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Old April 16th, 2010, 05:11 PM   #1
Thrak
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Air cut off valve

Has anyone removed the air cut off valve from the carbs? If so, what are your impressions?

Thanks!
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Old April 16th, 2010, 08:06 PM   #2
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what's an air cut off valve?
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Old April 17th, 2010, 06:57 AM   #3
Thrak
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Its the little valve on the left of the carbs, works kind of like the petcock with a little diaphragm. It injects (or not) air into the carbs under certain conditions.

I'm not sure what those conditions are, or what its purpose is. Emissions?
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Old April 17th, 2010, 11:32 AM   #4
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I think that's the coasting enrichener.



http://faq.ninja250.org/wiki/How_a_c...a_Closed_Mouth
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Old April 17th, 2010, 11:55 AM   #5
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Quote:
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I think that's the coasting enrichener.
You are correct. It is also called an air cut off valve by some. It's purpose is to reduce popping when you close the throttle at speed. I don't know of any performance advantage by removing it other than saving a couple ounces of weight. I've seen a lot of 250 Ninja race bikes over the years and all the stock carbs have had the coasting enrichener left in place.
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Old April 17th, 2010, 12:11 PM   #6
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from what I've read in that link I posted, I don't know why you would want to remove it.
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Old April 17th, 2010, 01:28 PM   #7
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My bike will never be on the street.. so things that benefit street riders (like a coasting enricher) are of no use to me. Hopefully, I'll never be coasting.

Also it seems like this may make it more difficult to fine tune the a/f mixtures screws. Rev it up and see how it comes back to idle but this adds fuel, making the mixture not entirely dependant on the a/f screw setting.

Or, does this thing only come into effect during engine braking?
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Old April 23rd, 2010, 04:32 PM   #8
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So I removed it today and it made a HUGE difference.

It starts up in less than a full crank and it "idles down" so much faster.

May not be the best mod for the street cuz it did introduce a very small amt of off-throttle popping, but its not a big deal. The positives far outweigh the negative for me.
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Old June 15th, 2021, 03:23 PM   #9
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Hod did you remove it? Where do you rout the hoses?
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Old June 16th, 2021, 04:58 AM   #10
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If you must ask....I'd suggest to leave an otherwise functioning valve well enough alone.
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Old June 29th, 2021, 02:39 PM   #11
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Quote:
Originally Posted by Sandr View Post
Hod did you remove it? Where do you rout the hoses?
can you describe how you removed it???
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Old June 29th, 2021, 04:08 PM   #12
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Quote:
Originally Posted by Thrak View Post
So I removed it today and it made a HUGE difference.

It starts up in less than a full crank and it "idles down" so much faster.

May not be the best mod for the street cuz it did introduce a very small amt of off-throttle popping, but its not a big deal. The positives far outweigh the negative for me.

Sorry I meant to quote you. Can you describe how you removed it?
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Old June 30th, 2021, 08:08 AM   #13
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Doubt you'll get an answer, OP last seen here in 2013.

For non-Ca models....simply remove valve and applicable hoses and cap off ALL hose vac ports....2 are between carbs, 1 on outside LHS carb, and the RH carb main vac port. Done.

Suggest to use proper sized, quality caps...please NOT bolts in the ends of the hoses (sloppy)
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Old June 30th, 2021, 01:10 PM   #14
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Quote:
Originally Posted by ducatiman View Post
Doubt you'll get an answer, OP last seen here in 2013.

For non-Ca models....simply remove valve and applicable hoses and cap off ALL hose vac ports....2 are between carbs, 1 on outside LHS carb, and the RH carb main vac port. Done.

Suggest to use proper sized, quality caps...please NOT bolts in the ends of the hoses (sloppy)

Makes me seem like a complete moron. I only looked at the most recent comment on this thread from 2021 and didn't realize the one before that was from a decade ago. I was thinking to just cap off the vacuum ports. My Triumph CVK's has the intake vacuum ports capped off and then theres a hose that runs between the two carbs. I assume thats a balancing vacuum hose. do these GA15's not need a vacuum hose running between them like the CVK's on my Triumph?
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Old June 30th, 2021, 01:32 PM   #15
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What brand CV's on your Triumph?

Balancing is achieved through synch of throttle plates. Perhaps the hose you refer to was a common vent or fuel delivery hose?
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Old June 30th, 2021, 02:13 PM   #16
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The 2000s Triumphs used dual CVK40's. I have those carbs perfectly synched. I have a vacuum gauge I bought just to synch those every year or so. You just connect the hoses to the intake nipples on the carbs.

Here's the picture of my carbs on the Triumph. I'm currently rewiring the Triumph. I was t-boned in January and it's almost back together. But, now looking at them the "coasting enricherner" looks like it's part of the carbs. The hose runs to a nipple on the other carburetor. So that means I could just cap off that nipple on the Triumph Carbs also?? link here --> https://i.ibb.co/mGF1j4k/IMG-6567.jpg


Also do these look correct like you said? I capped 5 spots. 2 on top 1 on the side below the enrichner and 2 in between.

https://i.ibb.co/M2cyjKR/IMG-6563.jpg
https://i.ibb.co/rbLzrhX/IMG-6564.jpg
https://i.ibb.co/bHj0D5J/IMG-6566.jpg

Sorry about the links. I posted them as pictures and when it loaded the pictures were giant on the forum and I had to remove the [IMG] brackets so they could easily be seen.
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Old June 30th, 2021, 03:46 PM   #17
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I believe we've missed one. In the 2nd 250 pic (#6564) there is a vac take-off right below the K (in CVK) Cap that one as well.

