Topic: CB550F carbs on CB500

[Matte Black]

I've dialed in a 69A rack from a 550F on my 500 with pods/4-1. It's close but hesitates around 1/8 throttle. Above that very responsive. It's jetted at 627B CB500 carbs stage 2: 40 slows and 120 mains.

Originally the 627B's factory needle clip pos was on the 4th groove. The 69A's on the 2nd, where it currently resides.

Should I move em to 4th groove?

I dread moving the clips, and can't get to it for a few days, so I thought I'd ask y'all.

Thanks

[Deltarider]

Originally the 627B's factory needle clip pos was on the 4th groove

Unfortunately this is an error copyied over and over again. Source of this evil is an American Honda Motor booklet (1977).
I'll explain why I believe data in that American Honda Motor booklet is flawed. In all other media 3th groove was prescribed as standard for the CB500. Something has gone wrong in the US specs and I believe I've found the origin of this mistake. Have a look at p.165 of the Honda Shop Manual CB500-CB550 if you will. There's a socalled Carburetor setting table with a comparison of the models CB550 and the CB550F-A. I believe Honda made an error here and typed CB500 over the left column where it should have been CB550.
First: there were no CB500s ever with 022A carbs (CB550s yes, CB500s no) and
Second: one would expect here a comparison of the CB550K and F models and not so much of the CB500 and CB550F. I've therefore deducted that forsaid American Honda booklet has bluntly copied this error and as we know from the ever echoing internet an error can go a long way by copying and copying it...
Having said that, there can be good reasons to have the needle in 4th, especially where intake and/or exhaust has changed, but it is my believe that a completely stock CB500 from the factory also in the US had the needle in the middle (3rd) position*. It makes even more sense when you consider that needle set 16012-323-004 was especially designed for the CB500.
All this is not much help for you. I personally think main jets 120 is crazy, but that's my opinion. My suggestion would be to experiment with various settings of the airscrews first and see what that does. Keep in mind that these models require a rich idle for a fluent acceleration. Don't be tempted to adjust the airscrews aiming for the highest idle in rpm. This may be a good practice for other motors, not for ours. I can do it with mine and the engine will purr like a kitten, but... acceleration will be miserabe. Just try to find an exceptable idle and good pick-up/driveability by adjusting the airscrews and there may be a good chance you don't have to alter the position of the needles at all. Remember also that the needles of the 069A carbs (stamped in number 273004) have a different taper than the needles of the CB500 (stamped in number 272304). So 2nd or 4th position on these different needles may be incompatible.
* However the possibility remains that American Honda had 4th groove in the data on purpose. That could explain the two turns setting of the airscrews (to compensate) in stead of 1 +/- 1/8 but personally I find it hard to believe that the American importer has opened all CB500 carbs on arrival to change the needle position. If they had left the factory with American Honda Motor settings carbs would have had a different stamped in carb number.

[Matte Black]

TYPO!!?? Thanks for pointing this out as I've read hundreds of posts on these racks over the years and somehow never heard anyone mention it. That booklet from 77 needs to be quarantined.

So the 500 factory setting was 3rd position? Here's a shot in the dark. What if I were to use the my 500 needles because of the taper difference? That crazy talk? A while back I compared the tapers, and they looked identical to me. Of corse I may be wrong as I simple lined em up. Is there a big difference in slide cutouts?

Yes I hear ya 120 sounds big, I had 110s, then 115s, and here I am. And I feel she's strong up to WOT. Once I get the slow circuit dialed in I plan on plug chops this spring to iron it out.

I'm happy to hear you mention the need for a richer slow. I tried 42s, but that was way too rich and hesitated worse. I've been carrying around a screwdriver for a week adjusting pilots. I'm currently at 1 3/4 out. I'm going to try 2 and see it my commute this morning improves. Honestly I can't get the science of the airscrew adjustment right without a tach. I'm literally opening them 1/8 before each ride in hopes.

Thanks for your great response delatrider!

[Deltarider]

What if I were to use the my 500 needles because of the taper difference? That crazy talk? A while back I compared the tapers, and they looked identical to me. Of corse I may be wrong as I simple lined em up. Is there a big difference in slide cutouts?

As far as I know slide cutouts are identical. Talking about the needles is talking about the needle jets too. They come as a set and yes they differ, but it doesn't mean your 500 can't run with them.

