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Help...breaking up/misfire under half to full throttle

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  • Help...breaking up/misfire under half to full throttle

    Hey guys, well I’ll try to keep this short. Anyways me and the wife are on a road trip currently down the blue ridge parkway. We are currently in West Jefferson, NC and came all the way from Dillsburg, Pa.
    So my issue started about mid day today where any throttle input over about 1/4 the bike would aggressively backfire/misfire and not accelerate. Like just very unhappy.
    But it will fire up fine and seems to come off choke fine and I can definitely get where I’m going but it just takes much longer as I can only ease into the throttle. It’s very frustrating as all the work I’ve done and tried to be meticulous about setting the bike up for the trip.
    The bike did seem to be running good before our trip as I road it daily to work, but it did always seem to lack in top end. I was still kind of playing with the PMS and seeing what changes it made.
    At this point I’m thinking possibly my float setting possibly something ignition related??? As it runs ok at 1/4 throttle and under. Idk guys we are planning to ride the Deals Gap tomorrow 6/4 lol and do the tail of the dragon but it will be just miserable if the bike is like this. And then 6/5 we will be in Nashville for two days.
    So far I did the old gas station tear down today to raise my pilot needle to notch 5 and the pms is probably now at least 4 and 1/2 screws out. Made no change except it seems to idle better lol. Pulled the number 1 plug and it was not wet right after an aggressive ride with misfiring. I was paranoid that I was set up too rich.

    Anyways I’m open to any and all suggestions to how I might get this right on our road trip lol.
    Current set up: (I’ll do my best)
    99 Road Star 1600
    K/N drop in air filter
    Cobra Slash Exhaust
    Dyno Jet jet kit (pms probably now 4 and 1/2 screws out. 5 notch down on pilot needle) Can’t remember what size main jet but it was the biggest in the kit.
    Went pumpless with suggested latest Yamaha float needle.
    Set float level even with rear top of float bowl with a clear hose.
    Pulled out stupid little screen/filter from carb inlet
    New fuel filter
    New Oem Clutch Kit w/Barons Pressure Plate
    Upgraded oil gear
    Inspected and installed new driver gear sprocket nut and lock ring
    Inspected and added lock tite to starter drive gear/stator

    My problem is I changed so much at once, I wanted to cover all my basis and now it’s biting me cause I’m having to back track over everything. I’m just pulling my hair out wondering what changed from a few days ago to now. I’ve also hopefully ruled out potentially bad fuel as I’ve filled up twice today. Also my mpg was around 26 for the first leg of the trip...bad? Good?

  • #2
    first thing screw the PMS in about a turn. AT 4 1/2 turns out it does not have enough tension on the spring under the screw to keep the screw in place and it will vibrate and fall out. You do not want to lose that screw because you will NEVER find another while you are on your trip.That usually happens at about 4 turns out. Did you clean any of the jets while you had it apart? Did you check the vacuum port on the top of the intake manifold to see if the hose/vacuum cap is missing or damaged?

    Comment


    • #3
      Ok will do on the pms. Cleaned all jets that weren’t being replaced and all ports that I could while the carb was apart. Vacuum port seems ok, still has a piece of rubber hose that is blocked on the end.
      I will say the intake manifold does have some exterior cracks that had me a bit worried. But if a vacuum leak was present would it not run like crap all the time?

      Comment


      • #4
        DYNA JET KIT INSTRUCTIONS: for a 1600 with exhaust and aftermarket air cleaner....
        jet it the same as if it was a Barons kit and I don't think you will know the difference. It will still need a "Mikuni" 37.5 pilot jet, The 37.5 dyna pilot that comes in the kit flows the same amount of fuel as the stock 35 Mikuni pilot jet. If I remember correctly the Dyna needle set in the 4th groove would be the same as a Barons needle set in groove 3 1/2 so it would be just a Tad leaner than the Barons needle. You can always just add a shim washer for a total of 2 under the clip to make it almost exact to the barons needles

        After turning the PMS screw out and the bike warmed up idling, use a tachometer, or listening very closely while turning the PMS screw in or out to find the highest idle. After you find the highest idle, turn the PMS screw out 1/8 to 1/4 turns. Your done.
        If you have to turn the PMS screw out more than 3 1/2 turns, then change the pilot jet to richer pilot.

        Did you do anything with petcock? Remove little screen/filters? You kept the stock inline fuel filter? Have the 3mm "grizzly" needle-valve? Vent the gas cap?

