Topic: CB550 stalls while coasting

[SamP]

Your mods never indicated a need for jet changes. There's not much that's really breather a great deal more air into your system. I'd suspect that all along the issue of "rich" was maladjusted carbs, not incorrect jets.

It would also be really advisable to replace the plugs with clean plugs every time you foul them. Or at the least, clean the fouled plugs. Using a "weak link" trying to troubleshoot that system is making things much harder on your diagnosis.

Info from another thread posted here the formula (can't link it here cuz I'm on mobile) to figure out what your jetting needs are based off of mods. I followed that to get 45 slow and 100 mains.
My logic right now is go back to stock and new plugs - worst case scenario is it runs lean, which won't foul plugs. But keeping the same jets I run significant risk of fouling again, since I haven't changed anything other than syncing correctly. If it DOES end up being too lean, I can order new keihin jets and see if that solves my issue.  Does that sound reasonable?

Before any of that, I'll be checking for vacuum leaks, because even with the right jets, vacuum leaks need to be identified or it will run rich regardless.

[calj737]

Sounds like a good approach. If too lean with stock jets, adjust the needle 1 clip position before swapping jets.

[SamP]

Well, I got the chance to raise the fuel levels in 3 and 4, and while I was down there I swapped out the mains and idles I had installed last fall (100s and 45s) with the stock jets that were in there when I bought it (90s and 42s). Was a real pain in the ass to start, not sure what bogging down or loping sound like, but it wasn't pretty - sounded worse when I rolled back on the throttle. Thought I'd taken 5 steps backwards.
Once warmed up, however, I was able to tweak the idle speed to a stable level and it sounded ok. Tested for vacuum leaks, sprayed carb cleaner all over boots and intake manifold, no increase in rpm. Good sign, so I took her for a spin around the block. Really gunned it up the hill right before the stop sign to really test my coasting stalls, and as I pulled the clutch in once I had crested the hill, the engine kept idling. Went around once more because I couldn't believe it. Did not stall. Drove up my driveway kinda fast, pulled in the clutch - didn't stall.
Swapped out the plugs with new ones, and while I was waiting for the engine to cool down a bit, I was examining the old plugs. It looked as if they were starting to clean themselves, with the leaner mixture and resulting higher heat, some of the carbon looked like it was starting to come off. The oily residue on plug #3 seemed to be gone, and I am wondering if that wasn't just gas, because after I took a ride around the block once , came back up and removed all the plugs, there was no residue on #3. In fact, the only plug that was starting to show any signs of anything, was #4.

You can't really tell much from these photos since the plugs were only run for like 5 minutes, but here they are.


Left is 1, right is 2.


This is 3 on the left and 4 on the right.

Should I run it a little bit longer and check again? Or is this diagnostic of it running well enough? Little concerned about 4, but I'm wondering if I should do another vacuum sync or not, then check again.

Next question is, how do I know if I've got the right mixture ratio? Theoretically I could have had the right mixture, just bad jets. So how do I know if it's too lean now, and I really DO need to increase jets a la the jetting formula, just replace them with Keihin?

[Jimsun]

Youre looking for more of a bronzy goldy colour when u pull the plugs

People suggest riding and when the bike is at 5krpm. Chop the kill switch and check each plug.

[flybox1]

#4 looks great, the others are super lean.

[HondaMan]

There's a caveat here for plug 'color', if you are running Conoco-Philips or Shell gasoline: these have, in most of the USA, nitrogen detergent aboard. This cleans the plugs a lot more than most fuel, so the readings come out much lighter than expected when the engine is set up right. Lately, this has thrown a lot of confusion into the "tuning" efforts of many SOHC4 riders.

One example: the normal colors for my 750 plugs has been, for 36 years until nitrogen showed up in the gas, a medium-to-dark tan. With these fuels, they come out plain white. Switching to Sinclair or BP locally will produce the "old" colors again, but it washes back off when I go back to the Shell, making the plugs look largely unused at all.

[SamP]

Just wanted to update - sat on all this for a while until life slowed down enough for me to give it another go.
I figured with the jets smaller than recommended for my set up, I opened the mixture screws to 2 full turns out to enrichen the mixture a bit, and after discovering how to properly use my syncpro ("So that's what those little brass things are for..."), I synced again and got a whole new baseline for the carbs. Idles smoothly at just under 1000 and while it still sounds a little starved at 1/4 throttle (not sure how to describe what it does, but it sounds like the engine is stuttering - loping? Bogging down?), I'm gonna see how the plugs look after riding for a few days. If they look lean, I'll bump the idles to 45s and test again.

