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Thread: Blast mikuin carb

  1. #1
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    I've been doing a ton of research on the subject and I'm pretty much 100% set in wanting to put a mikuin hsr42 on my blast. The only question I have is do you think the bike will run ok with just a exhaust and open intake? I ask Bcs it will be awhile tell I have the funds to port/polish the head, stronger valve springs, cams and ultima ignition. I like the mikuin carb Bcs the easy of tuning, quicker throttle response and smoothe running. I don't want to throw money at the stock carb if I'm just going to get rid of it anyways.

  2. #2
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    Assuming your upgrade components are matched for each other, you will benefit most from the HSR42 after making the performance upgrades to the heads and valvetrain. It should at least be driveable in the meantime, but how driveable? I really don't know.

    Will this be a daily driver??? You could always keep the stock carb on your Blast until you're ready to do the performance modifications.

    FYI: the Mikuni HSR42 can flow 213 CFM, whereas the stock Keihin CV40 flows ~159 CFM, according to a document by "bwoltz": Carb Shoot-out

  3. #3
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    Thanks for the reply. It will be a street blast. I'm in the process of saving money and figuring out what exactly I'm wanting to do. I got ahold of nrhs and asked them the same question. They said I'll be fine, just have to make sure to put in smaller/correct jets.

  4. #4
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    There's no point to switch from a CV40 to an HSR unless you're racing it.

    Being a non-CV carb, your throttle response will stumble and tuning will be a pain.

    A Blast at redline moves 58.3 CFM.

    31ci * 6500RPM / 2 / 1728 = 58.3 CFM

    They said I'll be fine, just have to make sure to put in smaller/correct jets.
    Smaller jets? Smaller than what?

    I'm in the process of saving money
    Then why are you putting a different carb on the bike? The carb costs money, the jets cost money, the tuning costs time (which is money) and your fuel mileage goes down (more gas used = more money spent).

    If you're doing it to be different, cool. If you're doing it to "save money", you won't. If you're doing it for performance, you're doing it backwards; the HSR requires more modifications (see above) before it becomes an upgrade, it will be a headache until then.


    Direct from NRHS' website:
    Quote Originally Posted by http://www.nrhsperformance.com/tech_mikunivscv.shtml
    On a mildly modified bike like this one (883 to 1250 conversion with stock 883 heads), the Mikuni just brings a little bit to the top of the dyno sheet. We've seen this result over and over, anytime we test it on a mild bike, it's hard to justify the cost of the Mikuni with the dyno sheet.
    That was 1.6whp increase and they agree that it's not worth it.

  5. #5
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    Thank you for the information. I guess I'll have to do some more researching

  6. #6
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    I'm not trying to dissuade you from your goals, just want you to be fully informed before spending the time and money and possibly ending up hating it resulting in a bad opinion of the Blast. I've seen it dozens of times.

  7. #7
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    I understand that and appreciate your honesty. This is my second blast. My first one was my first real street bike. I put on a velocity stack, jetted the carb and it came with a vance and Hanes exhaust already on it. Loved the bike besides a few stupid issue I had on it. Traded that in for a xb9, then a xb12, triumph speed triple, 3 supermotos, and last bike sv650. I decided to come back to a bladt Bcs it's pretty similar to a supermoto (being its cheap, small, decent power, and I don't care if it gets slightly beat up) but can handle long distance rides and I wanted to get my hands dirty on building the motor.



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