Feelin’ A Little Outta Sync?

Pandemonium Custom Shop Tech

Article by: Daniel Donley – Pandemonium Custom Choppers – pandemoniumc2.com

Originally Published In The March 2015 Issue of Cycle Source Magazine


Got a bike with two or four carbs? Engine not running so well? Well it might be time for a good carburetor cleaning and synchronization. Synchronization, what’s that? Well, it’s the adjustment of the carburetors so they work the same. When they are not right, your engine is basically fighting its self and will be running like SHIT! You can synchronize carbs a few different ways; the best way is with a synchronization tool that reads the vacuum on each cylinder while the engine is running, allowing you to tune each carburetor to the same vacuum reading. This tool will give you great results, but that tool is $100 or more. I have come up with a way to synchronize carbs without using the vacuum reading tool and have had great results. This method only works on carbs that are linked by one common shaft with an adjustment screw in between, which pretty much covers most multi carb set ups.


This is a set of carbs off a parallel twin engine commonly used in the 70’s and 80’s. I’m not going into the carb cleaning part for this tech, your manual will help you through that. I’m going to focus on the bench synchronization process here. So with a cleaned set of carbs, let’s get started. You will notice there is an adjustment screw in-between your carbs, this is used for the synchronization adjustment of them.


This is your idle adjustment screw, which sets the level of idle for your engine.


Remove the idle adjustment screw and take the spring off and set it aside.


Reinstall the idle screw and fully seat it.


With the idle screw fully seated your butterfly in the carb will be slightly open.


Got a small drill bit set? Your gonna need a small drill bit like a #50 drill or smaller.


We are gonna use the drill bit as a feeler gauge. By putting the drill bit in between the butterfly and the carb body you will then adjust the idle screw until you have a very slight drag when removing the drill bit.


This is the adjustment screw that adjusts the butterfly in the other carb.


By adjusting this screw it will open or close the butterfly allowing you to use the drill bit as a feeler gauge and making both carburetors butterfly position the same. Your carburetors are now bench synchronized. You can now remove the seated idle screw and install the spring. I have found that a good base line adjustment for the idle screw is to make the screw just touch the throttle arm and then give it two full turns. Well for next month’s tech, I’m gonna take this set of bench synchronized carbs and show you not only how close they are but also show you how to use the vacuum synchronization tool. So if you have any questions about this month’s tech feel free to give me a call at the shop. 419-576-6812 info@pandemoniumc2.com Daniel Pandemonium Custom Choppers www.pandemoniucustomchoppers. com


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