I'm happy to hear you mention the need for a richer slow. I tried 42s, but that was way too rich and hesitated worse. I've been carrying around a screwdriver for a week adjusting pilots. I'm currently at 1 3/4 out. I'm going to try 2 and see it my commute this morning improves. Honestly I can't get the science of the airscrew adjustment right without a tach. I'm literally opening them 1/8 before each ride in hopes.

Believe me, the last thing you need for setting the idle is a tach. Forget about looking for the highest rpm by setting the airscrews. On mine they are one turn out. I wouldn't recommend #42 slow jets. #40 is max and some prefer #38. Just try to achieve a fluent pickup/driveability by experimenting with the airscrews setting. I have the feeling a CB500 must run OK with a 069A set.

[Matte Black]

Wow, couldn't have been more right man. Opening up the airscrews 1/4 turn each this morn was the magic number, she accelerated much better. Gunna test another 1/8 and see what happens.

If I can't get the airscrews just right, shall I attemp moving the needles up a notch to 3rd groove?

It's only been bench synced since I rebuilt it last, I'll do a dynamic today, I think that should help a little.

Your only 1 turn out on youse? How's it jetted?

[Deltarider]

If I can't get the airscrews just right, shall I attemp moving the needles up a notch to 3rd groove?

Hard to say for me. I usually take the diagrams showing what jet does in what section of the range with a grain of salt. It's much more a dynamic 'mix' than what people think. For instance, nobody so far has been able to explain why it is that when I set my airscrews richer (supposed to affect mixture at idle only) even when I ride on the Autobahn at 120 km/h+ constantly mileage then is also affected.

Your only 1 turn out on youse? How's it jetted?

CB500s in Europe (France and UK excepted) had 649A carbs that were jetted differently.
We have the same slow jet #40, main jet is #78 and airscrew is recommended 1 turn out +/- 1/8. But these models have a cover over the airfilterbox as shown below.
Interesting is that although UK and France CB500 models have 627B carbs that have the same jetting as US have, like ours, airscrew is 1 turn out +/- 1/8. These 627B carbs with main jet #100 also had the needles in 3rd position.
Forsaid Amercan Honda Motor booklet is the only publication that recommends two turns out for the airscrews. Probably to compensate for needles in 4th. All the other documents have 1 turn out +/- 1/8. But what is standard prescribed is of less importance for you since you have a different set of carbs. This means you have to experiment and do plug chops. But 120 for the main jets seems excessive to me. Make sure the little O-rings around the main jets are still OK and seal well. You could also check the float height with the clear tube test but think twice before bending any floattangs. All the floats that I've seen were always correct.

[flybox1]

For instance, nobody so far has been able to explain why it is that when I set my airscrews richer (supposed to affect mixture at idle only) even when I ride on the Autobahn at 120 km/h+ constantly mileage is also affected.

I'll take a shot...
...because there is no 'mechanism' in your carbs to prevent flow through that passage at any throttle position above idle.
Same with the pilot and needle jets.  Nothing prevents them from supplying fuel when you get above the throttle position in which their through-put is maxed.

[Deltarider]

I'll take a shot...
...because there is no 'mechanism' in your carbs to prevent flow through that passage at any throttle position above idle.
Same with the pilot and needle jets.  Nothing prevents them from supplying fuel when you get above the throttle position in which their through-put is maxed.

I agree. Still people think that airscrew settings affect idle only. BTW, my apologies that in my post above I put it a bit confusing.

[Matte Black]

Yeah, seems half the jet to throttle graphs online illustrate pilot/airscrews bow out before 1/2 OT... Prob came from American Honda Motor booklet

I see, yours has factory settings, air box, etc. so 1 out, is norm, I though yours had similar setup. I have 4-1 exhaust, pod filters, hence the 120 main and 2 out pilot.

Similar to a slight vacuume leak, the hotter it gets the higher the idle gets, and hangs up instead of idling. The longer I ride the lower I have to keep adjusting the idle. I'm sure there's no leak, is it possible that adjusting the airscrews precisely can remedy this too?

[turboed13b]

Yeah, seems half the jet to throttle graphs online illustrate pilot/airscrews bow out before 1/2 OT... Prob came from American Honda Motor booklet

I see, yours has factory settings, air box, etc. so 1 out, is norm, I though yours had similar setup. I have 4-1 exhaust, pod filters, hence the 120 main and 2 out pilot.

