Throttle shaft wear and TwinMax calibration (was ABS)

[Ben Barkow <dr.ben@xxxxxxxxx>]

I've been riding around with my dual vacuum gauges recently. With  
liter-sized engines, you get an awful lot of vacuum during engine  
braking. It goes beyond 20 inches of mercury. I'm not sure how far  
since you need to use heavy needle damping (AKA "snubbing") and so  
brief transients are hard to catch. Folks who only have TwinMaxs can  
check this using the Min scale with the meter connected to just one TB  
- - see below. Using a TwinMax as a vacuum gauge might destroy your  
TwinMax meter so work carefully.

If my understanding of pressure is correct, since an inch of mercury is  
like .5 psi, and with butterflies about 2 sq inches, you can have 20  
pounds tugging on the little butterfly shaft. So, I'd expect lots of  
shaft wear, as Paige has noted. And for fueling to work right, you need  
to have some degree of precision at small openings.

I borrowed a TwinMax recently. Although I think dual vacuum gauges are  
the right way to tune, the  9 volt unit I borrowed was very nicely  
behaved and fair to the two sides - checked yours recently? Why not...  
do you believe in the Tooth Fairy?

Here's how this unit was calibrated:

Max: each meter number is one inch of mercury (plus or minus 3 for full  
scale)
Middle: each number is 7 inches
Min: each number is 10 inches

I'd say you are well-synched when you have deviations within plus or  
minus half an inch, and particularly at the point that matters the  
most, that first take-up of the cable slack.

Don't forget to re-connect your TB balance tube when the synch is over.

Cheers.

Ben                                                                      
                                               
Ben Barkow, Toronto... 39 seasons on Beemers, 44 as a biker

1961 R69s/rod, 1967-1999... really sup'ed up and fast

1984 R80RT/rod, 1998-2005  5 extra peak ponies in a wider flatter power  
band,
   much modified 2-into-1 exhaust, CR 9.5, Keihin PJ 34mm oval carbs,
   Uni filter, dual-rate springs with cartridge emulators, BT45/S11,  
Saeng fairing

1999 R1100S, 2004- Leo Vince exh, JetHot coatings, Techlusion 1031,
   large sticky foam filter, TB balance tube, 26 inch windscreen, air  
horns, Diablo Stratas

On 2005 Nov  12 , at 4:47 AM, oilheads-digest wrote:

>
> Date: Fri, 11 Nov 2005 22:44:27 -0500
> From: plpklt@xxxxxxx
> Subject: Re: ABS
>
> A while back on the list there was mention and even a like to  
> replacment of the TB butterfly shaft.  Can anyone send me that link  
> again, and how hard is it to replace it?   My right Throttle body is  
> making so much noise with the rattling from the trottle cable plate  
> that the shaft must be very loose... It shoulds like I have never  
> adjusted the valvles but is just the plate making all that noise.  I  
> wouldn't believe it but if you touch it the noise stops so I'm  
> convienced.
>
Paige

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