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Cafe racer build/carb swap

Discussion in 'XJ Modifications' started by Mustangmaster98, Feb 14, 2018.

  1. Mustangmaster98

    Mustangmaster98 New Member

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    Hey everyone I just picked up another 1982 Yamaha xj750 maxim as a parts or repair bike, originally I just wanted to used the carb rack for my other 82 maxim as my previous rack had a cracked carb. The more I think about it though I want to build this bike into a cafe since I have a clean title. The issue is the old airbox doesn't fit the look and pods are a no no on CV carbs. so my question is can I get a rack of carbs to fit my bike that will work well with pods or velocity stack filters? If I save this bike it'll be fully custom so a little work doesn't scare me but I'm not willing to keep this airbox. If I can't buy a different carb rack is there a proven pod combo I can use? I live in Iowa if that tells you my elevation and weather. Thanks for any help
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    Flat slide carbs are an option but you have to get correct size to fit boots I think 32mm but you run into problems with spacing , and figuring out jetting to name another hurdle . You would be WAY ahead of the game sticking with stock carbs and airbox it is less to fool with . Pods may look "cool" but to many issues to sort out.
     
  3. Simmy

    Simmy Well-Known Member

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    Although not my recommendation I'll go against the grain here, only because Dynojet do offer a kit for the XJ750.
    You'll notice in the pic (not certain if this IS the actual XJ kit or a generic pic) they supply a drill bit of the correct size to enlarge the hole in the throttle slide which leads to the diaphragm chamber. (actually 2 bits, one I suspect is for removal of the plug hiding the mixture screws) This is very important because when you eliminate the air box you change the pressure, actually increase the pressure at the carb inlets. Although I don't see a replacement diaphragm spring included they likely recommend snipping a specified portion of the OEM spring shorter. This allows the throttle slides to open with the changed pressure. So many here mistakenly believe it is just a matter of getting the jetting correct, that is the easy part. If your throttle slides don't correspond with your wrist your bike becomes a complete turd and one no one wants to ride.
    If you have help from a professional dyno operator complete with exhaust gas analyzer it can be set up properly.
    Budget at least $300-500 for the dyno though.


    s-l1600.jpg
     
  4. MattiThundrrr

    MattiThundrrr Not a guru

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    Ooh! It comes with stickers!
     
  5. Minimutly

    Minimutly Well-Known Member

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    Interestingly, those needles are vitually parallel. I have k&n pods on my kawa 750 trike, dropping the fuel level improved things a lot, but still not quite there. The carbs are keihins but the needles (tapered) are dynojet I think.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    put the airbox in and wrap screen around the carb boots it will look like pods.

    you could try fuel injection

    if you just want to putt around town go for the pods my 82 came with pods getting an air box po claimed a lot but he was very wrong.
    lose of power when you need it low top end 85mph. no rapid response from throttle when needed just a few problems. low gas milage
    the 82 still pulls hard at lower speeds and is great to ride
    my 83 flys by comparison.
     
  7. Minimutly

    Minimutly Well-Known Member

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    I don't quite get the anti pods sentiment common here. Sure they screw up the fuelling, but as has been said dynojet have done the homework for most models, and even if their kit is for a 650, and you have a 550, the difference is only likely to be a jet or two? Compared to the amount of work some people here have obviously put in to their machines this shouldn't be too onerous.
    And before someone says what do you know about it - I have gone through this on my kwak 750, so I have some idea.
    So my advice would be, if your build needs them go for it, but don't buy cheap chinese ones, k&n would be my pref, and then I would oil them properly, and reshape the inside lip to form a radius.
    Quick edit, just read through the thread on air box swapping, and the item on resonance and how the airbox can help torque at some point in the rpm range. Even though the explanation is a little simplistic in places essentially I believe it is correct. Putting this aside, the point at which it works best will be fixed, but that best point could be different for all sizes of engines. So, airboxes work for containing noise, standoff, maybe adding torque at certain rpms, but most of all, they work because that's what yamaha or whoever jetted the carbs for?
     
    Last edited: Feb 23, 2018
  8. XJ550H

    XJ550H Well-Known Member Premium Member

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    first the 650 carb kit would not fit the 550 carbs

    the anti pod sentiment comes from the fact that if yamaha thought the cv carbs would run better with pods they would have gone with pods.
    my clymer tells how to put pods on a 550 starts with buying a set of slide carbs.
    as far as dyno jet they send you a kit which is claimed to give the best performance possible not better performance . most here who are podding do it because they think they will get a faster quicker bike.
    I have asked podders on face book what they did to do pods and best answer was nothing to went up a jet size, then when I discribe my pod bike and its stumble at cirtain rpms and lack of top end speed they say they dont drive that fast or notice the stumble.
    another reason for the nopod thing is you should get the bike running the best you can before podding to give you a base line and help diagnose problems. many just tos the air box ang go pod then say why does my bike run like this. answer is because you did not get it right before converting to pods.
    most people do not have a dyno at home or access to one to do a proper poding
    but hay go for it if you want to

    Ignore the people who make a living designing bikes and motors podding would have been cheaper for Yamaha if it would work with cv carbs, and yamaha was concerned about cost and pricing in the US
     
    Last edited: Feb 23, 2018
  9. kosel

    kosel Active Member Premium Member

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    A friend of mine kept the airbox, but made side covers with half of a pod filter mounted on each. The effect was a hidden airbox and the cosmetic appearance of pods.
     
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  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    faux pods instead of faux pas
     
  11. JetmechMarty

    JetmechMarty Active Member

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  12. XJ550H

    XJ550H Well-Known Member Premium Member

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    Last edited: Mar 5, 2018

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