Topic: 76 cb550 running rich

[xhevi]

hello all.

i realize this topic has been beaten to death in this forum and others, and believe me, for the last 2 days i have been searching all over but i cant seem to find answers to my questions.

issue i am having is blackened plugs, strong gas smell trailing me and black smoke at high revs.

bike has a stock air box with a 4 into 1 exhaust, the air screw is 1 3/4 out. carbs were cleaned, rebuilt and vacuum synced.

PO did not make any changes to the carbs for the 4 into 1 exhaust. (main jet=100; pilot jet = 38; slide needle 026 and clip location= 4th from the top)

from what i gather a 4 into 1 exhaust requires a richer mix and the solution is to go +2 up on the jet size OR raise the needle by one clip. is that correct?

how will any of that help me when its already rich??

also sound like this a trial and error work - keep changing jets and needle height till it runs ok.

i see how swapping the jets is sorta doable with the carbs on the bike by dropping the bowl and floats with some sort of a container under to catch any falling parts.

on the other hand dropping and raising the needle is not something i wanna do more then once. the whole carb assembly has to be pulled off, taken apart, re synced etc.

taking the carbs off and then back on the bike is a PITA on its own.

any thoughts? 

thank you



some background:

its a 76 CB550 K2 with aprox 14000 miles on it, i have owned for a couple of years and rode it last summer approximately 200 miles after rebuilt below

1) top end work (honed cylinders, new rings, decarb head, lapped valves etc)
2) all new gaskets, o-rings, and some seals
3) rebuilt carbs with all new o-rings and gaskets. kept the same jets. stock carbs settings. main jet=100; pilot jet = 38; slide needle clip location= 4th from the top: air screw 1 3/4 out
4) carbs bench synced and vacuum synced afterwards
5) stock air box
6) 4 into 1 exhaust (that's how it came to me)
7) timing: looks good. i have gone through the electrical components from points to the spark plugs and all checks out. timing chain tensioner was adjusted and valve clearances were set.
weather temps: spring to fall. from 50s to 90s F.
9) altitude: from sea level to say 1000 ft.
10) new clutch, tires and so on

[jonda500]

Assuming float levels are good I would advise starting with getting the main jet / full throttle mixture correct as all other part/no throttle mixtures are affected by the main jet size. If it pulls harder with the throttle 90% open than fully open then try one size bigger main jets. Verify first that the main jets in there are actually 100 with a 1mm drill bit - it will be a very snug fit in genuine 100's.
John   

[Deltarider]

Any cloth under the seat that is partially blocking airintake?

[river]

I'll also add that the needle position on the slide CAN be changed with the carbs on the bike. I tuned for a long time messing with jets and needle height to get mine to run right at 9,000'.

[calj737]

Clip position “4th from the top” as you describe it puts it 2 from the bottom. That is VERY RICH.  It should be stock, 2nd from top. Confirm that is correct.

[xhevi]

Any cloth under the seat that is partially blocking airintake?

Nope, nothing that does not belong there. Just the tool roll.

[xhevi]

I'll also add that the needle position on the slide CAN be changed with the carbs on the bike. I tuned for a long time messing with jets and needle height to get mine to run right at 9,000'.

That sounds better.

[xhevi]

Clip position “4th from the top” as you describe it puts it 2 from the bottom. That is VERY RICH.  It should be stock, 2nd from top. Confirm that is correct.

I found a post on here from Two tired with a snap shot from some manual with a table showing stock settings for different CBs. That table called the clip to be at 4th from the top. Will look for it again.

Mine are set at 4 from the top.

[xhevi]

Clip position “4th from the top” as you describe it puts it 2 from the bottom. That is VERY RICH.  It should be stock, 2nd from top. Confirm that is correct.

I found a post on here from Two tired with a snap shot from some manual with a table showing stock settings for different CBs. That table called the clip to be at 4th from the top. Will look for it again.

