Topic: Air/fuel mixture

[eastern]

Perhaps an inane question. 

Still working through the new to me bike.  1974 CB 550.  I rebuilt the carbs, did the valves and now today had to go at the air fuel mixture to sort out low RPM bogging.  Seems to be good now, but I noticed I am only 1/2 turn out on the screw.  Should that be too rich, or does it not matter at all as long as it’s running well?

[eastern]

Further…. Stock pipes stock airbox.

[HondaMan]

Start at 1-1/4 turns. That should more closely match our modern gasolines: use Regular grade of that with today's gas because it burns much slower than 1970s gas did (so as to help light off the catalytic convertors found in vehicles). In the 1970s we needed premium for these bikes, today not so.

[eastern]

I did try that.  Started at 1 1/2 out.  Bike was bogging at low rpm.  Trimmed the ends of the wires which seems to have fixed some missing.  Cleaned and gapped the plugs which are NGK 8 temp.  Used 87 octane.  Timing set, valves done, carbs cleaned.  Kept riding and making adjustments 1/4 adjustments till throttle response was best and low rpm bogging seems to have stopped and wound up at 1/2 (or less) from fully seated.   I can’t seem to read anyone else having the same results so I’m not sure if it’s something still out.  My air filter box is open on top as I don’t seem to have a lid for it.  Not sure if that is an issue. 

[eastern]

Pics

[eastern]

Last thing.  Have some D7EA plugs arriving tomorrow to replace the NGK 8 Resistor plugs in it now.  Will see what if anything they change in operation.  After the current tuneup, my bike will now idle at 1100 or so RPM without sounding like it is going to come apart.   Previously, if I had the idle at under 1500 RPM, it sounded like it was going to grenade itself with head rattles.  Pretty thrilled with the progress so far. 

[dave500]

have the carbs had a vacuum sync?if out of sync itll rattle at idle,bench sync eye balling the slides gets it running,vacuum is final trim.

[BenelliSEI]

have the carbs had a vacuum sync?if out of sync itll rattle at idle,bench sync eye balling the slides gets it running,vacuum is final trim.

+1 to above. Only an accurate vacuum sync gets them running really smoothly.

[HondaMan]

Your airbox should work fine with the tool tray in place, even at speed.
Do you know if (or for sure) it jets in your carbs are Keihin's own? If they came from a rebuild kit, then they (and the needle in the slide) will not be the correct calibration, which will mess up the settings.

When you cleaned the carbs, did you also set the float depths, and at what [n]mm depth?

The D7E (or X22ES-U) plugs are better in the 550, for many reasons: they were the original ones. The D8E are too cold for all but interstate riding at all-day type speeds.

The noises you hear are just coming from the loose primary chain (it is a little worn) jumping around a bit when the engine isn't yet 'even'. This causes the cam chain to also wiggle its looseness, which makes the cam timing jump a bit, which causes interruption in the intake flow from the carbs - because of the long intake tubes in this design. When the carbs (and very importantly, the spark timing) get set right, things start to settle down quickly.

Since you had the carbs off, I have to ask this as a known 'bug', too: did you change the O-rings in those 4 intake manifold pipes where they bolt to the head? They are old and hard as plastic now, and don't seal for beans. They are the same size as in the valve caps. Reason I ask: often when these bikes are revived, these seals get disturbed after their long dormancy when someone starts moving stuff around on the bike, and they instantly lose their [old and hard] seal. The result is: the carbs act like they are running rich (even when they are not) because the vacuum leak at these seals dilutes the incoming air-fuel charge in an uncontrolled way. The "hint" here to me is: the bike runs better at 1/2 turn on the idle-mix screws, which is a VERY lean setting: this indicates that in the carbs the air is moving even slower than the screws' setting.

[eastern]

Thanks.  I did the bench sync with a 1/8 drill bit while putting the carbs back together.  The knocking is now gone and I can idle at 1100rpm smoothly.  I am still getting a very quiet rattle out of the clutch area, not nearly sd   Tomorrow's Amazon haul includes a carb sync kit and the D7EA plugs.  I'm a bit excited to see how that goes process goes and how close I wound up on the bench sync.   Will report back. 

