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Discussion Starter #1
To sync carbs you have to have a pair of vacuum gauges or a dual carb sync tool (or quad tool if you have 4 cylinders). The sync tool is a clear tube for each cylinder filled with mercury that connects to the carbs' vacuum lines and are bought from motocycle accessory shops.

You hook your carb sync tool (or vacuum gauges) up to both carbs, start the engine and check to see if the readings (the height of the mercury drawn up by engine vacuum) are the same for both carbs. Check it at different throttle settings. They usually aren't the same at different throttle settings, so you just have to do the best you can to get them as close as possible to each other. You change the setting with some sort of screw that connects the two carbs to each other. I don't have a shop manual yet and don't know where it is on the 500R but you can usually find out from the shop manual.

It's important that you note where the adjusting screw is set to before you start, in case you have to set things back if you mess it up. Maybe paint a line on the screw and always count how many turns (or parts of a turn) you move it. At least with an EX500 you only have two carbs to sync, my VMax had four and a CBX1000 has six. And if you had a '66 Mustang with a 289" engine you could have eight carbs that need syncing. :)



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Just to add one thing.... you will need to supply fuel to your carbs manually because the vacuum fed petcock will not supply fuel without it connected to the vacuum line
 

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or you could literally suck on the end of the vacume line & pinch it closed with a set of locking pliers.... but you don't even really need to do that... it doesn't take all that long and you should be able to complete the job before the float bowls run out of fuel.
 

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Where on the carbs do you connect the hoses? Is it where the suction valve and fuel tank vacuum hoses attach?

That is where I attched mine during the last tune up. I noticed that at idle the vacuum was not steady with the needle bouncing a bit, but it got steady with just a little bit of throttle. Is this normal?

The bike in question is a 2005 - having had all of it's previously scheduled maintenances done on time by the dealer.

thanks

davyyd
 

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Where to connect hoses

Yeah Davyyd, the suction valve and tank vacuum lines plug into the vacuum plugs on the carbs. This is where you hook up the vacuum gauges. Its actually better if you sinc the carbs with a partially open throttle.
 

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hi i put sarachus on my bike. inoticed more exhaust coming out right pipe than left. when reved right side really racks off left dosent. is this carbs out of sync. or weak left cylinder? bikes 06 5000 miles.thanx jojo very worried?
 

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Just finished a valve adjustment.
Question on the carb sync. Is the adjustment between the carbs
and adjusted from above with a vertically held screwdriver.
See the idle adjust from middle below carbs. Not to easy to get to also.
Confirmation re Idle adjust screw appreciated.
Thanks, Alan
 

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yes, its on the throttle spring thingy (thats a very technical term) adjusted from above.

make sure you dont push down on it while you are turning it, or you get a false reading.

i found the best way was to reach under with one hand and hold it up so i didnt push it down, then use the other hand to operate the screwdriver.

go slowly. make small turns.
 

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More questions on sync-ing carbs.
Used a large open syringe stuck vertically into fuel line to hold extra gas.
As engine cold reluctant to take it up to far.
Would like to check at 6000/7000 revs as range most operated in.
Next time I have tank off I will put capped T fittings in vacuum line just above carbs. This will allow the hook-up of my Twinmax so I can check it
on the fly..What are thoughts on this? Will look for a flexible screwdriver
(if such a thing) to assist getting to adjustment with tank in place!
Alan
 
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I have one of these... http://www.carbtune.com/index.html

But I have the Carbtune II version. Works excellent. I figure I'll always have a bike (or two or...) so why not spend a little extra $$ on good tools; one DIY valve adjust and carb synch. pays for the tool instead of paying the dealer to do it.
 

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I use a small gas can with a screened petcock and some fuel line to gravity feed fuel to the carbs. All lawnmower stuff. I also made a vacuum gauge years back with fuel hose, two stroke oil and a yardstick for tuning my ultralights. I care less about the actual vacuum number and more about the difference. Oil jumps some because it's lighter than mercury but also makes it more precise.

I fiddle with a lot of engines so having something like this is useful for more than just the bike. You don't need much time to sych up the carbs so the volume of fuel in the can is more than needed but man if you're trying to get another season out of your POS Murray lawn tractor then it's a treat to work with the engine running off the machine.

The spec is to tune at idle but FOG pointed out that there is flex in the carb linkage so I twist ever so slightly take that out.
 

