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  • Backfire threw carb...

    Have had my 06 R* since new,and on the dyno to make sure new jetting isn't too lean (168 main and 38.5 pilot, needle slide on 4th clip) and adjusted the pilot mixture screw ,looked to be ok in all RPM ranges w a max. power of [email protected] 4.6k RPM and max torque of [email protected] 3.4k RPM. Bike runs strong and has 10.5k miles on it, BUT, have always delt w this ANNOYING stumble/backfire thru the carb. after decel. Would def. ride more often it didn't always do this.Have tried different jetting, had a few different MC mechanics look at it for this issue, Speed sensor replaced,and still have not been able to shake this cough/hiccup. Even had one guy tell me "this is the best your gonna get it and your just gonna have to live w it" which i don't believe is the case. I tried adjusting the accelerator pump,thinking that could be part of it,but that seems to be working fine and sprays a jet of fuel into the carb as soon as you start to twist the throttle,and the accelerator adjustment screw is almost 1/4' from the pump cam before any adjustment,as set from factory?? Am almost resigned to the fact that,this bike,in this configuration is always going to have this stumble...kind of frustrating

  • #2
    For a 1700, with aftermarket intake and exhaust we normally recommend a Barons needle, and a 40 Mikuni Pilot. A 172.5 Mikuni Main. Clip in the 4th with a single shim and the fat plastic spacer under the clip. 2 1/4 out from lightly seated on the PMS.
    Make sure the idle is set to about 900rpms.

    Are you saying that if you’re sitting at a light and rapidly and repetitively twisting the throttle, the carb spits or coughs, or do you mean if you are using the motor to slow the bike, while the bike is in gear.....a hard decel, the bike is spitting back through the carb.

    Comment


    • gary1717
      gary1717 commented
      Editing a comment
      yes,when sitting at a light or if i twist the throttle before take off. Even just normally taking off, it will do this some of the time.
      The sound of a backfire in the middle of town,isn't the kind of attention i want to attract! lol

  • #3
    Sounds like the idle is set too low.
    Scott B.

    Comment


    • Flashback
      Flashback commented
      Editing a comment
      this would be my guess as well..

  • #4
    Mine does this same thing, has for 5 years now. I don't give a shit what kind of attraction it gets. Be gentle with your throttle movements ( no snapping) and this will help some. But, even at that, you will still get the occasional spitting. There may be something to what your mechanic says about being the best you can get. The big V-Twin is an antiquated design and given to fits of bad behavior. I don't know if the F.I. guys see this as much, maybe so, I have never ridden or been around an F.I. Road Star. But that don't confront us, right, 'cause we ride carbed bikes ( more antiquated technology) and we don't need no stinking fuel pumps!


    Comment


    • Bikerron
      Bikerron commented
      Editing a comment
      “ I don't know if the F.I. guys see this as much, maybe so,...”

      Oh, yea. My ‘09 hates to be blipped. She’ll pop back through the throttle body 50% of the time.

  • #5
    Mine does it at start up... So what do the great minds say about that?

    Comment


    • SKWEARpeg
      SKWEARpeg commented
      Editing a comment
      It’s not something that happens every time, but mine will do a little crank/bang on start up ever so often. Nature of the beast.

  • #6
    What is the idle set at? People have a tendency to turn the idle down, so the bike has a lope in the idle. These bikes will idle as low as 650 rpms when they’re warmed up, but the factory recommends 850 to 950rpms. Most shoot for 900.

    It sounds to me like there are two separate issues. A lean issue or possible low idle, causing a balky off idle throttle response. The bike spitting through the carb
    It also sounds like you’re getting a backfire out of the exhaust. The kind that causes concern with the cops.

    Things I’d do.

    Verify the idle is set correctly.
    Start looking for a possible vacuum leak at the intake manifold to head flanges. I’d even think about removing the intake manifold, surfacing the flange faces, and reinstalling it. If this is the problem, then you can get a lean condition off idle, and maybe even a backfire out of the exhaust.
    I’d check for an exhaust leak where the pipes mount to the heads. If you have an exhaust leak, it can cause both a backfire, and off idle throttle issues. OEM exhaust gaskets are recommended.

