Carb synch: Advise please

[Dave_A]

Ok, I ordered a 4-gauge carb-synch kit from JC Whitney.

I *know* I need to synch the carbs on my 850, and plan to check the 450 as well.

As I understand it, I am supposed to remove the screws from the carb boots on the 850, or the cyl head on the 450, and attach one guage to each cyl.

To adjust, IIRC, one turns the screws on the throttle linkage to bring the needles to the same reading accross the board.

Anything more?

Is more vacuum better than less - should I try and synch with as much pull or as little, or is there a specified pressure?

[daveo]

you want them all to pull the same vacuum....at both idle, and 3-4K rpm, be careful when you back off the throttle that you don't suck the mercury into the engine!

[Dave_A]

you want them all to pull the same vacuum....at both idle, and 3-4K rpm, be careful when you back off the throttle that you don't suck the mercury into the engine!

No mercury.

Mechanical Vac Gauges.

Should I try for MORE vac or less? Or does it matter?

[daveo]

doesn't matter, just the uniformity

[Anonymous]

Remember, on the 850 everything has to match carb #2 since that is the main driven carb. Fine adjustments can be made to the other three.

Good luck!
JV

[Dave_A]

DONE.

450 was off a tad, don't know how much diff it will make on a twin...

850 was all over the place... I kind of expected this, as I had just taken the whole carb rack apart... I see what you guys mean about synch being important, the 850 actually holds a ~1300rpm idle now, instead of having to be wound up between 2-3k to stay running...

Now, 850 oil leak finding time...

[Anonymous]

how do you set the carbs on the 450 ? steps from beginning to end and what tools needed ? and what screws on the carbs are for what ?
thanks

[Dave_A]

how do you set the carbs on the 450 ? steps from beginning to end and what tools needed ? and what screws on the carbs are for what ?
thanks

You need:

Set of 2 long screwdrivers, socket wrench to loosen the lock-nut, and either mercury carb-sticks or a gauge-set like the one I used.

First, loosen the lock-nut on the adjusting screw (Adjusting screw is on the throttle linkage between #1 & #2 carb.

Then Warm up the motor... Choke + carb meters -> not good...

Behind each intake boot (on the head) there is a single 5mm screw. Take these out and connect one of your mercury sticks/guages to each side. Be careful with the sticks (if you use them), if you hook them up wrong you can suck mercury into the motor...

Then, start the bike and turn the adjusting screw while watching the indicator on your device. Rev a bit after each adjustment to re-settle everything and see where you sit... Once you have the vacuum set at idle, run the bike up to ~4000 rpm, and adjust if needed...

Finally, turn everything off, and let the engine cool. put the screws back in the head, and tighten the lock-nut BY HAND or with the blade of a flathead screwdriver. If you use a socket wrench you will inevitably move the adjusting screw & mess up your synch...

[chuckycheese]

Idle

I've got a question....I've never synched my carbs but my bike idles really well at 1000RPM....does that mean they're in synch, or not necessarily?? Thanks!

[80gs1000e]

Re: Idle

I've got a question....I've never synched my carbs but my bike idles really well at 1000RPM....does that mean they're in synch, or not necessarily?? Thanks!

Not necessarily. #-o