Thanks again for all your help!

 

[eastern]

Your airbox should work fine with the tool tray in place, even at speed.
Do you know if (or for sure) it jets in your carbs are Keihin's own? If they came from a rebuild kit, then they (and the needle in the slide) will not be the correct calibration, which will mess up the settings.

I don't know if the jets are Keihin or aftermarket.  I could read 100 but not on the other.  I only cleaned the hard parts and installed new o-rings.  I didn't adjust the needle.  I wouldn't be surprised if they are aftermarket.  The bike is a 74 with now 16K miles so it must have spent some time sitting.  The tires were 24 years old but the bike has clearly been looked through fairly recently, paint and so on.  The insides of the carbs were actually quite clean.  The emulsion tubes weren't properly pressed in, they basically dropped out of the bottom almost on their own.  Were completely clean though.  Someone was in there before. 

When you cleaned the carbs, did you also set the float depths, and at what [n]mm depth?

I did.  24mm.  I also note that my bike isn't peeing while on the kickstand now.  One float was a bit sticky.  I think it's fixed now. 

The D7E (or X22ES-U) plugs are better in the 550, for many reasons: they were the original ones. The D8E are too cold for all but interstate riding at all-day type speeds.

The noises you hear are just coming from the loose primary chain (it is a little worn) jumping around a bit when the engine isn't yet 'even'. This causes the cam chain to also wiggle its looseness, which makes the cam timing jump a bit, which causes interruption in the intake flow from the carbs - because of the long intake tubes in this design. When the carbs (and very importantly, the spark timing) get set right, things start to settle down quickly.

Thank you for this.  That totally makes sense!  When the bike was running more poorly, it sounded like chain rattle, and was mostly when the engine would hesitate and miss.  I am sure I was also getting some missing from a bad plug connection, but also at least one jet was clogged with debris. Further, the PO has installed two in line filters, one of which had a severe kink in the hose due to it that MUST have impacted gas flow.  New fuel lines from petcock to carb now installed.  Bike is now running quite well at idle.  Was just stumbling a bit starting and at low RPM after the carb re-install, even after, but not as badly, once I fixed the spark plug wire ends which took care of the missing (cyl 1) after as well.   I could unplug Cyl 1 with basically no diff in running.  Trimmed end, reseated the end, and the bike is clearly running on all 4 cyls all the time.

 Some clutch noise maybe, (as it goes away when lever is engaged) but not excessive (and a lot less than my Ducati 998!)

Since you had the carbs off, I have to ask this as a known 'bug', too: did you change the O-rings in those 4 intake manifold pipes where they bolt to the head? They are old and hard as plastic now, and don't seal for beans. They are the same size as in the valve caps. Reason I ask: often when these bikes are revived, these seals get disturbed after their long dormancy when someone starts moving stuff around on the bike, and they instantly lose their [old and hard] seal. The result is: the carbs act like they are running rich (even when they are not) because the vacuum leak at these seals dilutes the incoming air-fuel charge in an uncontrolled way. The "hint" here to me is: the bike runs better at 1/2 turn on the idle-mix screws, which is a VERY lean setting: this indicates that in the carbs the air is moving even slower than the screws' setting.

I was under the understanding that 1/2 counterclockwise from fully seated would be a rich mixture rather than lean, and that the mix is leaner as you go counterclockwise out, ie, 1.5 turns out would be more lean than 1/2 turn out.  Is this incorrect?

I did not.  You mentioned them in an email when I ordered your ignition.  I intend to grab a set and put those in. 

I think I may have mentioned it... but I really appreciate the knowledge being passed so generously.  Thank you!

I'll report back with the 7 plugs in and the carbs synced tomorrow.  Hopefully it doesn't come too late in the day (for the neighbors!)

