I've read many articles and threads about synchronising carburettors on type 4's and I wonder why articles always state that the engine must be running between 2500 and 3000 rpm I've read the in depth article in TheSamba.com (1972-1974 Dual Solex PDSIT Carburetor Adjustment Procedure) very in depth indeed! I know that the Bentley manual states the same procedure i.e. run engine between 2000 and 3000 rpm. Question is WHY does the engine have to be run at this speed to synchronise the carbs? WHY can't they be synchronised at tickover?
I'd guess it's because tickover runs through the central idling system in a different part of the carbs.
You need to synchronise both. Idle: You are setting up the throttle stop so they both idle at the same speed. 3000 rpm: You are setting up the cables to make sure they open the butterflies at the same time. If you don't do both, it won't run right.
in a nutshell, different jets & orifices control the fuel available at different airspeeds through the carb...as dictated by the requirements of the engine at different rpm.... idle, transition, mains....by synchronizing the carbs you're simply trying to ensure that the amount of air and the time at which it's drawn through the carbs is the same for both... in a perfect world, you'd have one carb per cylinder jetted to suit that cylinder (as no two cylinders are identical) Multi point Fuel injection is about as close as it gets....
Throttle stops for tickover, linkage for driving. 3,000rpm is driving mid-range revs. Makes a ruddy racket.
Thanks for the input, im slightly deaf from yesterdays carb synchronisation exercise, the right hand carb was miles out, now to go for a test drive, hopefully its made a noticable difference!
When it's really out it sounds like it's firing on only three cylinders. Although I've got a carb synchroniser, as a check I've found that if you twiddle with the adjustable link on the right hand carb until it sounds right, it usually is.
andyv thats EXACTLY what my engine sounded like!, now the right hand carb is adjusted its like driving a completley different van, bluething it made a huge difference!
