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  • low throttle stumble

    I tried to locate my earlier post on this issue, but was unsuccessful. My problem, after cleaning the carb multiple times, going pumpless and installing the Grizzly float valve continues to be that at , up to @ 1/4 throttle,even after warming up and riding a considerable distance, my bike spits, cuts out and stumbles until I increase the throttle to half or more, regardless of gear. This makes light to light travel (NOT drag racing, just plain travelling) in city traffic quite dangerous. Although I have the recommended pilot jet in my carburetor, I'm wondering if I need to go larger. As it is, once I get on the highway and can wring it out, the bike seems to run fine. It's just when I'm back down to start off from a stop with lower throttle movement that continues to be the problem. I'm almost to the point where I will 'take the bike to the dealer', because, frankly, I'm stumped!

  • #2
    What groove in the needle do you have the clip in? Count down from the flat end and it should be the 4th groove with a plastic spacer and a silver washer under the clip. Might also want to make sure the pilot circuit isn't plugged somewhere. Pull the pilot jet and spray some carb cleaner thru the ports. Check the vacuum port on top the manifold for cracks in the hose or rubber cap if the AIS has been removed.

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    • #3
      If you pull the choke out when it's warm. Does it stumble worse that would indicate it's running too rich a bike that doesn't snap back to idle usually means too lean. It could be that your float level is too high or low. or your choke cable is sticky.. check the vacuum nipple on top of the intake manifold is not broken and also check the throttle cables are not arcking out the positive lead to the coils

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      • #4
        That grizzly valve Has and o-ring around it when you install it that keeps gas from going around the outside of it did you install the o-ring. You do not have to remove the carburetor to access the bottom of it

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        • #5
          Having the same problem with mine have all new jets and float seat+valve Adjusted the float level, curious do you have a hypercharger installed? Mine is when the throttle is barely open like a centimeter of a twist on the throttle(regardless of ambiant temperature . Any more than that and runs like a scalded dog. Dave helped to get it running as good as it does, take his advice.

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          • #6
            No hypercharger, just a BAK.

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            • #7
              I have checked all the connections, pulled each jet, individually and inserted the straw of a can of carburetor cleaner, spraying each passage, adjusted the PMS screw with carb off the bike, and carb settings as per my profile. I'm wondering if I need to replace the diaphragm on the accelerator pump, due to the low throttle response.

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              • #8
                i suggest you do my DUCT TAPE TEST. its always best to warm it up first. place duct tape over the outside of air cleaner to obstruct air flow , 25 % obstruction is a good starting point. run the bike , see how it runs, no change, add more tape. if u see an improvement, you are too lean to begin with, because tape lets in less air causing a rich state. vice versa.
                notes.
                1. i like to check the float level while bike is running, using the tube method .
                2. you really should replace the fuel in you tank and dry it out on intervals, the more u use it, the more ambient air enters and condenses inside tank. but do that later.
                3. i had low throttle stumble for years, found out the choke cable was not retracting at the carb end, i replaced it.
                4 .you can adjust pms with carb on bike if needed.

                AFTER YOU DETERMINE IF IT IS LEAN OR RICH, then we can proceed from there.

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                • #9
                  Does the acc pump start to squirt as soon as you start to twist the throttle and continue to squirt thru about 1/2 way thru to WOT? If it dribbles or spits fuel in the beginning of the throttle twist instead of a good solid stream of fuel when you first start to twist the throttle then you found the issue at the acc pump itself. If it don't start to squirt immediately then it may just need a acc pump timing adjustment. When you check it don't twist real fast. Just a nice slower steady twist. Also if you twist more than a couple times when checking ,start the bike for a few seconds to clear out any extra fuel that may flood the bike. then continue you test if needed.

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                  • #10
                    I just read your profile and seen you have a speedstar needle. I checked my file notes and dynos and when I was using a speedstar needle I used a 180 main 40 pilot and ran the clip on the 5th groove, pms at 2 3/4 and had good dyno results with that jetting. I think your 175 main will be OK though but change the clip groove to the 5th with plastic spacer and 1 silver washer under the clip.

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