Similar to a slight vacuume leak, the hotter it gets the higher the idle gets, and hangs up instead of idling. The longer I ride the lower I have to keep adjusting the idle. I'm sure there's no leak, is it possible that adjusting the airscrews precisely can remedy this too?

Too rich on main you would have to have some extensive mods for 120's.

[Deltarider]

Similar to a slight vacuume leak, the hotter it gets the higher the idle gets, and hangs up instead of idling. The longer I ride the lower I have to keep adjusting the idle. I'm sure there's no leak, is it possible that adjusting the airscrews precisely can remedy this too?

Yep, although a somewhat higher idle after warm up is normal for CB500/550s. Many owners simply turn the central idle knob for a higher idle when starting the cold engine and return this knob when the engine has warmed up for an acceptable idle. It can be done with gloves on. I do it every time. If idle keeps hanging up, it's an indication of a too lean mixture. If there's no airleak (the O-rings between intake and enginehead are suspect) I'd screw the airscrews in (clockwise) somewhat. Again: don't be tempted to aim for a higher idle in rpm by leaning out or you'll be 'rewarded' with a high hanging idle. Idle should be around 1100 rpm.

[Matte Black]

Good to hear, I've always had to raise and lower the idle as she warms up. I can accept that.

Funny you mention the o-rings at the engine side of the manifold... The reason I know that I don't have a leak, is because I did have a bad o-ring that didn't leak pressure until the engine was very very hot. It would only appear after a 30 min ride, and never while I was spray testing or vacuum synchronizing. At the point I finally found it, I've already sealed up the boots with silicone hah. I just replaced em a week ago. #1 was in pieces.

Could the hangups also be caused from a rich condition in the slow cycle? I'm wondering because the leaner I adjust the airscrew the less it hangs up.

[turboed13b]

Your main jet is flooding out all the other circuit. You should be hearing pops in the exhaust when you screw the mixture needle out if you don't you are too rich.

Your hanging idle is probably from the idle screw being too far in reducing vacuum and causing a lean condition because fuel can't get sucked in.



How does it run when you shut off the petcock mid ride?

[Matte Black]

Main flooding slow circuit? A concept I haven't heard. It's never popped through carbides or exhaust actually. I have 110s and 115s in which I've tried before but we're too lean, but could have been other issues at the time and not the mains. When it warms up around here I'll do a plug chop and sort it out. I actually have access to a dyno I may test instead, but need the slow circuit to improve a bit first.

I've never shut off the petcock mid ride but I have ran out of gas?

[Deltarider]

I've never shut off the petcock mid ride but I have ran out of gas?

Can you clarify us a bit more? Are you suggesting you may have a fuel delivery problem? Any 'extra' fuelfilters that might hinder fuel flow?

[turboed13b]

Main flooding slow circuit? A concept I haven't heard. It's never popped through carbides or exhaust actually. I have 110s and 115s in which I've tried before but we're too lean, but could have been other issues at the time and not the mains. When it warms up around here I'll do a plug chop and sort it out. I actually have access to a dyno I may test instead, but need the slow circuit to improve a bit first.

I've never shut off the petcock mid ride but I have ran out of gas?

If your mains are too rich they can flood out all the other circuits and you will never get the tune right.

When riding turn off the petcock. This will lean out the mixture and if your bike runs better than you are too rich.


Make sure you do that while in a neighborhood where you have stop and go so you can test the low end.


On a stock bike you can lean out the mixture screw so much that the exhaust will pop or make popcorn noises. Don't run it like that but is just an indication that you are close on jetting if you can replicate it.

[HondaMan]

The "stumble" you are feeling is due to too much mainjet.
When the engine goes from one mix range to a sudden different change, the flamefront cannot automatically cope with the sudden drop in oxygen content for the same amount of mixture. The 120 mainjet is too rich for the 750, let alone the 500/550. The 500 and 550K bikes had 90 mainjets with the needle in notch 3 for the 500 and 4 for the 550, on the same carbs.  This became the 100 mainjet in the later PD-style carbs for the 550F bikes, but that's about all the richness the intake valve can cope with. Above that, it will produce erratic throttle response, wet sparkplugs, washed-off cylinder walls (which will drastically shorten ring life) and soon burned exhaust valves, because the unburned fuel is still burning as it passes out of the engine, heating up those poor exhaust valve faces.