[Deltarider]

For the American way of riding these bikes, a D7 sparkplug is best. In Europe many choose the D8ES-L advised so by dealers. I've always had them before.
It seems you have adressed the issue. You're one of the many that had to fix the HT route to the sparkplug. That has always been the CB500/550s Achilles heel. Since it is so very easy to check, I always advise owners of a CB500/550 to look there first.
Is it possible for you to make a little video so we can judge the sounds?
A true 1100 RPM at idle is fine. Personally, I wouldn't aim for less than that.
For your airscrews: turning clockwise is richer, counterclockwise is leaner. If you have a float height of 24 mm, it is a bit off spec, but it could indicate to non OEM parts and then maybe it is fine. You may want to perform my simple test which is valid for all CB500/550s with oldstyle carbs. It is here: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647

[dave500]

I care less for idle,im rarely there anyway?a slightly faster idle is ok if it smooths things out,youll be over 3000 rpm all the time if your riding the bike properly,dont be scared to rev the bike or hold a lower gear in slow traffic ready for a quick burst to get you on your way,too many just loaf these older things along?they like the higher rpms,never lug these motors.

[HondaMan]

The carbs: the idle-mix screw controls the amount of fuel-air mixture that is admitted during the intake stroke. The idle jet itself controls the mixture of air & fuel.
Turning the idle-mix screw inward delivers less fuel-air mixture during the intake stroke by pinching down on the air passage size enroute to the idle-mix jet.

To prove this to yourself, once you get the bike running: fill the tank with gas and run to reserve and note the mileage. Then turn the screws inward (or outward) 1/4 turn, live with the idle results for the test, and check your MPG at the next time you hit reserve. You will prove what I said, to yourself, in the process. I have done this 'test' with more than a dozen SOHC4 bikes of all the types, and with the old Honda singles (90cc, 125cc) since the 1970s as well. They all correspond, despite the PD carbs having the idle-mix screw downstream of the pilot jet. In my own 750K2, on which I just finished this test AGAIN because of the recent fuel changes here in the Denver metro area, I get 28 more miles before reserve for setting the air screws inward an additional 1/8 turn to 5/8 turn, when I have been running them at 3/4 turn since 2016 when the last fuel recipe changes were installed at the local refinery.

In the older Honda shop manuals that were [poorly] translated in Japan to [what we Honda wrenches dubbed 'Jinglish' translations then) they sometimes mentioned the carb idle-mix adjuster screw settings (usually in the manuals for Singles). In most cases, the phrase was, "For richness, turn the screw in". As I worked with the Japanese at Honda, Suzuki, and later SONY and Panasonic for decades, I got to meet many Japanese engineers and techs, and noted their 'Jinglish' phrases as well: what the Honda translator(s) were saying, based on the sentence structure and the context of the explanation was/is: "If the engine is running rich, turn the screw inward" (to lean it out). This fits with the structure of the rest of the correspondence in those sections, which is how the Japanese speak, and the implication, by context, that the carb is being vibrated by the engine which may change the screw's setting. It will always turn itself outward with vibration because of the spring that the screw is compressing.

[eastern]

Honda man, very interesting. Thank you.  I haven’t gotten as fine as 1/8 adjustments but your 5/8 would actually be quite close to the 1/2 out that I found was working best. 

As it stands this evening. It has gotten dark and is raining. I did receive the seven plugs and installed those as well as the vacuum synk. I did have some challenges with the vacuum synk, but do you have them all synced now. However, I am not sure that the bike is running better than when I started from the bench synk. They were all quite close when I began. Had some trouble with one of the gauges and wound up, moving a lot of them out then hopefully back in but to a different Inches of mercury than the start I believe.   

I will have a look at it again in the morning and also try riding the bike

[eastern]

… that you had a bike running at four eights, or 1/2 out actually answers my first posted question which was is anyone running at approximately 1/2 out as it seemed a lower figure than I had seen anyone else mention. 

[dave500]

were you adjusting the idle mix screws doing the vacuum sync?

