Author Topic: 1977 CB550F 069-A Carburetor Help Needed (Read 2823 times)

rsank · « **on:** June 18, 2015, 05:49:04 PM »

Hi Everyone,

Following up on my earlier post with the carburetor trouble on my bike. I managed to borrow the jaws of life from the local Fire Dept., we
were able to cut through the frame and get the carbs out. I'll deal with the frame later...lol

The main issue I had was the bike was running lean on all cylinders. Running stock air box, Uni Foam Filter.

I was asked a bunch of information by the gurus which I couldn't provide until I had taken the carburetors off the bike.

So here it is.

Mains 98
Idle jets 38
Needle Clip is 2nd position from the top (on carb #1, I haven't checked the others yet)
Number on needle is 279004

The floats were not at 22mm. They were at least 2-3mm lower which could explain why it was running lean on all cylinders.

Two of the main jets were quite worn looking, they were so worn out that I couldn't read the numbers on them. The rubber on the gasket was fine though. The idle jets were in good shape.
One of the emulsion tubes fell out by itself but I haven't yet removed the others. All the parts look clean, no blockages.

Please advise.

jonda500 · « **Reply #1 on:** June 18, 2015, 06:09:20 PM »

I can't find any mention of the exhaust system- does the bike still have the original 4 into 1 with the original super quiet muffler? -if the muffler is a less restrictive one it will run lean with stock carb settings

rsank · « **Reply #2 on:** June 18, 2015, 07:42:10 PM »

Muffler is also the 4into1 stock one.

Thanks

Tews19 · « **Reply #3 on:** June 18, 2015, 07:59:57 PM »

Do the clear tube method for adjusting the float level. Also you did not mention where exactly the bike is running lean? Have you done a plug chop to determine where the leanness is coming from? Also what are the A/F screws at?

rsank · « **Reply #4 on:** June 18, 2015, 09:37:00 PM »

Yes I plan to do the clear tube method before putting it back on the bike. When measuring with the clear tube, where should level be?
A couple of weeks ago, I put a set of new plugs and took the bike on a 10 mile ride. I then took the plugs out and photographed them. Didn't do any plug chops.
And air screws are out 1 1/2 turns.

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Deltarider · « **Reply #5 on:** June 19, 2015, 12:10:04 AM »

Quote

The floats were not at 22mm. They were at least 2-3mm lower which could explain why it was running lean on all cylinders.

Now what did you measure and how?

Quote

Two of the main jets were quite worn looking, they were so worn out that I couldn't read the numbers on them.

Doesn't mean much. What counts is the inside and that hardly gets damaged ever.

Tews19 · « **Reply #6 on:** June 19, 2015, 06:19:05 AM »

I am not a fan of the short 10 mile runs with new plugs and trying to read them. This is just me though. I did around 200 miles and my plugs looked awesome but the bike would have a hesitation at low speeds. Than the plugs went to real rich. Ended up being the needle position was the culprit. Delta is correct about the insides. OEM brass is the best and will last forever. If the carbs are off give them a good cleaning. Make sure your tank is clean as well.

rsank · « **Reply #7 on:** June 19, 2015, 07:56:22 AM »

The insides of the jets seem to be all good. The previous owner has cleaned and serviced the carburetor, however, when I first got it, the air screws were 1/2 turn out of seated position, the bike was fouling all plugs, and later I had a stuck float needle on carb#2. I did the 3000 mile tune up and, reset air screws etc., and then started having the lean condition.
When I measured the fuel levels using the clear tube with the carburetors on the bike, all levels were about 1/2cm below the lip of the bowls.
Now that I have thr carbs out, I measured the float height as per instructions in the service manual.

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Duanob · « **Reply #8 on:** June 19, 2015, 08:14:03 AM »

Quote from: rsank on June 18, 2015, 05:49:04 PM

Hi Everyone,

Following up on my earlier post with the carburetor trouble on my bike. I managed to borrow the jaws of life from the local Fire Dept., we
were able to cut through the frame and get the carbs out. I'll deal with the frame later...lol Serious? I hope you're joking. Its pretty simple. Take out the filter box, remove the cables, take the clamps off the inlet rubbers, push them inside the venturi box, take the 8 bolts off the intakes, pull the carb/intake assembly straight back and twist downward and pull out to the left. Done.

The main issue I had was the bike was running lean on all cylinders. Running stock air box, Uni Foam Filter. Uni filter can cause lean condition. Also do you have the stock air horn, also restricts air flow more than not having it.

I was asked a bunch of information by the gurus which I couldn't provide until I had taken the carburetors off the bike.

So here it is.

Mains 98
Idle jets 38
Needle Clip is 2nd position from the top (on carb #1, I haven't checked the others yet)
Number on needle is 279004

The floats were not at 22mm. They were at least 2-3mm lower which could explain why it was running lean on all cylinders. No it does not. Did you check the o-rings between the intakes and the head? They get cracked and brittle and are a common cause for vac leaks.

Two of the main jets were quite worn looking, they were so worn out that I couldn't read the numbers on them. They don't really 'wear out' they get corroded from sitting in ethanol fuel. The rubber on the gasket was fine though. The idle jets were in good shape.
One of the emulsion tubes fell out by itself but I haven't yet removed the others. All the parts look clean, no blockages.

Please advise. Clean, clean, clean. Get a K&L carb cleaning kit or some steel guitar strings and make sure the pilot jets are clean all the way through. Clean the needle jets with fine brass wool. Measure float just as the tang hits the float needle from the carb base to the top of the float with carb inverted. And figure out how to take the carbs off without damaging the bike.

rsank · « **Reply #9 on:** June 19, 2015, 08:24:40 AM »

I was just joking about cutting the frame. The carbs were quite easy to remove. The rubber boots between air box and carb and between carb and intakes are new. Nice and soft.
Okay thanks for that explanation about the jet. Two of them looked like someone had taken a pair pliers and tried to get them off. But they are not so damaged.

