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  1. #1

    Default HSR42 on a Virago XV1100

    I recently installed an HSR42 on my bike that I'm having difficulty with. This is on a 1996 XV1100 Virago with a 2 into 1 single carb conversion manifold. The engine is rebuilt with 200psi compression on both cylinders and a stage 2 cam. The air filter is a round foam type that doesn't block a lot of air.The exhaust is a black widow. The idle circuit is good with a 17.5 pilot. After twisting the throttle, it's rough. I can only get it to run decent with the choke all the way pulled out and with a 117.5 Mikuni (1.25mm) main jet. It will still stutter a little from 1/8 to 1/2 throttle but after 1/2 throttle, it screams like a bat out of hell(only with the choke pulled out, choke in it runs bad). The needle jet is a y4 and the needle a 98. The pump jet is 50. The choke effects the performance throughout the throttle range. If I push the choke in, anywhere through the range, it sputters and wants to die. Pull it back out and it runs pretty good. I put a richer 130 (1.38mm) main jet on and it got worse. I didn't have anything else smaller or in between. I'm thinking this HSR42 is way too big but I was hoping to make it work. There are no leaks in the manifold for sure, I double checked. I'm thinking the carb is just way too big but I was hoping to get the HSR42 to work considering I have lots of money invested in it. Any suggestions which way I need to go on the main jet, needle jet and needle? If I need to go lower on the carb, what do you think? Mikuni TM33? Thanks.
    Last edited by Hellacious; 02-05-2021 at 6:41 PM.

  2. #2
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    What did your intake manifold manufacturer/reseller recommend for baseline jetting when you contacted their tech support? Why is their name a secret? (ALWAYS post maximum detail to help others help you.) Having to enrich the mixture (HSRs do not have a choke, which means an actual physical butterfly) means it's generally lean but main jets don't fix everything across the operating range. HSRs work on 883 Sportsters so they're not too large.

    Is it one of these? https://vtcportal.com/home/43-single...arburetor.html

    I'd also call Mikuni tech support since they've been used successfully on XV1100s. Parts sellers want happy customers and someone somewhere has already solved your problem, most likely the kit maker.

    https://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf

    Since you're running a Black Widow exhaust I'd contact them too. Many people spend gobs of money but don't interact with the manufacturers to get the most out of their parts. If you contact the kit maker, carb maker and the exhaust maker that should narrow things down considerably and there's no point in redoing what they spend dyno time sorting out.

    Post your results since there's not a lot of info online and it will help the next guy.

  3. #3

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    I bought the manifold 3 years ago on ebay for cheap. Bought the carb and manifold separately. The guy doesn't sell them anymore but I saw the exact ones being sold on ETSY here. Contacted them, no response

    https://www.etsy.com/listing/7426584...-1&pro=1&frs=1

    I have called several companies and most have said to weld an 18mm bung to fit an O2 sensor and meter. I guess I might have to do that. I understand the inner working of the carb pretty well but still learning. The tuning manual from Mikuni off their website says choke system, so that's why I call it choke. I have only seen 2 people on the internet with the HSR42 fitted to anXV1100. One from Thailand, I messaged him no response. Another on here named swampthing. I just posted to one of his old threads, maybe he will respond. The Thai guy had a video of it idling and just revved it a little, seemed ok but did not sound crisp to me. Kind of like mine with the choke on. No video anywhere else. So until I see video proof, who is to say this carb works on a Virago. I read several threads about the Mikuni choke. The info there contradicted my hands on experience. It said the choke only has effect at closed throttle. I understand that the choke only works with the throttle closed for starting, but the effect of the choke is throughout the throttle range on my bike for sure. Maybe I just misunderstood it. Someone actually said pulled choke at WOT is leaner than no choke but not sure if I believe that.From my understanding, when open, the choke shoots gas behind the flat slide bypassing the slide. Not sure though. I read the tuning manual before starting this project. The issue with the manual is this. Please correct me if I'm wrong. I have found the Main Jet size and needle jet size effects every circuit from idle to WOT, so I have come to the conclusion that you can't properly tune anything else unless you get the main jet and needle jet right first. I guess I will keep drilling the main jet until I get it the closest, then do the needle jet

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    As mentioned, choke is not a 'choke' but an open port to allow fuel to flow, regardless of slide/throttle position. Main jet does not affect idle or 1/4 throttle, but starts to affect fuel ratio from about 3/4 throttle, depending on needle jet and jet needle sizes and needle taper, to WOT.

    Did you check your float height first - need to do that before any other carb tuning.

    found some info here:

    Tuning Tips & Manual Downloads
    Here’s our simple outline for basic tuning to get you started.
    Click image for larger version. 

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    https://www.mikunioz.com/tuning-tips...v=3e8d115eb4b3


    Mikuni HSR Tuning Manual;
    https://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf
    Last edited by TriNortchopz; 02-06-2021 at 1:41 PM.

  5. #5
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    The kit you have looks like the one vtcportal sells so I'd contact them.

    If no joy, you could begin with the needle and jets which work on an Evo Sportster for a similar displacement baseline. HSRs have been used on 883s as well as 1200s (to which 1000 is close, and someone probably stuck one on an 1000 Sporty too.

    xlforum has many HSR threads and one 1100/1200cc vee-twin air pump is fairly similar to another. (For example some Drifters used the same basic Keihin CVs as on HDs.) Not all the threads list the jets and rather than digress into the Virago question I'd just ask about the jetting for a given displacement.

    Here's an example thread from hdforums:
    https://www.hdforums.com/forum/sport...42-1200-a.html

    Example jet/needle kit: http://power-barn.com/mikuni-hsr-car...s-045-khs-048/

  6. #6

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    Set the float first thing. Had a 20 pilot and a 160 main when I bought the carb. Bike would not idle, just pop and die. Only changed the main jet to 210 then it would idle, good actually. Didn't even Change the pilot jet. Go figure that one out. So I did the deed and bought a wideband air fuel meter and a programmable ignition. I'm installing the 18mm bungs now. Still might buy a Mikuni TM36 pumper if I can't get the HSR42 dialed in. When it's all said and done, I'll post the results.
    Last edited by Hellacious; 02-24-2021 at 4:50 PM.

  7. #7

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    Update:
    I welded in the bungs and installed the air/fuel meter and have some interesting findings. First I will say, and I know some will disagree, the main jet does effect the air/fuel ratio throughout the entire throttle range. Call my meter a lier, not me ok? It's not dialed in yet. Right now I have a 50 accel pump needle. A 37.5 pilot jet. A 6 needle jet, a 95 needle, set at the middle slot and a 128 main jet.

    The pilot is still lean, I will need to drill it larger. The needle and needle jet are close around 13 AFR. The main jet is too rich at 10 AFR. I'm guessing it will need to be around 122..

    I'll post the final results when I'm done, should be in a couple weeks.

    Installing a meter is most definitely the way for me, I highly recommend it if you are doing this sort of thing. Well worth the $170.
    Last edited by Hellacious; 02-24-2021 at 5:16 PM.

  8. #8

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    I could never get the HSR42 to work. I ended up using a Mikuni TM36 pumper with a 138 main jet. I also had to buy a programmable TCI from ignitech and used a power timing curve similar to a 1200 sportster. The stock TCI will not work very good with a single carb. Doesn't have a ton of power but good enough to cruise.

  9. #9

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    Of course you wont get a carb with drilled out jets to work. Jets are reamed, not drilled. Its a too imprecise method no matter what other guys tell you.

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