Author Topic: 175 Dual Twin Carburetor Throttle Valve Synchronization  (Read 1939 times)

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Offline paul25g

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175 Dual Twin Carburetor Throttle Valve Synchronization
« on: June 10, 2010, 10:15:27 AM »
Getting ready to synch my carbs.  Page 37 of the BS 175 Technical Handbook describes the procedure.  It says to use a throttle valve adjuster (special tool).  Since I don't have this tool, is there a suggested procedure of making sure the throttle valves are synched between the two carbs?  Thanks!

1958 BMW R60, 1966 BMW R50/2, 1972 Triumph TR6R

Offline disc_valve

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Re: 175 Dual Twin Carburetor Throttle Valve Synchronization
« Reply #1 on: June 10, 2010, 12:21:19 PM »

I always balance the carbs on mine by ear.

Stage 1:-

Fire up the engine and leave it idling, then listen at the silencer outlets. You will be able to hear if one cylinder is "lazy" - in that case, turn out the throttle stop of the lazy cylinder slightly. Keep tweaking until both exhausts sound the same, and if the idle speed is then too high or too low, turn both throttle stop screws in or out by the same amount to set a nice idle.

Stage 2:-

If you have an assistant stop the engine and set the throttle so that one slide is just disappearing from view at the top of the carb bore. get you slave/assistant to hold the throttle there while you go round at check the position of the slide on the other carb. Adjust the carb top cable adjusters as necessary until both slides disappear from view at the same time. This gives a rough balance close enough for normal riding. (Without an assistant stage 2 is nigh on impossible - in that case move on to stage 3!)

Stage 3:-

At the handlebar end of the throttle cable, unlock the adjuster and tighten it until the engine speed rioses to a fast idle (about 2500 rpm). Then listen at the silencer outlets again, but this time tweak the cable adjusters on the appropriate carb top until both exhausts sound the same.


Offline wonkyworks

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Re: 175 Dual Twin Carburetor Throttle Valve Synchronization
« Reply #2 on: June 14, 2010, 11:25:49 AM »
I use a #30 or #29 drill bit shank as a feeler gauge for adjusting the carb slides for idle. I then twist the throttle open and use a 1/2" rod as a feeler gauge for synchronizing the slides by adjusting the throttle cables. This works well for me. Doug



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