        Sure sounds like your starving for fuel. Did you leave stock airbix on and unmodified with just a drop in K&N? Would have been same price to eliminate airbox assembly and just get a K&N RA066V air cleaner (and flow more fuel)
        LET'S RIDE

        Comment


        • #5
          Thank you guys for the reply’s.
          So no change to petcock. Still running oem new Yamaha fuel filter. Since I deleted the pump my fuel lines kind of run down and that back up hill to the carb. Would that cause issues? It’s not extreme but it does have to go up hill a bit.
          I put in the latest suggested needle valve, which I believe is the grizzly one? Did not vent gas cap though...could that cause fuel starving? Could I try riding with no cap and see if it makes a difference? And no mods to air box. Just put in the k/n and called it a day

          Comment


          • #6
            Since your pumpless and no vented cap… you might try removing the hose from the fitting on top of tank which goes to the rollover valve… you may be pulling a slight vacuum due to the line being clogged…. A quick check is try running the high rpm speed with gas cap removed (test only) to see if the bike now runs normally…. Eliminate the obvious first…

            Comment


            • #7
              Don't ride the bike with no fuel cap, run a fuel pipe from your petcock into a fuel can leave the filler cap on run at least half a gallon keep your eye on the flow, run in on position and try again on res, there should be no difference in flow, if the flow stops remove the vent pipe at the top of the tank and try again , maybe the vent pipe is blocked? if all ok move down to the carb,
              I run a baron needle 4th clip down,175 jet and a 0.040th pilot air which makes the bike run better at slow speeds , 2 3/4 turns on the pms, and of course have you checked the enricher cover for cracks? ,fix a pipe onto the carb drain outlet unscrew the drain screw see if you have a healthy flow maybe the needle valve has a problem

              Comment


              • #8
                When the bike does this, pull over, shut off the bike, and remove the gas cap. If air whooshes in, you have a tank vent issue. I did everything you did except I run no filter and I vented the gas cap.

                Comment


                • #9
                  Ok guys good things to try out. We are currently an hour and a half away from the dragon. What’s the best way to vent the cap if that turns out to be the issue?

                  Comment


                  • #10
                    Ok pulled vent pipe and tried to blow through and it was damn near impossible. Followed it down and it looks like it goes into a filter? And then exits down under the bike. I pulled the hose off the inlet of the filter and it can now be blown through. I’ll take the bike out once we’re done eating and see how it does

                    Comment


                    • #11
                      The filter you are talking about is called a roll over valve. It is there to keep gas from coming out of the tank in the event of a lay down of the bike. You shouldn't be able to blow thru it but if you sucked on the hose you should have had air flow.

                      Comment


                      • #12
                        Yeah my bad...haven’t been thinking clearly. And pulling vent hose off made no difference. I’m really thinking it’s something with float needle or something clogged in the carb. We made it to Tapoco Lodge for the night. I’m debating if I want to pull the carb off here and tinker with stuff. We’re planning to be in Nashville tomorrow for two days so that might be a better area to get parts if needed.

                        Comment


                        • #13
                          You never said what main jet you are using. Also the 5th groove is wrong. If you are running Cobra slashcut mufflers on stock headpipes and stock airbox with a K/N drop in filter you should be jetting it as if it was a stock bike. The needle clip should be in the 3rd grove (4th at the most) with a Dynojet needle and the mainjet should be a DJ 165 maini jet. I'm getting that right from the Dynojet installation instructions. If you have a Harley dealer near you, get a Mikuni mainjet 165. Don't try to explain to them what you are installing it on they won't understand. Tell them it is for a Mikuni HSR42 carb.. Your carb isn't an HSR42 but it takes the same main jet.

                          My guess is that if you pull the spark plugs they will be very black. I have a feeling you are jetted extremely rich and that is the issue.

                          Comment


                          • #14
                            Had the same problem on my trip to Virginia last week. Check your battery ground. I found that when I sat back on the seat and took pressure off the seat AKA The ground terminal the bike performed perfectly I got a new battery and bent down the connection as ran like a champ since. But I tossed around the idea it was a garb issue for weeks before I realized it's most likely electrical

                            Comment


                            • #15
                              I scanned thru pretty quick, but, crack in the enricher cover?
                              It's not that life is so short, it's just that you're dead for so long.---unknown.

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