Topic: CB550F idle circuit update- HOORAY IT'S FIXED!!

[jonda500]

The bike is a 75 550F that I have put together from parts, the carbs are reconditioned 627B's with used oem 069A needles that I got from ebay clipped on the #2(from the top). The mains are new oem #98's and I have just changed the pilots from #38 to #35(new oem) without removing the carbs from the bike- I had to cut off halve of the handles from a stubby phillips head and a flat blade screwdriver and grind the flat blade thinner to fit the pilot jet slot (thanks riverfever for reassuring me that it can be done!).

The bike has always run better when not entirely warmed up- after 10 miles or so it would develop a bad flat spot at 1/4 throttle meaning I couldn't maintain steady speeds between 30 and 50 mph - most annoying. If I putted around a carpark just above idle with the throttle barely cracked open at all it ran perfect!

With the #35 pilots in things have improved markedly- It now likes the idle screws 1 turn out instead of 1.5 turns and the 1/4 throttle dead zone now has less of a decelerate effect, more of a lack of acceleration rather than actually slowing the bike down like before(with the #38's).
I am thinking next to try putting the oem solid mixture screws from my 069A's in, but I think I'm still gonna have a flat spot...

recap: standard 4-1 exhaust with aftermarket muffler, standard air filter, new manifold rubbers and o rings, new ignition coils and points plate (timimg set & advance checked w/timing light), reconditioned carbs-
mains #98
pilots #35
needles #2
idle screws 1 turn out

Still feels rich when I find exactly the right throttle position a small amount above idle could it be possible I need even smaller pilots??

[Duanob]

At 1/4 throttle I don't think the idle mix screws will do anything. My first thought is go back to the #38 pilot jets because that's what they came with. Just make sure they have't been drilled out. Did you do a 3000 mile tune up? Mostly thinking of your timing and points settings. Everything else sounds skookum as far as Honda settings. How do your plugs look after riding around for a few miles? Lean? Rich? You kind of need to know which direction to go.

[jonda500]

I initially had #100 & #40 jets in, then I changed to #98 & #38 (stock for this bike) but also added needle shims as the plugs looked very lean. Although it didn't fix it, this had a good effect on the super rich idle/pilot circuit(#40>#38), but made it too lean on W.O.T.(#100>#98). Finding and installing an oem air box cover snorkel thingy totally cured the lean on full throttle issue.
Next I fitted correct oem needles (#273004) clipped 2nd slot, no shims. This made no noticable difference.
Changing the pilots from #38 to #35 has made it run MUCH BETTER at 1/4 throttle and has narrowed the unresponsive range of throttle opening down to just a tiny, tiny bit either side of 1/4 open which is also a great improvement.
I have ridden 1100 miles since putting the bike together, I have tightened the cam chain, set the timing twice, set the tappets 3 times, changed the oil 3 times, and I do declare that I have vacuum syncronised the carbs 3 times (every time I pulled the needles out). The muffler is a straight through fibreglass packed type that has to be much less restrictive than an oem one (I haven't been able to find a genuine oem one for sale).
Airbox has the recirculation breather tube and I cut a square of filter foam to replace the disintegrated bit down the bottom, but the drain tube from underneath the bottom is missing.
Compression is low but it has good acceleration regardless. (#1-120,#2-90,#3-90,#4-70)- I havent done a wet compression test to confirm - but I believe the rings are worn (It uses a small amount of oil).
I have tried these carbs on my 500 with good compression and the same flat spot was present.

I have two unrestored spare racks, poor condition 069A's and nice looking 022A's. I am considering having a go at rebuilding the 069A's myself, whereas the 022A's look nice enough to just give them a try as they are. Are these carbs all the same except for the different jets, needles, clip positions and idle screws?

[jonda500]

I just swapped the idle mixture screws for the oem solid's, set them the same 1 turn out and took it for a ride (after warming it up for a few minutes!)- it started raining so I only went 11 miles. As I thought it runs about the same - it always feels like it's fixed until it warms up properly then the flat spot starts to rear its ugly head gradually. If I had to pick between better and worse, I'd say the solid screws made it better. The bike idles a little faster despite not touching the idle speed screw, so I was able to back out the screw a little which I believe is a good sign (being able to achieve the same idle speed with the slides slightly lower would have to be a good thing?).

