Bench Syncing Carbs... please explain

Ok guys, I feel like an idiot asking these questions, but hopefully you people won't be quick to judge. This is my first bike. I bought it a few weeks ago. When I purchased it, it started up nice, drove it home with the airbox off, about 3 miles and noticed that it seemed to bog down at low RPM. (Figured it needed carb adjusting or it was getting too much air).

Now I installed the airbox, and it starts hard. It will idle for about 5 minutes and then stalls and smells like gas. After looking at the plugs, plugs 2 and 3 are dark and sooty, while 1 and 4 are clean. I'm confident that it needs a carb adjustment. However, I'm thinking about just pulling the carbs and cleaning them.

After research, I have seen becnh syncing and checking the fuel levels. I hate to ask, but what does bench syncing actually mean, and what does the fuel level (clear tube method) mean.

So once I pull my carbs out, I should bench sync them... then what else do I need to do.

Thanks so much for your help!!!

 

When you get the carbs CLEAN, you bench sync', which means getting the butterflys to open as near as poss' at the same rate, this only gets them in the ball park to run the motor, the carbs have to then be vac' synced with the motor running.
You might check the coil on 2 & 3 & the pick up.
Float levels, push a short piece of clear plastic tube onto the carb drain, holding it vertical & loosen the drain screw, the fuel will rise up the tube to the level of the fuel in the bowl.

 

Here are the write-ups if you need the step-by-step, never hurts to have some pics

Bench synch

Float levels

 

How do you vaccuum sync carbs. is this where you get a tool.

 

You obviuosly have a set of cylinders doing the opposite of
the other two, it may be as simple as a pilot screw adj-but it's most
likely more then that.

So.....stop at this point. Read and learn (right here on this site)
all you can about how the carbs work-how to clean them-
how to tune them, because your going to get a zillion "it could be this
or that". and thats very much the truth, it could be.

All the info you need to make your bike scream is on this site.........
but it will be a hundred times easier for you if you take a little
time and get familier with parts and terms.

Believe me,you'll have to post a whole lot less "what do you mean
by this or that if you understand what the guru's are advising you to do.

good luck
ron

 

Yes, you use something like a Morgan Carbtune, or similar. IF you happen to be near the Utica NY area, come down and I'll do it for you. If not, at least put in your avatar where you are. I'm sure someone near you can help.

Dave Fox

 

You can get the tool or make one.

A vacuum synch is done with the motor warm and running.

If you have a 2 tube tool:

Warm engine
shut off
connect tubes to cylinder 1 and 2 vacuum nipple
start engine let idle
Turn screw in the middle of carbs 1-2 until fluid/gauge is even
shut off motor
replace vacuum caps
Switch tubes to 3 and 4 vacuum nipples
start engine let idle
Turn screw in the middle of carbs 3-4 until fluid/gauge is even
shut off motor
replace vacuum caps
Switch tubes to 2-3
start engine let idle
Turn screw in the middle of carbs 2-3 until fluid/gauge is even
shut off motor
replace vacuum caps and petcock hose

You may also want/need to adjust your idle mix now as the cylinders are getting slightly more/less air through the butterflys. Then synch again and repeat until you have no more changes to make.

For the tool you can but a carbtune tool ($100) search this site for baby bottle synch tool or make the one I have for about $6.

Here's what you need:

8 feet of clear plastic tube 1/8" ID
1 yard stick
duck tape
ATF fluid

I use ATF because it's easy to see, responds well to the vacuum and if some should get sucked into the motor it'll burn off with no damage.

To make tool:

Make a big U out of the tube with both ends even.
Tape to bottom of U to bottom of yard stick.
Tape tube up sides of stick
Tube should look like this /\/\
Add ATF (I found a vacuum fitting on my Jeep worked well for this. One end on the fitting one end in some ATF and crank the motor)
Hang yards stick and let fluid settle to bottom of U
Once fluid is settled you're ready to synch.

 

I am from Lynchburg VA. Thanks iwingameover, I'll pick those parts up tonight. I guess I will have to pull the carbs since the bike won't start now, but I have never had a problem I couldn't fix... so lets give this a try.