As it is she runs decent, idle doesn't hang or drop or stall out like before, so I know I'm headed in the right direction.

Thanks everyone. Will hopefully update again with more good news.

[Duanob]

Did you ever mention where you needle clip position was? I think if you changed from 4 X 4 exhaust to 4 in 1 you might only need to change that. Try it one position at a time. I would try and raise the clip position which will lower your needle. That is based on theory for leaning out the mix for the change in exhaust. But your plugs already show lean so maybe try enrichening the mix by lowering the needle position? Remember every time you remove the slides or mess with them you will have to do a vac sync. That will be good practice. Also while you have the needle out you can clean it as well.

I'm not too familiar with the PD carbs but I know that's the basic difference between the older 550 K and F models is just clip position. It doesn't cost anything but time to try it and see. Good luck.

[SamP]

Did you ever mention where you needle clip position was? I think if you changed from 4 X 4 exhaust to 4 in 1 you might only need to change that. Try it one position at a time. I would try and raise the clip position which will lower your needle. That is based on theory for leaning out the mix for the change in exhaust. But your plugs already show lean so maybe try enrichening the mix by lowering the needle position? Remember every time you remove the slides or mess with them you will have to do a vac sync. That will be good practice. Also while you have the needle out you can clean it as well.

I'm not too familiar with the PD carbs but I know that's the basic difference between the older 550 K and F models is just clip position. It doesn't cost anything but time to try it and see. Good luck.

I forget which notch the clip is on for the needles, but I do recall moving it down one notch from wherever it was, which would have lifted the needle (this was before I had any working concept of what this would do, I only thought "more gas = faster!"). I have a vague recollection of the clip being on the first, uppermost seat, so I'm pretty sure it's one below that, which should enrichen the mixture (unless I've got it wrong).

Thanks for the advice. I'll try that if swapping out for bigger idles don't resolve the issue at 1/4 throttle.

[cwchan]

I have this exact problem too.  I think i need to adjust my float heights.  I couldn't find any actual instructions online or in the manual. 

How do i go about this?

78 550 pd46c carbs too

[cwchan]

Do you just bend the tang?

[DaveBarbier]

Do you just bend the tang?

First, I'd verify your float heights by the "clear tube method". Do a search in the forums of what's in quotes. No need to remove carbs or even take the bowls off just yet. Fuel level should be ~3-4mm from bowl seam.

As for adjusting floats, I was trying to find a step by step on the forum but couldn't find it. I know it's around here somewhere. Maybe someone else can post it.


---
1978 Honda CB550K

[SamP]

I have this exact problem too.  I think i need to adjust my float heights.  I couldn't find any actual instructions online or in the manual. 

How do i go about this?

78 550 pd46c carbs too

It really depends on what changes you've made to your intake/exhaust, or jetting alterations, if any. From what I can surmise from my situation, my mixture was way too rich, and suddenly closing the slides from WOT had the effect of flooding the engine to a stall. Use the clear tube method to see what level your fuel is at, check your plug color and take it from there. And yes, you just bend the tang - it really doesn't take much to drastically alter the fuel level, so don't do anything too extreme in any direction. Be sure to hold both sides of the float while you adjust it, or you could torque it and it'll be uneven in the bowl.

[SamP]

Now that I'm insured, registered, and inspected, I've spent the past two days riding around town. Can't turn the idle below 1000 or else it might dip too low and stall, but at 1100 there is a consistency to how she runs and I'm liking it.

I've come to discover that the 1/4 throttle issue really only ever happens when it's cold. Once the engine has warmed up, there is no hesitation anywhere on the tach. So I'm just going to chalk that up to the cold natured-ness of these bikes. Hopefully the transistorized ignition will help with that.

Now that I've synced those carbs up nicely, I decided to pull the plugs and take a look. #4 was carbon fouled all too hell, and I think that was due to an improper sync from user error early on, but I've replaced the plug in that cylinder and will check it again in a few days. The other 3 are posted below.

Cyl #1


Cyl #2


Cyl #3


I think they're looking pretty good, so changing jets doesn't look necessary. Fingers crossed that #4 looks identical in a few days' time.

[HondaMan]

With our ethanol-laced gas today, those are beautiful plugs!