I just put a link below to my haphazard build thread in project shop, John

[jonda500]

Oops, I have jumped the gun- I just realised I haven't performed the clear tube float level verification yet on these carbs, so I will have to do that and some plug chops and report back when I have some plug chop pics - at least I don't have to do any more full throttle plug chops they are downright scary!

Also I suspect a rocker shaft issue as after setting the tappets spot on twice I'm still hearing a ticking tappet
-so I guess the valve cover has to come off to check that... I'll see if the clearances have changed again first..

[Duanob]

As I mentioned before the mixture screws are pretty much out of it by 1/4 throttle. It's either a pilot jet issue or needle issue if everything else is running correctly. If you have two other racks I would try those as a comparison. If the 022As work then go with that, same bodies and jet sizes just different needle position. Its funny how that airhorn makes such a difference on this bike's air mix ratio with the 4into1. I bought a MAC muffler that worked similar to the OEM because they are impossible to find not all rusted out.

FWIW I had the same issue as you on my F model where it would run fine when cool but rough just above idle speed when warmed up. I racked my brain for months until the final time I took the carbs apart I noticed the pilot jets on two carbs were different then OEM. All four were #38 but 2 after market jets were shorter and therefore not work like they should. The pilots should be #38 or #40 X 28mm in length. Something to check the next time you tear into the bowls. After 4 new pilot jets from jetsrus.com the bike ran perfect even after it warmed up.

These bikes can be noisy when they start getting up over 20,000 miles probably form wear but they will keep on going if you don't mind a bit of top end rattle. I have a friend with a 550 and only 10,000 I am always envious of how quiet his motor is.

[jonda500]

Update: I now have the needles clipped in the top #1 slot. I vacuum synced the carbs after changing the clips and can confirm that pulling the slides out DOES mess with the sychronisation as it was quite a bit off.

   I reset the tappets and found to my relief that they weren't far off this time, so I am just trying to ignore the random ticking noise.

   I have ridden over 100 miles with the #98mains/#35 pilots/#1 slot clipped 550F needles combo and the improvement is VAST! I can hold a steady speed at ANY throttle opening now with no bogging down. The problem I am having now is: if I snap the throttle closed to allow the engine to slow down from a high rpm and then open it back up again I get a poor response. If I crack it open a decent amount there's just a very slight hesitation and then it pulls fine, but if I roll the throttle gently back on the flat spot is quite noticable and irritating. As it happens after using engine braking (and zero throttle) I tried leaning out the mixture screws, but it didn't like that so I put them back at 1 turn out. I think I'll try a richer mixture screw setting next even though it seems to me like a too rich issue still.

   Here's a pic I just snapped of my plugs after a ride mainly on the freeway. They are almost soot free now with the lowest compression cyl #4 plug having just a little. (120 90 90 70)
John

[jonda500]

Trying to solve a rich issue by screwing the idle screws in seemed like a dumb idea so I turned my attention to the emulsion tubes instead. I pulled the emulsion tubes out of my 069A parts carbs - I was surprised how easily they came out, I just sprayed WD40 in them and pulled them out the bottom by jamming a match into them. I should confess I also installed my last 4 main jet o rings on a set of #100's with the intention of using them instead of the #98's - but when I checked with my glasses realised that I had accidently waisted the o rings on aftermarket jets - they're very hard to get off without breaking the suckers! I still thought I'd use them at this point as I thought the emusion tubes wouldn't make much difference.

I used my cut down stubby phillips head to pull the bowls off without removing the carbs from the bike. I used the throttle screw on the switch block to lock the throttle wide open and tried my match trick to pull the tubes - but it just broke off in there... so I had to pull the slides out so I could use a drift and a hammer to drive them out. One of them was particularly hard to get out and I'm not sure but I think it was in upside down! I am guessing they are probably not oem but don't know - they have the same two rows of holes but they are all the same size holes. The 069A tubes have various different size holes in the rows all smaller than in the tubes I removed, and two extra single holes in the middle 90 degrees around from the two rows of holes - plus they are a smooth shiny finish and they fall out when the jet is removed.

Luckily for me the #100's were too loose a fit to use (smaller than oem!) so I have obeyed the rule of one change at a time and put the #98's back in. Then, of course, I had to vacuum sync the carbs - this took longer than normal and I was starting to get really puzzled - then I realised my little mower fuel tank was running out of fuel! All went well from there apart from an alarming cracking noise toward the end when she was getting a bit warm.

