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Carb Tuning Success Story

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  • #1

    Carb Tuning Success Story

    I received the '79 mechanical advance from Scott last week and installed it successfully. Instead of going with known good carb settings after a perfect timing, I messed with them causing a bad low end bog. I kept pulling the plugs here and there to check color. Looked lean. I left a plug socket at work and home to check each day (20 mile commute). So, after I got home from work I set out to go for a good tune. I ended-up playing around with the Colour tune and the #1 cylinder was way outta whack. I called it quits for then to spend the evening with my girlfriend, and figured I'd reset all to 2.5 turns and start over.

    Girlfriend gone: game-on. Ended-up going four turns out and went for a ride. Pulled plugs. Black on 3 of 4. #1 cylinder was a little gray. Turned them all a half turn and another ride. Pulled the plugs. Two of four black, #1 was okay, #2 was gray. Synced carbs (very little adjustment necessary). Turned another half turn and another ride. #2/3/4 was gray. 1/4 turn and put the Carb Tune on again. No adjustment necessary. No more lowend bog. Plugs all look silver right now. I hopethe color comes down the road. I think I am used to the full advance I had, as I'm surprised that the bikeis not very strong till 3k when I assume the full advance kicks in. I'll keep an eye on plug color to see if any more fine tuning is necessary. I have tank filled-up to the tippy top, and will hopefully see better fuel mileage with the vacuum pod attached now.

    I was surprised to see the variation of tuning between the #1/2 carbs compared to #3/4. I think I may be a whole screw turn from 3/4 compared to 1/2.
    1979 XS1100F
    2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.
    Tags: None
  • #2
    Sounds like your slowly getting them tuned.

    the 3k power ad is because the main jets are kicking in. Every XS11 I have ever ridden you can feel that boost kick in at 3k, at 5k is where the REAL power band hits. If you have any weak clutch components, WOT at 5k or so will identify them for you.
    Life is what happens while your planning everything else!

    When your work speaks for itself, don't interrupt.

    81 XS1100 Special - Humpty Dumpty
    80 XS1100 Special - Project Resurrection


    Previously owned
    93 GSX600F
    80 XS1100 Special - Ruby
    81 XS1100 Special
    81 CB750 C
    80 CB750 C
    78 XS750

    Comment

    • #3
      I'm guessing your pilot circuits are still plugged up, or you have to go to bigger pilot jet...although there is definite change from pilot to main, correctly tuned motor should pull hard from idle to WOT
      just my .02
      Nick

      1979 XS11 F,Yamaha fairings w/hard bags, TC's fuse box, K&N air filter

      1982 Virago 750 (it's alive!)

      1979 XS 11 F, Windjammer IV, Samsonite luggage cases(another rescue)

      Comment

      • #4
        I agree with you Nick. After I get some color on the plugs and monitor fuel mileage, I'll check into current pilot jets. I guess I always assumed that you increased main jets first before ever having to increase pilot jets
        1979 XS1100F
        2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

        Comment

        • #5
          Originally posted by IanDMacDonald View Post
          I agree with you Nick. After I get some color on the plugs and monitor fuel mileage, I'll check into current pilot jets. I guess I always assumed that you increased main jets first before ever having to increase pilot jets
          Careful.......if that grey look stays on any one plug, your shortly headed for a ventilated piston. The grey can be actual alumunum pulled from piston. WOT for mains first...it needs to pull hard and fast ALL the way to redline. If about 7K, tach slows a bit compared to up to that point....too lean in the mains. The motors 36-3800rpm range and under will be approx. idle circuit range. Float levels can affect this rpm range to, besides pilot jet size, so make sure all eight of those floats are dead nuts on first. If ALL jets are NOT Genuine Mikuni having their little curly-q thing stamped into them, you WILL be chasing your tail till the cows come home....just a FYI.
          81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

          Comment

          • #6
            Not to discourage you, but you are at the BEGINNING of success, but not there yet. AS BA80 has said in the past, the earlier carbs ARE a bit easier to tune and more forgiving eliminating the slight stumble from idle circuit to main circuit since they pull fuel from both circuits. Hence, the larger main jetting for the earlier carbs and the smaller main jetting of the later carbs. The later model having no actual help with the transition to main circuit as they are pretty much seperated, even though a small amount may come through main circuit from the vacuum draw. Float levels, AND final fuel levels in bowls have to be all the same. It's actually very simple. Fill a glass with water, put a straw in the glass, and the water will be the same height in the straw as in the glass. Now blow across the top of straw to draw the water up out the top of it. Drop that water level in the glass to halfway, putting straw back in glass. Blow across top of straw and see how much harder your gonna have to blow across it in order to fill that larger vacuum created blowing across the straw to get the water to come out the top of it. Same principal on ALL carbs., whether they be automotive downdraft, motorcycle sidedraft/downdraft or farm tractor updraft. Hope that helps.
            81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

            Comment

            • #7
              Tune from top down.

              Like motoman said, get your big jets dialed in first and then move on to the other stuff. But make sure everything else is right before you tune your carbs. See the link below for a great procedure that works.

              http://www.factorypro.com/tech/carbtun.html
              Mike Giroir
              79 XS-1100 Special

              Once you un-can a can of worms, the only way to re-can them is with a bigger can.

