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Air jet cut off...or not?


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I'm getting a little tired of the constant popping when I let off the gas. I was going to plug the AJCV but read that it will make the bike feel like it has an engine break. I don't do any track riding and a lot of my miles are on dirt roads and open trails. For those of you that have done this mod, how much have you noticed the drag on decel?

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I'm getting a little tired of the constant popping when I let off the gas. I was going to plug the AJCV but read that it will make the bike feel like it has an engine break. I don't do any track riding and a lot of my miles are on dirt roads and open trails. For those of you that have done this mod, how much have you noticed the drag on decel?

wuts ur jetting???

the ACV richens the mixture on closed throttle decels...helps to prevent popping(lean pop)

typically 68s is sufficent...or a 70 pilot w/ the ACV disabled.

๐Ÿ˜

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I'm getting a little tired of the constant popping when I let off the gas. I was going to plug the AJCV but read that it will make the bike feel like it has an engine break. I don't do any track riding and a lot of my miles are on dirt roads and open trails. For those of you that have done this mod, how much have you noticed the drag on decel?

It's similar to a Jake brake on a big rig.

When removed it's good for flat tracking down fire roads and ice racing.

If you do a lot of street riding than leave it on, but for dirt riding engine braking can come in handy.

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I have a 70s in there now.

u may be too rich...:ride:

did u test ur pilot per the sticky on the jet'n board? ๐Ÿ˜

...and/or u may have an exhaust or maybe even an intake air leak.

:cheers:

P.S. with the ACF disabled it's really not a huge difference...increased engine braking is minimal AND u may get a little better engine response when

get'n back on the throttle. ๐Ÿ˜

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wuts ur jetting???

the ACV richens the mixture on closed throttle decels...helps to prevent popping(lean pop)

typically 68s is sufficent...or a 70 pilot w/ the ACV disabled.

๐Ÿ˜

So if I block the ACV I should fit a larger pilot...but does that mean I can't tune the Idle Mixture as before? Can you confirm that with the ACV blocked and with an over-rich mixture(at idle) the mixture screw will no longer tune correctly?

I would like to try this mod but don't want a permanently over-rich idle...but I'm thinking this would be the result.

Sorry to hijack the thread but we need a definitve answer for future reference...this would save a lot of fruitless trawling...thanks.

Edited by rogervize
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u may be too rich...:ride:

did u test ur pilot per the sticky on the jet'n board? ๐Ÿ˜

...and/or u may have an exhaust or maybe even an intake air leak.

:cheers:

P.S. with the ACF disabled it's really not a huge difference...increased engine braking is minimal AND u may get a little better engine response when

get'n back on the throttle. ๐Ÿ˜

I did, and I'm about 1 turn out with the 70s...guess I could go to the 68s, but I didn't think 1 turn was too bad.

I'll double check for an air leak. I just replaced the isolator with the upgraded one, maybe I didn't get it seated the whole way...but I don't think that is the case.

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So if I block the ACV I should fit a larger pilot...but does that mean I can't tune the Idle Mixture as before? Can you confirm that with the ACV blocked and with an over-rich mixture(at idle) the mixture screw will no longer tune correctly?

I would like to try this mod but don't want a permanently over-rich idle...but I'm thinking this would be the result.

Sorry to hijack the thread but we need a definitve answer for future reference...this would save a lot of fruitless trawling...thanks.

with the ACV disabled typically a 70/70s pilot is required...the fuel screw is still active.

I did, and I'm about 1 turn out with the 70s...guess I could go to the 68s, but I didn't think 1 turn was too bad.

I'll double check for an air leak. I just replaced the isolator with the upgraded one, maybe I didn't get it seated the whole way...but I don't think that is the case.

wut happens if u turn the screw all the way in? ...does the idle drop significantly and/or idle roughly or even kills the motor??? ...if there is not a significant change at "zero turns out" compared to one or more turns out that indicates that the pilot is too large. ๐Ÿ˜

see the sticky on the jetting board and more info on the ACV can be found here>>> http://www.borynack.com/XR650R/index.htm

๐Ÿ˜

P.S. a little "burble" on closed throttle decel is not necessarily a bad thing tunning-wise...

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I can turn it all the way in and not have it die. It does stumble a bit, but won't stall. between 1 1/2 and 2 out is where it starts to choke going the other way. I think I'll order a 68s and give that a try before I plug the ACV.

On a side note...if I check the plug color at idle, it will give me an idea of the pilot jet...correct?

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I can turn it all the way in and not have it die. It does stumble a bit, but won't stall. between 1 1/2 and 2 out is where it starts to choke going the other way. I think I'll order a 68s and give that a try before I plug the ACV.

On a side note...if I check the plug color at idle, it will give me an idea of the pilot jet...correct?

that's not testing too bad(1-1.5 turns out)...maybe a tad rich BUT 68s shud be plenty w/ the ACV operational :cheers:

the 68s is the proven "go-to" pilot size for the R(on hundreds if not thousands of bikes)...also a pilot on the leaner side(vs richer) seems to have less issues w/ bogging when wack the throttle off idle ๐Ÿ˜

i'm not a plug test guy...but u might be able to get a reasonable idea w/ a new plug.

wut needle clip position and main jet r u run'n???

๐Ÿ˜

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  • 2 weeks later...

As a 'before and after' comparison this comes close.

I have done a few mods so it is not conclusive..

I found my bike('92 XR600R) had a 165 main jet fitted probably by the original owner when it was opened up. I now have changed this to a 160. PJ was 62 which is standard but the original MJ is 152 so I think this explains why the bike would stumble under full throttle at speed.(mild exhaust pipe and altitude 3000ft)

Anyway I decided to bypass the ACV to see what happens.

When I 'gun it' at low speed and then throttle off...instant wheel lock.

Not good for traction and this instant breaking is very undesirable I think.

After this brief test I am thinking that I will unblock the ACV.

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OK I blocked the ACV with RTV but this wasnt strong enough as it got sucked through. I managed to block it permanently after breaking a pointy object in there. Sealed it up again and retested the bike. I cant really ride the bike much here in the 'burbs but it appears normal and throttle response good. Strangely the mixture screw now seems to do very little..maybe just a slight reduction in idle when fully in. My SJ is 62, MJ 160, and I raised the needle a notch(4 from the top). But I thought the ACV mod would make the idle leaner and require a larger SJ?

Edited by rogervize
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OK I blocked the ACV with RTV but this wasnt strong enough as it got sucked through. I managed to block it permanently after breaking a pointy object in there. Sealed it up again and retested the bike. I cant really ride the bike much here in the 'burbs but it appears normal and throttle response good. Strangely the mixture screw now seems to do very little..maybe just a slight reduction in idle when fully in. My SJ is 62, MJ 160, and I raised the needle a notch(4 from the top). But I thought the ACV mod would make the idle leaner and require a larger SJ?

the ACV only activates on high engine vacuum conditions...i.e. closed throttle decelerations...not steady state operation.

the info given here and on Bornyak's page is for XR650R...but basic principals shud apply to simular carbs.

:banana:

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But I thought the ACV mod would make the idle leaner and require a larger SJ?

The air cut valve makes the pilot circuit richer by cutting off air that goes through the pilot jet's emulsion holes. Like Kenzo said, it only closes under high vacuum conditions like deceleration.

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