Topic: CB500K2 Stock Carb Settings

[mrmunsell]

I am working on my carbs and trying to determine the stock configuration as a point of reference.

I have a CB500K2 (US) with 627B carbs.  I found most of the information I was looking for in the shop manual as well as 'CB500/550 Carb Specs' page on this site.

http://www.sohc4.net/cb550-faq/indexphp/cb500550-carb-specs

However, those resources did not answer one question I had... and created another.  I tried to find answers within the forums, but found multiple answers in one case and none in the other.  Maybe someone here can help with those...

1. What is the stock jet needle position?  The chart has this info for some configurations, but not the CB500K0-K2.  Mine is currently in the middle (3rd position).  Some threads I found indicate that this is the stock position, while others indicate it is the 4th position.  A post in one thread indicated it is a function of the market.  I have not been able to find that post again, but I think it said the standard setting was 4 for all markets except the US where it was 3.  If that is true, is that to compensate for other tuning differences between the markets... or was that some type emissions compliance / performance trade off?

2. What is the 'Air Jet'?  The shop manual and the site carb spec page both indicate #150 is the standard size for my motorcycle... but I have not been able to determine what this jet is and where it lives in the carb.  I have the carbs apart now and identified every jet / needle / valve that I removed (main jet, slow jet, jet needle, float needle / seat, throttle valve)... so either I am completely overlooking an additional jet somewhere or maybe it is something I identified by a different name.  Is it the emulsifier tube (one end resembles a large jet )?  My jet needles are marked 272304, which I understand is stock from what I have read here on the forums.  I haven't found any markings on the tubes yet... but they were much dirtier than everything else and I am still working on getting them cleaned up (I think they skipped them in the last carb overhaul done by the PO).

Thanks!

[shawn57nomad]

I think what you are referring to is the air screw.  I'll see if I can dig up the picture quick unless someone else chimes in.

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[shawn57nomad]

Or check this link part way down it shows items 1, 2, 3, 4 with description in picture.
http://forums.sohc4.net/index.php?topic=49763.0

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[mrmunsell]

Thanks for the prompt responses.  I had removed the air screws as well... and they look similar to the picture in your post.  I had not heard them referred to as air jets before... but I guess that does make sense given their function.  There are no size markings on mine as far as I can tell... but they do have the Keihin insignia and look to be of similar age as the other jets (which were all the stock sizes).  So I think you answered my second question.

[mrmunsell]

Back at my computer and doing some further reading on this.  I found an image that labels the air jets... Post #30 of the carb FAQ thread: http://forums.sohc4.net/index.php/topic,5410.msg741454.html#msg741454.

I am guessing those correspond to the 'Slow Air Jet' and 'Air Jet' in that carb spec page I referenced earlier.  In any case, I don't think any of these are something that is likely to have been altered or replaced by a PO... which is what I am trying to assess while I have the carb apart.

[CycleRanger]

My tiny Honda spec manual dated 1974 says:

Float level: 22mm
main jet: 100
slow jet: 40
Std. needle position: 4th groove from top
Idle mixture initial setting: Two turns from closed.
Idle speed: 1000 rpm.

Although these settings assume original exhaust.
You may have to to some experimenting to find the sweet spot with that new exhaust.

[mrmunsell]

Thank you for that information.

The Honda shop manual I have is consistent with that information... except it doesn't mention the needle position at all (that I have found anyway) and indicates the initial air screw setting is 1 +/- 1/8 turn from closed.  That is also what the carb spec page on this site indicates.  I have been reading through many threads on this subject here, and some indicated the initial setting should be 1 turn out, others indicate 2 turns out.  I am wondering if those two different values correlate with the two different stock needle positions.

I found an image in another thread which lists 500 / 550 specs (attached).  It is dated 1977 and looks like a scan of some pages from a booklet or something... perhaps a newer version of the tiny spec manual you referenced.  The 500 specs are all the same as what you listed.

As you noted, I just installed a new exhaust (Delkevic).  Still have the stock air box.  And aside from the uncertainty of the jet needle position, it looks like the rest of my carb configuration is stock.  The current carb setup seemed to be working reasonably well with the aftermarket exhaust the bike had when I purchased it (Kerker).  Although both exhausts are 4-1 with megaphone mufflers, the Delkevic down pipes are smaller in diameter and probably have other differences that will effect tuning (down pipe lengths, internal muffler design, etc).  So I figured it was best to start with the stock carb configuration and then go from there...

[CycleRanger]

Yes, that image looks like scans of pages from a later version of the same book I have.
You are correct, if your bike was running well with the Kerker then you should use the same settings
with the new exhaust and see how it runs.