[jonda500]

When I refurbished my 2nd CB500 with all original parts and setup it ran uber rich at idle and lean at full throttle. It took a long time to get it running well - I ended up with bigger #105 main jets, needle clips in #4 from the top (I did try 3rd slot too but it lacked power), smaller #35 pilots (with #38's it had a stumble that I couldn't get rid of by playing with the air screws), and air screws at 1/2 a turn out. While I don't personally have an exhaust analisis sniffer I still firmly believe that screwing the air screws in richens the mixture.
John

[HondaMan]

Honda man, very interesting. Thank you.  I haven’t gotten as fine as 1/8 adjustments but your 5/8 would actually be quite close to the 1/2 out that I found was working best. 

Well, my numbers/settings apply to the round-top CB750 carbs, which normally set at 1.0 turns out when new. I also live at 6000 feet altitude, which by itself is a 1/8-turn-inward adjustment on the 750, and about that much (e.g., slightly more than 1/8) for a 500/550K1-2 carb setup (different for the later PD carbs). So, instead of 1.5 turns (at sea level) the 500/550 becomes about 1-1/4 turns here.

For other readers:
The same setting (between 1/8 & 1/4 turn inward) applies for the 1979/80 CB650 carbs, if anyone is trying those monsters. I just finally got a troubled CB650 running after a local 'vintage' shop had it for 4 months, messing with its carbs: they had the mix screws at between 1 and 4 turns out on the various carbs. Ridiculous... I set them all to 1/4 turn less than stock per the manual and the bike started up, warmed up on choke, and rode off just fine.

[eastern]

Hello All,

I return from a test ride with a huge smile.  New plugs (7, non resistor) went in.  Vacuum sync completed.  (on top of timing set + Hondaman ignition, valves adjusted, carbs cleaned, timing chain tension set)   IT IS A NEW BIKE.   Sharp throttle response.  NO bogging anywhere.  No missing/stumbling.  Obvious power gain.  NEW BIKE.  Idles smoothly at 1000rpm indicated.  Will idle lower but some clutch rattle, so 1000 it is.  It even sounds different while riding.  I finally know what a properly running 550K feels like.  Amazing difference from purchase state.

I'll have to ride a bit more to check plug colour, but at the moment I can't imagine a bike running better.

If I had to put a word on the feel, I would describe it as "athletic".  Turn the throttle and it just goes.  This was not the case at all previously.

Thank you for all the continued help and advice.  It is appreciated and invaluable!

[eastern]

were you adjusting the idle mix screws doing the vacuum sync?

I put it at 1 turn out.

[eastern]

https://youtube.com/shorts/IDXKzuAKEPg?si=XUNBKx9I0PD13Wln

[eastern]

I care less for idle,im rarely there anyway?a slightly faster idle is ok if it smooths things out,youll be over 3000 rpm all the time if your riding the bike properly,dont be scared to rev the bike or hold a lower gear in slow traffic ready for a quick burst to get you on your way,too many just loaf these older things along?they like the higher rpms,never lug these motors.

The bike I have beene riding exclusively the past few years had the tach covered below 10000rpm to remind me to stay above it.  I'm back to road riding but not a stranger to wringing a bikes neck

Cheers

[eastern]

[...] I love the way we do bikes and so called "muscle cars" and I am not alone at all in that sentiment. 600 wheel hp is better than 300 wheel, and 1000 wheel is even better than 600 wheel horsepower :-). Adding refinements so the car will both turn and stop makes it even better ;-).

Yep and right after Helene there's Milton approaching your shores... But no doubt some orange ape will blame the Chinese for it...

Landfall is expected basically on top of my shop and house.  Can we talk bikes instead?

[scottly]

Please try to stay on topic, and NO POLITICS!

[Deltarider]

https://youtube.com/shorts/IDXKzuAKEPg?si=XUNBKx9I0PD13Wln

To me it sounds like less than a true 1000 rpm.

[jlh3rd]

sounds fine to me

[eastern]

Plugs were a bit sooty after a ride today.  Maybe felt a bit rich.  Went to 1 1.4 turns out.  Will see how that does.

