Author Topic: cylinder 2 not firing 1976 cb 550 (Read 3413 times)

Kreb · « **on:** July 20, 2020, 11:12:24 AM »

I just started up my '76 CB 550 for the first time this year. Starts fine, Idles (albeit a little rough) but it seemed to be lacking power in acceleration and seemed a little bit shakier than usual. After the ride I checked the cylinders to see if they were all firing and my second cylinder was moderately cool. I checked the plug and it seems to be fine (when I pulled off the cap the idle fell dramatically). I'm not sure what the issue could be and I was hoping some one could provide some insight. The carbs were rebuilt and the coils were replaced last year.

Thanks

Deltarider · « **Reply #1 on:** July 20, 2020, 11:27:11 AM »

Quote from: Kreb on July 20, 2020, 11:12:24 AM

I just started up my '76 CB 550 for the first time this year.

A few questions first. How long has your bike been inactive? How old is the gas? Have you added a fuel stabilizer before hibernation in case it has been longer than 6 months?
Carbs have been rebuilt, you say. Why was that and what parts were used, OEM or aftermarket?

Quote

... and the coils were replaced last year...

What made you think you needed new coils? What ignition do you run, original or aftermarket? How old are your plugcaps? Do you know how to measure their resistance? What type plugs do you run?

Kreb · « **Reply #2 on:** July 20, 2020, 11:34:18 AM »

Bikes been inactive since December. Was fueled up then, with stabilizer. The carbs were rebuilt because when I bought it last year it was barley running. I didn't do the work myself but I went to a shop that specializes in old hondas. They put in new gaskets, jets and cleaned 'em not sure what the parts were. I had the coils replaced later in the season because the first coil burned out and cylinders one and three weren't firing. The plug caps were replaced then.

Deltarider · « **Reply #3 on:** July 20, 2020, 11:47:02 AM »

I trust you know that one coil fires cyl 1 and 4 and the other cyl 2 and 3. Provided plugs and plugcaps are fine, there's a little test you can do. Have it idle. Now - with a screwdriver - turn the airscrew in the side of carb #2 in all the way. Do this carefully and remember how many turns it takes. Probably around 1¹/₂. Does this make the rpm drop? Then, when you turn it out again, to where it was, does that increase rpm again? Any inline fuel filters that may hinder fuel flow?

Kreb · « **Reply #4 on:** July 20, 2020, 11:53:52 AM »

Sorry yeah it was 2&3 which weren't firing last summer!

Bankerdanny · « **Reply #5 on:** July 20, 2020, 03:48:56 PM »

If the issue is just one cylinder then the issue is with the plug wire, plug end, plug, or fueling for that cylinder. If it is 1-4 not firing or 2-3 then the issue is in the ignition chain.

If you have a clean spare plug, you can unplug all 4 wires, then test one at a time by inserting the spare plug into each plug end, grounding to the head or cylinder block, turning the ignition on and pressing the starter button. You should see a visible spark as the engine spins. If you have spark at all 4 then you need to pull the plug for the cold cylinder and check the condition of the plug. Is it dry, is it black, white? Does it smell like fuel?

Have you checked to make sure the intake valve is opening? I had an adjuster back off on my 550 so the valve wasn't opening.

This type of issue can be a pain to track down, but be systematic and you can figure it out.

ekpent · « **Reply #6 on:** July 20, 2020, 06:29:50 PM »

Simple test is put in a new plug and see if it works better. Danny gave you a good rundown on potential problems. Sometimes a plug just goes bad.

Kreb · « **Reply #7 on:** July 21, 2020, 07:30:18 AM »

I performed Deltarider's suggested test and nothing happened. I turned the air screw in on carb 2 and the engine idle remained constant. I'm assuming this means theres a fuel issue?

Deltarider · « **Reply #8 on:** July 21, 2020, 08:37:21 AM »

This could indicate the slow jet (aka idle jet) is (partially) blocked. This is a common problem that many members here are familiar with.
Just to be sure, I advise you to repeat the same procedure for the other carbs. Take good note of the initial position of the airscrew by counting, so you can reposition the screw exactly where it was.
If, after you've done this, the #2 carb turns out to be the only one that does not show a drop in rpm, you could try this:
after removing the airscrew completely*, you could pour some WD-40, carbcleaner or brakecleaner in that opening and pray it will - by gravity - free the passage of the slow jet. Chances are little however, as the idle circuit has no less than 4 orifices: 1) the - in your case blocked - slow jet, 2) the airscrew (now open), 3) the intake opening in the carbs throat (shown in the picture below as: pilot system air jet) and 4) the small orifice in front (engine side) of the carb slide. The last two are usually open and not problematic, unless you run open (not filtering) pods. Maybe the fluid will free the slow jet just enough and fuel can afterwards do the rest.
Again, not much chance, but who knows. If the symptom remains, I'm afraid you have to remove the float chamber for further inspection, which you have to undertake anyway when the other carbs also have blocked slow jets.
This problem of (partially) blocked slow jets occurs often when the bike has been inactive for a long period of time.
* Note that in the orifice of the airscrew, there's a little spring which does not necessarily have to be removed. Just pay attention, it doesn't get lost.

