pops on decel - jetting question

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  • Guest
    #1

    pops on decel - jetting question

    '80 850 (CV carbs)
    stoch airbox with k&n filter
    4-1 exhaust which is pretty open
    carbs are clean with all new o-rings and the jets are in good condition

    bike was always popping on deceleration a little, but it got much worse since i upgraded the coils and coil leads / caps. i guess this could be considered an improvement

    turning out the pilot mixture screws doesn't help. when screws turned out more than 4 turns, the bike starts stumbling when slowly accelerating just off the idle while the popping remains. (though, at 2.5 - 3.5 turns, it runs like a champ but pops a lot.)

    when i add a little "choke" (with the engine fully warmed up) the poping goes away (but it's difficult to get it completely right as the bike also starts stumbling on slow aceleration).

    i'm thinking of putting in a larger pilot jet. stock size is 45 (this is a size larger than on the US models).

    do you think this is worth a try or do you have any other suggestions?
    what size to go with?
    maybe go with 47.5 for a start and see what that does?

    thanks guys!
    Tags: None
    • spyug
      #2
      Popping on deceleration is a classic symptom of air infiltration on the exhaust side. I'd be looking for holes in the exhaust pipes (connectors maybe). Are downpipes tight At the head and are there gaskets?

      It can also appear with a too lean carb situation usually when pod filters are installed and jets are not upped (richened) to compensate.

      In simple terms it is a too lean condition.

      As you correctly suggest, the first step would be to richen your jets a size or two. Do check your pipes for holes as well.

      Do your upgrades and tell us how it works out for you.

      Good luck with it.

      cheers,
      Spyug

        Comment

        • Joe Nardy
          Forum Guru
          GSResource Superstar
          Past Site Supporter
          • Jul 2003
          • 5849
          • East Tennessee
          #3
          You have somewhat verified a lean condition by proving that the popping lessens with a bit of choke applied, which richens the mixture. Larger pilot jets might help as well as shimming the needles. If your exhaust is very free flowing you may not be able to get the popping to go away.

          Thanks,
          Joe
          IBA# 24077
          '15 BMW R1200GS Adventure
          '07 Triumph Tiger 1050 ABS
          '08 Yamaha WR250R
          "Krusty's inner circle is a completely unorganized group of grumpy individuals uninterested in niceties like factual information. Our main purpose, in an unorganized fashion, is to do little more than engage in anecdotal stories and idle chit-chat while providing little or no actual useful information. And, of course, ride a lot and have tons of fun.....in a Krusty manner."

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            • Guest
              #4
              Originally posted by spyug
              I'd be looking for holes in the exhaust pipes (connectors maybe). Are downpipes tight At the head and are there gaskets?
              yes, forgot to say, the downpipes have no holes and seem to fit perfectly onto the exhaust ports and yes there are gaskets there. when building the bracket for this exhaust i bolted it firmly at the head and only then made the bracket so pretty sure it's sealing well. but it is puzzling that i would get so much popping while using the stock airbox.

                Comment

                • Guest
                  #5
                  Originally posted by Joe Nardy
                  as well as shimming the needles.
                  Oh, I forgot to say that, too - The needle is already up a notch.

                  Originally posted by Joe Nardy
                  If your exhaust is very free flowing you may not be able to get the popping to go away.
                  My worry as well . Would like to replace the exhaust with something quieter anyway but no dough at the mo with all the work i've done to it so far

                    Comment

                    • Guest
                      #6
                      Go with the 47.5s. It'll stop the popping.

                        Comment

                        • Guest
                          #7
                          Originally posted by chef1366
                          Go with the 47.5s. It'll stop the popping.
                          bless your words chef i ordered a set of 47.5s

                          will post the results

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