Well I have been for two test rides and I still can't believe it - flat spot issue is SOLVED! Living in the city this bike until today has been a right pain to ride, with its flatspot exactly in the throttle range most used in slow traffic and the hesitation after every slow down making me not even want to ride it any more.
John 

[jonda500]

Update: I was less than impressed that it was taking 2-3 kicks to start when hot and got to wondering if changing the pilots to #35 and dropping the needles to #1 was treating the symptons rather than the cause of the issue (the emulsion tubes!). So I changed the pilots back to #38 (new oem). This fixed the hard starting when hot issue, got it purring very happily at idle (screws 1 turn out) and had no negative effects.

Then I decided based on my seat of the pants dyno that although running really well, she was a little lacking in power. I decided I didn't trust the ebay 550F needles in the bike, even though they're the right number genuine needles they are very shiny and a brass color. So I pulled the slides/needles out of my 069A parts carbs. The needles look a coppery color with some staining. I didn't clean them! I checked they all had the correct number stamped in them and that they were all clipped #2 slot. The slides looked great so I put the needles back in them and one by one swapped them with the ones in the bike. Performed a vacuum sync.

Well the power is back! Normal riding she runs great - better than ever. Performance just off idle is worse again now though, with it needing a quick blip of the throttle to clear it before expecting any power at just above idle - but I really I would rarely ride it that sedately any way so apart from leaning out the mixture screws a little, I am just going to live with it for now and turn my attention to the oil leaks...
John

[PowerMax]

Just my 2 cents worth, so value accordingly - but, until you resolve your very low compression issues, you're going to be chasing your tail forever.  I can't believe the bike even starts when hot.

[jonda500]

Well I was so encouraged at how fantastic I had it running as far as riding it goes, that I thought I could get it to idle better too. Leaning out the idle screws didn't cut it- it was still rich at idle, so I took out the #38 pilots and put the #35's back in. I am now 100% happy with it - it starts first kick, idles well and has no flat spots. It will happily pull from as low as 1100rpm (although naturally I don't suddenly snap the throttle wide open from such low revs!). At high revs with a big handful of throttle the clutch is now prone to occasionally slipping again so the power's definately back. p.s. I got the order wrong by doing the pilots before the needle clips as the needle clips then affected the pilot circuit and so yes I did some tail chasing.

I of course want to fix the low compression eventually, but there was no way I was about to put money into new rings until I had a properly functioning set of carbs for the bike first and it goes so well that I am still in no hurry. I want fuel, electical, brakes, etc, etc all 100% sorted before I take the engine back out to rebuild it. Then when It comes to bedding in/running in the new rings I wont have any dramas interfereing with the process of running in my newly rebuilt engine!! p.s. I have only done one compression test on this engine and it was way back when I had only just picked it up from the local wrecking yard where it had been sitting under a pile of engines at the back of the shed for probably 20-30 years, and I had only ridden it ~100 miles. I expect the compression may have improved since then with the over 1300 miles that I have on it now, but it does use oil and I do conceed that the low compression may cause it to run a little richer than otherwise...

Below is a picture of the emulsion tubes that have given me so much trouble, see how big the holes are?- the 069A tubes have much, much smaller holes! Thanks to harisuluv for pointing out that 069A carbs have different emulsion tubes as that was the turning point for me (well that and finding an airbox snorkel and realising that I dont have to remove the carbs from the bike to remove the slides or take off the float bowls).

Below that is a picture of the 069A parts carbs I scored cheap off ebay from Phillip island Australia! You virtually never see SOHC carbs on ebayAustralia, and I took a punt that I might get some good bits from them -and well this was a fantastic stroke of luck- although battered and rough on the outside, they had 100% original brass and seem quite clean and unmolested inside with no wear or damage at all that I can detect. They cost me less than ONE new oem needle jet set and that's if I could even find any for sale! Bargain!
The slides below the carbs are the ones I took out of the bike which have the suspiciously shiny needles in them, the slides, needles, emulsion tubes and idle screws out of the those carbs are now in the 627B carbs in the bike. 

Recap- With the correct needle jets(emulsion tubes), and the airbox cover fitted, it now runs perfect with almost stock settings:

mains #98, 069A needles clipped #2, 069A needle jets, pilots #35, 069A solid idle screws 1 turn out,
original air filter witrh snorkel, original 4 into 1 with aftermarket straight through muffler.
John