Kreb · « **Reply #9 on:** July 22, 2020, 11:35:22 AM »

Update: It's worse... I followed delta's advice and squirted some wd 40 in the air screw pocket to reach the screw I took off the tank. I put everything back together and started the bike up, got about a half mile down the road and it stalled out on me. I looked under the bike and gas was pouring out of a tube (I'm assuming this is the carb overflow line?). Not sure if its the same issue or I messed something up taking the tank off.

Deltarider · « **Reply #10 on:** July 22, 2020, 11:57:52 AM »

Carb peeing fuel out of its overflow tube, indicates its float needle doesn't close the valve. This is often seen when bike has been inactive for a long period of time. It can be caused by even a small particle of dirt between the float needle's tip and the valve or the float itself is hindered in its movement.
1. Detach all 4 overflow tubes from their brass pipes to identify which carb it is.
2. Tap with the stub end of a screwdiver its floatbowl and hope this will help to get rid of the dirt.
3. If not, close the petcock, unscrew the drain plug completely. Now with the drain plug removed, open and close the petcock a few times, to create a flush of fuel that can flush out the dirt between the float needle's tip (that is now down) and the valve.
4. When needed, combine step 2 and 3.
In most cases this does it. Ofcourse you will collect all the fuel - inspect it for dirt or excessive rust - and pour it in your tank again.
5. When the above steps don't help, it is necessary to remove the floatbowl for further inspection.

Kreb · « **Reply #11 on:** July 24, 2020, 02:14:22 PM »

It turns out it was carb #2 which was the original problem. I knocked it and flushed it a few times and it seemed to stop overflowing for a while. I let it idle for a bit and then I rode down the street and back and it was leaking again when I got back. Should I take off the float bowl? Do i need to remove the carbs entirely to do this?

Deltarider · « **Reply #12 on:** July 25, 2020, 03:01:30 AM »

You could repeat the treatment you did, once more. You could also - very careful and very gentle! - blow (use your mouth) some air into the fuel line that feeds carb 1 and 2. When all that doesn't help, the floatbowl has to be removed for further inspection. If it had been carb #1, I had given you step by step directions how to do this with the carbs in situ. But to even access the interior of floatbowl #2, you'd had to remove floatbowl #1 also. I do it, but for you it's probably the first time. Then it's better to have the carbs removed and have them upside down on the bench. Much better to get familiar with them. Also you can check and clean all four. Take your time to do it. It will be an enrichment!
To remove the rack, loosen the 8 clamps, disconnect the throttle cables, loosen the airfilterbox so it can move backwards and give way. Ply the plenum-to-carbs boots just enough, so you can push them a cm or two into the plenum. All in all, it's a time consuming job. Practice Zen.

On a CB550 the rack is easiest removed towards the left (CB500 towards the right).
By all means, once removed, do not separate the carbs from the rack! All maintenance, all cleaning can be done without separating the carbs. Removing the floatbowls is all what it takes.

Kreb · « **Reply #13 on:** July 25, 2020, 01:40:34 PM »

That sounds like a good way to spend a day or so. Are there any parts I should be replacing as I wor, gaskets etc... The insulator boots look pretty worn especially on the airbox side. I'll probably replace those. It seems like 4into1.com is out of stock is there anywhere else you would recommend for buying these parts?

And thanks for all the guidance thus far!

Deltarider · « **Reply #14 on:** July 25, 2020, 11:54:41 PM »

Normally the brassware (jets, needles, etc) on these models, live forever and do not need to be replaced. Warning: don't be tempted to replace by aftermarket! I'd have a critical look at the small O-rings around the main jets. They must seal well. If not, the engine will happily suck extra fuel. Now for the O-rings, an aftermarket set will do. The boots between the plenum and the carbs are not that critical. See if you can repair with what ever sticks. The boots between carbs and head must be 100% airtight however. You can test this by having the bike idle and then spray some carb- or brakecleaner there and listen if the rpm changes. Also spray between the intake manifold and the head. Between forsaid manifold and the head are O-rings. They can harden over time, become brittle and then leak air. If rpm doesn't change, all is well.
When you have the carbs upside down on the table with the floatbowls removed, I can give you further directions. I forgot to ask you, when you had the airscrew out, was it the cross drilled one like shown in the first pic or the solid tip one, liek in the second pic?

Kreb · « **Reply #15 on:** July 26, 2020, 07:32:35 AM »

they are cross drilled.

Deltarider · « **Reply #16 on:** July 26, 2020, 10:59:42 AM »

Then you're in line with other owners of a CB550K2 with the 087A carbs. It remains a mystery why the K2's carbs got a new number stamped in (087A) and not the 022A carbs the previous models CB550 and CB550K1 had. There seems to be no difference between 087A and 022A carbs.

