Can you sync carbs on the bench?

This may be a dumb question, but is there a way for me to sync carbs on the bench? Ive got 5 sets of Gen2 carbs to rebuild, and I'm trying to figure a way to assembly line these bitches. thanks

 

Five sets! WOW.

No you cannot sync them on the bench.
But here is one thing you can do.
Make sure the screws that control the throttle shafts are all closed all the way
then turn each one open 1/4 turn. Make sure #1 and 3 screws are the same amount of tension. So open one, 1/4 turn and then just open the other one till it starts to get some pressure.

As you know there is only 3 screws because one is not adjustable. #4 cyl.

Then they will at least be in the ball park.

 

Yes, a bench synch will get you started fine, and sometimes quite close, but a gauge synch on a fully warmed engine will get you the smoothest possible idle.

Yes it works, but it can be improved on a running engine.

 

+1. The only way to really dial in the carburetors is to synchronize them using a manometer.

 

The FSM says to bench sync by 1st aligning the #4 butterfly plate with edge of the bypass hole at the bottom of the venturi. Then adjust the remaining 3 butterfly plates the same, at the edge of the bypass hole. I tried this method the 1st time I had the carbs off and it worked very well, engine idled good on 1st startup. I made minor adjustments by the old "ear sync" method and obtained a very good smooth idle. I had the carbs off again a couple of days ago and this time, I used a .002 feeler strip to adjust the butterfly plates, that is, placing the feeler strip under the throttle plate and adjusting the screw until there was a slight drag, just like adjusting a rocker arm. When I adjusted the idle screw so that the #4 butterfly was at the edge of the bypass hole, surprise, the remaining 3 plates were at what appeared to be the same correct position. When I reinstalled the carbs, the engine started up immediately and settled into a nice smooth idle. I had set the pilot screws to 2 turns out, but some fiddling provided best idle at 2 1/4 turns out. Engine runs great, good throttle response off idle, settles back into idle quickly with no rpm hanging.

 

Hmmm....i should have bench synch'd my carbs before installing them.

 

Performing a bench synch is valuable as this gets you on the right page. I would consider this step one in a two step process.

Manometers are a key piece of equipment for owners of bikes with carburetors.

Once you have some good weather try out your new synchronizer. You'll see the difference first hand.

 

sucks that mercury is a "life-threatening substatnce."

Bench Sychronizing is dah way to fly...need some other manometer than that motion-pro one with the fake mercury shite!

 

When you sync carbs what it is doing is getting the slides to open at the same time.

The dial type gauges are MUCH easier to use than the fluid filled type.
If you do not believe me try both.

 

I have used a vacuum tester used for testing leaking valves on cylinder heads with an adapter to fit the carbs. It is very accurate but it does not allow for the differences in the individual cylinders of an engine in operation.

 

I loaned my sync tool out to a friend who was working on his Venture Royale. He had a boo boo and the engine injested the mercury (yummy). So since it is darn near impossible to get that substance anymore, he was forced to buy me a new tool. I haven't even removed it from the box yet.

As others have said already, the bench sync is only the first step in the process. To truely achieve a proper sync, you need to perform an operational sync with a good tool, be it gauges or manometer type. I too have had solid results from a proper bench sync but it really isn't a sync, it is more of a base setting to get the engine running so you can do the final tuning. You should also be sure that the valves are adjusted properly as tight or loose valves will throw off the vacuum as much as a disparity in idle mixture. I also bought the Motion Pro carb adjuster tool woth the 90deg drive on the end so I can reach all the adjuster screws without burnng my tender fingers. It's a very nice tool for the V4!

On two stroke twins I use a home made manometer that is just a long loop of fuel tubing connected to the carb boots (engine side of course)with about ten inches of coolant in it. You attach the fuel line to a board so it forms a loop where the coolant can sit in the bottom and observe whether the coolant climbs towards one cylinder or the other (simple) cheap and effective. It gets more complicated with tripples and V4 2 strokes but the principles are the same, just use on carb as the reference.

Just a note on gauges. These are mechanical devices and as such they can vary in accuracy and wear out or get sticky over time. I find it helpful to attach your gages to a single source to see if there are any disparities between them before you start. Record the deviations on the gauge face with masking tape as +1 or -3 so you can see that you need to add or subtract from the actual reading. This will prevent you inducing a mismatch between your carbs.

You have all winter to get it right so take your time and have fun with it.

 

This kind people.
Google Image Result for http://www.saber-cycle.com/blog/wp-content/uploads/2010/01/08-030-2.jpg

 

This doesn't work for me Donald.

http://www.saber-cycle.com/blog/wp-content/uploads/2010/01/08-030-2.jpg


Ahh I just copied too much!
That is a nice set of gauges but personally, I prefer the sticks. Probably because my eyes aren't what they used to be LOL.

 

Morgan Carbtune all the way folks! < www.carbtune.com > I found the Carbtune to be less cumbersome than using a friend's mercury manometer. You have the added benefit of not having to mess with mercury or worry about fluids getting sucked up into the engine if you're not careful. To top it off, it's only a couple of dollars more than the Motion Pro tool at about $100 shipped. I opted to add brass barb adapters to the order and permanently installed them on the bike for faster carb syncs when required.

I don't work for them or anything, just very happy with the purchase. Wish I had bought it before I screwed around with trying to make my own sync tool... that's an evening I'll never get back!