[mrmunsell]

About to get back to working on the carbs... and I still needed to settle on the needle position to continue.  I wanted to start with the stock carb configuration... but was still uncertain if that corresponded to a needle position of 3 or 4.  I just did another round of searching here and found the posts below by Deltarider (both from a common thread).  The theory outlined there sounds plausible to me.  It fits with everything else I had read and I certainly don't have any better theories. 

So I am going with that and starting with the 3rd needle position and with the air screw 1 turn out.  When I pulled the carbs, the needles were at the 3rd position and the air screws were out 1.75 +/- .25 turns (but my emulsion tubes were pretty dirty, the float levels were a off by about 2mm on average, and one carb had overflow issues - I believe due to float / needle issues which I hopefully fixed).

Thanks for the help everyone!

http://forums.sohc4.net/index.php/topic,155383.msg1779542.html#msg1779542
http://forums.sohc4.net/index.php/topic,155383.msg1779684.html#msg1779684

[Deltarider]

I am wondering if those two different values correlate with the two different stock needle positions.

Yes, they do. I've experimented. Standard was 1 turn out for the airscrews and 3rd (middle) position for the needle clip. For some reason Honda America choose two turns out and 4th clip fot the needles. Why? We just don't know.

[TwoTired]

 627b carbs use different settings from the 649a carbs.

Were it me, I'd use the U.S. model settings.

Cheers,

[mrmunsell]

Thank you both for the followup.

I believe that second post I referenced by Deltarider indicates that the 627b carbs in other markets (UK and France) had the same jetting as the US, yet they used those non-US settings (3rd needle position and 1 turn out).  Based on the bits of information I have found around the forum thus far, it seemed that the 4th position / 2 turn config is unique to the US market (and not the 627b carb)... fitting with the typo theory in the first post I referenced.

But as I reread the second post I referenced, it is not clear if that air box cover difference also noted in the post is applicable only to the Euro models with 649a carbs or also those with 627b carbs (UK and France).  Perhaps other US market specific differences outside the carb such as that factor into this as well.

So then... I am taking TwoTired's suggestion and starting with the US settings after all (4th needle position and 2 turns out) and will go from there.  I was just about to install the needle on the first carb...

[Deltarider]

I believe that second post I referenced by Deltarider indicates that the 627b carbs in other markets (UK and France) had the same jetting as the US, yet they used those non-US settings (3rd needle position and 1 turn out).

Correct.

Based on the bits of information I have found around the forum thus far, it seemed that the 4th position / 2 turn config is unique to the US market (and not the 627b carb)... fitting with the typo theory in the first post I referenced.

Correct.

But as I reread the second post I referenced, it is not clear if that air box cover difference also noted in the post is applicable only to the Euro models with 649a carbs or also those with 627b carbs (UK and France).  Perhaps other US market specific differences outside the carb such as that factor into this as well.

The airbox cover was exclusively on models (ED, G, H) of the CB500, CB500K1 and CB500K2 for some markets on the European continent that had the 649A carbs. UK, France and other markets (US excepted) had the 627B carbs with the airscrews at one turn out and needles clip in 3rd slot as you can read in any Honda document from the very beginning. Why Honda America suggests a different setting (mind you that booklet being the only source) remains a mystery. I don't rule out they were misled by an error in the Honda Shop manual CB500-CB550 on p. 165.

[mrmunsell]

Deltarider, thank you for the additional information.

I got my carbs reassembled and installed.  I went with the '4th needle position / 2 turn' configuration as a starting point.  This configuration was in the ballpark: started easily, stable idle, rideable, but on the rich side.  Acceleration was uneven at lower throttle angles (plugs fouling, I think).  Smoothed out at higher throttle angles, but acceleration seemed lacking.  Backing out the air screw about 1 full turn (achieved in multiple iterations / steps) helped things, but not enough at the lower throttle angles.  I have only taken it out on an initial test run so far...  still probably have a bit more testing and tuning to get it all sorted out.  No plug chops yet... but I did pull the plugs after my test run (rural roads with little stopping / idling) and they were fouled.  Once I get things sorted out, I'll post an update here.  Maybe this weekend with any luck.

Thanks everyone!

[Deltarider]

You're doing a fine job and I admire your thorough approach. Is your airfilter stock?

[mrmunsell]

The bike still has the stock intake boots / plenum / filter box.

I believe the air filter is an aftermarket stock replacement.  It looks just like the one at the link below - it even has the removable little red foam dot (still in place).  It was on the bike when I got it.  PO claims it was replaced about two months prior to my purchase... and it looks consistent with that to me (very clean).

http://4into1.com/uni-foam-stock-air-filter-cb500-cb550/

[mrmunsell]

I just wanted to update this thread with my progress on this.

