However, a mixture of jets, needles, and screw changes coupled with poor performance from the ignition certainly will.įuel level in your bowls should be set to the proper height, irrespective of your plug colors. Non-stock needles will effect the fuel performance, but I can't imagine as much as you describe. Looking for thoughts and opinions even if you feel I am not on the right track.Ībsent of jet gauges, you can not be certain someone prior to you has not drilled open the orifice diameter of the jets that are installed. I have checked the coils and they ohm out good, Dyna S Ignition System and the air screws need to be set at 2 1/2 turns out or it will not idle at all. I’m not real jazzed about the second option. Buy an aftermarket set of emulsion tubes or used if they can be found or buy 022A needles. Installed the factory Mikuni needle and it was corrected. The other reason is I chased the same issue with another motorcycle when I blindly installed the Factory Pro needle with a stock emulsion tube and fuel economy was horrible afterward. I pulled a couple emulsion tubes out but there was no part number stamped on them. Two reasons: The 100 main jet that was in the carbs when I bought it, I think the PO bought the wrong kit and replaced the emulsion tube with the wrong one. What I am highly suspicious of is the needle jet/emulsion tube, that it could be for a 550K 022A model. The carbs also have the stock needles with the Keihin part number 273004. The carbs originally came installed with 100 mains (from the PO) and have since put in the proper 98 mains. Full throttle the bike pulls hard and has no surging. I bought the bike this spring and it has run poorly and comsumes a lot of fuel ~26-27 mpg with a lot of surging from 1/4 throttle to 3/4 throttle and black sooty spark plugs. Hope I've helped a bit.1975 CB550F with 069A carbs, stock exhaust, stock airbox, properly set up carbs etc.

I am not an engineer but I get a bit baffled that terms for parts (emulsion tubes/needle jets) appear to change mid-explanation. Maybe you could suggest a 'group buy' discount? I'm going to try an persuade the lad to fork out. The Factory Pro replacement tubes ('now nickel plated') are part numberĬRZ-EMU-100120K and cost £40.00 per pair + VAT + 'a couple of quid' postage. I called their UK agent this morning about buying a pair of their emulsion tubes. Note that, with fuel level adjustments, you can make some mixture adjustments with the 'fuel level', as adjusted by 'float height' changes.' (end of quote - see this link ) Replace the emulsion tubes / needle jets if there is more than 10k miles of varied use or 5k miles of in town driving on the bike before trying to tune. Additionally, the fuel that does get released is in larger, less burnable droplets. The needle, stock or aftermarket, will wear the needle jet orifice oblong - causing excess fuel to flow at cruise and low rpm. 'Replace worn bare brass needle jets in stock carbs with Factory Pro's own stock replacement nickel plated needle jets. I have no connection with them, but they seem to have persuasive 'evidence.' They provide quite a lot of information to back up their claims for their product. I tracked down a patented replacement emulsion tube from an American dyno company called Factory Pro Tuning. I did a bit of research on Mikunis because of my son's misbehaving CV 38s on his M600. The emulsion tubes are prone to wearing oval which affects performance and fuel consumption, worth checking out and replacing if needed.

Factory pro emulsion tubes