I would suggest using 100 mainjets with the needle in either 3 or 4 notch, and the idle air screws set to 1.5 turns, give or take 1/4 turn from there.

[Deltarider]

Have the same suspicion as Hondaman. Have to correct his typo's however,

The 500 and 550K bikes had 90 mainjets with the needle in notch 3 for the 500 and 4 for the 550, on the same carbs.  This became the 100 mainjet in the later PD-style carbs for the 550F bikes, but that's about all the richness the intake valve can cope with.

Read: The 500 and 550K bikes had #100 mainjets with the needle in notch 3 for the 500 and 4 for the 550, on the same type of carbs. This became the #98 mainjet for all CB550F (also known als Super Sport) models.

Carbs 627B (on: CB500, CB500K1, CB500K2), 649A (on: CB500K2 [ED,G], 022A (on: CB550K, CB550K1), 087A (on: CB550K2) all share the same needle set (needle and tube) parts no. 16012-323-004. Needles have stamped on number 272304. Needle position differs. As said, standard was: 3rd for CB500 models, 4th for CB550K models.

Carbs 069A (on: all CB550F models) have needle set 16012-390-004. Needles have stamped on number 273004.

Needle sets 16012-323-004 and 16012-390-004 do differ, both needles (different taper) as well as holes in the tubes (in metric it's Ø 0,9 for the 16012-323-004 set and Ø 0,7 for the 16012-390-004 set).

Again, not even Honda is perfect. It's my believe they made a mistake on p 165. of the Honda Shop Manual 500-550. That 'CB500' over the left column is a typo as I see it. It should have been 550. My believe is this mistake is copied over and over again.
Note: Above information concerns old style Keihins only.

In the later much different PD-style carbs for the CB500K3/550K3/K4 (4-4 exhaust) models we find different shaped mainjets #90.

If you think this is already an unbearable load of info, realise we haven't even discussed the different shaped airscrews...

Matte Black, don't despair. All the above does not automatically imply your bike can't run well with a 069A set. Differences are small but... 120 main jets is way too much. Could it be you were tempted by a poor fuel supply or malfunctioning floatvalves? Have you checked for a good fuel route, not hindered by any kinks or inline fuel filters? Fuellines should be 17 and 28 cm in length. Ideal diameter is  Ø 5,5 mm.

[Duanob]

Yeah, seems half the jet to throttle graphs online illustrate pilot/airscrews bow out before 1/2 OT... Prob came from American Honda Motor booklet

I think you're getting your terms mixed up. The pilot jet is the slow jet (the size 40 jet). the Idle/air mix screws are only only for adjusting the idle and that's about it. The needle position/pilot jet take over after that. I think your pilot jet is fine, the main jet is way too big, after that you will need to play around with needle positions to get it right, depending on how free flowing your exhaust is. If it's restrictive like the 550F then I would set the carb up like a 550F as a starting point. Also make sure if your needles are old there isn't some corrosion or gunk towards the top of the needle preventing them from sitting all the way down in the emulsion tube. Remember everytime you mess with the needles you will have to vac sync again. After market intakes and exhaust are always an experimental thing to get it running right.

[Deltarider]

the Idle/air mix screws are only only for adjusting the idle and that's about it. The needle position/pilot jet take over after that.

Don't you think that the airscrew and pilot jet are linked and work together then? I repeat: these models require a rich idle for a fluent acceleration. Don't be tempted to adjust the airscrews aiming for the highest idle in rpm. This may be a good practice for other motors, not for ours. I can do it with mine and the engine will purr like a kitten, but... acceleration will be miserabe. For the silkiest idle I'd have my airscrews 2 1/2 turns out. For both a fluent acceleration and acceptible idle it has to be 1 turn out. Try to find an exceptable idle and good pick-up/driveability by adjusting the airscrews and there may be a good chance you don't have to alter the position of the needles at all.

[turboed13b]

the Idle/air mix screws are only only for adjusting the idle and that's about it. The needle position/pilot jet take over after that.

Don't you think that the airscrew and pilot jet are linked and work together then? I repeat: these models require a rich idle for a fluent acceleration. Don't be tempted to adjust the airscrews aiming for the highest idle in rpm. This may be a good practice for other motors, not for ours. I can do it with mine and the engine will purr like a kitten, but... acceleration will be miserabe. For the silkiest idle I'd have my airscrews 2 1/2 turns out. For both a fluent acceleration and acceptible idle it has to be 1 turn out. Try to find an exceptable idle and good pick-up/driveability by adjusting the airscrews and there may be a good chance you don't have to alter the position of the needles at all.

