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air cut valve on carbs

Old 06-14-2019, 07:12 AM
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air cut valve on carbs

Has any one done this mod ? blocking off the port on side of carb ?
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Old 06-14-2019, 10:02 AM
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Originally Posted by wheels View Post
Has any one done this mod ? blocking off the port on side of carb ?
Im sure some one has, but not seen it done.
Why? what are you hoping to gain be removing the valve and blocking the port?
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Old 06-14-2019, 11:47 AM
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eliminating have to replace the diaphragm later I have read ,it can also cut down on popping inside the exhaust on decal
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Old 06-15-2019, 04:46 AM
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Originally Posted by wheels View Post
can also cut down on popping inside the exhaust on decal
Only if there is an air leak... its pretty simple to correct that iit really can be only one of a few things O ring, tube and clamps, or diaphragm.
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Old 06-15-2019, 05:37 AM
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Here is some great info on the what why of the air cut off valve and circuit should anyone be interested

https://www.motorcycleproject.com/te...alve_more.html

Bottom line, its removal is a short cut to avoid the cost of maintenance. Removal has no other benefit. The air cut off works very well to eliminate lean condition and backfires during hard decel..simply put It Works, when it works.
a new OEM valve assembly for the VTR is about $55 internet pricing in the US.... I have 6 pair of carbs for the VTR ranging from 1997 to 2003, all of the air cut off valves seem to be working ..none leak vacuum (diaphragm failure) all upon applying vacuum actuate the valve (so nothing is seized or binding)

On the three carb sets I've done total rebuilds on now, all had some cracking seen on the rubber vac lines feeding the air valve. I did not confirm if they were actually leaking vacuum or not..In hindsight that would have been good to do just for the info.
few mm in quality silicone hose, 4 Oetiker clamps, and 6 O rings is all I have seen is needed (plus cleaning) to restore the air cut off system to full serviceability and ready for another 10 years of riding.

$55 per valve is not cheap... if needed, but the system is a benefit and I think should be retained unless it s pure track bike and you're looking for perfection in jetting for specific circumstances and the least number of failure points possible.
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Old 06-17-2019, 06:03 AM
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I was annoyed by popping back through the exhaust bad, in have been through the carbs and snyc them ,replace all o rings and checked clamps on intake. Any other suggestions? I jetted it like your set up 175 frt 178 rear needles the same . pilots 21/4 turns . its so close just wanted it a little closer lo
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Old 06-17-2019, 08:44 AM
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I was annoyed by popping back through the exhaust bad


Check for loose or perished vacuum hose , or unplugged hose if balance hose is fitted on front pot. Dodgy gasket in manifold header or header/ link pipe connection. Carb intake manifold rubber not seated properly...
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Old 06-18-2019, 06:13 AM
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For me I got the thumb adjust fuel screws and was able to dial out the popping. I don't mind a little but mine was offensive.

Have you turned your fuel screws at all? Mine was almost totally the front carb causing the issue.
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Old 06-19-2019, 01:10 PM
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have experimented with fuel screws and will double check intake flanges thanks for everyone's help ,especially carb article
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Old 06-19-2019, 03:41 PM
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Originally Posted by Wicky View Post

Carb intake manifold rubber not seated properly...
Wouldn't that also cause driveability symptoms due to a lean condition?

I'm also having a lot of popping on decel. I had the exhaust and carbs off and now it is a lot worse than it was before. If it were an exhaust leak, wouldn't there be evidence around the area of the leak?
I also did the idle drop procedure. I'm going to try turning idle screws out a small amount.
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Old 06-20-2019, 02:29 PM
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check very closely the fitment of carbs to intake boots ,
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