Topic: Cb550f slow jet question

[Fattyflathead]

I cleaned and rebuilt the 069A carb on my 76 CB550f project bike, the bike is running but with  problems idling and all plugs black indicating running rich. The only non original parts I put into the carb were the slow jet 38 and main jet 98, I'm thinking  of trying to clean the OEM l jets and reinstalling instead of the aftermarket parts before I try and sort out the idle/ rich problem.

 My question is if I hold the slow jet up to the light , should I be able to see a pinhole of light through it at the screwdriver slot ??, as i currently can not pass a piece of wire down through the jet even after soaking in carb cleaner!
Appreciate any replies

[paul_D]

Yes you should be able to see a pin hole down the slow jet. The hole size is equal to the number on the jet. (40 equals 0.4mm) Try a brass bristle from a brush, spin it in your fingers while applying some pressure. Anything harder than brass will damage the jet pin hole. If you have no luck, soak it in something stronger to break the build up down.

[Fattyflathead]

Great thanks for the advice.ill try that.

[Fattyflathead]

As a lot of threads i followed ran out before i could find out how the OP fixed the problem, i just thought i'd reply to why my project bike wasnt running well after fully rebuilding the carbs.

I used aftermarket idle and fixed jets in the rebuild( rookie mistake no1), so i decided when it wasnt going great to replace the jets with the OEM parts i took out.

When i opened the float bowls i found dirt in them , i obviously fed bad fuel back into them after cleaning them (rookie mistake no 2)

It was still running rich so i vac synced the carbs this time at low rpm, i realised i also put too much oil in the uniair filter foam (rookie mistake no 3) hence the rich or choking.
After fixing all that and turning the idle screw out to 1 3/4 she runs nice and happy having being off the road for god knows how many years and the plugs are looking good. I want to thank " Two Tired" for all the effort and details in his threads without which i would still no doubt be down the shed scratching my head.

good luck and thanks.

Steve

[Duanob]

Glad to hear you got your issues fixed.
I am having the same issue with my 550F. Burns very rich at idle up to about 1/4 throttle. Blows black smoke, coughs and sputters until the mains kick in then it runs great, nice and smooth all the way up the RPM range. I leaned the idle air screws out as far as I could and have the bike still run and it still runs rich. I even ran it with the filter out and it is a bit better but at this point it should be running lean, not rich at all. Still running rich. I've been through the carbs before and know the needle is in the correct clip position and the floats are set correctly. I know all air passages are clear and the emulsion tubes are clean.

I took the carbs off the bike and pulled a pilot jet and compared it to a pilot jet I had from a set of doner carbs. The pilot jet from my F is shorter and has smaller air-mix holes in it. It also doesn't have the Keihin logo stamped on it either. So I am cleaning the carbs and throwing in the doner jets with the Keihin logo and rechecking the float height. I am hoping the pilot jets I took out are aftermarket and that's my problem.

Update: I got into my carbs and found two after market pilot jets. I measured the OEM jets I had and they are 28mm long and other two or 24. I also speculate that all the pilot jets were drilled out. A #38 pilot jet will only fit the smallest cleaning wire from a K&L wire kit. All four pilots in my carbs would fit the third smallest which I've never seen before. I replaced all pilots with good 38s but it's raining and haven't put the carbs back on yet. I like discovering what could possibly be the problem.