Topic: Simple carb problem

[arblebang]

Hey there we are restoring a 77 cb550 with a history of poor maintenance. I have been through the carbs and cleaned them up nice, however we still have an irregular idle and the bike doesnt like to come back down after revving. I'm sure it is in the carbs, specifically what should I look at?

Thank you

[Johnie]

Did you complete a bench sync before you put the carbs back on the bike?

[Deltarider]

Running lean can cause this problem. Are all your jets clean, are settings according to Honda's data?

Check for airleaks between carbs and engineblock. Spray some brakecleaner when idling and listen if RPM changes. Also the O-rings between head and inletmanifold are suspect. Again: spray some brakecleaner (some use WD-40) and see if RPM changes. If so, you've found a leak.

[arblebang]

Carbs synched with professional tools and methods, and the boots seem good to me. I tested for an air leak already and found none, altho I will test again. We have ordered new jets because the slow jets seemed to have much smaller holes compared to my 81 GS850, and granted that is a bigger engine but I suspect there might be some gunk in the jets despite my most ambitious efforts with carb spray and a needle. Could that be the source of the 550's inability to return to idle speed?

[Alan F.]

How's the float height?

[dave500]

those minute slow jets ,poked with a needle however carefull,can be damaged,im guessing the carbs have been blown through with compressed air with all jets removed?eyeballing 81gs850 jets as a comparison isnt really gonna help,,was there any white corrosion in these carbs on the honda?might just need another blow through.,no kinked fuel hose?not just a sticky cable,the push and pull cables are set correctly?with the tank off make sure the linkages are free,you said the bike has had a poor maintenance history,wd 40 all the rack linkages(im guessing thats been done already?)

[campbmic]

Did you check slide needle height? I have a 75 550 that had a similar issue but was running WAY out of whack. I rebuilt the bottom of the carbs three times. I finally looked at the slide needle and all four carbs were set to something different.

[arblebang]

Slide needle, thats a good idea never checked that.

Linkage, fuel flow, all good. Float height was a little high as per the ambitions of the previous owner, the carbs were hopelessly overflowing every time I turned on the petcock. At first I thought the float needle wasn't seating, but it was clean so I did my best using a children's ruler to set the float heights and now they don't overflow so I was satisfied with my efforts, but it would probably be a good idea to reset them with a more specific measuring device. I have an original manual which is very helpful.

OK so my plan of action is new slow jets, slide needle, float height. Thanks a lot guys, if there is anything else you can think of pls let me know.

[Johnie]

Just a thought...you mentioned this 77 had poor maintenance. How does the fuel tank look? Even the smallest crap in there will cause all sorts of carb problems.

[Deltarider]

OK so my plan of action is new slow jets, slide needle, float height

.
Why? Are they damaged? Just clean them and make sure you do it with something softer than the messing of the jets like copper wire. If it's an old style Keihin (069A) all parts are easy accessible.

[JBMorse]

Sounds like you've got a handle on things, but did you check the float heights correctly?  Apparently, on the later carbs, you're supposed to measure from the lips of the float bowls:
http://www.salocal.com/sohc/tech/float_tool/float_gauge.htm

I'll second the tank check.  You don't need much fuel flow interruption to give you problems
Also, have you already done the other tune up stuff?  Valve clearances, timing, etc?
Good luck!

[arblebang]

After synching the carbs I left the tank nearby on a sawhorse connected by a long, clear 1/4 inch tube. The amount of rust coming thru the tube is astonishing, altho the filter seems to trap it all. This weekend or next I think we are going to throw it into a saline solution and try and blast all the rust off of it with my battery charger, altho the owner of the bike wants a "professional" to "take all his money" and "do the tank cleaning properly."

Thanks for all the great ideas guys, I have a lot of food for thought for this weekend. I'll post the results.