If you're up for some more experimenting (I call it 'fine tuning'), consider this:
First, as a test, set the points plate back a few degrees so the timing is "late" an equal amount on both coils. Using low-octane gas, ride it a while a see if the hestitation goes away and stays away. If it does, the "fix it" step is to put the timing back where it belongs, AFTER you clip off 1/2 turn from at least one of the spark advancer springs (if not both), and re-bend that last loop to hook it back onto the advancer post.

The 500/550 Fours in particular tend to heat-anneal their spark advancer springs. This lets the timing then advance too soon. It should never reach full advance before 2500 RPM: most of the ones I see today are FAR sooner than that, and stumble until I "fix" them this way.

[SamP]

Ethanol free at my local gas station.

Thanks for the advice on the test, hondaman. I might give it a go later this season when I've run out of things to tinker with  .

As is, she runs smooth when warm, and if it ain't broke...

[SamP]

Well, as is the case, not so good news. Plug on #4 was fouled all to hell again, even after a good sync. Pretty bummed. Plug looks dry, so I don't think it's oil, but I'm not gonna rule that out. Could it be oil?



Before I go digging deeper, I'm gonna be checking my valve clearances, possibly sync again just to see if it is as synced as I think it should be. I'll be checking for vacuum leaks as well (only on #4 though).

On a suspicion a few weeks back I pulled off the cam shaft end cap covers just because...the one on the #1 side oozed oil as soon as I pulled it out, however the side on #4 did NOT do this. Under the tappet covers I can tell the whole cam is pretty well lubed, as are the valve springs. Could it be an oil leak from the channel on that side? Should I check the torque on the head cover bolts around #4? Really pretty lost here.

Lastly, there is a chance, albeit a small one, that I installed an oil ring upside down. The last time I broke down the top end, I had a hell of a time trying to find the word "top" on the damn ring, and being a noob, I hadn't marked it (don't ask why I took the damn rings off in the first place, I don't have an answer for that). I am 90% sure I saw the end of the letter "P" on the corner of the ring, but it's entirely possible I got it backwards.

Obviously breaking down the top end is not something I want to embark upon just yet (a last resort, really), so give me what you got.

[SamP]

So after a bit of deliberation and rumination, I've convinced myself it's not an oil leak (deposits are dry and fluffy), so top end tear down probably won't do anything. I decided to check my spark advance that was WAY OFF (didn't fully understand how to set that before, but I researched it and got the timing set with an old turn signal.) Bit of an issue, I had set the point gap long ago but double checked it and it was good. Tried to set timing and got 1-4 timed right, but it was at the end of the free play in the plate, so then I couldn't set 2-3 correctly. Reset the point gap at .016 (up from .013), and was able to set advance on 1-4 and 2-3. Went for a ride, got back, checked again and it was off (!!!). set it AGAIN and this time it's stayed put.
Since I've corrected the timing, I've been noticing quite a bit of spitting back through the carbs, pretty consistently when warming up. This leads me to think my mixture is a bit on the lean side, and that I should try upping my slow jets (mixture screws are turned out to the point where they stop changing anything: 2 1/2 turns out, I believe?). But I don't wanna mess with that until I've got my #4 plug consistent with the rest, which all look great.
So, back to the point at hand. I checked the valve clearance on #4, and the intake valve was at .0025, so I closed it down a bit to be within spec. Between that and the spark advance correction, this has not addressed the carbon fouling.
Which leads me to think it's A) weak spark from coil, B) problem with idle, main, needle, emulsion tube, or mixture screw on #4, C) clogged passage within the idle mixture circuit not letting air through, or D) an issue relating to minor corrosion in #4 wherein the emulsion tube sits lower in the float bowl because the tube cannot go any further into the carb body. I suppose I could add that the butterfly valve on the choke could be failing, however they are failing in the other direction - when I hold the choke closed while starting, they tend to flap open. Still starts no problem, but I know that they tend to stay open rather than closed.
Currently checking A by swapping 1-4 coil with 2-3. If #3 becomes carbon fouled, I'll assume the issue is with increased resistance in the wire from the coil to cylinder #4, reducing spark enough to carbon foul the plug. If not, I'll check B by swapping out one by one, all the components between 1 and 4 and see if that affects #1 plug. C will require pulling the carbs and dipping them to ensure all passages are clear, and for D i'll need to measure how far the jets/emulsion tubes sit from the main body in comparison to one another.
Any other insights from anyone else would be appreciated.
Edit - I also vacuum synced again, and they were all even at idle. Turning the throttle a bit and they seem to pull unevenly, but once I let off the throttle it balances right back out. Don't know if this is normal behavior or not.

