Topic: Carb slides and needle

[Badboy]

I am in the process of fixing the carb problems on my 1972 CB500four.I have looked through some of the tech sites ,but so far can't find the info. The trouble I had with my carbs when I had it going,was that it run rich at about 35 to 40 mph at nuetral throttle. I tried about everything [I know now that the carbs were not syncronized right]but I am not sure that is the only problem.
Can anyone tell me what the number on the slides should be or what the cutaway should measure and the number on the slide needle. It ran good at full throttle idled not to bad but took more gas than it should[sparkplugs to dark]. I live at about 1000 ft above sea level,so there is not a problem with high altitude.

[TwoTired]

The stock CB500 carbs had a setup number stamped onto the carb body mount flange, top right.  The setup number for the the CB550 with stock airfliter and exhaust system was 627B.  These carbs had a #40 slow, #100 main, and , according the the shop manual, #2.5 needle.  I never suspected the slides or cutaways were different beteen the CB500, CB550K, & CB550F that used the same style carb bodies with different setups; 627B, 022A and 069A respectively.  So, I haven't compared the slides themselves beteen models for dimensional or number stamped differences.  I'll make some notes next time I need to take them apart.

One technique for machine repair is to correct anything known to be out of spec.  Do enough of this and the bike will generally run like new.  Of course, this assumes a bike unmodified from book referenced specifications.  If your carb sync is out, sometimes the plugs will show different deposit types.  At any rate, you can compare the plugs to the pics on:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
Also, unbalanced carbs can show different head pipe temps, particularly at idle.

You also might consider marking your throttle with tape, temporarily, while you sort out the troubles.  This is so you will know where 1/4, 1/3, 1/2, etc, throttle posistions are during tests.  This will better help you focus on what part of the carb operation to address, pilot jet, air bleed, slide needle, or main jet.

Hope this helps,

[Badboy]

I have done some careful measuring. The main is about .040 in,don't know what that would be in a #. the pilot is .017 in says 40 on it.Slide needle is 2.5mm down to .125in tapering to .050in at 2.150 in. Slide is 1.620in long,1.520in on the cut out side.A 7/64 drill will go in 3/8in or better [.111in] on the top of high speed emulsion tube. Are they worn out.How tight should the needle be in them? There is some numbers on the slide needle,but can't make it out ,maybe 2/ something. There is a reason that it is runnig fich, but at this point I do not know why. What do you think  on this one? The slide has numbers 103 on the bottom and 2.5 accross from that on the bottom

[Dennis]

Don't know about all of those numbers ......
but did you try lowering the needles?
Also are your floats at the correct height?

[TwoTired]

Being a Japanese motorcycle, the engineers used the metric system for all the measurements.  A #40 jet is .4mm (about .016 in.).  A #100 jet is 1mm (about .0393 in.)

I admire your diligence measuring the needle profile.  However, worn needles generally have wear marks where they rubbed against the needle jet.  Likewise the jet would be shiny at the wear points, or the opening is oval shaped.

I've never seen any profile measurements printed or posted anywhere.  It would be nice data to have, I admit.

Cheers,

[Badboy]

I think that I have tried everything,lowering fuel level,lowering the slide needles ,changing the idle air bleed,etc. It still run to rich[the sparkplugs to dark]at about 35 mph or so. Wide open it run good,idle not the best but I could live with it. I have been told by one who works on these kind of carbs that being out of sync would make it mean at less that 1/4 throttle. I am think that it is taking fuel though the high speed jet to soon. When I put the slide needle into the emulsion tube I can see light by it [there is over .010in clearence there. Is that to much?

[Einyodeler]

I have had 2 cylinders running rich before and changing the needle settings had no effect , turned out to be the o-rings on the main jets were almost gone and fuel was seeping up past the jets.Another thing is make sure that your float heights are set at 22mm.

[Badboy]

  My post about the diameter of the slide needle and the relation[in the down position,slide closed] in size to emulsion tube,.011 in clearance [I can see light though it with the needle in place]. Is that okay or is the tube worn out? How tight should the fit be?
I know it can't be to tight or it would bind.

[Dennis]

I don't think anyone on the board knows the answer to your question and I would guess that is why you did not get a response. There must be some space there to allow fuel flow. How much space - only Keihan and Honda know for sure I would think.