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This is the other procedure I was going to do tonight after adjusting the valves.

I built the two container assembly with a hose between them and a hose from each to the carb vacuum ports. I didn't have any small jars handy but what I did have were two clear plastic water bottles. I purchased some clear flexible tubing and drilled some holes in the lids of the water bottles, carefully hot glueing the hoses into the lids so they were leak free. I then put enough water in so that I could suck it from one to the other with the water level dropping enough that it wasn't able to be taken up by either of the vacuum hoses. I tested this carefully and then connected it to the carbs after removal of the fuel tank.

I fired the engine up and with some amount of dismay, watched the water bottles instantly collapse under the vacuum and just as instantly, the water being sucked up both the hoses due to the now higher level in the collapsed bottles.

Shite!

Shut the engine off and after a bit of cranking, got it to fire up despite the water. Not really the way I intended to decarb the cylinders.

I guess I need some stronger containers.

BCmcrider
 

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I tried using oil in a clear tube and it turned to froth within a few seconds and just stuck to the side of the tube with all the air or vacuum running through it. I'm getting a pair of vacuum gauges from McMaster-Carr to retry it.
 

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BCmcrider said:
I fired the engine up and with some amount of dismay, watched the water bottles instantly collapse under the vacuum and just as instantly, the water being sucked up both the hoses due to the now higher level in the collapsed bottles.

Shite!

Shut the engine off and after a bit of cranking, got it to fire up despite the water. Not really the way I intended to decarb the cylinders.

I guess I need some stronger containers.

BCmcrider
yeah glass is a bit stronger than plastic :) go down to the corner store and get 2 snapples, or iced teas... hell even corona bottles would work :)
 

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psyco1 said:
I tried using oil in a clear tube and it turned to froth within a few seconds and just stuck to the side of the tube with all the air or vacuum running through it. I'm getting a pair of vacuum gauges from McMaster-Carr to retry it.
I found that a u tube water manometer was next to useless in trying to sync my carbs. The problem is that the vacuum pulsations cause the same problem you describe, that is, the water gets more and more air entrained in it with each pulsation and eventually (ie 3-4 seconds) gets sucked out one end or the other. Maybe it's the diameter of tubing that's the problem. After air gets entrained, it takes about 3-4 minutes to get all the bubbles out of the tube so you can start again.

Since my previous post, I made the two jar device http://faq.ninja250.org/index.php/Is_there_a_carb_sync_tool%3F using glass jars and have to say it works great. I hung it from the ceiling above my bike with the hoses all connected up. This made it very easy to watch as I held the throttle slightly open between small adjustments.

The other thing I did was to run long clear fuel and vacuum lines from my mc to the connections on the gas tank sitting on the workbench next to the bike. This way, I didn't have to worry about running out of fuel while trying to figure out the best setting for the sync screw. This also allowed me to test my petcock operation.

To test the petcock in all positions, I started with the fuel line connected to the carb fuel connection and the vacuum hose connected to the tank but disconnected from the carb. Using my mouth to draw a vacuum I was able to verify that no fuel came out when in the off position. With the same connections but the petcock in the on position, a bit of vacuum draw caused the petcock to start providing fuel. The same test in reserve position also verified the petcock operation.

At the time of these tests I had about 2/3 of a tank of fuel so the result may be different with a nearly empty tank.
 

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Also this is my setup to sync the carbs with



two glass arizona iced tea bottles, with rubber stoppers in them, 2 holes drilled in each rubber stopper. The bottle on the left goes to the left carb, right to right.

The long rubber tubes going to each carb barely make it into the bottle past the rubber stopper, I dont want oil to have any possibility of pulling into the carbs.

The smaller rubber tube shared between teh 2 bottles goes all the way to the bottom and exchange oil between the two bottles.

I was able to suck oil from one to the other with some effort.


I am not sure which is the screw i need to turn to sync them, I am guessing it is the one in the picture in the post above, and where the green screwdriver is in the synctool picture

The plastic water bottle on top of my engine will hold the fuel. I have to siphon fuel out of it and when it enters the tube (before i drink any) I squeeze the tube and connect it to the fuel filter.

There is my complete carb sync tool.
 

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Can anyone confirm that that is the screw?

I am adjusting it, and the left carb sucks tons more than the right one, so much that it empties the bottle in about a minute and transfers all the oil to the other one.



Confirmed it is the screw

My carbs are now synced
 
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