I do have the stock air box the uni foam filter is in place of the stock paper filter.

Thanks for the advice on measuring float height.

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jonda500 · « **Reply #10 on:** June 19, 2015, 09:05:50 AM »

rsank, you didn't say if you still have the original airbox cover snorkel/horn piece in place?

Question for the gurus who always ask for the number stamped in the needles- my 69A carbs have needles numbered 273004, whereas rsank's needles are 279004 - does one of us have the wrong needles in our 69A carbs??

rsank · « **Reply #11 on:** June 19, 2015, 10:24:23 AM »

I didn't quite understand your question before, but I get it now. Yes, I have that snorkel attached to the top of the airbox.

rsank · « **Reply #12 on:** June 19, 2015, 10:31:58 AM »

The online service manual available from sohc4 says the following about the 069 A carburetor:

Jet Needle 2.4953Φ -- 3° 00'-- 2 grooves
I wonder how this will translate to those numbers?

Deltarider · « **Reply #13 on:** June 19, 2015, 10:35:33 AM »

Quote

my 69A carbs have needles numbered 273004, whereas rsank's needles are 279004 - does one of us have the wrong needles in our 69A carbs??

My guess is rsank misread that 3 for a 9.

rsank · « **Reply #14 on:** June 19, 2015, 10:45:50 AM »

absolutely right! old age is catching up on me, it is indeed 273004, just used a magnifying glass on it...

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przjohn · « **Reply #15 on:** June 19, 2015, 01:35:40 PM »

I thought the "Jaws of Life" line was actually pretty good.

rsank · « **Reply #16 on:** June 19, 2015, 01:47:26 PM »

Can't work on my bike worth a crap but at least I still have a sense of humor left...

przjohn · « **Reply #17 on:** June 19, 2015, 01:52:43 PM »

Yup, along with patience a sense of humor is a great asset to have when working with vintage bikes.

jonda500 · « **Reply #18 on:** June 20, 2015, 02:07:33 AM »

I had to use my new non prescription glasses to read those teeny numbers - I don't need them to read normally - third time I've ever used them!
+1 before goin out to the shed to do battle with the carbs, I first work out every day at the gym for a month, then I put on a bullet proof vest, bandaides on all my fingers & welding gloves over them, kevlar pants, knee-pads, wrist guards and a gas mask, oh and bionic arms...

(just kidding all I take out with me is patience & determination)

jonda500 · « **Reply #19 on:** June 20, 2015, 04:15:17 AM »

Correct me if I'm wrong but I don't think there's any easier way (CB500/550) than this:- ?

Remove the battery and battery cage
Remove the fuel tank and the throttle cables
Undo and remove the two brackets that hold the airbox to the bike frame
Fully loosen the clamps on the four airchamber rubbers at the back of the carbs
Fully loosen the four intake rubber clamps at the front of the carbs (the carb ones only - leave the engine side ones tight!)
Carefully ease the airchamber rubbers off the carbs and remove the clamps (or they may get bent during the next step!)
Pull the carbs backward out of the inlet rubbers and carefully patiently manouver the carbs sideways past the airchamber rubbers without tearing them

Although possible, I have found no advantage in seperating the air box and the air chamber from each other

I have found it is not possible to remove the air chamber with out removing the carbs first!

Putting them back in you must have the air box and chamber sitting in the frame first!

Best tips I have learnt from this forum:
- slightly lube the intake rubbers & warm them up with a hair dryer
-when you get one side pushed in stop and temporarily tighten the outer inlet rubber clamp on that side so it can't pop back out when you push the other side in

Any ways my 1975 CB550F is also running lean (apart from the pilot jet - rich at 1/4 throttle) so I'll be watching this thread closely even though I am still an oem muffer away from having the completely original setup rsank has.

Stev-o · « **Reply #20 on:** June 20, 2015, 06:38:59 AM »

Quote from: jonda500 on June 20, 2015, 04:15:17 AM

even though I am still an oem muffer away from having the completely original setup rsank has.

FYI - there is a nice one for sale in the for sale section

rsank · « **Reply #21 on:** June 29, 2015, 08:13:39 PM »

Hi everyone! I just wanted to post an update. I reset the float heights (they were set too low), the jets and needle didn't need much cleaning as they were in good shape (I have always used ethanol-free Shell V Power 91 on this bike), bench synchronized the carbs, checked the fuel levels in the bowls using the clear tube method - all were about 2-3mm below the junction of the two halves. I read previous posts on what the correct level should be and it seems to confirm that.

I put everything back together on the bike and it started up with two kicks and full choke. I took it out for a short ride but it was going so well that I went for around 100 miles in 95 degree heat. I have not yet pulled out the plugs but it ran very smoothly all day and there was no issue with power, I took it up to 80mph on the highway. It was revving nicely too. Of course, every time I stopped, just for sanity check, I made sure it was running on all four cylinders, which it was. I have to do a final vaccum sync and buy a new set of plugs to do my final checks. Thanks for all your help. It wasn't too hard. These 069A's are easy to work on. I just took my sweet time and didn't want to hurry up and make mistakes.

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Deltarider · « **Reply #22 on:** June 30, 2015, 02:40:54 AM »

Good to hear. Personally I'm always surprised how well designer fuels like Shell's V-Power and BP's Ultimate clean and keep clean.

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Author Topic: 1977 CB550F 069-A Carburetor Help Needed (Read 2823 times)