Carb Sync Tool

427cobra · Post by **427cobra** » Fri Jan 18, 2008 11:58 am

I got a Uni Sync carb tool so I could sync my own carbs. However not sure exactly how to use it...ha

Anyone have directions or any tip for me so I can get my Trailfire sync'd...(just kidding..

:blink: )

I wanted to sync my LF before the ride. So any help would be appreciated.

-Eric

MuskyBear · Post by **MuskyBear** » Fri Jan 18, 2008 12:33 pm

Some damn good info on this link, here is some of it.
http://snowmobile.off-road.com/snowmobile/...b%20sync%20tool

Rough Tuning Adjustment:

- Remove the airbox for free access to the carburetors.

- Unscrew the idle speed screws, (big knurled knobs on the side of the carburetors you can turn with your fingers), so they are no longer touching the slides. You will feel the resistance change as you are turning counter clockwise. The slides should bottom out in the carburetors. If not, the cables may be too tight. In that case, use a wrench to loosen the locknut on top of the carburetor, and spin in the adjuster so the slide comes all the way down, and the cable is slightly loose.

- Adjust the idle screw in on each carburetor until it just touches the slide. Now turn it in another four (4) turns. The carburetors are now roughly balanced at idle. (Another way is to lift the slide, install a pencil, turn the idle screw in till it just lifts off the pencil on each carburetor.) The actual idle speed will need to be adjusted when the motor is running.

- Now squeeze the throttle slightly, (just off idle is enough), and look/feel the slide lift. Adjust the throttle cable up on the "slower" carburetor, until they both lift at the same time. Now you are done with the rough "off idle" adjustment.

- Next test the "freeplay". Squeeze the throttle slightly until you are just lifting the slides. How much clearance is there on the throttle lever? The manufacturers specify this as it affects the throttle safety switches on many models. The width of a credit card is about right. You will need to loosen the nut on each carburetor, and adjust in/out the same amount to get the freeplay correct. Now go back and check the synchronization at "off idle".

- For the final test, squeeze the throttle full on. Feel inside the carburetors; are the slides all the way up? If not, check the throttle cable condition, routing, and your previous adjustments. Also check for interference with grips, thumb warmers and the like. Repeat for 3rd/4th cylinder, then move on to fine tuning.

Fine Tuning Adjustment:

- Dig out your synchronizing tool.

- Put the sled on a stand, (very important for safety).

- Start your sled and warm it up, shut it off.

- Ensure the airbox is installed. Hook up your synchronizing tool to two carburetors, using the port on the "engine side" of the carburetor. (The ports will be covered with some type of rubber plug.)

Note: Some carburetors may have a smaller fitting requiring adapting. In this case, use a couple of pieces of smaller diameter (primer type) tubing forced inside of the carb tools larger tubing. Be careful to keep the lengths the same and ensure an air tight fit. (See picture.)

- Start the sled but do not touch the throttle.

- Ensure the carb sync tool is level, and adjust the idle screws to balance the antifreeze from side to side. You will need to adjust the screw on the carburetor with the coolant at the lowest level, in a clockwise direction. Adjust both carburetors up or down evenly to get the idle you want. Shut the sled off, swap the synchronizing tool lines, re-start, and double check your readings; they should read the same. (If the lines are not the exact same length, you will get different readings, adjust your line length.) On sleds with more than 2 cylinders, match the remaining cylinders to one of the first two.

- Next start the sled again, and squeeze and hold the throttle to bring the RPMs just off idle. Turn the throttle cable adjuster counter clockwise on the carburetor with the coolant at the lowest level, to even the coolant. On sleds with more than 2 cylinders, match the remaining cylinders to one of the first 2.

Note: Don't let the sled idle to the point of overheating. If you adjust idle in the summer, you will most likely have to readjust in the winter.

- That's all there is too it. Now go amaze your family and friends!

427cobra · Post by **427cobra** » Fri Jan 18, 2008 12:56 pm

That has some great info....Thanks!

I have the type of sync tool that you need the air box off to sync the carbs. You place it on the carb and read the level of a red ball that is in a tube.

