Why sync carbs? (need education)

[J///Kidd]

So I pulled my carbs off and cleaned them (to the extent that you can without disassembling them as a unit). Reassembled and now ready to put back on the bike. So next would by syncing them.

I have some questions:
1) If nothing was changed (other than gaskets, new stainless steel screws and new fuel lines), why would I need to sync them? (ie. what would cause them to be out of sync at this point)
2) Sync refers to what? Equalizing the vacuum/pressure for each carb to make sure they all pull the same?
3) When I go to sync them, I understand I need to get the bike up to operating temperature.
a) Do I attach the airbox at this point (or leave it off)?
b) Do you guys just lay the gas tank across the frame (horizontally) while doing this?

Thanks for any information/education/understanding/advice you might be able to send my way. I just want to have an understanding of WHY I am doing things instead of just going through a set of instructions.

-John

[Lykkan]

So I pulled my carbs off and cleaned them (to the extent that you can without disassembling them as a unit). Reassembled and now ready to put back on the bike. So next would by syncing them.

I have some questions:
1) If nothing was changed (other than gaskets, new stainless steel screws and new fuel lines), why would I need to sync them? (ie. what would cause them to be out of sync at this point)
2) Sync refers to what? Equalizing the vacuum/pressure for each carb to make sure they all pull the same?
3) When I go to sync them, I understand I need to get the bike up to operating temperature.
a) Do I attach the airbox at this point (or leave it off)?
b) Do you guys just lay the gas tank across the frame (horizontally) while doing this?

Thanks for any information/education/understanding/advice you might be able to send my way. I just want to have an understanding of WHY I am doing things instead of just going through a set of instructions.

-John

If your carbs were pretty dirty, you should have honestly tore them down and dipped *each* carb for 6 hours + sprayed them with carb cleaner then reassembled and replaced the o-rings. If it was in need of cleaning it most likely needed a deep cleaning. I don't want to admit how many times I've had to tear carbs apart to fix something I overlooked. The entire problem the whole time was making sure the carbs were clean, most importantly the o-rings were sealing off well, and the holes in the jets were clear.

edit: I remove the jets, and soak them in the bowl. I dip everything but the float, the float needle thing, and obviously I don't dip the rubber boot or the boot cover.

If your carbs aren't 100%, not synching them will result in the cylinders firing with different power than the one next to it. This can cause vibrations at high RPM's, shitty sounding exhaust notes, hot-running cylinders, cold-running cylinders etc.

Synching them is REALLY not that hard. Does this contraption look that hard to make?

instructions: http://en.650wiki.org/index.php/12.19.1._The_$2.05_Carb_Syncronizer_%28premium_edi tion%29

You do the 2 passenger-side carbs, then the 2 driver side carbs, then the 2 middle carbs. When the liquid in the bottles isn't rising or falling, those 2 are in sync. When they ARE rising and falling, turn the screw between those 2 carbs (in the middle) until the liquid settles.

As for the tank, I fill the carbs up, then just set the tank away from the bike, and the carbs have plenty of fuel for me to sync them (if you're slow you'll probably have to refill them a couple times)

Also, if your carbs are dirty, they may be in sync at idle, but won't be in sync at higher rpm because your jets are clogged etc

[J///Kidd]

Thanks, Lykkan.

Let me clarify. I did tear each carb apart (removed main and pilot jets, needles, bowls, emulsion tubes, etc.). I took all the metal parts (jets, needles, float bowl bottoms) and soaked them in Berryman's for 24+ hours. I took the carb bodies (all 4 still connected as one unit) and cleaned them with carb cleaner and a tooth brush to get the majority of the junk off and then soaked them in a proprietary mixture of Pinesol and Dawn (dishwashing liquid) for 24+ hours. I used my compressor to blow everything out. I then replaced all the gaskets with new sets (thanks for the link, Arsenic) and reassembled everything. Honestly, the carbs looked in surprisingly good shape. The only thing I really noticed was trace amounts of sediment in the float bowls. I figured at 20 years, it couldn't hurt to give them a good cleaning

I was just trying to get an understanding of why a sync would be necessary if nothing had changed. I really didn't even have to adjust the float heights (a little bit on carb 3...but barely) - they were right at 14.6 mm.

