Topic: 1978 cb550 with 74 carbs. Need carb help.

[eric11]

So I bought my bike a little over a year ago and have slowly been restoring it. It is a 1978 Cb550 with a freshly rebuilt top end. 

After some research I believe it has 74 carbs on it. The carbs are running a 110 main jet. And a 40 slow jet with the needle in the 2nd clip position from bottom. I cleaned, bench synced, float adjusted to 22mm, and put new gasket kits on them before installing them. The bike is also running Uni pod filters and a Jardine 4 into 2 exhaust with mufflers installed. I put it all together and started the bike for the first time and these are the symptoms.

It will only run with the choke on at 1/4 open. When I close it the bike dies

I had to lean the air mixture screws out 4 and 1/2 turns to get it to idle even with the choke open.

I've checked the spark plugs and the have a ton of soot on them.

Sometimes I would get a pop through the carb body.

The idle hangs when I rev it.

So this is my initial thought after reading. I didn't clean the emulsion tubes when I cleaned them before. And those are known to cause problems. So I have the carbs off now and re cleaning everything.

In your opinion what jetting and needle position would work best for my Uni pod filters and 2 into 4 exhaust??

I know that they came with a 38 slow jet and mine has a 40 in it. Is that jet too big for my setup? And does my bike need the 110 main jet or would the 100 be closer. I know carbs are trial and error. And I'm willing to put in the time. I just figured since I had them apart I'd ask for some wisdom. 

Thanks!







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[Deltarider]

No 500 or 550 needs a main jet wider than 100, unless it has been seriously, seriously modified. These bikes with the oldstyle Kei-hins were jetted filthy rich from the start. Cleaning the needle jets can help. Luckily you have the old style Kei-hins. You can remove the needle jets with the carbs in situ. Just remove the float bowls. If the needle jets (aka emulsion tubes) don't come down rightaway after removal of the main jets, here is what to do.
Again, carbs can be left in situ. After removing the main jets twist the throttle at least halfway in order to raise the needles and with your other hand insert from below a match or wooden toothpick into the needle jets. When that is snug in the needle jet, cant or turn the wooden toothpick a mm or so and you can wiggle the emulsion tube out easily.
Some WD-40 at forehand can help.
Essential in this procedure is that you open the throttle to raise the needles.
Has worked for me, but many times they just dropped after the main jets were removed. Very simple. And again: it can be done with the carbs in place. Keep the parts separate in containers or boxes 1,2,3 and 4 and make sure you assemble them correctly and not upside down (if possible at all). Check all little holes in the needle jets are open. You don't need fancy stuff. It is important to check the little O-rings around the main jets still seal. If they don't seal well, raw fuel is happily sucked in by the engine. These carbs are easy to work on. No need to remove them let alone separate them from the rack (a spreading disease in this forum, don't be tempted, the linkage just doesn't need maintenance). For maintenance removing the floatbowls is enough, the rest is to fill pages in manuals. People are better of inquiring mechanics that have actually worked on these machines instead of absorbing all kinds of academic possibilities in manuals. Piece of cake.

[eric11]

Thanks for the replies. Yeah I have no intention of disassembling the whole rack. I'm just cleaning those emulsion tubes and putting the smaller 100 main jets in.

When rebuilt everything I put new gaskets on the intake manifold and inspected the boots. Which I haven't vacuum tested it yet but my jets aren't even close to do so.

So Cali737 you think I should drop my needle clip position to the bottom position ( the richest it can go ) and get 38's for the slows and run the 100 mains?

I was thinking of setting that needle clip position back to the center position ( which would lean it out a little more ) considering I'm running the 40 slows and use the 100 mains. Is that the wrong thing to do?

Thanks again!! 


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[eric11]

My needles have 5 clip positions. Mine is set at the 4th from the top right now. My understanding is the middle position (third from the top) was the stock position on these carbs.


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[turboed13b]

I disagree with a cb500 or 550 not needing bigger main jets. I have four of them with open pipes and pods and one runs with a 110, two with 105, and one with 100.

[mrfish2]

Stock position on those carbs should be second from the top.

Second from the bottom for K model carbs (which is what it looks like he has).

[mrfish2]

The F model carbs were set at 2cd from the top, but the K model carbs are set at the 4th position stock.

