Announcement

Collapse
No announcement yet.

Carb tuning for dummies?

Collapse
X
Collapse
 
  • Page of 2
  • Filter
  • Time
  • Show
Clear All
new posts
Previous 1 2 template Next
    #1

    Carb tuning for dummies?

    Finally got the beast running, after almost a year! A carb teardown/rebuild, a new coil, new exhaust, timing adjustment, and about a hundred other things and it now runs pretty dang well! Except I need some help in the tuning department. I started out with the pilot screws at 1 turn out, and the air screws at 2 turns out. This setup is trashing my brand new V&H pipes! It seems to run very well with this setup but the plugs tell me I am lean and the pipes are turning dark gold and 3 of the 4 are starting to blue a bit. I followed V&H's suggestions and went to 115 mains, and upped the pilot jets to 17.5s. I double (and triple) checked and I have no air leaks at the airbox, and I replaced the intake o-rings so those are good. Running down the street on the pilot circuit (putting along at 20mph in 2nd) it chugs and pops and sputters from the carbs. On the main jets, it takes off like a cannon, like it should. The chugging sounds and feels exactly like it is running out of gas, like when I forget to turn on my pingel petcock ;-). I should make it clear that the problems I am having are due to tuning the carbs, as all I did was set them to what was suggested after cleaning them. I tried to turn the screws out another half turn (can't tell exactly how far I got them to turn) and it seemed to make it run a little worse (?). Its ridiculously hard to tune the pilot screws with them being UNDER the carbs. Also, watching my pipes turn yellow and blue is a very damaging way to tell what is going on with the mixture.

    What settings should I shoot for? Sorry for the long winded post. I just want to cover the bases and get it back on the road, as I won't ride it like this so I don't damage something.
    Tags: None
    #2
    Float levels should be rechecked. Sounds like a serious lean condition not due to jetting.

    Personally I would have left the old pipes on to make sure the carb rebuild/other repairs went well and saw the bike run stock OK before embarking on a rejet with the VH. This way you have a baseline to work from. At this point it is hard to guess if it are the pipes that are leaning the engine out or is it a carb problem because more than one thing changed.

    I don't mean to beat you up, I know it really sucks to have pipes turn blue.

    I bet floats or a plugged passage. I don't think three carbs would plug at the same time so floats are my first choice.
    1981 GS650G , all the bike you need
    1980 GS1000G Power corrupts, and absolute power corrupts absolutely

    Comment

      #3
      Gotcha duaneage. I wouldn't normally have made so many changes at once, but I would have never gotten it tuned right with the old exhaust because it was completely gutted. It would have been so much more lean with the old exhaust. Guess I will have to pull the carbs and check the float levels this weekend :-(

      ANy other suggestions if that fails?

      Comment

        #4
        Check fuel flow into the carb rack. Filter OK? kinked line or too small? Petcock flowing OK? is the vacuum line to it snug, ( might be cuting fuel off)

        Fix this before anything else. Lean burning is hard on the valves too. They sell stuff to remove the blue color from pipes, check out a dealer and see what they have. it may work. Mine are a little golden from leaving the choke on but they look kinda good like that.
        1981 GS650G , all the bike you need
        1980 GS1000G Power corrupts, and absolute power corrupts absolutely

        Comment

          #5
          Fuel flow is excellent. No stock petcock, in my first post I mentioned that I have a pingel petcock in place, working well. I am looking into the blue remover stuff, it is called "Blue Job". Sounds like it should do the trick. Anyway, tomorrow I will have a look at the float levels, but I sort of doubt that is the problem. Since this is for the initial tuning of the carbs, I think I just need a little help as to what steps I should take towards remedying the problem.

          Thanks for the insight, I will post some results tomorrow.

          Comment

            #6
            Lift the needels!

            Comment

              #7
              OK I spelt that wrong, litf the needles!

              Comment

                #8
                Well guys, I checked the float levels, they all looked good. I did go ahead and raise the needles one notch. It seems to have pretty much cured the lean problems (the rest I think can be handled with the pilot fuel screws). A couple things though- after raising the needles one notch, the idle will not go below 1500, even with the throttle adjuster screw all the way out. is this normal? also, the bike now seems to lost some of its punch. You used to have to hold on when hitting the throttle hard, and it really would take off like a rocket at around 5-6k. now, it just doesn't have that same "oomph" anymore. plugs are looking better (except one which is pretty rich, i need to mess with that). should i reset the needles to where they were before and just crank the pilot fuel screws all the way out? or is there something else I can do to remedy the current situations? Also I have noticed that the engine is noticeably cooler, I don't immediately burn myself on the cases anymore, and the pipes are not a more reasonable temperature (no more yellowing/blueing like before) which is a good thing. I guess I just need some guidance as to where to go from here.

                Thanks guys!

                Comment

                  #9
                  Lifting the needles was the way to go,but it does not effect the idle.
                  Make certain they are put together ok, check the cable adjustment, check carb balance,readjust pilot screws.

                  Comment

                    #10
                    I will be sure to check the cable adjustment tomorrow. I think with playing around with the air and fuel adjustment screws I can probably get things closer. Obviously the carbs can't be synched yet until the mixtures are correct, right?

                    Oh, and the whole raising the needles deal was a lot easier than I thought... it's really fairly simple!

                    Comment

                      #11
                      No it's ok to balance your carbs,you may have to do them again later,but balance is very important.

                      Comment

                        #12
                        I have a Morgan Carbtune but have not gotten to use it yet. Basically once I get the mixtures close, I hook up the carbtune and run the bike, adjusting the air screws till they are all within a 2cm hg of each other, right? I guess I am not sure of if it is adjusted by using the air screws. The "manual" that came with it really doesn't explain this at all. It just says "adjust carbs until they are within 2cm of each other".

                        Comment

                          #13
                          No it's not adjusted by the air screws,what balanceing does is to make the vacumn drawn in the same for each carb,if you have cv carbs there is a locknut and screw on three of them on the throtle linkage,one is fixed so you adjust the rest to that.Not sure what carbys you have got,if they have a largish top they are cv,if they are narrow just slide carb's .
                          Not certain what you have,if they are slide I think there would be a locknut and adjuster under the top covers.
                          Run the motor at 2000rpm (aprox), the value your gauge will show is not important as long as they are all the same.
                          By the way every time you change your jets you put your carbs out of balance.
                          Hope this help's!

                          Comment

                            #14
                            Can anyone confirm what screw is used for synchronization adjustment on my stock VM26ss carbs?

                            Comment

                              #15
                              Inside the top's of the carby's.

                              Comment

                              Previous 1 2 template Next
                              Working...
                              X