    Comment


    • gary1717
      gary1717 commented
      Editing a comment
      My idle after warm up is right at 1kRPM Used to have it a bit lower. Around 850 to 900,and a low or loping idle condition will def. contribute to this problem with the motor having to catch up to itself,and lazy throttle response. Also have somewhat of a backfiring thing going on when I'm coasting down a hill and after a bit,I hear some light,pop pop pop,which sounds normal .
      Have used the WD-40 metohod for checking for leaky manifold seal.

  • #7
    Sounds like accelerator pump squirt when the throttle is cracked is not there. ie: lean condition back fire through carb.
    Is the word PICTURE a picture?

    Comment


    • #8
      Another reason I'm loving my HSR42
      2000 Roadstar 1600 - BAK, Pumpless, Curt's manifold, Mikuni HSR42 Freedom Combat Pipes Jumbo Strong bags, PPG 'HellFire' Paint.

      Comment


      • SKWEARpeg
        SKWEARpeg commented
        Editing a comment
        Mmmmmmm

        I wouldn’t be so quick to throw shade on the stock carb. I think this may be something else.

      • Spydr
        Spydr commented
        Editing a comment
        So do I, except when that 42 backfires at start up.
        Other than that, it's awesome!

      • Jaybo
        Jaybo commented
        Editing a comment
        Oh it likely is something else, the jetting sounds pretty good, so there could very well be some other issue. Since I put my HSR on it now instantly revs, it starts perfectly ev ery time, has yet to stumble even when I go full open from idle, etc. CV carbs are fine, but a mechanical slide is always going to outperform them. My only complaint is the 33-ish MPG I'm getting from my old 43-ish MPG. Might be because I'm digging on the throttle response though now

    • #9
      Jetting may be too lean??

      Comment


      • #10
        WD-40 is a really crappy thing to use for finding a vac leak.
        The best is a mapp gas torch like one used for sweating copper fittings..
        Put a hose on the end, and just enough gas coming out. Move the end of the hose all around the flange to head joints while the motor is running. The mapp gas is a lot more flammable then WD-40.
        Don’t forget to turn the mapp gas off when you’re done.
        Manifold flange leaks are pretty typical, and can be really difficult to find. Most just bite the bullet and go to work.

        Comment


        • #11
          I think you better check the number on your main and pilot jet again because no such thing as a 168.5 main or a 38.5 that I have ever heard of. Also put a 172.5 mian jet along with a 40 pilot needle on the 4th groove. Get a Barons kit and only use Mikuni jets. I don't know what AFR numbers you seen but it had to be lean as hell with anything close to what you said.

          Comment


          • gary1717
            gary1717 commented
            Editing a comment
            Hmmm. Was gonna get a new jet kit and step it up a bit richer,and try that,but does the brand (Dynojet,Barons,Mikuni) make a difference and which is the preferred kit for a Roady?

          • SKWEARpeg
            SKWEARpeg commented
            Editing a comment
            Yes. Mikuni and DJ Jets are sized differently. See the chart in the Tech Articles section.
            Mikuni jets(it’s a Mikuni carb) will have the square in a square and “R” trademark stamped on them. If it doesn’t say Mikuni, and you didn’t buy the jet kit, you probably have no idea what’s in there.
            Barons uses Mikuni jets.
            You’ll have to order a 40 Pilot
            N224.103-40

        • #12
          My Roadie seems to run pretty hot as compared to my HD riding buddies in NYC traffic in the summer heat,and was considering a fan assisted oil Cooler. Anyone running one of these? And are they effective in stop and go traffic?

          Comment


          • #13
            30 mpg is the best i get. 172.5 main and stock pilot 3.5 turns out

            Comment


            • Rodzim
              Rodzim commented
              Editing a comment
              Even with a stock pilot?. How many turns out is yours?.
              I have v&h long shots and a k&n

            • SKWEARpeg
              SKWEARpeg commented
              Editing a comment
              Opening up the idle mixture screw(PMS) is a poor substitute for adding fuel to the Pilot circuit. It’s on the wrong end of the hose, so to speak.
              Going to a 40 Pilot with a 1700, gives more fuel across the whole Pilot circuit, without requiring you to run rich at idle just so you can have a bandaid later on.
              Cruise speeds below 70mph, can be pretty well handled just by the Pilot circuit. If you’re lean in the Pilot, you’ll be bumping into the Main more and your mileage will suffer.

