Saturday, January 18, 2014

Walkthrough on balancing the throttle bodies on a GSF1250

Here's a walkthrough on adjusting the throttle bodies on a GSF1250.  Works for the FA and the GSX650F and water cooled injected 650 Bandits.  As with anything mechanical, this is my experience, yours may differ, and you do this at your own risk etc.

There's 3 options to balance the TBs.  The first is what is recommended in the Haynes Manual, which gets you to put the bike in dealer mode with the switch above and connect the balancer.  This has the IAP sensor (number 1) disconnected and it throws fault code C13.  It works OK.

The second is to use the suzuki SDS software and follow the steps in the dealer manual.  The problem is most of is don't have the SDS.

The third is to apply vacuum to the IAP sensor so the bike thinks its pulling vacuum.  What I am showing is a variation on this that gets the bike to pull its own vacuum via a T piece on the Carbtune.

In short there's a few ways to do this.  What you can't do is pull the vacuum hoses off and just connect the Carbtune, as the vacuum hose to the IAP won't be there and the bike will have a tantrum about it and not run properly or idle.

Firstly, remove the right hand side cover and connect the Suzuki test switch (cheap on line and a good investment) and check for fault codes.  You don't have to do this, but it's peace of mind and your bike will tell you if there's any fault codes. I will post the codes in a separate post.  Here's the connector:


and here it is with the switch connected (a paper clip works too)


You turn on the switch and if the TPS is correctly adjusted, you get -C00 as you see below.  I have how to adjust it elsewhere on the blog.


You then remove the fuel tank.  I suggest sitting it between two chairs as it won't sit on a flat surface


To prop the tank up on the bike you can use bits of wood or get the tank props from Scott at Metrick Metal (www.metrickmetal.com)


Get a carb balancer.  I recommend the Morgan Carbtune.  Remove the 4 vacuum hose connectors off the throttle bodies, and connect number 1 (left side), to number 1 on the Carbtune, and so on.  What I did was put a T in the number 4 hose and connect this to the vacuum on the IAP sensor.  This means no messing round putting the bike into test mode or trying to pull a vacuum on the IAP.  The bike does it for you, and in my view it most closely replicates normal running conditions.

I am pointing at the IAP (number 1) here


And here it is off the bike and connected to the Morgan Carbtune (I have an extra IAP sensor that lives with the Carbtune). 


Connect the  number 4 line in the normal manner and connect the electrical connector to the IAP as well.  You will see that the number 4 line pulls vacuum to the IAP so the bike thinks it is all connected.  Simple.

Once connected, prop up the tank, and turn on the bike.  I then go and do things like lube the chain until the bike warms up enough to trigger the fan.  


After the fan kicks in, wait for it to turn off again.  The bike is at operating temperature.  Check the readings.  This wasn't too bad, but still room for improvement.  I use no. 2 cylinder as the base line


Use a small screwdriver and gradually adjust each cylinder.  The bronze screw is shown below in the middle of the pic and there's one on each throttle body.  Screwing in makes the tube rise. Just a fraction of a turn and you will find each throttle body has an impact on the others so you need to go back and forward a bit.  If your bike is out you will hear the idle smooth consideably.

When you think it's right, blip the throttle.  Don't do any adjusting when the fan is on either.  When you blip the throttle, the tubes won't settle evenly, so there may be more adjusting to do.  Take your time.  It's not hard, but check each time you think all is good by blipping the throttle.

If you stuff up, screw the number 2 air screw in till it seats, back it out 1.5 turns and adjust the others to that.  There's no vacuum reading as such, just get them all the same.



Here's where I got mine to this afternoon.  These things are out of whack from new and it makes a lot of difference to idle, clutch rattle and low speed running.


After you finish, reconnect the vacuum lines, check and check again, reconnect the fuel line, electrical connector and vaccum hoses and bolt the tank back on.  Make damn sure the fuel hose positively clicks on, as if they part company under pressure, it means fuel on a hot engine and your back tyre - i.e. potential crash and burn scenario.  Be safe and make sure all fuel lines are well clicked on.

Once you are all connected up, check the bike runs OK (rough idle, failing to idle is either a vaccum hose off or you forgot to reconnect the IAP)  Go to a friend's for a barbeque and go for a ride in a 1912 Renault.

It was a good day.























1 comment:

  1. I plan to buy a Morgan Carbtune and sync my Bandit 1250 soon using the T connector in the #4 hose and connecting to the IAP for vacuum method. To splice in the T, did you cut off the end of the Carbtune's #4 line and use that to connect to the IAP? If so, about how much did you cut off? Also, is the advantage of this method because it provides a smoother idle so the tool gauges are easier to read during the sync, or does it actually provide a more accurate sync and a better idle after the sync is done?

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