Carbureted motorcycle jetting questions?
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  1. #1
    Seat Tester
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    99 xvs 1100 vstar custom
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    Question Carbureted motorcycle jetting questions?

    ok, so i have a 99 xvs-1100 v-star custom. I have modified the factory exhaust. Rear baffle has been removed and the forward 2 have been drilled full of holes. So very little back pressure. I have removed the factory intake and have installed pods. Removed the ais system. I am having trouble Jetting the carbs. I have synchronized them and adjusted the valves. I have 17.5 pilots, 150 mains, 3 turns out on pms screw. 3 washers under the needle as well. the rear cylinder takes awhile to catch when its cold. Both cylinders have 130 ish psi of compression. I do not know if this is lean or rich. It pops through the intake sometimes. it did exhaust pop on decel untill i turned the pms screw out slightly. My has a batwing, hard bags and a trunk. my last tank i got 30mpg, but i was driving "spirited" and checking top speed. Which was higher than before. I also do not believe it has aftermarket cams. Any help is appreciated. will answer any questions yous guys have. Thanks.

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  3. #2
    M-J Lifetime Achievement Award
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    Just to clarify what is the pms screw you refer to.

    The cold start problem may be the idle jets being blocked. A good dose of carb cleaner may solve this. As for the popping any mod on the exhaust...esp baffle removal will almost always cause some of that. It isnt a good idea to run with straight through pipes...most of the silencing is to appease authorities but a degree of it is to provide good exhaust flow.

    You should get some idea of how rich the motor is running by doing a plug chop. The needles being raised by three washers seems a bit extreme. As for the mains and other jets it would be wise to find out what the specs are and if necessary doing small changes from those.

    good luck
    Smoke me a kipper I'll be home in time for breakfast

  4. #3
    Seat Tester
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    i think its called a pms screw. it adjusts fuel throughout the whole throttle range. The exhaust still has some restriction. I had drilled the pipes before the rejet and it ran fine.(although it was a tad on the rich side) only rejetting because of the intake change and ais removal. I suppose i may have dislodged something in the fuel line and it plugged something. there is many idle circuits on these carbs. It only does it when cold. i have removed one spacer from the needle. each is 2 thou thick. the kit i purchased recommended 22.5 pilots, 150 front 147.5 rear mains, and 4 shims. The rear cylinder did not want to ignite at idle. and was blowing black smoke. the flames were cool though. so i dropped 2 in pilots and it helped. im a nube at jetting. (can you tell) so you recommend a plug chop? How exactly do i go about doing this.
    Quote Originally Posted by Aussie Steve View Post
    Just to clarify what is the pms screw you refer to.

    The cold start problem may be the idle jets being blocked. A good dose of carb cleaner may solve this. As for the popping any mod on the exhaust...esp baffle removal will almost always cause some of that. It isnt a good idea to run with straight through pipes...most of the silencing is to appease authorities but a degree of it is to provide good exhaust flow.

    You should get some idea of how rich the motor is running by doing a plug chop. The needles being raised by three washers seems a bit extreme. As for the mains and other jets it would be wise to find out what the specs are and if necessary doing small changes from those.

    good luck

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  6. #4
    Ditch Magnet
    My Bike(s)
    2002 SV-650N, 2007Yamaha 1100 custom
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    https://sites.google.com/site/vstar1...r-must-do-list read this must do list. never give it throttle when starting.. and check the mid shaft nut it sometimes comes loose and can lock the rear wheel.. there are sections on tuning and jettings. everything you need to know about the 1100 is here.two shims with pods.17.5 or 20 pilot jets 3 turns out on the screws and you can turn them out until the decell popping stops. in the jetting section there is a chart which tells about how to jet for pods and pipe mods.

