Carb Synchro

[PAULYBOY]

I havea suzuki gs850. 4 carbs + 25 year old bike = really rough running.oes anyone have an easy homemade way that someone with moderate mechanical skills can equalize the carbs?

[Navy_p503]

I consider myself a pretty competent mechanic, but I just didn't have the tools or the type of shop to complete a synch. You're going to at least need a vacuum gauge and a big fan. If you've already cleaned or rebuilt the carbs and it's still running rough, good luck

[IrocRob]

The right tools are a good place to start, I use this one: Morgan Carbtune - carburetor synchronizer for balancing motorcycle carbs

[themeatmanlandry]

I made my own with a yardstick, a piece of clear tubing, some oil and some bailing wire. I already had a squirrel cage fan. You also need about 10' of fuel line to hook up your fuel cell (it must be removed from the bike).

$1.55 Carb Sync Tool by Marty Ignazito

Pretty easy to use. You just hook up to the first two carbs and adjust; then you hook up to the second two carbs and adjust; then you hook up to the two commons (or whatever they are) and adjust. The only time-consuming part is to figure out how much difference is (close enough." Using oil instead of mercury amplifies the pressure differential (due to the extreme differences in density between mercury and oil). I found it fairly easy to do.

[PAULYBOY]

Okay, I thought it was more NASA caliber stuff. Sounds like I could use the same idea as a spirit level in construction. Now, can somebody give me some details in how to do this, i.e. should the engine be warm, should the choke be on, off or in the middle? Assumong the carbs, looking forward as in sitting on the bike would be 1,2,3,4 from left to right, am I doing 1&2, then 3&4, then 2&3, or what?

[themeatmanlandry]

Originally Posted by PAULYBOY

Okay, I thought it was more NASA caliber stuff. Sounds like I could use the same idea as a spirit level in construction. Now, can somebody give me some details in how to do this, i.e. should the engine be warm, should the choke be on, off or in the middle? Assumong the carbs, looking forward as in sitting on the bike would be 1,2,3,4 from left to right, am I doing 1&2, then 3&4, then 2&3, or what?

The bike should be warm, and you should have a service manual. I'm sure all bikes are probably the same, but you should check your Haynes (or Chilton's, or manufacturer's service manual) before you start just to make sure. You sure as heck don't want to get them all out of whack.

You also have to adjust the idle to a certain speed. I think this depends on teh bike, so you really need a manual.

While you're doing the test, you need a good fan (or so I'm told) to keep the bike from overheating. Not sure if this applies to liquid-cooled bikes or not. I used a squirrel cage fan that was left over from a job many years ago. I *knew* I'd use that booger someday!

What type/year bike are we working on?

[87gsxrnut]

It's not like a carb synch tool is THAT expensive. Geez.

- Nut

[themeatmanlandry]

Why buy something for almost a hundred bucks and wait on shipping when you can make it in an hour for <$20?

[PAULYBOY]

I'm working on an 81 GS850. I've finally got the tank off puttin flames on it and thought I'd go ahead and synchro the carbs if I could. The guy that sold me the bike put new plugs and oil& filter and air filter on the bike, and told me the reason it ran a little rough and needed a lot of choke was because of this. I don't have reason to doubt him, and figured if it aint rocketm science, I could maybe save myself 100 bucks or so.

[themeatmanlandry]

Originally Posted by PAULYBOY

I'm working on an 81 GS850. I've finally got the tank off puttin flames on it and thought I'd go ahead and synchro the carbs if I could. The guy that sold me the bike put new plugs and oil& filter and air filter on the bike, and told me the reason it ran a little rough and needed a lot of choke was because of this. I don't have reason to doubt him, and figured if it aint rocketm science, I could maybe save myself 100 bucks or so.

Sorry, I somehow missed the bike info in the first post. My mistake.

If an idiot like me can do it, pretty much anyone can. I highly recommend getting a manual first, though. Not only will it tell you how to synch carbs, but you never know what you'll learn just by reading it.

When you say "runs rough" are you referring to a surging, or a bad idle?

[Aussie Steve]

Hey Landry that pic of you?????

[themeatmanlandry]

Originally Posted by Aussie Steve

Hey Landry that pic of you?????

Sadly, yes.

[PAULYBOY]

Right now the way the choke is on, it runs at about 2800-3000 rpm. Even after it warms up, if I take the choke off to where it should run at about 1200-1500 rpm, it runs really rough like not all the carbs are getting fuel. Sometimes when I'm driving, the bike surges and stumbles occasionally. Then, once in a while, I can cut the choke almost all the way down and it runs a lot smoother than usual. I figure if I synchroes a dual carb car 35 years ago in my teen, preknowledge (what do you mean I have to change the oil?) days, I should be able to do this now. In the interveninig years, I've learned how to strip the heads off a V6, take em down to nothing, then reassemble the car engine after the valve job was done. If I can do that with a fool injected engine on a late 90's car, i stink I could do this!

[themeatmanlandry]

I'm sure you can. I don't know much about carbs and stuff, but I seme to remember that unbalanced carbs will cause a surging when the engine idles. I may be wrong.

Are you sure the carbs are clean?

[eb77k]

After sitting for so long, and the fact it doesn't want torun unless choked leads me to believe you need to clean the carbs completely prior to sync'ing them.

[PAULYBOY]

The guy I bought the bike from said the carbs had recently been cleaned and rebuilt, he just didn't have the time to tune them.

[Clint]

What does "recently" mean? A few weeks are sometimes enough to crud them up again. I think you're right in assuming it needs a sync, but run some cleaner through the tank, at least.

[PAULYBOY]

I'm painting the tank right now, but I think I'll hook up a IV type bottle with enuff fuel and cleaner to synchro the carbs while the tank is finished and cleared. I figure if I run a quart bottle like a Gatorade bottle with a siphon type tube going to the feed line it'll be like an intravenous bottle in a hospital . Yeah, kinda like M*A*S*H* in my side yard, only for the motorcycle.