Gotta go with Delta lean that air screw out and your slow acceleration from a stop will most likely be very choppy.

[Matte Black]

Yeah, seems half the jet to throttle graphs online illustrate pilot/airscrews bow out before 1/2 OT... Prob came from American Honda Motor booklet

I think you're getting your terms mixed up. ...

Not mixing anything up, I know air screws adjust the pilot/slow jet, hence the slash, it's commonly mentioned together in charts too. I was just agreeing with Deltarider saying some "take the diagrams showing what jet does in what section of the range with a grain of salt" because I've always noticed that half the diagrams you see don't show the slow jet extending from idle to WOT:

First chart shows slow jet bowing out before half OT...

So I have great news! This morning I turned my air screws out 1/8 and it improved immensely with only a little hesitation at accel. Pulled over, did another 1/8, and man she is SMOOTH! Now only the tiniest bit of hesitation, almost unnoticeable. 100% responsive? No, but close. Gunna keep doing 1/8ths until no improvement, then back one. I'm prob out 2.25 at this point, honestly lost track.

So all ya'll fellas think my mains are too big:

I personally think main jets 120 is crazy

120 for the main jets seems excessive to me

The 120 mainjet is too rich for the 750, let alone the 500/550.

Too rich on main you would have to have some extensive mods for 120's.

120 main jets is way too much

I'm open to that, but let me point out my mods again: Un-oiled UNI pod filters, 4into1 de-baffeled exhaust, base jet main jet #100, Needle clips second groove.

Once the slows are perfectly dialed in I'll do a plug chop and see if ya'll are right. I have #115s ready in case. I have to go by a shop that has a dyno tomorrow, perhaps they'll hook her up and save me some time.

Thanks fellas

[Matte Black]

Hey fellas, sorry for the delay.

Recap:
Hotter it gets, the faster it idles/hangs up. As it warms, I'm constantly having to lower the idle so it drops back to a reasonable idle. The only way I can get a smooth acceleration if for the idle to be set perfectly, otherwise slight acceleration and it will drop RPMs and stall. After riding for about 30-40 minutes, I'm having to have the idle so low that it does a little surging and doesn't perform good.

Here's an update...
After all ya'll kept saying that my mains were too big, AKA mains flooding out other circuits, I dropped it down to a #115. Nothing noticeably changed.

Then I decided to drop to a #38 slow (factory CB550 size). Nothing noticeably changed.

Unless my problems have something to do other than the carbie, the only thing I can imaging to do is start moving around the needle clips. Currently it is at the 3rd groove...

Where should I look next? Ignition? Valves? Stumped...

[harisuluv]

This thread is too hard to follow for me to be of any assistance.  Things are changed seemingly on a whim, and multiple changes at a time.

I have a feeling that you need to go back to the basics and do some more reading about setting these carbs up.  The fact that you were setting the air screws based on RPM makes me think that you are really a novice.

Are you using the air screws to do your vacuum syncs also?

[Matte Black]

This thread is too hard to follow for me to be of any assistance.  Things are changed seemingly on a whim, and multiple changes at a time.

No whim. This thread is full of requests to go down a size on the mains, so I gave it a try. I was fine with the #120s and may put em back in later after I figure out the big issue and a plug chop.

Single changes only. After each change, I vacuum sync, adjust IDLE screw, THEN adjust AIR screws. Test ride. Revert change if it doesn't improve.

Note: The only reason I went to #38 slows was because my AIR screws were open 3+.

I have a feeling that you need to go back to the basics and do some more reading about setting these carbs up.  The fact that you were setting the air screws based on RPM makes me think that you are really a novice.

No. I never mentioned AIR screws. I said the IDLE screw (knob) is what I adjust when I ride... I couldn't ride it daily, without.

Are you using the air screws to do your vacuum syncs also?

I've never adjust the air screws while vacuum syncing. Are you asking or suggesting?

Moving forward...

Basically. Before it heats up, it runs great. Smooth. Responsive. Fast.

Degrades over time. 0-1/8 OT dead spot occurs.

Perhaps a vacuum leak is occurring when things get hotter, that's not showing up in the sync. AKA Expanding o-ring. I dunno.

Thanks