Otherwise, good to give a try. Report please?
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Old June 30th, 2021, 03:58 PM   #18
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I will definitely report back. Probably tomorrow. The float bowl gaskets I ordered arrive tomorrow I'm pretty sure. The original ones had turned solid. So I should be able to test them tomorrow.

The one you pointed out leads nowhere. its not used so that means I'm ready to test.

Also on the Triumph. I'm going to buy some more caps and try and cap off that vacuum line and see how it runs without the hose.
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Old June 30th, 2021, 05:14 PM   #19
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So I took the hose off of the Triumph carbs and it ran pretty rich. rich enough that after my ride there was smoke coming out of the velocity stacks. another thing is that taking it off made the idle adjustment screw not do anything at all. I couldn't adjust the idle. it also made the two cylinders run slightly differently and it used to pop a lot when engine braking and now it doesn't pop much at all and it doesn't return to idle as smoothly when riding.

so I'm not sure what it does but when riding and on the the throttle it runs fine.
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Old June 30th, 2021, 05:22 PM   #20
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I'm very excited to get the ninja running though. my grandmother bought it for me right after I graduated high school. it's the first on road bike I have ever owned. it's sentimental since she bought it for me. I have been riding since I was 4 and have had many bikes but I cant get rid of this bike or my Triumph. Some idiot about 8ish years ago was riding in my lane around a bend really fast for no reason and I had to ride off the road down into a deep holler. the bike is fundamentally fine but the fairings are ugly. I'm just going to cut the rear end off and put a flat style seat on. I have an old KZ650 tank that I sat on there and it fit so I am going to make it into a light trail bike that I can do very light trail riding for fun.
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Old July 1st, 2021, 10:25 AM   #21
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Also without the vacuum hose running from the top intake nipple on the carbs to the petcock will the fuel still flow?
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Old July 1st, 2021, 03:50 PM   #22
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UPDATE:

I got the gaskets in and tested it out. I cant seem to get it to idle nicely it well idle good for a about 10 seconds and then start to dip verryyy low but not die. it revs fine and nice most of the time but its VERY slow to return to idle. like 10-15 seconds. I have tried 110 jets and 115 jets. 115 was way to rich. I'm not sure what the stock pilot jet is but maybe I need to go up on it? I have never really had to change out pilot jets before on my bikes. only main jets.
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Old July 1st, 2021, 04:28 PM   #23
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Stock pilot is #38. Doubtful whether increasing size would help at all HOWEVER adjusting pilot screws on each side for highest idle may improve your situation. Worth a try, no?

Are carbs equipped with any other mods, as in needles or shims?

Did you confirm fuel levels in each bowl to be correct?

Are pilot jets and circuits genuinely, fully clear?
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Old July 1st, 2021, 05:45 PM   #24
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I have the stock needles shimmed currently at 3mm I started at 1mm then 2mm now I am at 3 to keep it from dying but it doesn't seem to work. I am currently also at 4 or 5 turns out on the AF mixture screw. I am at 110 mains and all the caps are on the nipples we talked about before. The carbs are perfectly in sync. I did it by eye when I was first putting it all together and when the bike was hot I put the gauges on and somehow I had it in sync just by luck.. I don't have any air filters on the bike but that shouldn't really matter. I am running open intakes on the Triumph and it runs just fine. It's hot enough here right now I dont need the choke. it doesn't really do anything anyway when its this warm.

So currently:

•110 Mains (Genuine Keihin Jets)
•38 Pilots (Stock)
•All 5 vacuum nipples capped
•Carb bodies in sync
•Stock needles shimmed to 3mm
•2 Brand new float valves
•Floats set to 17mm


Thats what I have done and it just idles all over the place and takes forever to come down to idle and it will die after idling for 20-25 seconds so I'm thinking it's running out of gas with the 38 idles. It revs so I'm pretty sure the 110 is fine.

The only variable that hasn't changed is maybe getting some 42 idle jets. Surging and slow return to idle is a running lean problem so thats all I can think of. I'm definitely not lean at 110. I was pretty rich at 115 but still it ran.

42 seems big for this bike. Thats whats in the Triumph and it's a 790cc.

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Old July 1st, 2021, 06:21 PM   #25
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Had no idea you're not running an airbox. Also assume you'll be installing pods then? Oversized mains, shimmed needles and now oversized pilots? With the decel valve delete?

I dunno, just too many variables. I'll fade back outta this one.
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Old July 1st, 2021, 07:05 PM   #26
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Yes the pod filter is on its way. I stole the 42 pilots out of my other bike and threw those in and they didnt make a difference. I'm going to try some more adjustments on the AF screws tomorrow with the 42 Pilots in there. Might make a difference.

I was ran off the road a number of years ago and the fairings are ugly so I am making it a naked bike with a different tank and some slightly knobby tires. theres probably a variable that I havent thought of yet. I'm sure I will get it running eventually


EDIT:

Just as a test I put the enricher back on and it ran worse. it revs super high. It's got to be a vacuum problem. This bike has never ran that well and I'm starting to suspect theres something wrong with the carbs and or the vacuum with the carbs.

Before you dip could it be something other than carbs that you can think of?

Last futzed with by marshallsmith27; July 1st, 2021 at 08:39 PM.
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