Carb balancing on the cheap (pictures!)

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Skier
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Carb balancing on the cheap (pictures!)

Unread post by Skier » Wed Mar 23, 2005 11:51 pm

Finally got around to taking care of a lot of schoolwork so I have some time to do this, as promised.

Gathering the parts
For this project, you will need:
* standard airline tubing (check the pet aisle of your local grocery store, or a pet store. My 20 feet of it was less than $4 American)
* tape (masking or duct, I used masking since it was what I had)
* ATF (automatic transmission fluid - just buy the cheapest stuff you can find)
* something long you can tape the tubing to (I used some wood lying around the house, a yard/meterstick would work fine)

Putting it all together
You want to put the tubing so it makes a U around the long item, which I'll refer to as the yardstick from now on. Basically, you want to make the tubing have a good two or three feet of extra tubing from the top of the yardstick. This will let you run the tubing to the carb boots without moving the thing around too much. Tape the tubing into place.

Now, stick one end of the tubing into the ATF and suck on the other end of the tubing. Try to get about 3/4 of the way up the yardstick on either side. Let the device sit for a bit afterwards for an hour or two to let the fluid settle. If you have too much in it, you can either blow out the excess or, if you haven't cut the tubing to length yet, make a loop at the bottom with the excess tubing.

A picture is worth a thousand words, so here is an example one (not mine):
http://www.screaming3d.com/pics/cb/synchtool.jpg

And here's a picture of mine:
http://www.screaming3d.com/pics/cb/balancer.jpg

If you have a vacuum operated petcock like my Radian and want to use your gas tank, cut up an extra section of about two feet or so of the airline tubing. This allows you to have a longer reach to the gas tank when you move it from its mounting location.

Balancing the carbs
Read this page for some background: http://www.dansmc.com/balancecarbs.htm . I put my bike up on the centerstand, pulled the tank off to the side so I could access the nipples on the carb boots and attached the device. Fire the bike up with the lines attached. Basically, if a carb is pulling more ATF into it than the other, you need to adjust them. I balanced carb one against two, then three, then four. Might not be the best way to do it, but it was sure better than it was. You might want to balance one to two, then three to four, then one to three (or four). This ensures the banks of carbs are balanced against each other.

The screw you are looking for is this one:
Image

There are a total of three of them. One for carbs one/two, one for carbs three/four and one for the left carb bank (one and two) and the right bank (three and four).

Here is a quickie diagram on how to set up the lines for balancing carbs one and two:
Image

And one and three:
Image

(Please forgive my lack of art skills, I'm a computer scientist for a reason. ;) )

While this guide is for four cylinder bikes, a bike with two or three carbs should be quite similar. Any questions, please feel free to ask. And forgive any typos and whatnot, I'm exhausted from school.

Many thanks to ronboskz650sr for giving me instruction on how to build and use one of these myself - saved some money on it, that's for sure! That's also his balancer pictured in the walk-through.

(3/24/05: added a picture of my balancer)
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Unread post by sabbath » Mon Mar 28, 2005 1:35 am

Excellent post. Any suggestions on how to get fuel to the engine safely with the fuel tank out? The whole deal sounds kind of dangerous.

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Unread post by ronboskz650sr » Mon Mar 28, 2005 6:29 pm

You should be able to put an extended tube on the pitcock and prop the tank up or hang it from something.
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Unread post by beerbaron » Mon Mar 28, 2005 10:15 pm

On my service manual it is said to sync carbs 1-2 then 3-4 and then use the center screw to sync both pairs. Which I already did and it went fine.

Did the manometer described above but used 10-w30 oil , it was a little slow to move but it did the job anyway.

Justs did it today, really helped my idle speed and throttle response.