[eric11]

Oh wow so this means the 40 slow jet is stock on these carbs as well..


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[mrfish2]

Oh wow so this means the 40 slow jet is stock on these carbs as well..


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My carbs are 087A's (for a 76 550K) and they had 38 slow jets stock. I'm not sure where they got 40 as being stock for the 74-76 carbs.

[Deltarider]

I disagree with a cb500 or 550 not needing bigger main jets. I have four of them with open pipes and pods and one runs with a 110, two with 105, and one with 100

.
Who wants open pipes and pods if you can have the real thing? 
Tested on the dynostand my standard CB500K2 (ED) '76 with #78 (!) main jets was still overrich at 9250 rpm in 5th doing 185 km/h. Ofcourse you will never reach that speed on the road because of winddrag.

[mrfish2]

Oh wow so this means the 40 slow jet is stock on these carbs as well..


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My carbs are 087A's (for a 76 550K) and they had 38 slow jets stock. I'm not sure where they got 40 as being stock for the 74-76 carbs.

Because the 40 is listed as stock for the 022 carbs. You're not paying attention to the model details. The 087 is not listed in that chart. But, you are correct, the 38 is stock for the 87 as confirmed elsewhere.

Ahhh, I did not notice it said 022A in the chart, that makes more sense now. The column header is written CB550k 74-76, that's what was throwing me off. 

[mrfish2]

I had to lean the air mixture screws out 4 and 1/2 turns to get it to idle even with the choke open.

Just so I don't seem like a jackass for contradicting Cal I'll contribute some helpful knowledge 

Somewhere on here (probably in the FAQ) Hondaman wrote that the air screw is really only effective from 1 to 2.5 turns out. If you've had to turn yours 4.5 turns out (and I didn't even think that was possible) then your carb settings are way off (which has already been established). If it were me I would go back to all stock settings using genuine Keihin jets to establish a baseline and tune for the pods from there.

[Deltarider]

CB550k 74-76, that's what was throwing me off

Another example of misunderstanding when you use 'year' in stead of model.
Models with 4-4 were: CB550K(0), CB550K1, CB550K2, CB550K3 and CB550K4.
Models with 4-1 were: CB550F, CB550F1 and CB550F2.
The last year the F2 was on the market it still was a F2 and not a F3. There never was a F3.
All you need to know is what model you have. The year is irrelevant and only leads to confusion.
In the various Parts Lists you'll find listed per model the corresponding engine- and framenumbers as well carbnumber. Very simple. You'll find forsaid Parts Lists here: http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb550
So from now on we'll have no more talk of year this or that but everybody will know what model he has so we can have things straight. Agreed?

[eric11]

I apologize. Yes it's a 550K model. And come to find out it actually has the 627B carbs on it?? Which might explain a few things. From that list that Cali posted the 40 and 100's are stock. The other thing that's confusing me now is it says that the needle should be #2.5 with no clip positions. So do I even have the right needles in there if I have the needle with 5 clip positions?? Here's some pictures 


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[mrfish2]

Finally found a better carb setup pic, this one has the needle clip info for the 627 carbs (which came on CB500's)

[Deltarider]

Although the 627B carbs were on the CB500 you can safely keep them as the only differences are in settings. For a CB500, CB500K1, CB500K2, CB550K, K1 and K2 the number on the needle should be 272304. 

[Deltarider]

Finally found a better carb setup pic, this one has the needle clip info for the 627 carbs (which came on CB500's)

I know but to me it is useless, for all CB500s in Europe with these 627B carbs had the needle in 3rd (middle) position.

[eric11]

Wow thank you guys so much. That's the needle I have. I'm going to put them back together with the needle in the 4th position even if stock was the 3rd just cause I'm running pods and not stock air box then I'll tune accordingly. I'll report back what happens. Thanks again!


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[b5rider]

Wow thank you guys so much. That's the needle I have. I'm going to put them back together with the needle in the 4th position even if stock was the 3rd just cause I'm running pods and not stock air box then I'll tune accordingly. I'll report back what happens. Thanks again!


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I'm in the same boat, except I have a big bore kit and 650 cam ( and a separate thread) I just printed out the guides. thanks