This is the carb configuration I ended up with for now:

Jet needle position = 3
Pilot jet size = #35
Main jet size = #105
Air screw position = 2 3/4 turns out

Bike config:  About 750 ft above sea level.  CB500K2 (US model w/627B carbs).  About 14K miles.  New Delkevic 4-1 exhaust.  Stock air intake system with new OEM paper air filter.  Dynatek 5 ohm coils.  New OEM points and condensers (Tek).  HondaMan ignition.  Points and valve clearances recently adjusted.  Carbs recently overhauled and synced (bench then vacuum, multiple times along the way).  Keihin needles / jets / air screws.  New OEM float seats / valves from Honda.  Float levels set to 22 mm during overhaul and then further adjusted on the bike to get the fuel bowl levels to 3 mm below the carb bowl flange.  New intake manifold O-rings and boot clamps.

I arrived at this carb configuration by starting with the stock configuration and changing one thing at a time based on feedback from the bike (behavior, performance, plugs).  Arriving at a satisfactory main jet size and jet needle position was relatively quick and painless, but it took many iterations to get to that same point with the pilot circuit.  It started out excessively rich… so I backed out the air screw one step at a time trying to overcome the excessive richness… until the air screw was all the way out (head flush with carb body - roughly 3 1/2 turns).  Then down to the next available Keihin pilot jet size and repeat.  #40 -> #38 -> #35.  As I found myself having to back out the air screws even with the #35s, I was starting to wonder if #32s might be necessary or if I might need to consider straying from the stock float height.  But thankfully things started looking better as I approached the vicinity of 2 1/2 turns out on #35s.

I think there is room for further improvement, but I am very happy with how the bike is running right now and will run with this configuration for awhile to establish a new baseline.  It is much better than when I got it.  The biggest difference is from 1/4 throttle to WOT.  When I got it, the fuel metering was okay in the first 1/4, but then leaned out beyond that.  Throttle response and power are good across the board now.  And it has been pretty well behaved with this jetting so far (nice transition through the 1/4 throttle region, etc).

When I got the bike, the measured float heights were about 2 mm higher than spec (except #4, whose float frame was twisted resulting in the two pontoons differing by about 5 mm in height).  I corrected the float heights when overhauling the carbs… and then found that the bike ran excessively rich in the first 1/4 when I got everything back together.  It was rideable, but I had to minimize time spent in the first 1/4 to prevent fouling the plugs.  I suspect a previous owner or mechanic had a similar experience after installing the Kerker 4-1 exhaust that was on the bike when I bought it... and they altered the float height to improve the first 1/4 without any rejetting (and at the expense of 1/4 -> WOT).

[dave500]

that photo shawn57nomad,whats with those solid looking airscrews?

[CycleRanger]

I just wanted to update this thread with my progress on this.

Great followup. Sounds like you've been busy!

[jonda500]

I just wanted to update this thread with my progress on this.

Great followup. Sounds like you've been busy!

+1  thanks for sharing

I have had a similar journey with my CB500 (1973 Australian model which is a K1 with a K2 engine).

I have original 4 into 4 exhausts, but apart from that I currently have almost the same set up as yours:

627B carbs
- main jets #105
- pilot jets #35
- needle clip position 4
- air screws 5/8 turn out
- float levels 4mm below seam

I have the little rubber spoiler on the front of the air cleaner box and the original tool tray.

I haven't tried running the needle clips in position 3 since I changed the mains to 105, but looking at your setup, I'm thinking I should try that again along with raising the float levels to 3mm.

Mine currently has good plug color, starts easily and runs well in most situations, however when cruising in top gear at highway speed if I close and re-open the throttle I get momentary hesitation. Also if I back off just slightly to slow down just a tad, it seems that it slows down a little more than just a tad...

I admire how you've done yours in what I believe is the correct order -float levels, -mains, -needle clips, -pilot circuit, I wish I'd had a similarly sensible approach when doing mine.

John

[mrmunsell]

I have original 4 into 4 exhausts, but apart from that I currently have almost the same set up as yours:

Interesting that you ended up with #35/#105 jets on the stock intake and 4-4 exhaust system.  Was #40/#100 the original jetting for your bike as well?

I have the little rubber spoiler on the front of the air cleaner box and the original tool tray.

I have both as well.  Well, I did until last night.  I just installed a NOS K&N air filter last night.  It is a single oval filter and mounting plate that mounts to the inlet of the stock plastic manifold.  In other words, it takes the place of the stock air filter box.

I admire how you've done yours in what I believe is the correct order -float levels, -mains, -needle clips, -pilot circuit, I wish I'd had a similarly sensible approach when doing mine.