[arsenic]

I was just trying to get an understanding of why a sync would be necessary if nothing had changed.

Every time you remove the carbs from the cylinder head boots, they twist just a tad. They don't change drastically, but they do change. I give you my word on that.

[Lykkan]

Every time you remove the carbs from the cylinder head boots, they twist just a tad. They don't change drastically, but they do change. I give you my word on that.

interesting info

[Kreylyn]

Every time you remove the carbs from the cylinder head boots, they twist just a tad. They don't change drastically, but they do change. I give you my word on that.

+1

Be a good time to do a valve check/adjustment before that sync too.

Do the sync with everything hooked up and together, except for the tank. Don't forget to cap off the vacuum line for the petcock so you don't sync to a massive vacuum leak.

I generally use an alt fuel source and set the tank safely to the side. leaving it turned on the bike= good chance it falls to the floor and you have a damaged tank.

Krey

[shpielers]

I dropped my tank doing that...
I use gear oil for chain lube. Comes in a nice 1L bottle with a tapered tip. Put a gasket in it, add a little gas (this is once it's emptied and clean of course) and it works great as an auxiliary tank.

[J///Kidd]

I dropped my tank doing that...
I use gear oil for chain lube. Comes in a nice 1L bottle with a tapered tip. Put a gasket in it, add a little gas (this is once it's emptied and clean of course) and it works great as an auxiliary tank.

That's a great idea.

So, to confirm, not only do I need to plug the external vacuum line (on carb 4 that goes to the back of the petcock), but I should also have the external fuel source feeding BOTH lines into the carbs, correct? Otherwise only one set of (2) will be getting fuel.

[arsenic]

correct

[J///Kidd]

Thanks everyone.

I almost feel competent enough to complete this properly and successfully

We'll see....

[Lykkan]

That's a great idea.

So, to confirm, not only do I need to plug the external vacuum line (on carb 4 that goes to the back of the petcock), but I should also have the external fuel source feeding BOTH lines into the carbs, correct? Otherwise only one set of (2) will be getting fuel.

wut

Umm, the lines you hook up go to the synchronizing tool you make. Those are vacuum lines, not fuel lines. There's only 1 fuel line that connects to the gas tank, and that's at the bottom middle of the carbs.

Imagine a long straw, filled with koolaid, and your significant other was sucking on one end and you were sucking on the other. The person with the most vacuum would win the koolaid.

With these carbs, you want no one to win the koolaid (please use water in the sync tool, not koolaid...)
When both of the 2 carbs you're syncing have the same amount of vacuum, they're sync'd.

[arsenic]

wut

Umm, the lines you hook up go to the synchronizing tool you make. Those are vacuum lines, not fuel lines. There's only 1 fuel line that connects to the gas tank, and that's at the bottom middle of the carbs.

He's saying hook up both fuel lines to the external fuel source. You do realize the pre 98 and 98+ carbs are different right? The pre 98 carbs have two fuel lines. It doesn't connect to the gas tank it connects to the petcock. Or in his case, they both connect to the petcock.

[Lykkan]

He's saying hook up both fuel lines to the external fuel source. You do realize the pre 98 and 98+ carbs are different right? The pre 98 carbs have two fuel lines. It doesn't connect to the gas tank it connects to the petcock. Or in his case, they both connect to the petcock.

oh ok

[maniac1886]

My first external fuel tank was a little rudimentary. I took a sheet of plywood just a little bigger than the tank, drilled 2 holes in it, and ran line from the petcock through the holes. Set the tank on the plywood and suspended it from the ceiling. Its really not a good idea. it didnt work to well so I ended up taking a gas tank off an old lawn mower, added a shutoff valve and a "T" fitting, ran the hoses to the carbs and hung it above the bike from the ceiling. Works quite well i might add.

[rschlegel]

Check amazon.com for an auxiliary tank. I got one for less than $25 shipped and brand new. The time you spend figuring out other options and parts will probably cost more. IMHO.