[jonda500]

Hi Sam, I don't think it's your coils- the coils fire once every revolution making a spark simultaniously in both 1 and 4 (or 2 and 3). The cylinders all recieve a spark when the piston nears the top regardless whether they are on compression or exhaust strokes. So I'd rule out the coils, although the issue still could possibly be #4s spark plug, cap or lead.

[SamP]

Hi Sam, I don't think it's your coils- the coils fire once every revolution making a spark simultaniously in both 1 and 4 (or 2 and 3). The cylinders all recieve a spark when the piston nears the top regardless whether they are on compression or exhaust strokes. So I'd rule out the coils, although the issue still could possibly be #4s spark plug, cap or lead.

Thanks for the input jonda. I was still concerned about the actual wire from the coils to #4, so I needed to test it. After the swap I went on a 15 minute trip around town and when I got back, had a look. Plug #3 was still nice and gray, so I've at least confirmed my wires are not the culprit. Plug caps are new and known good.

Put all the coils back where they belong and swapped out the emulsion tubes and mains between 1 and 4, so I'll take another little joyride tomorrow and have a look. Took the time to remove the mix screw blow canned air up into the seat for good measure. Also measured how far down the main jets went below the seam, and between 1 and 4 the difference is negligible.

Concerns to be addressed later is the spitting back through the carbs. Mostly happens when just barely rolling on the throttle when cold, or even just idling without throttle. Would that be too small idle jets or too low needle position? Air filter is freshly cleaned and oiled.

[calj737]

Did you ever verify your fuel levels via the clear tube method? If so, post up pictures please-

[SamP]

Did you ever verify your fuel levels via the clear tube method? If so, post up pictures please-

I did, but did not take pictures once I got #3 and #4 corrected. The last photos I posted they were 1 or 2 mm too low, so I raised them in both until they matched the others, and when they did I didn't take a pic. Can verify again, but I think I may be cornering the issue...

I swapped the emulsion tube and jets between 1 and 4 and rode it today like normal. About halfway through the ride it starts acting up, stuttering like crazy. I make it home and check the plug on #1, and it's wet with gas, whereas before it was nice and gray.

Swapped the tube and jet with some extras I had laying around in #1 (unfortunately aftermarket, but we'll see how they run in the meantime). Wasn't thinking clearly and took her for a ride instead of syncing, and the same issue came up, but made it home with lots of throttle blips at red lights. Now #1 is clean, gray and dry, but #4 is still all sorts of carbon fouled (I had cleaned it off, so these were all new deposits). I realize that this could be because I didn't sync before I went for a ride, so I'll sync it and see where it's at. Before I went for that last ride I knew something was wrong - it would idle well at ~1200 for 3-5 seconds, then dip to ~800 for a second, then right back to ~1200. Not sure if that's just an indicator that it needed a sync, or if something else with the spark advancer, which I needed to calibrate AGAIN. Think I need to replace it.

Further down the rabbit hole we go...

What's the consensus on aftermarket emulsion tubes? Yes? No? I know where the forum stands on jets, but what about those tubes? I've got 3 more to swap out with the other carbs, but I don't know if it's a good idea or not.

[calj737]

Do you have a quality brand ignition plate? I seem to believe I read you were out of adjustment, then it wouldn't hold, now it's off again? I've got a good quality stock unit if you need to swap yours off. Probably even an advancer if I look hard enough. Let me know- I'd rather see someone put them to use to solve a finicky bike than have them lying about in a parts bin.

[SamP]

Do you have a quality brand ignition plate? I seem to believe I read you were out of adjustment, then it wouldn't hold, now it's off again? I've got a good quality stock unit if you need to swap yours off. Probably even an advancer if I look hard enough. Let me know- I'd rather see someone put them to use to solve a finicky bike than have them lying about in a parts bin.

Yeah, my timing has been all over the place. It was set incorrectly after the rebuild, but I was able to static time it with a turn signal, and got it lined up right for both 1-4 and 2-3. Each time I take it out for a spin it seems to go back out of correct timing again, despite being clamped down firmly. Gap looked good, as did contacts, and the plate looks brand new. Not sure of the make, but I'll look it up tomorrow after I sync. If you had a spare plate/advancer I'd love to have the opportunity to try all this with some known good parts. Might end up trying hondaman's spring clipping technique, and it'd be nice to have a backup if that goes to pot. Let me know what you want for em.

[calj737]

Fire me an address via PM. I want them to help get your bike running. That's what I want for them.