Anyone around Lynchburg VA that is experienced, I would greatly appreciate any help to ensure that I don't screw anything up. PM if you would be willing to help.

 

Let me know if you want pictures of it. I'm going to be using it again hopefully tongiht if my new jets arrive.

Lynchburg is a 200 mile ride from me.

 

Yeah man, I would love some pictures or even a video or something of it. I'm sure alot of other people would use the technique if they saw it. I'm pretty sure that I know what you are talking about, and I've played around with the bike long enough to know whats going on.

I seriously appreciate all of your help. I'll post updates tonight to tell you where I'm at, if it worked, or If I hit any other problems.

 

If you make your own sync tool like that, be aware that a lot of them like that are a whole lot more sensitive and that can make them much harder to work with until the bike is pretty close to in sync. The one I have has restrictors on it to avoid having fluid sucked right up.

Do I know what I'm talking about? Well, yeah. Example, this past weekend at a carb clinic one carb rack was completely disassembled. I mean completely. After it was back on the bike, we used a homemade sync tool, which is a really well built one. However, the sync was so far out that it was impossible to get within a range that wouldn't suck the fluid all the way up. After fighting with that for awhile, we decided to get out my carbtune, and I had the carbs synced within a couple minutes. We did not go back to the homemade one at the time since it was getting late and we wanted to get our ride in. Long story short.....the bike worked well, LOTS more torque and power than before, and getting over 50mpg for the owner on the way home.

Personal feelings- yeah, I prefer homemade tools whenever possible, and hope to make one identical to what we were trying to use. But I would use the carb tune first, then go to the homemade one for finetuning.

YMMV

Dave Fox

 

I agree with dave. YOu do have to be careful I use ATF incase some gets sucked in. Also I only put about 18" of ATF in my tube. Enough to get a good balance but little enough that I've got about 3 feet of hose for it to get through before it gets into a motor. Mine have never been far enough out after the bench synch to have that probelm.

 

I got a friend tonight who has bench synced carbs before. He is coming over to help me out. He's got like a 300 dollar carb sync tool in his garage that we are going to use. I really wanted to do this myself, but I feel much more confortable having someone walk me through it the first time.

 

$300? Quick, tell him to sell it, and get the Morgan for 100, then he'll have 200 to play with.

We didn't have too much fluid in the tubes, but the carbs were so far out that I couldn't look at the tubes and adjust quick enough before it pulled right up the tubes and over the handlebars.

Dave

 

I think I'm missing something here - you rode the bike for the first time WITH NO AIRBOX and noticed it seemed to bog at low RPMs. Then, you put the airbox on and it hard starts, then stalls and gives evidence of really rich running (smell of gas, sooty plugs). Coincidentally, the two that look to be running rich are fired by the same coil / ignition system. And with all that, you're focusing in on CARB SYNC?

IMHO, you're putting the cart WAAYYY before the horse on this one.

Forget the syncing for now, on the bench, or with a vacuum gage. No form of carb syncing is going to correct rich/lean/possibly dirty carbs or a possible ignition problem.

Start with carb cleaning - making sure jets and passages are all OK.

As they go back together, you bench sync 'em. This just means setting the interconnecting throttle linkage so that the butterflies are all pretty close together. Not so that one is 1/8" open and the others are all shut, etc.

I'm just sayin'.... I think you need to go to the fundamentals rather than getting excited about your buddy's $300 carb sync tool.

Good luck with it, whichever direction you go.

Kirk

BTW, looking back, it looks like Wizard and parts gave you identical advice.

 

Yeah, I agree, thats whynI have pulled the carbs off of the bike for cleaning, the purpose of the post was a basic understand of all the process that goes into preparation.
So, I will continue with your advice and thoroughly clean these carbs up and get them ready to bench sync them with another tutorial on here. Also, this is literally my 2nd or third week with the bike apart, what seems like common sense to most may not be someone who has very little mechanical experience.

Either way, I thank you for your help, and I will keep everyone up to date on what I experience.