              If you’re still running the original needle and seat, I’d be replacing it as well.

            • gary1717
              gary1717 commented
              Editing a comment
              adjusted my PMS 2 1/2 to 2 3/4 out from a hand tight seated position. I think its a Baron PMS,But not sure. Will have to look back at past receipts.

          • #14
            This is usually a result of the idle being to low or the mixture being to lean or a combination of the two if your jetting is correct and you don't have a intake manifold leak. Try enriching with the idle screw a bit. The idle screen adds to or subtracts from over all mixture as evidenced by the AFR gauge. The RS does not like a slow idle and will back fire if idled to low. If that fails... remove the air cleaner and visualize the accelerator pump nozzle squirt to ensure it is functioning correctly and adjust/repair accordingly

            Comment


            • #15
              Originally posted by gary1717 View Post
              My Roadie seems to run pretty hot as compared to my HD riding buddies in NYC traffic in the summer heat,and was considering a fan assisted oil Cooler. Anyone running one of these? And are they effective in stop and go traffic?
              because you are extremely lean.

              Comment


              • #16
                Really do appreciate all of your technical and expertise opinions on fixing this!! or at least improving it. yes,even though the Dyno is saying I'm not running lean... i think it is a part of a lean condition , even w the excess running temps. time to re-jet again

                Comment


                • #17
                  The accelerator pump is adjustable and it might not be engaged soon enough.........I would check it if the idle is good
                  not all those who wander are lost......

                  Comment


                  • #18
                    Originally posted by gary1717 View Post
                    Really do appreciate all of your technical and expertise opinions on fixing this!! or at least improving it. yes,even though the Dyno is saying I'm not running lean... i think it is a part of a lean condition , even w the excess running temps. time to re-jet again
                    You say the dyno says you are not running lean. What do you think is lean. What are your AFR numbers at WOT and at cruising speeds and under what drum load?
                    I say whoever done your dyno don't know what lean is and shouldn't be doing dynos. I also don't believe those numbers on a sum what stock bike without internal engine mods.

                    Comment


                    • #19
                      not sure of how to read the dyno results on the readout sheet,but it says max air/fuel ratio 1= 15.7 at engine RPM = 4.8 and no other AFR #"s also Max power =77.7 at engine RPM = 4.6 Max Torque = 103.1 at engine RPM = 3.4 i don't know what the drum load/resistance was set at, but this guy has been doing this for a long time. Have #'s to compare this to from back in july of 2012. Bike was jetted different at that time, but #"s were better this time. (Max power 74.7 at RPM 4.6 and Max Torque 97.7 at RPM 3.4) his setup is a Dynojet model 250i The bike did do the cough/stumble a couple of times while he had it on the dyno,and he didn't think much of it,but did tell me he doesn't touch carburetors

                      Comment


                      • roadiemort
                        roadiemort commented
                        Editing a comment
                        Lmao, He dyno's bikes but won't adjust the jetting if required. He must know there one born every min.

                    • #20
                      Originally posted by gary1717 View Post
                      not sure of how to read the dyno results on the readout sheet,but it says max air/fuel ratio 1= 15.7 at engine RPM = 4.8 and no other AFR #"s also Max power =77.7 at engine RPM = 4.6 Max Torque = 103.1 at engine RPM = 3.4 i don't know what the drum load/resistance was set at, but this guy has been doing this for a long time. Have #'s to compare this to from back in july of 2012. Bike was jetted different at that time, but #"s were better this time. (Max power 74.7 at RPM 4.6 and Max Torque 97.7 at RPM 3.4) his setup is a Dynojet model 250i The bike did do the cough/stumble a couple of times while he had it on the dyno,and he didn't think much of it,but did tell me he doesn't touch carburetors
                      The 74.7 and 97.7 numbers sound more realistic. If the air fuel ratio at any point of running was in the mid to upper 15afr range it is extremely lean. At a WOT pull the afr should drop to mid 11's and the highest it should be at a steady cruise speed is mid 14's but around 14 AFR is about a perfect spot at cruise. At 15.7 WOT AFR your bike will be running hot and popping alot. Way to lean. The guy is tricking something on the results and testing. You need fuel to make power. You don't have enough fuel at 15.7 AFR to make that kind of power without trickery on the dyno.

                      Comment

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