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Unread post by ronboskz650sr » Mon Mar 28, 2005 10:23 pm

Good point..slide carbs and cv carbs are different. See manual for specifics. Also some slide carb set-ups apparently have a refence carb that doesn't adjust as much as the others, and you synch the other three to it. I read about this at another forum, so the manual is always the best way.
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Unread post by TechTMW » Tue Mar 29, 2005 1:42 am

Some CV carbs (Like the ones on an xj650) also have a non-adjustable carb.
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Unread post by Skier » Tue Mar 29, 2005 3:34 pm

sabbath wrote:Excellent post. Any suggestions on how to get fuel to the engine safely with the fuel tank out? The whole deal sounds kind of dangerous.
You could place a longer fuel line on the tank and move it off to the side or you could use a pop/soda bottle as a temporary gas tank. To do this, you will need to make some kind of fitting that runs from the neck of the bottle to your fuel line to the carbs. An idea I just thought of is you could drill a hole in the plastic screw-on top of the container, insert a fuel line and seal it up with a gasoline-proof sealer of some kind. Then, fill the bottle with some gas, flip it upside down (so the top part with your fuel line is facing down) and poke a hole on the other end so air can get in. Hang it somewhere and away you go!

Just remember, in case of disaster, have a fire extinguisher on hand.

I should really do that next time I fiddling with my fuel system. :oops:
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Unread post by poppygene » Wed Apr 06, 2005 9:55 am

sabbath wrote:Excellent post. Any suggestions on how to get fuel to the engine safely with the fuel tank out? The whole deal sounds kind of dangerous.
I use a fuel tank off an old lawnmower motor. The kind that have a shutoff are the best. Just attach a longer piece of tubing in place of the regular fuel tube and bungee it to the handlebar or the back of a chair, etc. Just needs to be higher than the carbs for gravity feed.
Let me get this straight... it's one down and four up, right?

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Unread post by 2 Wheel Virgin » Wed Apr 20, 2005 6:55 am

sabbath wrote:Excellent post. Any suggestions on how to get fuel to the engine safely with the fuel tank out? The whole deal sounds kind of dangerous.

I used a 20 ounce pop bottle with a nipple that comes on bottles of gear lube (threads match). Filled it about 1/3 of the way, stuck the nipple into the hose going into the carb, turned it on end and tied it to the frame with a piece of wire. I zip tied it the first time but that is a pain when you need to add more gas, so I recommend tieing. Also put a small pin hole in the side at about the half way mark for ventilation. Make sure it is in the middle so when you disconnect it and go to sit it down gas won't come out of the vent hole.
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Unread post by Skier » Wed Apr 27, 2005 12:33 am

Would anyone be interested in pictures of my syncer in action? My carbs are out of balance again ( :frusty: ) and I need to get them taken care of before a long ride on Saturday.
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Unread post by Telesque » Mon May 23, 2005 3:51 am

Skier wrote:
sabbath wrote:Excellent post. Any suggestions on how to get fuel to the engine safely with the fuel tank out? The whole deal sounds kind of dangerous.
You could place a longer fuel line on the tank and move it off to the side or you could use a pop/soda bottle as a temporary gas tank. To do this, you will need to make some kind of fitting that runs from the neck of the bottle to your fuel line to the carbs. An idea I just thought of is you could drill a hole in the plastic screw-on top of the container, insert a fuel line and seal it up with a gasoline-proof sealer of some kind. Then, fill the bottle with some gas, flip it upside down (so the top part with your fuel line is facing down) and poke a hole on the other end so air can get in. Hang it somewhere and away you go!

Just remember, in case of disaster, have a fire extinguisher on hand.

I should really do that next time I fiddling with my fuel system. :oops:
I've seen this idea done before with different things, but remember: Save the cap! You might not be able to use the bottle again (since it has a hole in the bottom, now) but you can always save your 'modified cap' for next time, and just find another bottle to use.

I prefer using this method over pre-made screw-on nipples (like gear lube bottles) because you can pinch off the tubing to stop the gas flow, even if it's not connected to the gas line.
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Unread post by CentralOzzy » Sun Jun 05, 2005 8:31 am

Carbies? ie. More than one??

They are like Chain drives....who need em?

Bah!








