mixture problems

OK, I'm hoping someone can help me out here... My carbs are sparklingly clean, new plugs etc etc. However the plugs are sooting up big time (which to me looks like too rich a mix) but I can't see this as logical as the bike has K&N filters and a Harris exhaust. The Jets are standard which in my book should run lean. I have not touched the mixture screw as the manual severely warns not to, but is it safe to play with the mix screw ? ( the one next to the cold start plunger under the little rubber cap )

Also I can start the bike with a tiny amount of choke , about 5 seconds and it then runs albeit way too rich.

Any ideas ?

UK XJ750 1982

 

just one question how did you clean the carbs sparkling clean if you never took out the mixture screws to clean that circuit??

Ok now onto your question. With the K&N and exhaust you are right at high rom and wide open throttle conditions the stock mains should be lean. But the mixture circuit can still be adjusted too rich. Adjusting the mixture is Key to getting a bike to run perfect. How does your bike idle when running is it really smooth or do you hear a little lope in it? Did you bench sync the carbs then sync them up when they were on the bike?

THe starting means that you did get the enrichment circiut clean which is one thing alot of us overlook the first time around. If you have rubber caps on the mixture screws somebody has already been there as from what I have read and seen the factory uses a metal plug that you have to drill a tiny hole then use a screw to pop them out. Most use a colortune tool to get close then do plug chops to do the fine tuning.
Find a safe place and do a full throttle run for a short bit maybe 1/8 to 1/4 mile hit the kill switch and close the throttle at the same time let the bike cool and look at your plugs. Are you getting any popping from the exhaust? or any bog? Bog is usually rich and popping is usually lean.

 

Really hard to make an XJ rich.

Almost have to have a leaking float needle or float level too high.

 

definitely too rich, chav, what do your plugs look like? are they all the same? have you got one that looks good? if so you can use a glass fuse as a depth gauge, drop it into the pilot screw hole of the one that looks right & mark it level with the top of the carb body, then set the others to that.

 

No they all sooty. I haven't had it synched yet. I didn't take the mixture screws out because the manual said not to. Apart from that they have been ultra sonically cleaned and refurbished.