Mine are set at 4 from the top.

this is post i mentioner earlier. the bike is a 1976 CB550 K2 matching engine numbers.

http://forums.sohc4.net/index.php/topic,118472.msg1339092.html#msg1339092

[calj737]

Clip position “4th from the top” as you describe it puts it 2 from the bottom. That is VERY RICH.  It should be stock, 2nd from top. Confirm that is correct.

I found a post on here from Two tired with a snap shot from some manual with a table showing stock settings for different CBs. That table called the clip to be at 4th from the top. Will look for it again.

Mine are set at 4 from the top.

this is post i mentioner earlier. the bike is a 1976 CB550 K2 matching engine numbers.

http://forums.sohc4.net/index.php/topic,118472.msg1339092.html#msg1339092

That is a misprint. Really easy to confirm. Move the clip up 2 places and run the bike.

[xhevi]

my carbs are off the bike at this time so i can not play with the needle setting just yet.

however here is some more info on my carbs.

1) carbs are stamped 087A.

2) all of the internals seem to have been replaced as some point. none of the jets have the K stamped next to the size.

how big of a difference is between Keihin jets and aftermarket? looking at jetsRus and they do not have the #38.

another thought is. if only the exhaust was changed and all else is stock, should the jetting for the same year CB550F would be a better starting point?

thank you

[river]

O87A?? Can you post a picture of those carbs? They should be O22A.

[xhevi]

O87A?? Can you post a picture of those carbs? They should be O22A.

i would if i could. for whatever reason is not letting me post.
i found 087A stamped on all 4 carbs on the flange that meets the rack/ plate, not sure what is called.
where should i look for the#

[Deltarider]

087A is right for the K2. BTW, so far nobody has a clue what the difference is between the 022A and 087a carbs.

[xhevi]

Is there any difference other then jetting between
087a and 069a ?

069a -  98 main, 38 pilot and clip position 2.
087a -  100 main, 38 pilot and clip position 4.

I got this numbers from:

https://motorcycleproject.com/text/specs.html

[Deltarider]

Not that we know, but realise the needles differ. See below.

[Scott S]

my carbs are off the bike at this time so i can not play with the needle setting just yet.

however here is some more info on my carbs.

1) carbs are stamped 087A.

2) all of the internals seem to have been replaced as some point. none of the jets have the K stamped next to the size.

how big of a difference is between Keihin jets and aftermarket? looking at jetsRus and they do not have the #38.

another thought is. if only the exhaust was changed and all else is stock, should the jetting for the same year CB550F would be a better starting point?

thank you

 #2 is probably your biggest issue. If whoever installed the "kit" also used the needles, then you really have no idea what position the clips are in. The aftermarket needles are different than Keihin and meter fuel differently.

 You said the carbs are off. Bite the bullet and and at least check one needle to confirm position. The emulsion tubes could be worn as well, compounding the aftermarket needles/jets issue.

 At this point, you really have no other option than to try leaning it out with the needles and/or the main jets.

 BTW, most 4-1 exhaust won't require a re-jet. It's the aftermarket carb kits.

[xhevi]

my carbs are off the bike at this time so i can not play with the needle setting just yet.

however here is some more info on my carbs.

1) carbs are stamped 087A.

2) all of the internals seem to have been replaced as some point. none of the jets have the K stamped next to the size.

how big of a difference is between Keihin jets and aftermarket? looking at jetsRus and they do not have the #38.

another thought is. if only the exhaust was changed and all else is stock, should the jetting for the same year CB550F would be a better starting point?

thank you

 #2 is probably your biggest issue. If whoever installed the "kit" also used the needles, then you really have no idea what position the clips are in. The aftermarket needles are different than Keihin and meter fuel differently.

 You said the carbs are off. Bite the bullet and and at least check one needle to confirm position. The emulsion tubes could be worn as well, compounding the aftermarket needles/jets issue.

 At this point, you really have no other option than to try leaning it out with the needles and/or the main jets.

