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  1. #1
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    Default Carb tuning problems

    Hey guys, i could use some of your infinite wisdom on how to properly tune my carb. Im new to bikes and carbs are definitely not my specialty. Ive read a bunch of other threads on tuning and tried tuning it a bunch of ways but it really mind boggling how no matter what i do it always struggles somewhere. Obviously everyones bike is different so it wont be the same for everyone, id really appreciate some guidance on what to try.

    Heres what i have done to the bike so you can get a better idea what might work for my situation

    - Filterwears pre-filter
    - 4 velocity stack
    - 6sigma Carb jets (48-175) *do not recommend kit*
    - Needle shimmed to .045
    - Dans Allen head bolt kit
    - Air fuel EZ-mix screw
    - Dans Superboot
    - Carb brace (carb springs)
    - NGK Iridium spark plug
    - Vance and hines exhaust (packing blew out)

    Last night i went on a group ride with some friends and i know its got to be running lean in the mid range because my carb blew itself off 3 times. Under heavy load it bogs down like its flooding the cylinder, and at high speeds i can barely hit 80 mph and then it will start bucking like its flooding and then all combusting at once.

    I want to order the yost kit to dial it in properly but have to wait until i get paid to order it this week. Obviously i know it needs to be re-jetted but i dont know what ones id be looking at changing to cure the problems. I have 42, 48, 162, 175, 180, 190 jets right now. Do you think adjusting timing could help at all? If so, could you share a link to that thread please?

    Thank you all for any suggestions and advice!

    Heres a pic of my velocity stack
    Attached Thumbnails Attached Thumbnails 95FAD859-BB4E-466C-BD79-78C5197546B8.jpeg  
    Last edited by NotSoFastBlast; 08-31-2020 at 04:29 PM.

  2. #2
    Racer styxnpicks's Avatar
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    don't adjust timing. its likely where it needs to be.

    start with tuning the main jet first. if you cant go faster than 80mph at wot than your main is either too lean or too rich... be methodical. try either a step up or step down.. better or worse? worse go back! better keep going

    if you really want to get serious about tuning put a wideband on it. it will tell you what your a/f is at so your not shooting in the dark
    Buell XBlast: NRHS Xb Stage 2 lite, 515 10.5:1, .551 cam, Daytona Twin 1005s-Ex, Vance Hines, Crossroads Fork Brace + Rearsets. Pirelli Rubber
    Buell XB9r: Race ECM/Muffler. K&N

  3. #3
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    Quote Originally Posted by styxnpicks View Post
    don't adjust timing. its likely where it needs to be.

    start with tuning the main jet first. if you cant go faster than 80mph at wot than your main is either too lean or too rich... be methodical. try either a step up or step down.. better or worse? worse go back! better keep going

    if you really want to get serious about tuning put a wideband on it. it will tell you what your a/f is at so your not shooting in the dark
    I was definitely thinking about a wideband. Ive seen kits for around $190. My only issue is that id have to find someone to weld the bung on.

    I tried taking off the pre filter today and its definitely A LOT better, but now surges at low speeds.

  4. #4
    Racer styxnpicks's Avatar
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    surging at low speeds could be the pilot but is more likely the needle shim. the shim really makes alot of difference in low speed ridability right around where you cruise if your lugging the motor
    Buell XBlast: NRHS Xb Stage 2 lite, 515 10.5:1, .551 cam, Daytona Twin 1005s-Ex, Vance Hines, Crossroads Fork Brace + Rearsets. Pirelli Rubber
    Buell XB9r: Race ECM/Muffler. K&N

  5. #5
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    Quote Originally Posted by styxnpicks View Post
    surging at low speeds could be the pilot but is more likely the needle shim. the shim really makes alot of difference in low speed ridability right around where you cruise if your lugging the motor
    I just ordered the yost kit today, im hoping that it will make fine tuning a lot easier, but ill take any and all suggestions! Lol

    I have read a TON of different threads on it and obviously we all need different tuning. So i had it shimmed to .45 before and it was really bad at hitting any high speeds. I dropped it down to .015 and it seems a little better but struggling in the low end.

  6. #6
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    UPDATE: i installed the yost kit and decided in going to get a wideband to tune and dial in everything properly. i orderd the aem wideband kit and the glowshift clamp on 1-3/4" bung so i dont have to try to weld a bung on my vance and hines exhaust. (ive seen people say it was really difficult because the metal is so thin) when i install the o2 sensor do i need to try to have it close to the head or will anywhere be fine?

  7. #7
    Racer styxnpicks's Avatar
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    my bung ended up about where the front tie bar is. maybe slightly higher. I had mine welded in by a competent independant local muffler shop. I think I paid 20-50ish to have them weld the bung in. carried the header in marked where I wanted it
    Buell XBlast: NRHS Xb Stage 2 lite, 515 10.5:1, .551 cam, Daytona Twin 1005s-Ex, Vance Hines, Crossroads Fork Brace + Rearsets. Pirelli Rubber
    Buell XB9r: Race ECM/Muffler. K&N

  8. #8
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    Id do it myself but i dont have a welder here, when i moved i went from a 6 car garage down to a tiny 1 car garage. Unfortunately had no room.

    So i moved the clip to the 4th from top and it didnt go to well. Was definitely running way to rich. I came back home and moved it to the 2nd from top position and used the included shim, DEFINITELY getting a lot better now. When im just cruising through the town it seems to be sluggish at low throttle, but really improved mid range.

    Im thinking if i drop the jet to a 46 instead of the 48 i have in it now it would help. Right?

    Wideband will be here tomorrow. But unfortunately the bung wont be for at least a week or so. I was looking at the header and i was thinking that it would fit right after the initial curve and be able to stay hidden (dont want some ugly botched exhaust) lol
    Last edited by NotSoFastBlast; 09-09-2020 at 07:17 PM.

  9. #9
    Racer styxnpicks's Avatar
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    the cv carb is kinda sluggish by nature down low. it could be jetting or it could be how it is. it kinda takes a second to build vacuum before it responds. the main thing is to remember to start with the main and work down from there. I found the needle and shim are effective for almost all cruising 1/4 throttle to 3/4. idle mixture screw actually only has an effect on idle mixture... and the pilot jet really only changes tip in.. making little difference by the time your at 1/4 throttle the wideband once installed will give you data you didnt have and youll be able to go from there. for examble I had a 180 main and was running pig rich 10.5:1 WOT... im down to a 160 now and still 12.5:1 rich at WOT
    Buell XBlast: NRHS Xb Stage 2 lite, 515 10.5:1, .551 cam, Daytona Twin 1005s-Ex, Vance Hines, Crossroads Fork Brace + Rearsets. Pirelli Rubber
    Buell XB9r: Race ECM/Muffler. K&N

  10. #10
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    Thanks styxn, to elaborate what i was trying to say. The bike runs fairly well, but when cruising in low to mid rpm and opening up the throttle to get it to really move (To get away from bad drivers) it seems extremely hesitant. It gets louder, lower pitched, thumps a lot harder, and seems like its having a hard time.

    EZ told me to drop down to the 45 instead of the 48. So im going to try that while waiting on the afr install. I started fabrication of a dash today (also adding a voltmeter i had from a previous build) when i get the bung ill get it all hooked up and see what it says. And obviously ill post some pics of my new cluster.

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