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Carburetors synchronization

Synchronize carburetors, what does that mean ?? When you twist the wrist, you open the throttle, which lets gas enter into cylinders. It is self evident that, in order that the engine works the best way, the same quantity of gas must enter in each cylinder. And a good method to evaluate this quantity is to measure the depression in each intake pipe. So, purpose of synchornization is to have the same rate of flow in each cylinder, that's all.

Let's start with a little tip : engine will run for a while with bike stopped. In order to avoid any cooling problem, if you have a fan, place it in front of the bike. If engine is cold, start the bike, and let it run until it reaches normal temperature.

moto et ventilateur

Then, as usual, you have to remove tank. It's time to have a look and to check where vacuum hoses are : they are necessary somewhere beetween carburetor and intake valve. There can already be an existing pipe, or one you have to screw on.

In most cases, there is already one hose on one of the pipes, it's the one of the fuel valve. On my XX, vacuum holes are here..

trou de prise de pression

Then screw the pipes, and connect balancer hoses. Check there is no air leaking.

branchement des prises de pression

Problem : how can we replace fuel tank. I use 2 clear pipes, quite long...not so bad, you can usually do the whole operation without refilling. Whatever is the system you use, make sure fuel won't leak on the hot engine or exhausts....

moto en réglage de synchronisation

Let's start the engine, and set up idle speed at 2000 - 2500 rpms. Make sure to not stupidly open throttle and suck up mercury in the engine. You can read depression of each cylinder on the instrument : purpose is to have all columns at the same level.

dépressiomètre en fonctionnement

It seems it isn't correct on that bike. Cylinder 2 is really higher than others. So you'll have to set up. Solution is to tighten or loosen little screw which define the setting from one cylinder to next one. You can see the screw on the picture here above.

vis de réglage de synchronisation

There is one 'reference' cylinder (usually #3 for in-line-four), which is directly leaded my throttle cable. So we'll set all others to have the same mercury level than #3. Be careful, on in-line-four, you adjust 2 and 4 on 3, but the third screw adjusts 1 on 2.

So, the method is to align 3 on 4, 1 on 2 and then 1-2 on 3-4 with central screw.

Once setting is OK at idle speed, open throttle a little to check it is still OK on dynamics. No need to be extremly accurate, usually 2 cm diffference beetween 2 columns is OK.

Once you're done, remove tooling and reinstall fuel tank. .