Carb sync and tuning

Wed Oct 6 21:02:23 EDT 2021

Kevin,
Tom Cutter gave me a handful of them years back when we were cleaning up his shop. I took them to SuperTech and laid them on the table with a “free” sign. To my surprise, I think I brought some back home. Send me your address and I’ll mail you a set.
Chris

Sent from my iPhone

> On Oct 6, 2021, at 8:23 PM, Kevin Fahey <faheykm at hotmail.com> wrote:
> 
> 
> Can anybody recommend a substitute for an old spoke for the spark plug to plug boot extender?  I've been wanting to give the shorting method a go IAW Matt Parkhouse's video but don't have any old spokes and nothing I've got in my 20 year drawer or see at the local big blue box store gives me a warm and fuzzy.
> 
> Kevin
> 
> From: Zwicky, Eric <ezwicky2 at gmail.com>
> Sent: Wednesday, October 6, 2021 4:15 PM
> To: mdairheads at casano.com <mdairheads at casano.com>
> Subject: Re: Carb sync and tuning
>  
> Also, it would be helpful to read up a bit on the procedure(s). 
> There's a few.   Shorting sticks, various gauges (I have the Harmonizer 
> and I love it).
> 
> But basically, after you have the timing and the valves sorted, you want 
> to baseline your carbs.
> 
> Start with the idle stop screws, which open the butterfly in the carb 
> body, at *just touching* the lever.  or Maybe one turn in.   But both 
> sides set the same way.
> 
> Then turn in the idle mixture screws (at the bottom of the carb body) 
> til they bottom out, then back them out a full turn, or a turn and a 
> half.   Different years  models have different starting points.   You'll 
> have to look at the Bing site, or maybe Snowbum's site, for specifics. 
>    Now you've got the baseline set.
> 
> Also, make sure your throttle cables at each side have roughly the same 
> amount of play, maybe 6 - 10mm, at the place where the outer cable 
> sheath sits in the little adjuster on the top of the carb body.
> 
> Then, I like to use the shorting-stick method to get the idle where I 
> want it (on my R90/6, around 1000rpm), and even on both sides.  This is 
> adjusted at the idle adjustment screws, not the idle mixture screws... 
> the ones that you level-set at the beginning. (The terminology can be 
> confusing).    Once it's roughed-in like this, I use the Harmonizer from 
> here on.      But I am assuming you don't have one, so let's assume 
> shorting sticks.
> 
> One I am happy that the idle is at the right rpm and both sides are 
> contributing equally, I will use the idle mixture screws to set each 
> side at their highest rpm.    You might have to turn one in a bit, and 
> the other one out a bit.   Turn the screw an 8th of a turn at a time, 
> slowly, waiting to hear an increase or decrease in rpm.    Or use the 
> gauge to see the rpms rise or fall.
> 
> Once you've got the idle mixture optimized on each side, go back to step 
> one and re-balance the idle stop screws (butterfly valve) as both sides 
> might no longer be in balance since you've optimized the idle *mixture*.
> 
> You might have to keep going back and forth a few times between idle 
> speed and idle mixture adjustments til you have them both optimized.
> 
> Once you're happy with those steps, you want to adjust the throttle 
> cable where it attaches at the carb.
> 
> start the engine and twist the throttle just off idle, and adjustments 
> to the adjusting nut until both sides are balanced *with the throttle 
> engaged a bit*.    Some people make the cable adjustments with the 
> throttle just off idle, some recommend running it up to 3000rpm and 
> checking.
> 
> This is much easier with a gauge than with shorting sticks btw.    For 
> somebody new to it anyway.   Old-timers with a lot of experience, and a 
> good feel and good ears love the shorting sticks method.    Me, my ears 
> are shot from a lifetime of loud music so I like the Harmonizer.
> 
> There's probably a lot of minor details that the gurus will pick apart 
> here, but this is the gist.
> 
> The thing is to read up and get a feel for it before you start.    Just 
> a few for starters:
> 
> https://bmwmotorcycletech.info/synchcarbs.htm
> 
> https://www.youtube.com/watch?v=5bmJ0iYBYgQ
> 
> And this pdf from Bing to see where to set your idle-mixture screws to 
> start:
> 
> https://www.bingcarburetor.com/uploads/9/8/7/9/98794296/bmw_jetting_chart_cv_carbs.pdf
> 
> Good luck.
> 
> eric
> 
> 
> On 10/6/2021 3:42 PM, Zwicky, Eric wrote:
> > Mac is right.   You need to get the timing and valve adjustments sorted 
> > before doing the carb sync.
> > 
> > I don't know where Lutherville is but there's a concentration of very 
> > helpful and knowledgeable airheads in the Annapolis area, and further 
> > west in Westminster.
> > 
> > If you were in Richmond I'd come on over :)
> > 
> > 
> > 
> > 
> > 
> > On 10/6/2021 3:37 PM, Mac Kirkpatrick wrote:
> >> Just an FYI, ALL other parts of a tune up must be satisfactorily 
> >> completed prior to doing a carb sync. Particularly adjusting the 
> >> valves, or the sync is useless.
> >>
> >> Mac Kirkpatrick
> >>
> >> On Wed, Oct 6, 2021 at 15:02 Porter Gieske via MDAirheads 
> >> <mdairheads at casano.com <mailto:mdairheads at casano.com>> wrote:
> >>
> >>     Does anyone have a carb sync tool and would be willing to help me
> >>     get my carbs in tune?
> >>     I have bought a kit of gauges and they are being delivered in a few
> >>     days- I am looking more for advice on mixture and idle.
> >>
> >>     I am in Lutherville, 21093.  Bike is 1981 R100.  Bing 40’s.
> >>     Thanks
> >>     porter
> >>
> >>
> >>
> >>
> >>
> >> -- 
> >>
> >>
> >> Mac Kirkpatrick
> >> Glenmoore, PA
> >>
> >> "After all, what is adventure, but inconvenience, properly regarded?"
> >> C. Donahue
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