  7. #5
    M-J Lifetime Achievement Award
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    A plug chop is where you ride the bike at moderate speed for around ten to fifteen minutes. Pull in the clutch and cut the ignition then coast to a stop with the clutch pulled in. This gives an indication of the fuel getting into the engine at mid throttle settings without any slowing down through the gears and thus lower throttle settings.
    Smoke me a kipper I'll be home in time for breakfast

  8. #6
    Super Moderator

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    Quote Originally Posted by Aussie Steve View Post
    A plug chop is...............
    Or find an old mechanic who still has an exhaust gas analyzer and knows how to use it.
    Don't believe everything that you think.

  9. #7
    Seat Tester
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    thanks for the help.
    Last edited by DivineChaos; 03-28-2019 at 03:11 PM.

  10. #8
    Seat Tester
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    well turns out i was lean at idle and way rich at wot.

  11. #9
    Ditch Magnet
    My Bike(s)
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    i have full cobra exhaust, 3 and a quarter on the screws.if i let the bike sit for an hour after a ride sometimes i'll get a pop thru the carbs. 20 pilots but some guys in the past couple years are running 17.5..mine have been in for about five years and no complaints. two shims 0.05 total,150 on the front and rear mains. k&n pods.my plugs are almost white ethinol burns clean so i backed the screws out until i got a little color.

  12. #10
    Seat Tester
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    Quote Originally Posted by nickbehavin View Post
    i have full cobra exhaust, 3 and a quarter on the screws.if i let the bike sit for an hour after a ride sometimes i'll get a pop thru the carbs. 20 pilots but some guys in the past couple years are running 17.5..mine have been in for about five years and no complaints. two shims 0.05 total,150 on the front and rear mains. k&n pods.my plugs are almost white ethinol burns clean so i backed the screws out until i got a little color.
    mine still pops through the carb sometimes. im running 20 pilots, 147.5 front and 145 rear. 2.5 out on screw. i was trying to figure out what shims were stock on it. it had a thick white one, a small silver and a really thin white one when i pulled it apart. so it had been messed with. i dont want to do too much till the temp comes up. if its on the lean side while its cold, it should ritchen up when the temp is in the 80s. its in the 40s now. what do you get for mileage?

  13. #11
    Ditch Magnet
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    https://sites.google.com/site/vstar1...g/carb-jetting if you scroll down there's a picture showing a needle with two shims below the plastic spacer. stock it comes with one shim when you go to pods you add one shim for a total of two. your pilot can be 17.5 or 20 people are running both. your lean on the screws you should be at 3 turns or more.. i'm getting about 45 mpg.i switch from reserve anywhere from 130 to 155.

  14. #12
    Seat Tester
    My Bike(s)
    99 xvs 1100 vstar custom
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    land of 10,000 lakes
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    Quote Originally Posted by nickbehavin View Post
    https://sites.google.com/site/vstar1...g/carb-jetting if you scroll down there's a picture showing a needle with two shims below the plastic spacer. stock it comes with one shim when you go to pods you add one shim for a total of two. your pilot can be 17.5 or 20 people are running both. your lean on the screws you should be at 3 turns or more.. i'm getting about 45 mpg.i switch from reserve anywhere from 130 to 155.
    so you have a 17.5 pilot? So i still have 3 shims on the needle. is your mpg at 65mph? or you running slower?

  15. #13
    Ditch Magnet
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    i have 20 pilots, i run two lane blacktop.60,65.rolling hills,4th gear most of the time,4,000 rpm. if i go on the interstate i'll keep it at 70,75.

  16. #14
    Seat Tester
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    Wel i got 40 mpg on my last trip. was 80 miles hwy, and 40 in town. before i was switching to reserve about 118 miles. now im in the process of making tru duals for it. will be loud (no mufflers) till i get my drag pipes.
    Quote Originally Posted by nickbehavin View Post
    i have 20 pilots, i run two lane blacktop.60,65.rolling hills,4th gear most of the time,4,000 rpm. if i go on the interstate i'll keep it at 70,75.

  17. #15
    Ditch Magnet
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    if someone messed with it they may have changed the needles if so it will be hard to tune it easily. with mikuni needles the jetting is written done if you have dyno needles you will have to try to match the jets and settings to each circuit by seeing how it runs.


 
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