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Unread post by txbadboy » Thu Jul 07, 2005 2:02 pm

as im still learning the different aspects of mechanical differences between cars and motorcycles...whats the difference on carbs? CV and slide is what ive heard..not sure if this relates, but on my carbs (theres 2) they say VB. theyre Keihin, of course. any ideas?? as far as cars, the differences are fairly minimal :P bear with me!
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Unread post by eugeart » Wed Jul 20, 2005 3:40 pm

This is a great series of posts and highly imformative. The tubing and ATF is a great direction to go in any case. No harmful mercury to be exposed to. I'm sure I'd rather not ingest any ATF though so be careful.

Concerning the fuel tank removal and alternate fuel source. I've always just edged the tank to the side but it made me nervous and I can see where it could be dangerous and even impractible.

Ever see a plastic bottle after its had gasoline in it for even a brief period of time? It begins to melt. Using such a flimsy container could have adverse effects in your garage I.E> explosions if it were to release and vaporize.

I thought, what would be a better, more simple and elegant solution? Well we've all seen those tiny plastic gas cans that hold a pint or two that are meant to store gas in! Go to a hardware store and find some sort of brass valve/petcock that will fit your longer fuel line, drill a hole in the lower side of the container and attach petcock. Rubber washers and or epoxy can seal the arrangement. It'll have a an airtight arrangement with a vacumn release already built in!

While not perfect and I'm sure there are flaws in this setup (I actually haven't made this device yet) I feel the approach is a safer, more usefull permanent addition to the garage DIY'r set of tools. Out on the road or in a pinch a coke bottle is a emergency solution and perfectly fine albeit a fire hazard.

Even better, if you have access to a broken lawn trimmer or the like the plastic gas tank of perhaps 10oz capacity might be a better choice for adaptation.

Just some ideas from a man who'd rather make his own tools...
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Unread post by Skier » Thu Aug 04, 2005 11:45 pm

eugeart wrote:(Truthful words).
I entirely agree with you. I was going to give a ring to a lawnmower repair shop the next town over and see if I can scavenge a tank, it'd sure be safer than a pop bottle.
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Unread post by revcbl » Sat Oct 08, 2005 9:55 am

Hopefully this isn't off-topic, but I balanced the carbs on my cb750 last weekend for the first time with a standard mercury manometer. The fluctuations were so large that I had trouble getting an accurate reading. In my clymer manual there's a drawing of a tin can damper (to be used with their diy water manometer). Looks like just a 12 oz. can with a hole in each end to accept hose connections. Would putting this in-line to the manometer level out the readings? Is there a better cheap option? Are those fluctuations just par for the course?
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carb balancinf cheap question?

Unread post by were trees » Thu Mar 16, 2006 5:23 pm

on carb balancing.
75 cb 550
putting the tubes in the 5mm holes at the intake?
any one have a cheaper option the buying the screw in tube adaptors?
and rejetting for buying new exaust how do i know if i need to and and which jets to get

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YICS

Unread post by padedwalls » Sat Apr 08, 2006 4:40 pm

This method is not able to be used with Yam's YICS correct? Unless you have the YICS tool, to isolate carbs,......correct?

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Unread post by Beach » Sun Aug 06, 2006 10:17 pm

Anyone know if I can use a sphygmometer, or a pair of them to balance carbs? Its a device used to measure blood pressure in MM of mercury. It goes up to 300 MM / HG. These are available for about $20 and up. I have some laying around.
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How do the carbs become out-of-balance?

Unread post by koconno2 » Tue Sep 12, 2006 2:19 pm

I hope someone is still answering this string. This seems like great information for old bike owners like my self. I have a 81 Honda CX650 with two carbs. I have very little experience with motorcycles and since I have the engine removed from the bike for an alternator R&R I thought I should tune the carbs after the reassembly.

What causes the carbs to become out-of-balance to start with? Are there worn out parts that should be replaced first?

Are both ends of the manometer attached to the carbs?

Do you attach the manometer to manifold vacuum or venturi vacuum?

Could I use vacuum gages instead of a manometer?

Thanx, KPO.
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