MuskyBear · Post by **MuskyBear** » Fri Jan 18, 2008 1:03 pm

I'm sure it is the same principle. On my 1981 LF the Mikuni's had a little pipe plug you could take out on the engine side of the carbs and put a little fitting in to hook your sync hose to them and then cap them off with a little rubber plug. I think your tool you just put the thing over the air box end of the carb and check one then check the other. It is more of a universal tool for carbs that don't have a place to hook a small hose to on the engine side of carb. You are measuring vacuum caused by how far each slide is open.

Danzig · Post by **Danzig** » Fri Jan 18, 2008 2:10 pm

BRING THAT FRICKING THING TO THE HOUSE NOW, YES I AM DEMANDING IT..

427cobra · Post by **427cobra** » Fri Jan 18, 2008 3:28 pm

That could be arranged....

Post by **ICCSF 108** » Fri Jan 18, 2008 3:35 pm

Eric & Paul: The main thing to remember when using that tool is to turn open up the adjustment wheel on the tool to let the most amount of air flow through the tool as you can& still raise the red indicator. If you don't then the idle will come down on the sled because your choking off the air to the carb your checking & it will give you a false reading. The idle needs to stay consistent to synchronize the carbs. if you don't understand what I mean give me a call & I'll walk you guys through it.

Kenny

427cobra · Post by **427cobra** » Fri Jan 18, 2008 4:43 pm

Thanks Kenny.

Thats kind of what I figured. I was messing around with it a little last night when I had my LF running. I will have to check it again and make sure it doesnt choke off the air supply when i am adjusting the carbs.

If it doesnt seem to work I will have to give you a call.

-Eric

MuskyBear · Post by **MuskyBear** » Fri Jan 18, 2008 5:16 pm

Using that tool with needing the air box off, how much do you compensate for having the air box off with the idle speed? Or once they are sync'd can you just adjust the idle with the air box back on as long as you turn the screws the exact same amount? Kind of seems to be defeating the purpose.

harleysportster · Post by **harleysportster** » Fri Jan 18, 2008 6:04 pm

ICCSF 108 wrote: Eric & Paul: The main thing to remember when using that tool is to turn open up the adjustment wheel on the tool to let the most amount of air flow through the tool as you can& still raise the red indicator.? If you don't then the idle will come down on the sled because your choking off the air to the carb your checking & it will give you a false reading. The idle needs to stay consistent to synchronize the carbs. if you don't understand what I mean give me a call & I'll walk you guys through it.

Kenny

To add to what Kenney has explained:
I would check both carbs at idle first, then raise the track off the ground and wedge the throttle open to achive 4000 RPM for the second part of testing.
Open the Air Flow control on the flow meter all the way, then place the meter on the right side carb with the engine running. Slowly close the flow control until the float in the tube lines up with a graduated mark on the tube. The meter must be in a vertical position. Place the flow control on the left carb and compare readings. If both readings are equal, all setting are correct. If they are different, adjust the lowest carb idle float reading to match the higher one.
When idjusting at 4000 RPM, use the flow meter as previous and loosen the lock nut on the cable adjuster on the carb of the lower reading and adjust the throttle cable sleeve to achive an equal reading of the other carb. Retighten the lock nut once the setting has been achived.
If any further idle speed adjustment is necessary, always turn both idle screws equal turns to keep the carbs in sync.

427cobra · Post by **427cobra** » Fri Jan 18, 2008 6:21 pm

Thanks for all the info. Hopefully have time tonight and give it another try!

Right now the sled runs good...just wanted to check things over before the big Eagle River ride.

-Eric

MuskyBear · Post by **MuskyBear** » Sat Jan 19, 2008 2:02 pm

BTW how much did that tool cost? I am planning on making the home made version. I heard that when you sync that way your sled really idles sweet.

427cobra · Post by **427cobra** » Sat Jan 19, 2008 2:52 pm

Thanks Guys for all the info.

WOW is it cold out today 5 deg...brrr

I think the tool was around $25 off of ebay..

Danzig · Post by **Danzig** » Sat Jan 19, 2008 3:03 pm

Well--

I now have the tool you sucker Eric. You're never going to get it back..

Today sometime I am taking the sled to work again and we will have to try this tool out and see how it goes. I gotta get them skis tightened up too. So hopefully I wont be too late tonight getting home..

427cobra · Post by **427cobra** » Sat Jan 19, 2008 4:46 pm

haha....have to let me know how it goes! you can do mine next!