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  1. #1
    CB750 Member ugly's Avatar
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    NEED OPTIONS!!!!

    So I have been tinkering with my carbs for the last couple days and I can't seem to get them right. I know I will never get them perfect but I need to get them to lean out and stop back firing throught the exhaust. The bike is a 1981 cb750k, running CV carbs, 4 into 4 exhaust that goes back just behind the motor. (Yes, its loud!) I also installed washers inside to help with back pressure. Good compression on all cylinders. I removed the vacuum lock off on the top and I am running straight into the carbs with an inline fuel filter and petcock. I have all for carbs bench synched and for jets I am running 74 pilot jets and 130 mains. Needle setting is in the stock position with the A/F screw turned 2.5 turns out. For my air filter I am running pods. Not k&n, but not the cheap-o ones from Ebay either.

    So my question for everyone is, what are you running for jets and needle setting that make your DOHC Honda running pods, run the best with little to no backfiring through the exhaust.

    And please dont waste your time telling me that it can't be done done because I know it can. There are plenty of people on here doing it. Thanks in advance.

  2. #2
    Moderator dirtdigger's Avatar
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    With that short of exhaust its always going to pop no way around it...short exhaust is an absolute killer of power on a street ridden bike. And I will waste a little bit of time saying you will never get them running correct, you may get it running ok but never as good as if you ran a proper exhaust and air box. That I can guarantee. With that said it is your bike and Im sure you are going for a "look" so it is going to be a trial and error to find the right jetting unless you have access to a dyno. Tuning the CV carbs is not like tuning a conventional carb, you think you need to richen them up but it just makes it worse, they are finicky and it will take some tinkering with more then just the jets.

  3. #3
    CB750 Member ugly's Avatar
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    i completely understand what you are saying but I know I can get it to run a little bit better than what it is now. you and I both know that these cv carbs are a complete PITA! if money was no option then I would have a nice set of cycle x carbs but seeing that I don't have that kind of money these will have to do. ill attach a pic of the exhaust on the bike. I would say its comparable to a set of drag pipes.
    Click image for larger version. 

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  4. #4
    CB750 Addict Wez_'s Avatar
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    Read post # 5 here

    http://www.cb750.com/threads/4295-Co...-SOHC-AND-DOHC

    He says this DynoJet kit works with Pods. I can attest that swapping back to the stock Air Box makes a hella difference. I just performed the swap this weekend and am still in the process of completion.

    Now with the stock air box installed, the bike basically almost jumps out of my hands with all the torque now in mid range. I am still going for 10k RPM as it's possible. But the little "side" door on the side of the air box/ filter was left off on my ride in today as I ran out of time looking for it. A guy at work told me that cover will make a big difference. Also, the intake "stack" in the back of the box no longer fits due to my electronics pan. Hopefully Ill get this all figured out quickly as the bike is a fuckin animal! Pulls like a SOB and sounds great. I rebuilt the top end and had the valves ground (my mistake) Otherwise I shimmed a few extra thousands of clearance in the valves and rebuilt the carbs per the manual here"

    http://www.cb750c.com/publicdocs/Sea...anual_revG.pdf

    Its a long process but you likely have done some of the steps already. Follow this carb rebuild to the T and your carbs will be worry free for sometime. Also, those rubber air cutoff if bypassed will cause a backfire. My bike farts every now and then as I bypassed mine but I love the sound. Im running a 4-1 into a Super Trapp Exhaust that sounds amazing when ripping!

    Today on the way in I got the biggest fist pump from a town worker admiring my bike! Thanks cb750.com!!

  5. #5
    CB750 Addict Skelee's Avatar
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    I think I have the same bike as Wez. I have a 4 to 1 exhaust, stock everything else. My bike sounds great and normally runs great. I went on small group ride and not much said during idle but once we hit the rode I got compliments! When you hit 5000+rpm it kicks ass
    82 CB750SC Nighhawk

  6. #6
    CB750 Addict Dave's Avatar
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    The carbs need to be synced on the running engine, "bench sync" is only a starting point.
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  7. #7
    CB750 Addict Wez_'s Avatar
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    So I put the side cover onto my airbox and it no longer stumbles at 4.5K as much and it redlines 9-10K now!!! Wow...what an animal !!

    Carbs not synced yet.

  8. #8
    CB750 Member ugly's Avatar
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    so after some trial and error i finally figured it out. havent been on a long enough stretch of road to really open it up but so far, so good. messed with the jetting, adjusted my "baffles" added more air, less fuel and it purrs like a pissed off lion! so to whoever says that you cant run pods on cv carbs, your wrong. it will work! maybe not as well as stock but with re-gearing, and knowing how to ride... all works well. thanks all for al the help!Click image for larger version. 

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  9. #9
    CB750 Addict Wez_'s Avatar
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    What RPM can you get the bike up to with your setup?

  10. #10
    CB750 Addict Dave's Avatar
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    Quote Originally Posted by ugly View Post
    so to whoever says that you cant run pods on cv carbs, your wrong. it will work! maybe not as well as stock
    I'm pretty sure people say exactly what you've learned. You can get it to work but not as good as stock (using the airbox).
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  11. #11
    CB750 Addict Skelee's Avatar
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    These work:

    https://fortnine.ca/en/emgo-clamp-on-pod-air-filter

    Sent from my SM-A520W using Tapatalk

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