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Old 05-10-18, 05:05 PM   #1
watsoc
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Default '99 SV650S Carb Balancing Issue

Hi all,

I've just attempted to sync the carbs on my 1999 SV650S for the first time since the bike has been in my ownership (therefore no reference as to what they were like before). The front cylinder seems to pull substantially less vacuum than the rear and to get the carbs anything close to balanced (still not perfect) I had to remove the adjustment screw completely.

I followed the blueproof guide to fitting extension lines and have checked all the obvious stuff like the fittings on the vacuum gauges and the vacuum hoses both in terms of condition and length. I have also tried swapping between the 4 gauges on the synchronizer to make sure that there was no error being introduced by the tool itself. This all checked out ok.

Valve clearances were checked about 800 miles ago with the front cylinder being tight on both inlet and exhaust. They were re-shimmed accordingly and when reassembled were bang in the middle of the specified tolerance range. Compression came back at just over 200psi per cylinder

I've had the carbs off cleaned the float bowls and jets (I think it might have been dynojetted as its running 144 mains) and checked the idle mixture adjustment against spec which was at 3 turns out from lightly seated rather than 2.5. the bike had been running smoothly and the plugs were a good colour so I was reluctant to change this.

I removed and cleaned the choke plungers and made sure that they were running freely and bunged some hi-temp automotive silicone around the front boot in a half-arsed attempt to seal up any vacuum leak resulting from a perished boot. Re-assembled rechecked and it's exactly the same. The only thing I did notice was that there is a bit of play in the front pivot of the throttle linkage is this normal?

Its a bit of a funny one as the bike is running smoothly I'm just concerned that there is something sinister bubbling away ready to rear its ugly head. Have I missed something really obvious?

Thanks in advance

Chris
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Old 05-10-18, 05:18 PM   #2
R1ffR4ff
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Default Re: '99 SV650S Carb Balancing Issue

There is some inaccurate information around on balancing these carbs.

Both tubes on your balancer must be the same length.If you have made them of different lengths they will give a false reading.

I use a Carbtune 2 that comes supplied with the correct restrictors that fit inside the tubes close to the throttle bodies.

http://www.carbtune.com

http://www.carbtune.com/carbcust.html

Without restrictors the pulses will be too much and give false readings also.
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Last edited by R1ffR4ff; 05-10-18 at 05:20 PM.
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Old 05-10-18, 05:26 PM   #3
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Default Re: '99 SV650S Carb Balancing Issue

Dunno, but: http://forums.sv650.org/showthread.php?t=96892

they mention the the linkage arm causing problems if sloppy (13553-19F00-000).

You covered the boot with silicone - did you see/suspect a leak? All rubber perishes with age but I would have thought a leak would have shown itself with exhaust popping.
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Old 05-10-18, 05:54 PM   #4
watsoc
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Default Re: '99 SV650S Carb Balancing Issue

The total tube length from vacuum take-off to gauges is identical but they are the dial type rather than the carb tune style. Its a set for 4 cylinders and I have substituted all the component parts for one and other (ball valves attenuator valves etc) and tried using different gauges and the reading is always the same so I'm fairly sure the tools aren't at fault.

Cheers for the heads up on that thread regarding the throttle linkage there is enough play for the revs to rise to 3-4k rpm from idle when the slack is taken up so I think this is the most likely cause. I hadn't discovered the play prior to taking the carbs off so the liberal use of silicone was a shot in the dark! I should have accepted that no increase in idle when carb cleaner was sprayed at the boot and no funny running probably meant it was ok! I'll investigate the linkage tomorrow.

Thanks for your help
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Old 05-10-18, 05:55 PM   #5
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Default Re: '99 SV650S Carb Balancing Issue

From the other thread also make sure there's no fault with the,"Choke Plungers" just in case but soak the screws well with rust release as they are very soft and just google them e.g SV650 choke plungers.I had no trouble removing mine as the heads were fine and I used a proper JIS Screwdriver after a good soaking and left overnight.
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Last edited by R1ffR4ff; 05-10-18 at 06:07 PM.
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