I was trying to follow advice I had read on the forum -  I believe I had read a post from TwoTired that recommended that order.  However, I didn't entirely stick to it because mine was running excessively rich over most of the throttle range with my initial carb config.  So I did deviate from the order a bit to get it a little easier to ride earlier in the process:

-float levels, -first pass air screw adjustment, -needle pos, -main jet, -pilot jet / air screws

Mine currently has good plug color, starts easily and runs well in most situations, however when cruising in top gear at highway speed if I close and re-open the throttle I get momentary hesitation.

I was experiencing a different symptom in what might have been the same condition.  When riding on rural highways in hilly areas, I think I sometimes created a similar situation near the bottom of bigger hills.  Increasingly closing the throttle as I descend a hill, sometimes completely closed by the bottom on the bigger ones, and then transition back to opening the throttle.  And at that point when I just started re-opening the throttle, I would sometimes experience what I think was a slight missing.  I was still on my pilot tuning journey when things were still too rich but closing in on where I am now.  I did not experience that symptom with clean plugs… it would develop that symptom after riding a while.  I think the issue was that the plugs were getting lightly fouled during highway cruising... perhaps enough to get away with under less challenging cylinder conditions... but not in conditions such as that.  I suspect that based on how the plugs looked after riding in that scenario, that the symptom developed / got worse with more highway riding, and that it went away as I leaned out the pilot circuit.

I wonder if your symptom might be that your pilot circuit is on the other side of ideal (a little too lean vs a little too rich).  I don’t know… just speculating and guessing based on my experience with mine.  I don't have much experience on the other side of ideal in the pilot circuit yet (lean vs rich).

[jonda500]

I first got this bike running with unrestored carbs borrowed from my other cb500. With these stock setup carbs fitted it ran almost perfect without changing anything despite having a 4 into 1 fitted!

So I sent the original highly corroded carb set that came with the bike to harisuluv to be reconditioned. They came back in pristine condition looking almost brand new.

I started with the original jets (100/40) and needle clips #4 position and initially still had the 4 into 1 with a rather loud muffler fitted. At first the bike would only run properly if it was stone cold - after 30 seconds it would start to blubber like as if the choke was left on full and soon after the plugs would stop firing and when removed, were found to be wet with fuel which had to be dried off to get them to spark again!

I bought second hand 4 into 4 pipes for it one by one hoping that they would make the tuning easier.... but it still took me years to get it to where it is now 
(on my low income I have to save up the money each time before being able to buy new different size genuine jets)

I agree I seem to be just on the lean side in my pilot circuit, but I have tried going back to #38's and the result is a rich pilot circuit once the bike warms up, even with the air screws 2 1/2 turns out...

John

[Deltarider]

I follow this thread with interest. First let's check if we all agree on what is a turn out. In my book one turn out is a 360^o turn. The reason I raise this, is that I'm puzzled by the turns out of your airscrews, the both of you: Jonda 2¹/₂ and Mrmunsell even 2³/₄ out. Stock it was 1 turn out ⁺/_- ¹/₈ out for European models with the needle clip in 3^rd position. In an American Honda booklet (the only source btw) we find 2 turns out, in combination with the needle clip in 4th (from the top) position. What I hope, is that you haven't turned out the airscrew so far out to achieve a highest rpm at idle. That may be common practice for most motors and will work fine for them, not for ours. I can turn my airscrews out as far as Mrmunsel has and I'll be rewarded with a silky engine that purs like a kitten. But the bike won't accelerate well anymore. Out of curiosity on my 100% stock CB500, I've raised the needles to 4^th and I discovered you have to compensate indeed by turning the idle screws out to more or less two turns to avoid hesitation in acceleration. Next spring I'd like to return to normal again: needles in 3^rd and airscrews 1 turn out. Needle and needle jet were designed for the CB500 and I therefore conclude the middle position would have been Honda's intention, although I admit it's not a very strong argument. Besides that, quality of gas has changed (again) and I'd like to see if I can get the max (both gas mileage and performance) from designer fuels like V-Power and Ultimate. What is important to know, is that all models CB500 need an idle that's on the rich side to facilitate a good acceleration, even if you would need to increase the idle rpm by turning the big idle adjuster. I know it's complicated and the fact that the quality of gas has changed over the years (more than once!) doesn't make things easier. Jonda, I'm as puzzled as you are. Are you sure the little O-rings around the mainjets seal well? That the slow jets are not accidentily widened?

[dave500]

im running 100/40 jets,with 4-1 and stock airbox,bike hauls,i have a fairly long muffler which helps,some are too short to be any good,i broke third gear few months ago and put a spare motor in,used the same carbs no changes,still hauled arse,the air screw in or out guys get too finicky with it,its not a be all and end all,technically each cylinder will require a slightly different setting.

[Deltarider]

Next spring I will teach myself to fine tune by listening to (and comparing) the sound of each exhaust. Uch, uch uch. I'd love to see a vid of this in practice.