Bankerdanny · « **Reply #17 on:** July 27, 2020, 06:51:37 AM »

My understanding is the different numbers correspond to the jet and needle combo that carb used.

My 550 drove me crazy with constant overflowing. I finally bought and installed a full set of genuine Honda parts. I measured the non- Honda parts that were in it and the needles were slightly shorter than the Honda parts, which meant the float wasn't closing them properly.

Kreb · « **Reply #18 on:** July 27, 2020, 02:35:04 PM »

So I opened up the carbs and the float seems to be working fine... Then again I'm not sure what I should be looking for!

Deltarider · « **Reply #19 on:** July 28, 2020, 01:12:45 AM »

Inspection time. I'd keep all parts together, so #1 carb parts in container #1, #2 carb parts in container #2 and so on.
Some members here have reported a cracked brass overflow tube that caused leaking. Maybe they had removed the overflow lines to roughly.
Does float swing smoothly? Could float have been hindered in its movement by touching the sides?
When in doubt, remove the float swivel pin, using your thumb- and fingernail. Sometimes you need pliers, but do NOT pinch the pin. Polish swivel pin without using any abrasing stuff.
Were float needles fitted correctly with their tiny pin resting on the tang? Verify float valve needle is the right one (OEM) and the little spring pin at its bottom actually works. Cones and the inside of the valve must be clean.
Unscrew slow jet and see if it is open. This is a bit tricky. Sometimes you think it is obstructed and it turns out, it is in the eye of the beholder so to speak, a trompe-l'oeil if you will pardon my French. To verify well the slow jet is clear, you need a magnifying glass, then vary its distance to the jet a bit, until you see a hole like in the pic below. I can only see it using a magnifying glass or... by taking a picture. When you see a perfect round hole, you can be sure the bore is clear. When it needs cleaning, use some copper wire like shown in pic. With slow jets removed for inspection, you can spray some carbcleaner up the orifice. Check if it exits at he other three orifices I described before in reply #8.
Now you're at it, you can check a few other things. Inspect the little O-rings around the main jets are in good order and will seal well. With main jets removed, you can get the needle jets (aka emulsifier tubes) out. You can do it by say imitating a full throttle by hand. Either the needle jets will come falling down by gravity, or they will need a little help. A wooden pick put in them from below will, when canted, enable you to extract them. Sometimes you'll find white stuff in the little holes in the sides. It is from water. Clean the holes.
What's your impression? Are jets etc. OEM? Please report the sizes of your jets. Do take pics.

Kevnz · « **Reply #20 on:** July 28, 2020, 03:02:15 AM »

Hi everyone,
I've just gone through this exact same scenario with my 550, paid METICULOUS attention to cleaning, polishing, making sure float is not binding on the tang etc, set level to EXACTLY 22mm, and carb1 still leaked. Is this a fuel quality issue? Back in the 70's none of my 4 bikes leaked a drop, fast forward to 21st century and all of them have leaked. Back in the day our fuel was leaded; did the lead somehow affect the performance of the float valves? Or could it be a fuel density issue? If the new fuel is less dense than the old gold, does the float perhaps not exert the same upward force on the needle, hence not shutting off reliably? Any thoughts?

Deltarider · « **Reply #21 on:** July 28, 2020, 03:27:23 AM »

Kevnz, that is a good question. First, let's realise that the quality of gasoline differs not only in time, but also from country to country, so we can not make generic statements. I doubt however the gasoline will cause leaks the way you have described. A change in the characteristics of gasoline can cause leaking where it concerns the seals, but that's about it.
I do have indication todays gas is causing more slow jets to become partially fouled especially when the bike is not used for some time. In particular the CB550K3 models seem vulnerable to this. A small dose of a fuel additive or kerosene (or lamp oil for that matter) might bring some improvement. I don't know how to put it, but modern gasolines seem to be less lubricious. It's a feeling I already have for a very long time, ever since lead was phased out, but I cannot substantiate it with science.

Kreb · « **Reply #22 on:** July 28, 2020, 01:01:03 PM »

Ive dissembled the carbs at this point and everything looks alright. Orings are in good shape as far as I can tell (the jets needed a bit of force and wiggling to come out). The only thing different about the carb in question, which is actually #3, not #2 as i had previously thought, was that the float seemed to sit a little bit lower when they were upside down. Jets are : Main 100, slow 38 and needle 1.8. I have no idea if they are OEM or not so ive attached some pics. also pictured is the carb in question.

scunny · « **Reply #23 on:** July 28, 2020, 03:59:58 PM »

Are all the float needles the same length ?

Kreb · « **Reply #24 on:** July 28, 2020, 05:16:44 PM »

all the needles are the same

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Author Topic: cylinder 2 not firing 1976 cb 550 (Read 3413 times)