS750/840 Suzuki
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