              Comment

              • #8
                I have a thought, and you guys tell me if I'm wrong: if the PO had this bike tuned perfect with current carb jets, but only modified the advance curve, would that not still hold true without the modified advance? Meaning, no need to mess with pilots and main jet, just a tweak of the float height (maybe), and maybe another quarter turn of one or a few of the mixture screws?
                1979 XS1100F
                2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                Comment

                • #9
                  In other words, the bike ran like a raped ape in a cage prior to swapping out the advances, and me adjusting mixture screws. Are you saying that same state of tune cannot be attained again with mixture screw settings?
                  1979 XS1100F
                  2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                  Comment

                  • #10
                    Went out to the garage and turned the mixture screws a quarter turn to the left. Black carbon build-up on three of the four plugs. So, at-least I know I am not running too lean. Turned them back a quarter turn and will note riding issues.
                    1979 XS1100F
                    2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                    Comment

                    • #11
                      Originally posted by IanDMacDonald View Post
                      Went out to the garage and turned the mixture screws a quarter turn to the left. Black carbon build-up on three of the four plugs. So, at-least I know I am not running too lean. Turned them back a quarter turn and will note riding issues.
                      Those mixture screws REALLY need to adjusted with motor running and on CENTERSTAND, or on some sort of centerstand being vertical upright. Also needs to be done at operating temperature, which WILL require you to put a fan in front of motor to dissapate some that cyl. heat away. Even with that, you may have to shut it down to cool during the setting process. Mercury stixs(manometer) are STILL the ideal way to sync and set idle mixtures, but vacuum gauges WILL work. Idle mixes set to JUST the highest in. vacuum on all four cyl., then sync each pair, then sync the pairs together. Something that many overlook doing the sync is while motor is off cooling inbetween adjustments, blip that throttle several times to seat the thread sync screws. Re-start and adjust, shutting bike off and blipping throttle several times to again seat the threads, no matter how minute the adjustment was. Do this inbetween each adjustment process till when throttle is blipped, the vacuum draw stays within a 1/4in. vacuum draw on all four cyl. Using mercury stixs, and blipping the throttle while running is NOT a good idea, as a small hiccup from a cyl. can and WILL pull the mercury out of tube and into that cyl., and most of the time quicker than you can jerk the hose off.....DAMHIK. A correct and good carb sync DOES take a bit of time and practice......practice away(DON"T forget the fan). Some say the sync doen't come into play above idle......tottally dissagree, as when cruising at a normal 4-5K range, or even above that, The throttle plate opening is still minimal. Hope that helps get to a smooth running point quicker than what your trying to do now. After all that, THEN start checking plug color for any jetting change, which of course will require you to go thru the sync and mixture adjustment again after R&R of the carbs. Patience and diligance will reap you the reward grasshopper........
                      81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

                      Comment

                      • #12
                        Are you cleaning the plugs between test, putting in new plugs, using the same dirty plugs, or what?
                        Nathan
                        KD9ARL

                        μολὼν λαβέ

                        1978 XS1100E
                        K&N Filter
                        #45 pilot Jet, #137.5 Main Jet
                        OEM Exhaust
                        ATK Fork Brace
                        LED Dash lights
                        Ammeter, Oil Pressure, Oil Temp, and Volt Meters
                        Green Monster Coils
                        SS Brake Lines
                        Vision 550 Auto Tensioner

                        In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

                        Theodore Roosevelt

                        Comment

                        • #13
                          Originally posted by natemoen View Post
                          Are you cleaning the plugs between test, putting in new plugs, using the same dirty plugs, or what?
                          A good point Nate..
                          81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

                          Comment

                          • #14
                            You guys underestimate me, lol. I put brand new plugs in after I got my final tune. I did not have my tan coat on the plugs yet after running it down to work and back the day before yesterday. So, after I got home, I turned the plugs a quarter turn (having a box fan on the engine, letting it idle), and the plugs instantly carboned. I cleaned the plugs with contact cleaner, turned the screws back to where they were, and that's where I am now. If I do a slow roll on the throttle, I have no hesitation, and the bike screams through all gears. But, if I WOT in-gear right now, I have a slight stumble. Runs great otherwise all the way up to redline.

                            I noticed nobody commented on my statement regarding the pilot jets, and my lack of needing to switch them.
                            1979 XS1100F
                            2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                            Comment

                            • #15
                              Originally posted by IanDMacDonald View Post
                              You guys underestimate me, lol. I put brand new plugs in after I got my final tune. I did not have my tan coat on the plugs yet after running it down to work and back the day before yesterday. So, after I got home, I turned the plugs a quarter turn (having a box fan on the engine, letting it idle), and the plugs instantly carboned. I cleaned the plugs with contact cleaner, turned the screws back to where they were, and that's where I am now. If I do a slow roll on the throttle, I have no hesitation, and the bike screams through all gears. But, if I WOT in-gear right now, I have a slight stumble. Runs great otherwise all the way up to redline.

                              I noticed nobody commented on my statement regarding the pilot jets, and my lack of needing to switch them.
                              ....no comment, as you actually never stated what size they were, or whether they were Genuine Mikuni or not, least not anywhere I've seen in this thread. Not underestimating your ability, but trying to set mix screws with bike not running leaves ability still questionable....least with carb tuning.
                              81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

                              Comment

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