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Bros 650 - carb issues - rich vs lean - help requested

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    Bros 650 - carb issues - rich vs lean - help requested

    (before I posted this, I did a search, couldn't find anything exactly as below, apologies if similar has been asked previously).

    Hi,

    First off, a brief summary of the bike:
    1988 Honda Bros 650
    K&N airbox filter
    Dynojet stage 1
    Supertrapp exhaust with about 8 plates (I think)
    Owned 23 years
    182,000km (almost all me)

    Owner:
    49, reasonably technical, but no access to a workbench due to location.
    I know how my bike feels, or should feel, to ride.

    Issue:
    About a month ago, I dropped it off at my garage, as it had been diagnosed as running rich. I have no doubt this is true, the petrol consumption has gone up gradually over the years.
    The carbs were torn apart, and diaphragms found to be ripped, and were replaced. They carbs were cleaned, and the bike put back together.
    It then exhibited classic lean running symptoms:
    -popping on the overrun
    -lack of power setting off, and in the mid-range
    -petrol consumption way too good (55mpg (UK) in town - very unlikely
    -running very hot - fan coming on way sooner than usual
    So I returned it to the mechanic. He raised the needles a notch.

    Now:
    -The immediate throttle response is back, as it pulls away from idle.
    -The bike accelerates well on an half to fully opened throttle
    -its the 1/4 to mid-throttle response that still suffers, but only a little - it's fluffy, there's a slight hesitation rolling on the throttle smoothly at 40-60mph.
    -slight backfire, but nowhere near as frequent, or bad as before.

    I'd like the bike to run perfectly, can you please suggest what to ask for next?

    Thank you!

    Humbug
    London
    UK

    #2
    your jetkit introduced alot of variables and may require repeated attempts to get it right. idle drop procedure will get 1/4 throttle response dialed-in. check sparkplugs for proper color (colour) ! study the tuning instructions that came with the jetkit.

    having someone else working on your carbs but not himself riding the bike makes things much harder to get right.

    sometimes you need to stretch the slide springs for the best results.
    Last edited by squirrelman; 07-28-2019, 03:51 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.

    Comment


      #3
      Borrowing below image from ParcNHawk, you could try to raise the needles a bit more - it is free and easy and if it doesn't fix the problem or even make it worse, you can just lower them again...

      Carb_effects.jpg

      Comment


        #4
        Might be worth a call to WE moto in Brighton to see if they can help. They are a parts supplier but stock most carb bits . Worth a try

        Comment


          #5
          As an aside I have a Supertrapp and got it repaired the discs at the end are stainless but bolt onto a mild steel collar which rotted away. Fixes through the end of the pipe if I recall.

          Comment


            #6
            Originally Posted by Bros Steve View Post
            As an aside I have a Supertrapp and got it repaired the discs at the end are stainless but bolt onto a mild steel collar which rotted away. Fixes through the end of the pipe if I recall.
            Maybe contact Supertrapp and see if they have a baffle end cap they'll sell ya. Actually your baffle may need replacement as well. Ask for both see what they say.
            "Hawk Porn" http://picasaweb.google.com/11124379...eat=directlink 1990 NT650-Penske 8981, Race-tech Springs & Gold Valves, Steve Lenac six-piston caliper & EBC rotor,SS Brake lines Ft / Rear lines through SSA ,VFR brake lever, F2 front wheel, F-120/70 R-160/60 Dunlop Roadsmart, Full-Supertrapp Exhaust, Stage 1 Jet kit, K&N Filter, Corbin Seat, Pro-Tec Clip-On's/ Past Rides...1986 VFR700F2 Interceptor / 1979 Yamaha Rd400 Daytona Special

            Comment


              #7
              Thanks Spa. I had a guy who does classic racing Honda's fit a new baffle here in the UK. Thought it might be useful info for Humbug if he needed his doing anytime. Sorry if I've caused confusion

              Comment


                #8
                Originally Posted by Bros Steve View Post
                Thanks Spa. I had a guy who does classic racing Honda's fit a new baffle here in the UK. Thought it might be useful info for Humbug if he needed his doing anytime. Sorry if I've caused confusion
                No worries
                "Hawk Porn" http://picasaweb.google.com/11124379...eat=directlink 1990 NT650-Penske 8981, Race-tech Springs & Gold Valves, Steve Lenac six-piston caliper & EBC rotor,SS Brake lines Ft / Rear lines through SSA ,VFR brake lever, F2 front wheel, F-120/70 R-160/60 Dunlop Roadsmart, Full-Supertrapp Exhaust, Stage 1 Jet kit, K&N Filter, Corbin Seat, Pro-Tec Clip-On's/ Past Rides...1986 VFR700F2 Interceptor / 1979 Yamaha Rd400 Daytona Special

                Comment


                  #9
                  Running hot means lean.He raised the needles.....made it richer .Now you have a mid-range hole.Go down to 4 rings on the supertrapp and ride it.Report back.
                  There are other ways to affect the mixture w/o fiddling with jets......you need to choke the exhaust a little.

                  Comment


                    #10
                    Originally Posted by behindthetimes View Post
                    Running hot means lean.He raised the needles.....made it richer .Now you have a mid-range hole.Go down to 4 rings on the supertrapp and ride it.Report back.
                    There are other ways to affect the mixture w/o fiddling with jets......you need to choke the exhaust a little.
                    That's worth a try - easy thing to mod.

                    I've been riding the bike in central London, and it's behaving nicely, but will try this before the next run out of town.

                    Comment


                      #11
                      Originally Posted by Humbug View Post

                      That's worth a try - easy thing to mod.

                      I've been riding the bike in central London, and it's behaving nicely, but will try this before the next run out of town.
                      Use some anti -seize on the disc bolts.....they can be sticky.

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                        #12
                        Originally Posted by behindthetimes View Post

                        Use some anti -seize on the disc bolts.....they can be sticky.
                        They can be sticky even with anti-seize. When I used to have mine, I broke off several of the welded-on nuts inside and that was with anti-seize.

                        Brian - Richland, WA
                        1991 Hawk GT
                        1997 VFR

                        Comment


                          #13
                          wonder if aluminum duct tape wrapped around the discs to block them off could be worthwhile... that way you'd know if it was worth snapping off then bolts that hold the discs before go down that path? Yeah, you'll likely have to clean up some goo mess, but I'd rather do that with cleaner and stiff brush than deal with exhaust nuts and bolts.

                          Comment


                            #14
                            Damn, wish I'd read your post before trying to take the exhaust apart, and snapping a bolt.

                            I also found the internal muffler is shot - rusty.

                            I can't even get the 5 remaining bolts out of the exhaust.

                            Took the whole exhaust off to try and take it to my motorbike shop, to find that they no longer do Supertrapp.

                            Can anyone let me know what parts to get, and where from?

                            Cheers,

                            Humbug

                            Comment


                              #15
                              After researching, I now know that I need a core. Thing is, I don't know the part number to ask for.

                              On the original AZ Motorsports invoice from 2000, they list this as p/n 623515. This might be their p/n, and not Supertrapp. Also, AZ Motorsports don't do Supertrapp, or motorbike parts any more.

                              I have emailed Mr. Hord, and Supertrapp, for help.

                              Ordered some copper grease for the bolts, and some exhaust assembly grease, in case I try and put it together as is (I'd rather not).

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