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I need some advice for tuning a pair of Mikuni carbs I have on my Morini 500. Previous owner fitted them and they work much better than the Dellorto’s that were on the bike. I have watched some videos on tuning the VM Mikuni and I have the idle jets were I want them. Video says get the main jet sorted for WOT before playing with needle and clip. Ignition is electronic Sasche and it’s set and forget. The carbs were set for sea level but I am at 2000+ above sea level, I knocked the idle jets down from 30 to 27.5 and the plugs now have a nice light brown colour. Bike idles and runs well but at WOT it just bogs and runs quite rough. How do I know if it’s trying to gulp more fuel or drowning from too much?
at WOT , slightly close the throttle , if it accelerates , it is too lean 130 sounds small , i run my V65 lario with 34 mm mikuni VM , i run 210 main jets.
Thanks! More to check today. One of the carb to head rubber boots ( a new one I bought from NLM ) has torn, need to fit an d hard rubber one in its place.
A 210 main is GIGANTIC! For example, the T3 is spec'd for a 130. My LeMans 3 and 4 are somewhere between 130 and 140. Even my BMWs are in that range. From all the evidence so far, it sounds like dropping the main size down a few notches should help.
by the way, on aliexpress you will find cheap jet kits for mikuni's, just buy 100 to 150 in small steps, they are stupidly cheap. saves you going to a shop to get the next set of jets, i bought the complete set of dellorto main and pilot jets, and a complete set of mikuni main and pilots. trying other jets is just grabbing them from the cabinet. makes setting up carbs so much easier.i wish i had those 20 years ago.
This is a good resource to have on tuning Mikuni carbs. I used it to help me setup my VM32s. Very detailed. Good luck!http://www.vintagebikebuilder.com/mikuni-tuning-and-jetting-guide.html