[jwurbel]

So you are taking the position that out is lean?  I will be interested in your results.  The in lean, out lean, in rich, out rich never seems to get clarified regarding results.  I am aware of screw location relative to engine side vs air box for carburetor settings. Not sure on your carbs where your adjustment screw is at.  I contacted Keihn some time back re: my CB 750 k2 carbs and posted their comments earlier.  In was rich, out was lean which is contrary to Mark.  This is NOT a criticism of him or his extensive writings on this subject.

[eastern]

I hear you.  Just going to try it at basically stock setting for a bit and see how the plugs look.

[dave500]

dont over think this simple adjustment,its not critical to the running of the motor once under way and using power,however the idle mix on these carbs does add to the overall fueling but only to a minimal amount,some carbs for example mostly on cars have a more complex system where the idle mix cuts out once driving along and adds no more fuel,if you think you have a rich condition when running i doubt its from the feeble fueling added from those idle mix screws.

[PeWe]

Small adjustments can make it.
From running well and screaming to the feeling of a wire attached to the front end that a high powered winch pulls hard 

A car gives the kick in the back.

[willbird]

So you are taking the position that out is lean?  I will be interested in your results.  The in lean, out lean, in rich, out rich never seems to get clarified regarding results.  I am aware of screw location relative to engine side vs air box for carburetor settings. Not sure on your carbs where your adjustment screw is at.  I contacted Keihn some time back re: my CB 750 k2 carbs and posted their comments earlier.  In was rich, out was lean which is contrary to Mark.  This is NOT a criticism of him or his extensive writings on this subject.

That would kind of tell us that the screw is letting more air bleed in as opposed to letting more fuel in ??

Bill

[eastern]

Fair enough Dave500 and PeWe.  I went back to the 1 1/4 more because when I went to 1/2 out, it was before the carb cleaning/sync and I wanted to start closer to recommended baseline.  Haven't had the chance to spend time working on mixture since the sync is complete, but that and the strip/clean was the money.
I need a few hours to install new spokes on the rear, then will take it for some proper shake down rides.  Hopefully in the next couple of evenings.
At city speeds, it is currently running flawlessly. 

[M 750K6]

On the question of whether screwing out or in leans the idle mixture. 750K6. I have plugs 1 and 4 showing slightly sooty. I unscrewed the idle screws on these 2 carbs to 1 1/4 turns out. I then went for a ride. I had difficulty starting the bike from cold. The bike was surging / missing at idle and in 1st and 2nd at low speed, below 3,000rpm and I had occasional exhaust popping when engine braking. This went away when I returned to 1 turn out.

I read those symptoms as running leaner at 1 1/4 vs 1 turn out, especiallythe exhaust pops.

After nearly a year trying to understand and fix the two slightly sooty plugs, I've been through the carbs, tappets and ignition and once the carbs are clean the bike has always run fine at exactly 1 turn out. As the plugs don't foul and as far as i can tell the exhaust pressure is the same on all four (my compression tester doesn't cope with the deep narrow spark plug position) I've decided to just live with it. Provided you're not running too lean, on a 50 year old bike, if it runs well, bank it as a win!

[dave500]

yours should have the early carbs,the air screw is behind the slide,turning it in cuts off air=makes it richer and visa versa,have yours got the hole drilled in them,i like the solid ones better,bit more control i think?you can solder them up solid.

[HondaMan]

Something to remember with these OLD carbs: they are soft metals. The mere act of having turned in the screw(s) tight (or snug, hopefully, instead) widens the hole of the taper just a bit. So, in many cases, the 1 turn setting is slightly more than 1 turn out, now.

Note that this change doesn't happen with the PD type carbs that use the tiny O-ring and flat washer to seal against: that was why those were created for these bikes, as the US DOT was really beating up Honda over how 'mushy' the settings actually are in the roundtop-type carbs. The O-ring and tiny washer are the seat in those later carbs, so 1 turn today is the same as 1 turn in 1976.

[Deltarider]

They look like this.