Topic: Problem with #2 cylinder on CB650

[destroyer]

   After completely rebuilding the carbs and replacing gasket, jets, diaphragms, etc, I put them back on my 1979 CB650.  She fires up, but is rough.   I noticed that the #2 and #3 headers are nowhere near as hot as the 1 and 4.  I checked the plug wires and they are all getting equal spark.  I switched the coils and she is still running the same.  When  I unplug the #2 wire while she is running, there is absolutely no change in rpms or idle.  When I unplug the 1 or 4, she dies, so they are definitely at full force.  When I unplug the number 3 wire, there is a slight change, but not much.  My motor only has 8,000 miles on it.  I know that the number #2 carb is the one with the accelerator pump and stuff.  Other than remove the carb and make sure there is nothing wrong with it, what do you suggest?  I will be checking cylinder compression this afternoon when I get an adapter that will fit my plugs. 

On another topic, what is the factory number of turns out on the idles adjustment screws?  Is it 2.5?

[kghost]

You check the points?

[destroyer]

Dumb question:  How do I check the points?

[eurban]

Well you would need to find a bike that uses points first Your 650 has an electronic ignition.   I don't know the factory setting of the IMS screws for the 79 650 off hand but I doubt it is 2.5 turns out.  These screws will only meter effectively till about three turns out so I doubt Honda's stock settings are close to the extreme end of the adjustment range.  Probably more like 1.5 as the baseline setting.  How about getting or downloading a manual for your bike?  Set your mix screws to the correct baseline setting  (perhaps someone else can tell you what that is) and then work from there.  Look at your plugs (their appearance will give you some useful intel) and swap them around if you want to test for more ignition related issues.    Most likely you still have some carb issues.  I would guess impaired idle circuits in the dead/deadish cylinders.  Did you pull your pressed in idle jets and clean them carefully?  You might also have insufficient fuel in the 2/3 bowls.  Should be easy to do a check to see how much fuel drains out of those bowls vs the outer two.  You can also use clear tubing on the overflow nubs to see what the actual fuel level is in each carb bowl.  Did you bench synch your carbs after the rebuild?  Have you set your valve clearances? Is your bike modified?

[jtrain]

Im with earban: carb probs at least it was on my cb650.

[destroyer]

I have not modified anything, my bike is 100% stock.  I have the 1979 Honda service manual, but it is vague in many areas.  As I said before, I took every single piece of carbuerator apart and soaked them in carb cleaner.  Then I replaced the gaskets, needles, and jets with new ones and put it all back together, so I am pretty certain all of the jets are clear.  I stuck sewing needles through them all to make sure they were clear.   I have replaced all the plugs, and the plug wires are all giving good spark, so I would think it has to be the cylinder itself, or the carbs.  I have not synced carbs yet, and need advice.  I have a mercury carb balancer that I use on my '07 Triumph T100.  It does not have the boots on the ends of the hoses though, just hose?  How do I hook it to my carbs?  Attached are pics of my balancer and my carb.  I am assuming that the balancer tubes go into where the flathead screw is in the right of my picture?  If not, please tell me what the hell that screw is for.Thanks for any additional advise.

[eurban]

You have pressed in idle (pilot) jets on your bike. The manual will likely tell you that they are not removeable.  However on bikes of our vintage, inorder to properly clean the idle circuits, these jets should be carefully pulled, soaked, and have something like a single strand of COPPER wire run through them. These jets have a single tiny up and down hole in them as well as crosswise holes. Everything must be completely clean.  The passageways underneath the jets are much more effectively cleaned with the pilots removed.   A sewing needle will damage them if used with much force.  So did you pull them or not?  A bench synch involves adjusting all the slides to be at the exact same height with the throttle open at a given setting.  #2 slide is not adjustable at the linkage underneath the cap so it is your baseline.  Take something like 1/8" drill bit and adjust the the idle speed knob (it moves the entire linkage so all carbs are affected) untill you can just slide the 1/8" bit between the #2 carb slide bottom and the carb bore.  Now adjust all the other carbs to have the same exact opening using the synchonization adjustment screws underneath the top caps of the carbs. This will put you at a good starting point from which you should be able to properly synchronize your carbs using guages while the bike is running.  . . . .Doesn't the manual tell you what the baseline setting is for setting your IMS screws??

[destroyer]

The idle yet is the on thing I did not remove because the manual said I would not.  However, I soaked everything and gently put needles in to make sure I was getting passage.  Thanks for the advise on the bench sync, I'll give that a try right now.  As far as the IMS screws, all the official Honda manual tells me is to record the number of turns out that they were before I took the needles all of the way out.  However, I am not sure that the previous owner had them set right, so I am still unsure as to how many turns I need. 

[cb650]

Haynes says 1.5 turns.   The pilots do come out just do it carefully.
My current bike I couldnt get to run right after several carb cleanings/checking.  Cleaned up another set I have and put them on and it runs great.  As for the ignition if you have fire you wont have to mess with the timing unless someone took the trigger/pickups off and didnt get them on right.

[eurban]

Your problem could be a number of things but you have the classic symptoms of impaired idle circuit(s).  You can ignore this if you like but my guess is that to fix your problem you will need to pull your pilots and clean them properly.  Keep sewing needles away from the tiny orifice in the pilot.  It can be enlarged very easily.