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88' Hawk backfiring after Mukini, Stage 3, and Pods

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    88' Hawk backfiring after Mukini, Stage 3, and Pods

    I first met this Blue Beauty in 1994, stupidly sold her in 2015, bought her back (+5 miles, same exact gas) a few months ago, and got her back on the road running like a top shortly after (carb clean, new battery, new tires, fired right up).

    I've got a little more budget for Hawk parts these days, so I also sprung for a new rear shock, a mukini fuel pump, and pods (already had a full M4 system on). Horde was temporarily out of stage 3 kits and I NEEDED to ride, so I took it out and had a lot of back-firing issues. I figured I had more air with the pods than the stock airbox, so I was likely running lean. I put the stage 3 in (bigger jets, stretched springs, clips moved up the needle) but am still getting backfiring.

    Any advice?

    #2
    Did you put on new intake boots? Id guess air leak.
    Don't spend money and buy, spend time and learn.

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      #3
      Solid maybe (boots look solid).. but the inspection might have found something.. I am assuming there is a mixture screw for each carb? Cause I don't see one on the right side of the bike. The one on the left seemed to be pretty backed out as well, might be I flubbed that in the deep carb clean when I got the bike back.

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        #4
        There is a pilot screw for each side. I think that's what you're referring to.

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          #5
          Backfiring on decel? How did the air cutoff valves look when you cleaned the carb? Where the valves seated correctly when everything was put back together?
          ASMA #139

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            #6
            Yes, backfire on decel, the more engine braking, the worse it was. I never touched the air cutoff valves; they likely haven't been touched since the bike was new.

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              #7
              What jets are you running, where are your clips on the needles, and how many turns out are the slow speed screws? JD usually throws out a rough 2.5 as a baseline on the screws but if you did pods and your jets are not larger than 158 or 160 then that may be your issue as well. Also, is your backfiring on decel? If so may be the Air valve, which people overlook a lot of the times when cleaning. Also worth asking, you did clean the carbs out well before changing the jets right? Sounds like it had fuel sitting in it for a while so good chance some passages are not clean and clear.
              88 Blue Hawk GT - Under construction but rideable (guest approved)
              89 BlackHawk 2.0 - On the lift and being assembled
              90 Hawk GT (color as to yet be determined) - Still on the shelf in crates

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                #8
                Originally Posted by Chrisvp View Post
                Yes, backfire on decel, the more engine braking, the worse it was. I never touched the air cutoff valves; they likely haven't been touched since the bike was new.
                I would give those a look.
                ASMA #139

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                  #9
                  Originally Posted by Chrisvp View Post
                  Yes, backfire on decel, the more engine braking, the worse it was. I never touched the air cutoff valves; they likely haven't been touched since the bike was new.
                  having done alot of carb work on various hondas over years, i've never yet found a bad one, so i believe it can be generally ignored .....unless some careless twit misplaced the spring in there while he was screwing it up........?

                  does your bike have good top end power and is able to redline in lower gears ?
                  Last edited by squirrelman; 11-07-2022, 11:41 PM.
                  "It's only getting worse."


                  MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

                  Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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                    #10
                    Clarifying: After getting the bike back from it's temporary owner, I drained the coffee colored gas out of everything and gave all of the passageways inside the carb (that I know about) a good cleaning. Everything went back together and the bike ran great. Full redline in any gear. No stumbling or backfiring. Full M4 exhaust. Stock airbox (minus the snorkel). Clips two clicks down from the non-pointy end on the needles. I don't know what mains went in. Mixture screws likely 2.5 turns out (based on something I wrote in the service manual) As far as I could remember, it was the same performance as previous. I know this is a dangerous assumption to make, but I would believe it was the mods AFTER I got the bike on the road that is causing the trouble.

                    Next, I put in a new fuel pump and pods. It would accelerate ok, and I could hit redline, but it backfired on hard decel. I figured it needed more jetting work.

                    Now, I put in Factory Pro Stage 3 (168 front, 164 rear but going by memory), clips on forth position from the non-pointy end, standard pilots, springs stretched to 8" and baked. Have not taken it out on the road, but seems to backfire exactly like it did before. The factory kit didn't make a difference.

                    Based on 6 advice to inspect the carb to engine boots, I found that the right mixture screw is gone. The left one was turned WAY out. This seems like the most likely culprit. Horde has some coming in so it might be a week or so before I can report back.

                    Anyone in the San Antonio area? Would love a second set of eyes on this

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                      #11
                      What kit did it have before the stage 3? -- Stock needles are not groved.

                      If you were looking for a support group you're barking up the wrong tree. This place is fulla enablers dude. - Shooter77us

                      The bitterness of low quality lingers long after the thrill of a low price has gone. - RacerX450

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                        #12
                        I'm guessing a stage 1 Factory Pro, back in 1998 when the M4 went on

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                          #13
                          backing the screw out any more than about 3 1/2 turns risks its falling out while you're riding.
                          "It's only getting worse."


                          MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

                          Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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                            #14
                            Update: I put a new mixture screw in the front cylinder carb and everything smoothed out nicely. Too much rain today to road test, but everything is feeling like it should. I also replaced the original spark plugs.. The plug wires seem fine but I bought some the the NGK wires from Hord while I had the credit card out. I'm assuming "if it ain't broke, don't fix it" and they can go in the parts bin?

                            Comment


                              #15
                              Update after riding. Smooth and fun! At least in the lower RPMs and with 1/4 throttle. Upper RPMs seemed slow to climb, and more throttle had no appreciable effect on engine effort. It is completely possible that it's normal for a Hawk to be slower to redline, but it seems solid up to 4K rpm, and then take awhile to go beyond, even in second gear. 168 main front, 164 rear, 42 pilots. Exhaust doesn't smell gassy. Not much change after the bike warmed up; maybe a little better power.

                              Possible my main jet is starved somewhere other than at the jet?

                              I've never synched the carbs, is that the next thing to do?

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