Stumble at 3k rpm after new exhaust with rejet - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 08-03-2019, 10:33 PM Thread Starter
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Stumble at 3k rpm after new exhaust with rejet

So I got a new set of Vance and Hines today. I put them on, and if I slam the throttle, it hesitates at 3k. If I go smoothly, thereís no problem. I put 140 jets with one shim in during the ear shave. How do I know how far I need to go up with the jets, without buying unnecessary jets? Thereís no exhaust leak that I could tell, and it worked great with the stock exhaust and even no exhaust


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post #2 of 12 (permalink) Old 08-04-2019, 08:54 AM
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Looks like you need to increase the pilot jet size to get a better transition from the pilot to the main.

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__________________________________________________ ____________
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post #3 of 12 (permalink) Old 08-04-2019, 12:28 PM Thread Starter
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Stumble at 3k rpm after new exhaust with rejet

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Originally Posted by Spockster View Post
Looks like you need to increase the pilot jet size to get a better transition from the pilot to the main.


I may have 40/142. I canít remember. I do remember I have one shim though. I heard that the shim helps smooth the transfer between pilots and mains. Is that an option? It is still super rich, and when it does start, it fires up immediately with no choke.
So youíre thinking 42/142?

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'86 VN750 with the following work done to it, after sitting for 19 years:
John 8:44
REV 2:9
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post #4 of 12 (permalink) Old 08-04-2019, 12:36 PM
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Rich? That's some new info.

40 pilot? New info.

I can't imagine making it richer will help at all. But that all depends on the actual situation currently in place.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
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Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #5 of 12 (permalink) Old 08-04-2019, 12:52 PM Thread Starter
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Quote:
Originally Posted by Spockster View Post
Rich? That's some new info.



40 pilot? New info.



I can't imagine making it richer will help at all. But that all depends on the actual situation currently in place.


I dug out the receipt.


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'86 VN750 with the following work done to it, after sitting for 19 years:
John 8:44
REV 2:9
REV 3:9
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post #6 of 12 (permalink) Old 08-04-2019, 02:01 PM
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Almost everyone jumping to 42/142 has been too rich.
ubertalldude and MSattler like this.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

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post #7 of 12 (permalink) Old 08-04-2019, 03:36 PM Thread Starter
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Which is consistent to the write up done. So should I try adding a second shim under the needles? Or no shims? I am surprised it didnít do this with no exhaust


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'86 VN750 with the following work done to it, after sitting for 19 years:
John 8:44
REV 2:9
REV 3:9
www.voat.co
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post #8 of 12 (permalink) Old 08-04-2019, 05:18 PM
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There's apparently enough restriction in the new pipes to make a difference.

Adding shims to the needles will make it richer. You can try to remove the shims and work from there, but you'll probably end up around 40/138-140. At any rate, you'll have to start over with the shims anyway.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #9 of 12 (permalink) Old 08-04-2019, 05:43 PM Thread Starter
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Okay. I will get those jets and let you know how it goes.


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'08 Road King Classic
'86 VN750 with the following work done to it, after sitting for 19 years:
John 8:44
REV 2:9
REV 3:9
www.voat.co
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post #10 of 12 (permalink) Old 09-23-2019, 12:06 PM Thread Starter
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So playing around with the hesitation when slamming on the throttle, I have found that using choke stops this, and it has a smooth transition. However, it pops on deceleration with the choke pulled. The exhaust is turning a nice blue as well. Doesn't the choke add more fuel, and restrict the airflow? That means it is making it even more rich than the 42/142...

'08 Road King Classic
'86 VN750 with the following work done to it, after sitting for 19 years:
John 8:44
REV 2:9
REV 3:9
www.voat.co
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