 BTW, most 4-1 exhaust won't require a re-jet. It's the aftermarket carb kits.

last night i dropped all the needles by 2 clicks tightened up the top end, hoping i am done with that part.
 
all needles were all set at 4 from the top. forgot to check size and whatever stamping they had on them, i assumed they are all the same.

the emulsion tubes have some very light scoring on outside. there is no stamping anywhere.

are the genuine emulsion tube and needles also stamped? how can one tell if genuine or aftermarket?

[Deltarider]

Needles are stamped, the tubes aren't. As shown in my overview ^ all CB550K models with oldstyle Keihins had the same needle the CB500 had: 272304. All "F" models had the 273004 needle. When the stamped in number begins with a D, it is a Keyster product.

[xhevi]

Great help. Thank you.

I think that's a D. Is Keyster any good?

[flatlander]

keyster is a common aftermarket brand. there's no guarantee that sizes match OEM (usually they don't) and their tolerances may vary. basically it's a gamble.

they might work with an adjustment of needle height. but you really need to run it to know.

if not, and if you're not too tight on money you may just want to get a keihin set from jets r us which would save you a lot of trial and error. if they don't have a 38 pilot, just get the 40. but now that you have the needles adjusted, why not give it a go and see how they do?

[Scott S]

Great help. Thank you.

I think that's a D. Is Keyster any good?

 That's a "before" pic, right? Because that clip is set towards the "rich" end of the needle.

[xhevi]

keyster is a common aftermarket brand. there's no guarantee that sizes match OEM (usually they don't) and their tolerances may vary. basically it's a gamble.

they might work with an adjustment of needle height. but you really need to run it to know.

if not, and if you're not too tight on money you may just want to get a keihin set from jets r us which would save you a lot of trial and error. if they don't have a 38 pilot, just get the 40. but now that you have the needles adjusted, why not give it a go and see how they do?

Other then the fouled plugs that make the start a pain I think it runs decent for my riding. (I mostly ride local rarely get it up to 60mph.) With cleaned or new plugs starts right up. It pulls ok but it takes only one ride to get the plugs fouled.

Was looking into jetsRus. Mains plus pilots seem to run about $70 total. Emulsion tubes about 80 total Can't find the needle unless it comes with the emulsion tubes.

All and all looking at around 150$ to 200$. Not that bad if it saves me all the trouble. But I also working on my 73 bmw R60/5 and that needs cylinders bored Pistons etc.

Maybe will just get the needles and emulsion tubes for now and see how it does.

[xhevi]

Great help. Thank you.

I think that's a D. Is Keyster any good?

 That's a "before" pic, right? Because that clip is set towards the "rich" end of the needle.

That's a before photo. I raised the clip by two. So it's now at second from top.

[calj737]

Other then the fouled plugs that make the start a pain I think it runs decent for my riding. (I mostly ride local rarely get it up to 60mph.) With cleaned or new plugs starts right up. It pulls ok but it takes only one ride to get the plugs fouled.

It is quite possible you are the cause of the plugs being fouled. If you ride this motor in low RPMs, slowly, you are "lugging" the engine. It wants to be ridden well above 4,000RPMs.

General riding that fouls your plugs tells you nothing. You have no evidence of where (throttle position) the fouling occurs. Time to properly perform some plug chops. IDLE first. Then WOT. Then MIDRANGE. Only then will you have evidence to what adjustments are needed in your carbs.

All and all looking at around 150$ to 200$. Not that bad if it saves me all the trouble. But I also working on my 73 bmw R60/5 and that needs cylinders bored Pistons etc.

Maybe will just get the needles and emulsion tubes for now and see how it does.

Stop believing spending money on "possibilities" and start spending some time doing what's necessary. If you have adjusted the needle 2 positions, assemble the bike, fresh plugs, and ride it properly (correct REV range). And be certain you are operating the CHOKE correctly. You would not be the first to operate it in reverse.