Question on syncing carbs on a 120

[Bradford]

I just want to make sure I'm going about this the right way. I want to sync my carbs and plan on building a manometer like this: http://www.powerchutes.com/manometer.asp

From what I understand, carb #3 is the fixed one and the other two have to be synced to it. first you sync #2 to #3 then #1 to #3. Using the manometer in the link above, do I connect the two tubes of the manometer to the vacuum connectors between the carbs being synced and the block? I assume I would connect the manometer between carb 2&3 and adjust carb 2 to have the same oil level in both sides of the manometer then repeat the process with carbs 1&3.

Also, are there hoses connected to these connections now? If so, do I remove them and plug them off?

Cheers!

Brad

 

[Len Todd]

Well.... a three holer could be a bit different. But, on the four-holer, there is a vacuum line to each carb. One of the manometer connections has to be connected each carb. You remove the hoses and connect the manometer hoses to the carbs. Then, the concept is to adjust the carbs so that the level of the manometer is the same across all carbs. This is sometime hard to see as the vacuum is not steady and the mercury jumps around a bit. But, you can get very close.

One of these vacuum lines, on my sled, also goes to the fuel pump. So, if you disconnect it and put on the manometer, you only have about 30 seconds to set it before you run out of fuel. A tee works well for this one connection to allow the fuel pump to still be tied into the line.

Also, you have to be careful to not have the mercury close to top of the manometer If you blip the throttle too hard and suck the mercury into the carbs, you will have a mess. My Manometer came with some "jets" to install in the connection tubing. While the holes in the jets are very tiny, you can still get a good read. It actually dampens the variations somewhat to give you a more accurate reading. It also precludes sucking a lot of mercury up through it and into the carb.

 

[RX1Jim]

When I am using a manometer to sync the carbs on the 4 stroke sleds and my 4 cylinder street bikes, I put a big warning note to remind me to NOT blip the throttle. On the sleds I put a block under the throttle to prevent me from hitting the throttle. Just too easy to forget and hit the throttle then end up with a toxic mess!!!!

 

[Bradford]

When I am using a manometer to sync the carbs on the 4 stroke sleds and my 4 cylinder street bikes, I put a big warning note to remind me to NOT blip the throttle. On the sleds I put a block under the throttle to prevent me from hitting the throttle. Just too easy to forget and hit the throttle then end up with a toxic mess!!!!

I guess that's why 2 smoke oil is recommended for these homemade manometers!

Brad

 

[Len Todd]

Actually, in some states you can not get the mercury. It is a toxic substance, and I guess they (some governments) don't trust us with it.

 

[vogelm1]

Yep, you pretty much have the method down. There is a rubber plug covering the port on the end carb; the other two have vacuum hoses connected at their ports which go to the fuel pump. I ran a "T" in these two lines so I could run the engine as long as need while adjusting. Only two of the carbs have an adjusting screw, so just turn each one in or out until all the carbs "line up". When doing mine I don't have to turn the screw much either way...it's a very fine adjustment, maybe a 32nd or even 64th of a turn.